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ALBERT R. MANN LIBRARY
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CORNELL UNIVERSITY
Cornell University Library OL 536.H85 V.
The mo: uitoes of Nor’
Te 3 1924 002 846 016 mm
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Cornell University
Library
The original of this book is in the Cornell University Library.
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http://www.archive.org/details/cu31924002846016
THE MOSQUITOES OF NORTH AND CENTRAL AMERICA AND THE WEST INDIES
BY LELAND O. HOWARD, HARRISON G. DYAR, AND FREDERICK KNAB
VOLUME ONE .
A GENERAL CONSIDERATION OF MOSQUITOES, THEIR HABITS, AND THEIR RELATIONS TO THE HUMAN SPECIES
WASHINGTON, D.C. PUBLISHED BY THE CARNEGIE INSTITUTION OF WASHINGTON 1912
A.eny coats CARNEGIE INSTITUTION OF WASHINGTON
Pusrtication No. 159, Vou. ONE
Gower of thig bak wore first issued
JA 21 1918
THe Lord Baltimore Press
BALTIMORE, MD., U. 8 a.
TABLE OF CONTENTS.
TNCTODUCEION® ¢5siyies cs tuciels v sediaie a Senin dale VR aaa Gatun o 4 ABR on ab eed aR eoE sas
Early accounts of mosquitoes............ 0.0. ccc ccc ceccceuseecceuceuueens 8
Mosquitoes a8 PeBt9... fas cs o3 eevee Gaede ca ere saacneuunsameeensvaudas 8
Early accounts of the biology and structure of mosquitoes............... 20
Structure of the adult mosquito............. ccc cece cece cece ceeceeeeneeuees 25
PMG TOA. 5a otise oak crate cher MePocs mtn ti Xan Scmed anach Gucalalala atenes ee 4 cies ae ymca ecu ae 25
PNG CY OG se cS octane yiabdeen da mii ook Mina artin oa tok akua ee Arete GweEo tes 25
The: antenne! eee sceerrrcaeret yenieraaendsdoaacanwiaecs eae saueacs 26
EHV: CLV DOU) hase cecaishariacesas avaunceich scans aiais sale renera- BG oie gees des Bia ger ake eS 36
DDE PrODOSCIS ise ssiesc ceria aides ws Wickes sack Guan Wes Hee was WS BAG RAS BA 37
FENG: Dall s:. oven avisam oa wag cae ee Nie acu da a Fates So SOLES kee ee 50
PNG: AMORA RS rast. Gate esas uve $4 Missy 4 CMR Ae 24 ME oe AERC oca ade oon Glens salon oa 55
The :prothorax: 2.0 xsd t-censcaiecwe daneviasw aveisoa 0:0 ohided. ie « Wea aiiw. tases sar RWndenee 55
DHE MESOEN OAR: i. varaiev eis Gudea ein s Bialena GAs noun Gis deawere leg Blea Ie ahaa’ 4 57
The Metathorax .. vreiece oaaancsieasioe'y 05 sae at4 Rede ba whe 64 eG awe oa aw EE 59
ENG WINES: 307s opis Sas Oe ws dag ease Wine’h <6 Big dM POA ARES ek RE ene 60
MOG MOBS oc aiccane g's atu oka tann a Gia esal x's. AIRS ew kone, See vamtaisoh EA cde Pan pa BS SHS 62
MN ADGOMEN. 55 sss 5 sivas 8 58 sacs: gie Saves a asacereie ew drew visww Shain 40.4: ¥eenwtsecd Widued ss 67
The abdomen of the female............. cece cece cere c cece evenenss 67
The abdomen of the male............c cece ce ecec cee eeeceecceceeees 69
PVG: SCAICS isch. isva Sages eansisse o< dedi sry Guat 8 ances si aA Sask RARE RPE TR Gl 71
The internal anatomy of mosquitoes........... 00 cc cece cece cece ee nen tenance 15
GLOSS AMALOMNY: 5 siisitis-s ssieraicn se acavenacavaievequsl Oca wpnbaie P sxaule Vand eae adeaton wedeataees 75
The alimentary canal......... 0... cece ccc e cece eee e ee neeeeeeeee 75
The TeprTOductiVe SYSTEM voc oe cen oa seus es ace cen eea ves cee ve cuaNRA 79
Ne fat DOY sass gir yawns vee eos O42 ¥ Goa £4 KE RR OEE iad sve Monee 79
The tracheal system ss sss scwe cd cee 24 sew a dba 6 soe wae wea cece o eeecne ® 80
FRISCO ORY <> se easii tee tise: 8 eoaaia id avsdar ode d.loneyh ch sib upaub dik. belies testa ask Gomeauetetad raters 80
The alimentary canal and appendages...............cceeceeceecees 80
The reproductive SySteM........... cc ccc cee nee tee cee ceeeerseccces 83
The larva, sae sis sess soe es eh sae ine tte 62s ae eG ApS BANE Hy Selec Dee e « 84
Head and mouthparts.............. cece cece ccc u se ese cence ree teneenes 84
ARNG: OY ES. cores bess. 6s oie cd a Heras eWee aera ee SHER ENN. yeh FRE EES 87
FENG CH OTAX. -y.cigee-g ai pide ele hye <cawlatars w@ slaylo ds Sache qualnetn’s ats 4 arene wd aries 88
The Abdomen. s.c's's-syan-c a ws a 38 4 oe vee ss ORE HOY CAA EBM SA Sa NE ae 88
The respiratory organs................. Sh oetaetre saat ah aed tPadon ba Gootysae Peed ena 89
Modifications of larval structures............ 0... ccc cece cece ee eee eens 91 Adaptations of the mouthparts of Culicid larve to the predaceous
A DUG aya arciserd eg ana ss Gees ea washes lead si aie Witte: ade wees 3 hs oe Es 95
Moulting and the number of larval stages.......... 0... 0. ccc cece ence reas 97
TENE UND Ae so. 9.5 ,5: es nee ead pes Maes WRG SG aun eed he cues Bed Deana levied alea auondavga scar 99
EXClOSION: OL CHE: TMA LO. esse psc eyes bo. cesunlig 3:4 stank # dea. seta ee. Sinn Heke Oma aie iwi arene ee 103
Habits: of adult mosquitoes ives scses sac wid vice gages & siete s wise cba Seach: w oh lorie ane Aiwa s 106
The £000: Babits ices: seek ces Hees a eag eeu dase Few 4a Tea ew RES a4 Say aHele es 106
Mosquito songs and their power of hearing............. cc cece eee eee 114
PTDINS OL, CCL VAC Vesa: 50.25 cos asge x snnbieteerces Gauans b iasdausgu gs HUGS grist gp ele Nd. favieag DUR yenlout ot Sl gviphtaveh aN allah 118
AsO MB OVC 665s 4 sar aiss ne scmiecar ese ee aaeca seared tas Sima Doasseaipeonsgoaicasig wihawer ane sacindcly ve hid lave ae abaee 118
Hibernation and eestivation.......... 0... cece cece eee cette tence 119
Mating habits ais¢seesecees i i caw sss mpw aes ie bed EA Os TER Ee A Ow 494 ee 120
Abundance of MoOSquitoes...... 6. cece cece eee e eee e teen nee 132
Mosquitoes in the far North......... 0. ccc ce ccc eee ree cee ree eee eae 135
Eges and oviposition. « «cies is nets sawed eeeeasa ele be oases ele nurs bed ge ea bese 140
Habits: of the: larvetsseeissxec4 i mw vss ews ce emnees snow aa wae ye asee eee ew eva eee 146
Food of mosquito larve.... 0... ccc cece tcc ee ete e eens Neti t aa tacos 150
Hibernation of MoSquito larV®..... cece ccc ee eee ee eee eens 154
The pupal Periods cvs.s0 ee ssa pesea neg aca ge sea te mange Seem OE Rea Ce eee RE 155
TABLE OF CONTENTS
Natural ionemies: cc vic gudielesulsag vey due oie dais 43g BON eye caw oes
Plants - 6 ec ysisig esd wow bs wae Bee ORE Se Kee 8S4.6 Ses 4a Wes hee ere abe ee a Fungi. and. bacteridis: sows sic ceascauiaias taeda dee Hees eee so EEF AMLIB 95 5 sictivce 2 -egsneaus dete sivanis ecard emus Od satayaeat aod gis gucie) pyalte eAbe de are REE DE DERE ESS
WETMES sscsktat beanie saison ccna iis shud alee giana Wal signe basins ad atacatee oe Insect, enemies +. ated. sexes vc ccees Fe deere ceed ea ees bee Medes eee es Mites: v.04 start ecadad eetamee aku tad Ree 86 4-TEt Oe ter ee Sem Yea MeR es SDIGOTS) 55.5. siete cp-atec ane. & Sach Senin’ b aniador ana avs WT Apacertade re: Graveneieee ecdiwusec es cauavece Od neseeuers Other arthropods ..0.4 5s week de ewes eat nd Seeds tas oe ae ew go Rhee BAtracWlans: a vec ceecca ihe wiapany atca arise cag aA wig wiles le leurs ptadoin aaa eymiaa eve wa ae Reptiles: favs Gece was be weg wins ye ails awe ee ena oouis eataatsciiae Birds jog ieiss sees 53a Shes a eeOS 8 OS BUS Bs KS oa Bees SEAR A Eee TS HES
Collecting, mounting, and rearing.............. ee ce eee eee eens sol desusun Seachean
Collecting adults ........ 0... cece eee eens ariets Seana reanere earn es js ate cadelygrewateuen Mounting adults sic o's sss d ccna. s teuien se eae eee Fe Res PpalinG es aeG cules Sending by miail:or expressi.c.s<sicades semen 64 Ores 54 GHEE a ee 8s HES am Rearing: ccc ass dine os cane he a4 cess se o4 tle es eens SADE ete hs oa See dks Sbide: MUO Unt: ete esis ysis. sass Seen se 8428 wiceod Soe Reariat visas salsa orn we Gani Bybebaro ud ed yattaig ea an Collecting Vary isiseccinaiscaicne bees oaieis 8 wena Oa sla Brg e oi Sale bee Shela ew Collecting 6228S" wesc cities oecen eastern dees oats tein SOs Sele Hee Oe e eh OR se
The relation of mosquitoes to MaN.......... cece cee eee eet eee ener t eee eees i
The carriage of disease by MosquitoeS........... cece cece eee een eeae Marly 1M CaS) aa ncthess-ais Xm vo sree toe eG eS Resa aye WAS Gitte DE OEE Sees Malaria xs. 3i earigne dnc imeue wes Gee cieliGw Neuse Sea heat autre anes ARS pete The malarial organisms.......... bad elaehs hago cerigics Oa Mean guemaness Ste ay wie The life-cycle of the malarial organisms.............-....2eeeee Scientific demonstration of the transmission of malaria............. The mosquitoes that carry malaria.......... 0. ccc seen eee ee eeee The habits of Anopheles mosquitoes.......... 0... ccc cece eee e eee eeee Resting position of adult Anopheles............. ccc cee ee cc eees Semi-domestic and wild species..............ccc cence cece reeuee Hibernation and estivation............. ccc ccc eee cee eee eens Feeding habits of Anopheles......... 0c cece cece eens ccc ecuseeee Nocturnal and diurnal habits.............. 0.0... ccc cee eee cece
The note of ANOPheleS..... ccc ccc cee ce ete cee cnenas Distance Of MSU so cdcisiy sels acgssse. esses: 0g Snevave rs Siotehas va diava te evaceenss
The behavior of Anopheles towards certain colors............... Breeding places of ANOpheleS....... 6... cece cece ccc n es ecaus
Habits and food of the larve of Anopheles....... 0.00. cece cue Resistance to desiccation.............. 0... cece eee eenceececcee
The scientific demonstration of the carriage of yellow fever by mos- CUITOCB iss nines Scns ain uranyl.
The New Orleans epidemic of 1905......... The death of Reed, Carroll, and Lazear The search for the causative organism....................... The yellow-fever mosquito............................0000000 0 Domesticity of the yellow-fever mosquito.................. Feeding habits Daideh a are Susie a ermuletlegs Wecdis 3.2 wale ca Gans Wie eons ooce e
TABLE OF CONTENTS
The relation of mosquitoes to man—Continued. Yellow fever—Continued. The yellow-fever mosquito—Continued. TIME) OF: ACHIVICY -o.. .ccsrsce careeqricin ages dade. ane nega balan ate Length: Of: litesof ima so sejed anv ano stun araates sanseeg niet ae wae Influence of temperature........... 0.00 ccc ccc cee cece ee eens The biting of cadavers............ 0. cece cece cece eee tenes Distance: Of: Nights. icc. s:e'¢scarvina darian 19) wea eucaresaual oacncdverel alia cevunavalenrs ate MCR erences Cncsee nario ior se sa era tne ia calehsdarts | alipre sheesh sper sonatas ees Relation of food to oviposition. ......... 0.0. cece eee e cece eeeeee OVIpOsltion: 6 evaies sawiged 4ahed TAKES COREE EGMAT RARE SARS sce $3 Breeding? WADitss cic sss sien acarbssudesn sued sasea te, bare ee SLIM mews anteen Bom dianeuwlawn snob PENN CG) OS BS ascii Sic arn aapesycist sd arn cien «anne avoidy vanes wear aucoa gabon ougeahaeuatonars Breeding: PACES: seis ehcoeds sang sad aiddnas Woden eer ruealas eleraakaa ele Behavior: Of Jarv®sasy caved sews ¥ia oe bens ee sk hasan medee
Duration of larval stage.......... 0... c eee eee cee eee
Resistance of larve to adverse conditions..................
The geographic distribution of the yellow-fever mosquito........ Original home of Aédes calopus........ 0. cece eect ee ee ne eee Distribution by artificial means.......... 00... 0c ccc cece eee
The yellow-fever mosquito in Hurope...............00 eee eeeeee
DOH BWC! er csccceeret Mayon oecae ara adnacsieash onus’ anid ies e@ulaniowalaues beuiader a FUlarlasiS: sche vexanes eros amass anew oewled 1 y eieas y ARES RG tes Rabe oe Transmission by mosquitoes........... 0. cece eee cee cee eee e teens The-filaria, WOrnis a bisceo ocd. sis doaadeusnd. saccade dot guns Saaastaas Gersenmayaleeuecaee as Periodicity Of THe ATi Biscsses eseccevccacesecanaiiecgsa a davsin Sosns even a Weave h dese Evolution in the mosquito.......... 0... cc cee ee eee cece eee eeee
Mode of transmission to the vertebrate host..............eeeeeeeees Mosquitoes that transmit filariasis.......... 0.0... cece eee eee eee Suggested relations of mosquitoes with other disease................005 HWffect, OF WOSCUICO: PILES. ove. ce ses casaice a everarntec ds water aye etapa eee ao ecelgiig ee grtiaies ea leleaee® Relative: SUSCEDUIDINGY 1o.nc 5d sctceieas ushaig ie oa od eRe S ee 2 Sees aes Economic loss from mosquitoes........... 0... cece eect eee ee enees OBS: AROMT: WAAL ais 5. sesece eset ediercdi scan Shard ogee aries yi addednn Gobusndhanmievamileireradevanedspaces LOSS. from: VellOW P6VEP <0. sn kis eae ei baed aiken we dere Run eae oe Endemic disease as affecting the progress of nations.................... Losses from mosquitoes aside from the carrying of disease.............. Reduced value of real estate...... 0... eee ee eee cence neaee EVOSS? CO: AS TICUICUTE aiip:aicoa Siacasins adzsdr ania: autxivaiieok iguanas avacs eno! SudRomie S SaeNCLO aS GOBER Of SCTOS DL IG sa cascicecocavsvcrc es hes erence deta ater ecnautes dia apters ona toc carton asastelariifeo The value of reclaimed lands............ ee eee eee ee ee eee ener Salt marsh lands in New Jersey....... 0... cece cece cece eee neees Influence of wind on the dispersal of mosquitoes...................00005 The carriage of mosquitoes by ships, railroads and other conveyances.... Mosquitoes in the courts-at-law........ ccc cece ce eee eee te eee e teenies Protective and remedial work against mosquitoes.............0. cece eeee Protection ‘from. Ditess.4....0406a 04 chara dsaies weed seer eeaes SCPCENS: ANG CANODLCS aise ccuccwce sgt eGeesne eos auiegiia cess inner ahdecdluanmen od weaonaieand Screening breeding-places ............ cece cece cece ener eens Protective: Jiquids: asia. sie-o ee Gan eas resin eerelas arsine wteceipty elnonus eas Smudges and fumigantss 6460.62 ceciessesses se ves caweoreesanss Pyrethrum or chrysanthemum...................e eee eens
Mimms culicide or camphor-phenol...................000 eee
PyTeOP WV «areas ca teasaterilyg aan sitaralsg a eggs iliorg dads laces a tewraidce Amanat
Sulfur dioxide: ... .scaccs.wcisse sesamiakd sia oesweg eecwes MerGUriG--CHIGPG Gs go: a:cies coco vas subscesiyies svouerenistign vend cuehe aiaiavsiinle udereegen
Other LUMIZANUS! «i cscciescs coma ware din wee aaa aten ed eden tas wales
Remedies for mosquito bites......... cece eee ee ee eee eens Apparatus for catching adult mosquitoes. ............. cee eee eee eee Destruction Of Warvib.. ccccccdacwe enced dsc e SEEMS CU Rae SES Ree cee Permanganate of potash......... ccc cece ccc ee eee e eens Sulphate: of COpPePsss4.34 eres Menai maaewnee deel eae a aie eave
Certain proprietary COMPOUNAS........... eee eee eee ete
CaCtis: pastel cc banca wetees ened e sete veins ehaeL Mees eee seuss
PetrG] GUI: aecieid ver ddsiandaainonice deddos soansconausichd MMadtier said SAREE AAS MONS
COED OL] scesoiigasass ta cenit ask wonnleauietiilars aaieleaaaien d aerarsae eee un droauacers
vi TABLE OF CONTENTS
Economic loss from mosquitoes—Continued. Protective and remedial work against mosquitoes—Continued. Destruction of larve—Continued. Phinotas: Oil ss00.02 sxe 4 eae ee ee SASSY ORE Eee e he eat e as
Sensitization to light. ....... 0... cece eee eee eee e eee ence etes Poisonous: DIANtS) .ci6.ccscawcen ce aacied a Saved sid atv etapde BOE Maeda Seeman ANE eae dade PA alee. dis chad sate Sania ae tO yee aie are Wanais Sa eins Fuentes Abolition of breeding places of household mosquitoes................ Prevention of sewer breeding.............c cece cece cece eee eeee Removal of bromeliaceous plantsS............ cece cece eee tence eee Drainage measures for non-domestic specieS.............02eee eee eee The practical use of natural enemies of mosquitoes................. Fish introduced into Hawaii.............. cee cee cee cen eee Fishes in the West Indies......... 0... cc ccc cece e eee e teen cence A Bragilian, NSD sisccistssceGels oa tewtolba eee wSmerehs tas aries sees
Alleged deterrent trees and plantsS........... cece cece cence nee ener FAUGa Ly DEUSE ace obiz ceeace s,5 Sey nse’ cays Ai dessb aie wguaeer ee. Seas ua a: Win fel Dosauaeae dosed. 8
Ricinus and Papaya........... Spblsadavansvanatan® i ilyal eid Sve ouaaenede-Ba tears QOPI 5 aisssis sce aatannniens iseidinia vee eh etree ee cles 1a aires Seen leads
China berry trees............ cc cece cece ee eens ee ee er
POS ba kasta sa ttaneteciea erecta Avie phen eira a aaees a inaie toa iageen Siete sched Weater“plants: ¢ vo. chtewe deals cain acs qareis a stags siaueled Bae s Aas Organization for community work.............00 cece cc eseee cee eeee The importance of interesting children..................0.0000-
Recent work in Germany..............00c ccc eeeeue ccc cueenneee
Work along river fronts..............c cece eect eee eeceeeanes Examples of mosquito control.............ccceeeceeees ase for aaah gaa ats egite Seer Work in Havana during the American occupation...............ee0eeees Work at the Isthmus of Panama..................ceeecee oRaaeessed see Work in Rio de Janeiro................... whee distal ss Hh y eciae waa eee ese Work in Veracruz and Mexico generally............cc cece ccceceececces WOPK: AN) Japan é osscctconcacny tg diaars nd lakes ha aniaw PaeancecneArsieedicadcae Cena oo
XIII. XIV.
LIST OF ILLUSTRATIONS.
Facing page. . Antennal sense-organ of Culicide........... 0... c cece eee eee eee 30 « Mouth:parts Of Culex’... accas .ccoaaaed savte dw anieria-swiln ew waneiere simmedare’ 36 « Thorax: Of PsOrophOT ais. os scisces sc wee csawnss vada eeammry daisuas eeuREE we 56 . Fig. 1. Heliconia champneiana Griggs. Eastern Guatemala.......... 156 Fig. 2. Bromeliads. Cérdoba, Mexico............cccce cece cece ee eees 156 . Fig. 1. Heliconia champneiana. Eastern Guatemala................. 156 Fig. 2. Epiphytic Tillandsia. Florida Keys............ccceeceeevees 156 . Fig. 1. Flower-spike of Calathea. Eastern Guatemala................ 156 Fig. 2. Bromeliaceous plant on trunk of royal palm. Porto Rico...... 156 . Fig. 1. Anopheles and Culex larve in natural position in water....... 158 Fig. 2. Adult mosquitoes destroyed by fungus...............2e0e0008 158 » Wigs. 1.2; Larva,.of Chaoboruss sacs. sance sg eeeessoenescasewecveaaans 168 Fig. 3. Larva of Corethra...... 00... cece cc cece cece e et eee e ee eeeeeee 168 . Fig.1. Crane Lake, Saskatchewan, June, 1907. Mosquito net for PTOLECtlOM:. OL “LAC Cs. css a seretiasg earns Sig ere wlera Reena hisos mune 252 Fig. 2. Destroying the yellow-fever mosquito by fumigation.......... 252 . Fig. 1. Covered rain-water tanks at New Orleans.................05. 282 Fig. 2. House at Pretoria, Transvaal, protected against ants by resting on water-filled metal panS............. ccc cece cece cece 282 Fig. 3. Mosquito-breeding tree-hole .......... 0... ccc cece e eect eee eens 282 . Mosquito breeding-places at Dallas, Texas.............. cece eee eeeee 286 . Operations of filling in salt marshes, Sheepshead Bay, Long Island.... 334 Draining the salt marsh, Hackensack Meadows, New Jersey.......... 336 Fig. 1. School children finding mosquito breeding-places, Worcester, MESS sy» Ze geascgccgs oy veudbicccrcecs ancien) tice ahvaria Yahoos sor avo ar uiarea jig aitaio em ghar 356 Fig. 2. Mosquito class-work, Worcester, Mass.............0 eevee eeee 356
vii
INTRODUCTION.
The discovery that mosquitoes are agents in the transmission of certain dis- eases, and especially the discovery by Sir Ronald Ross, in 1898, that mos- quitoes are the agents in the transmission of malaria, aroused a widespread interest in these insects. Hitherto the Culicide had been treated by ento- mologists with the other flies, and, being regarded as unimportant members of the order Diptera, were not especially studied and only such species as happened to find their way into entomological collections were described by systematists.
In the year 1902, when the Carnegie Institution of Washington began its im- portant work in aid of scientific research, the systematic and biological knowl- edge of American mosquitoes was slight. A bulletin published by the U. 8. Department of Agriculture in 1900 embodies our knowledge of the North Ameri- can mosquitoes at that time. Twenty-three species were distinguished in this bulletin, while a number of the descriptions by early writers remained unrecog- nized. For the first time, the full life-histories of two widely different species were given. In the same year Major George M. Giles, formerly naturalist of the Indian Marine Survey, published in London the first edition of his “ Hand- book of the Gnats or Mosquitoes,” which was the first attempt to bring together and codrdinate the knowledge of the mosquitoes of the world. This work in- cludes 48 species from North America and, although many of these were un- known to the author, the original descriptions were made available for students.
In 1901 the British Museum of Natural History published the first two volumes of “ A Monograph of the Culicide of the World,” by F. V. Theobald. In this work, 69 species were treated as North American and West Indian, but a number of these had not been studied by the author. At about the same time a volume entitled “ Mosquitoes; How they Live; How they Carry Disease; How they are Classified ; How they may be Destroyed,” by L. 0. Howard, was pub- lished. In this book 25 species were recognized and classified in synoptic tables by D. W. Coquillett. Considerable space was given to discussions of the habits of mosquitoes, their function in the carriage of disease and to the subject of remedies.
While considerable knowledge had accumulated about the habits of mosqui- toes in general, it became evident that the different species diverged widely in habits and detailed information on these points was needed. It is necessary to distinguish carefully in this respect. Only those species that are harmful to man, either as agents in the carriage of disease or as annoying by their bites, need to be considered in economic work. Much useless labor and expense can be avoided by an accurate knowledge of the habits of the species. For instance, Boyce (Mosquito or Man?, p. 96, 1909) refers to the mosquitoes living in crab- holes as “the chief nuisance in those houses which are situated near the sea,” and figures a tent for capturing these mosquitoes. Our observations prove that the crab-hole mosquitoes do not bite nor annoy man, and no consideration need therefore be given to their destruction. Again, the commonest mosquito during
1
2 MOSQUITOES OF NORTH AMERICA
the summer months in the Northern States is undoubtedly Culex territans, which is the only species breeding abundantly in a certain class of fresh-water marshes and pools at that season. We now know that this species does not annoy man (in spite of its name), and are enabled to state that such fresh-water marshes and ponds are not breeding-places of noxious mosquitoes.
Therefore, realizing the imperfect character of our knowledge and especially the very great need of a competent monograph of the species of Culicide of North and Central America and the West Indies, both from the biological and the sanitary points of view, application was made, in April, 1902, to the Carnegie Institution of Washington, for a grant which should enable the prepa-
tation of a monograph to include all possible information concerning all mos- quitoes of the geographical regions just mentioned.
The grant requested was made by the Trustees of the Institution in January, 1903, and organization work was at once begun. It was at first expected that the monograph could be completed in three years, and the grants made by the In- stitution covered that period. At the expiration of the third year, however, it was found that the material was by no means complete. Too much reliance had been placed upon the promises of volunteer observers, and important regions were, for this reason, not properly covered. The workers engaged in the prepara- tion of the monograph were not content to publish the material accumulated, since it was their earnest desire to make the work as complete as possible and as valuable as possible to biologists and to sanitarians. The investigations were, therefore, continued during 1906, 1907, and 1906, partly by the help of funds appropriated to the U. S. Department of Agriculture by Congress for the in- vestigation of insects affecting the health of man and animals, partly by the assistance of the Isthmian Canal Commission, partly by the help of volunteer observers in the West Indies and Central America, and partly at the expense of two of the authors (Dr. Dyar and Mr. Knab). While it is realized that the present work is incomplete, the additions gained by the work of the last few years has surely more than doubled its value.
In planning the work in the early months of 1903, it was decided to secure local observers advantageously situated in the different faunal areas of the United States, and to compensate them for observations during the summer months, in the course of which each should make as complete a collection as possible of the mosquitoes of the region in which he was located, should rear each species in all its different stages, and should submit all specimens and com- plete notes, with sketches, at the completion of the season. During the first year there were employed for this purpose Miss Isabel McCracken, of Stanford University, a graduate student and assistant of Prof. V. L. Kellogg ; Mr. Fred- erick Knab, of Chicopee, Massachusetts (one of the present authors) ; Mr. 0. A. Johannsen, of Cornell University, Ithaca, New York; Mrs. E. @. Hinds. at Victoria, Texas; Mr. John R. Taylor, of Las Animas Hospital, Havana, Chibex Dr. H. G. Dyar, of the U. S. National Museum (one of the present authors), at Kaslo, British Columbia; Mr. T. H. Coffin, of the Johns Hopkins Medical School, in the Bahama Islands; and Mr. Kenneth Taylor, at Minneapolis Minnesota. ,
INTRODUCTION 3
In addition to these observers, the following individuals made volunteer col- lections and observations which were transmitted to Washington: Mr. G. G. Coghill, of Pacific University, Forest Grove, Oregon; Major William M. Black, U.S. Army, Panama; Mr. H. C. Weeks, Bayside, Long Island, New York; Dr. J. B. Smith, State Entomologist of New Jersey, New Brunswick ; New Jersey ; Dr. Alfredo Dugés, of Guanajuato, Mexico; Dr. J. W. Dupree and Prof. H. A. Morgan, of Baton Rouge, Louisiana; Dr. José H. Pazos, of San Antonio de los Baios, Cuba; Dr. W. E. Britton, State Entomologist, New Haven, Connecticut.
The material brought together during 1903 was very encouraging, and many of the reports of the paid observers were full and contained many new contribu- tions to the knowledge of the early stages of mosquitoes.
With the opening of the season 1904 it was thought best to limit the number of paid observers working in the manner described above, and only two were so employed, namely, Mrs. Maurice F. Ricker, of Big Fork, Montana, the wife of Professor Ricker, the head of the summer biological station at that point, and Mrs. Hinds, of Victoria, Texas. Dr. A. Siegrist, of Puerto Angel, Pochutla, Oaxaca, Mexico, was also tentatively engaged. The sanitary officials of the Panama Canal Commission promised assistance, and two of them were promised compensation for expenses incurred in collections and observations. The results from Panama and from Puerto Angel were, however, nil.
The extreme importance of a most thorough knowledge of everything con- nected with the yellow-fewer mosquito (Aédes calopus) induced the grantee of the research fund during the spring and summer of 1904 to make an especial effort to determine its geographical distribution, and to learn as much as possible about its habits. In the course of another investigation he went to south Mexico in the spring, going as far south as Oaxaca, and studied the effect of altitude upon the distribution of the species from the seaboard at Vera Cruz up to Orizaba. The Mexican sanitary authorities were consulted, and his efforts were very intelligently seconded through the great courtesy especially of Dr. Eduardo Liceaga, the president of the Superior Board of Health of the Republic of Mexico.
Beginning with the middle of June, Mr. Herbert Barber, of Washington, was sent upon a trip to determine, if possible, the line of northward distribution of the yellow-fever mosquito in the United States. He began at Brownsville, Texas, and followed approximately the line of distinction between the upper and lower austral life zones as laid down by Merriam. He proceeded gradually as far as Louisville, Kentucky, where the work was taken up September 1 by Mr. T. H. Coffin, who followed it through to the Atlantic seaboard.
By the operations just described the main portion of the mosquito fauna of the principal inhabited regions of the United States was rather fully worked up, and during 1905 an especial effort was made to secure material representing the mosquito fauna of southern Mexico, Central America, the West Indies, and Alaska. The Canal Zone was again left to volunteer observers. One of the authors, Mr. Knab, left Washington the end of May, visited Key West and Havana, then Vera Cruz, Cérdoba, Orizaba, Santa Lucrecia, Rincon Antonio, Almoloya, Tehuantepec, Salina Cruz, and Acapulco in Mexico; Acajutla, San
4 MOSQUITOES OF NORTH AMERICA
Salvador, Sonsonate, and Izalco in the Republic of Salvador ; Champerico and San José in Guatemala; Puntarenas, Santo Domingo, San José and Port Limon in Costa Rica; and Corinto, Nicaragua. Mr. Knab collected a large amount of valuable material, and one important result of this work was to show that the yellow-fever mosquito occurs at every point visited on the Pacific coast. While it could be assumed that this would be the case, there had, up to that time, been no authentic record of the fact.
At the same time that Mr. Knab started for Central America, Mr. August Busck, of the Department of Agriculture, was sent to the West Indies, sailing from New York on June 1. He visited Grenada, Trinidad, Tobago Island, St. Vincent, Barbados, Martinique, Dominica, Guadeloupe, St. Thomas, Santo Domingo (Santo Domingo City, San Francisco Mountains and Samara Bay), returning to Washington early in October, having collected and bred a very ex- tensive series of mosquitoes and having aroused the interest of a number of local observers, who subsequently were of much assistance in the investigation.
Early in the summer Mr. A. N. Caudell was sent to Florida to work out the life history of a species not yet fully known, and in the spring Dr. Dyar and Mr. Knab went to western New England to study carefully the as yet little under- stood spring and early summer mosquitoes of that region. During midsummer Dr. Dyar visited the Adirondacks to work out some hitherto unknown points in the life histories of certain species inhabiting that region.
Early in June, while engaged upon another investigation, the grantee visited the Natural History Museum in Vienna to study the mosquito types of Wiede- mann, in the Wiedemann and Winthem collections. He took with him from the United States determined material of several species about which there existed some doubt as to their identity with the Wiedemann types, and cleared up several points of systematic importance. Returning to this country in the early autumn he was able to give many points of value in quarantine measures to the Public Health and Marine-Hospital Service, and in late October visited New Orleans and observed the operations of the closing days of the campaign against the yellow fever, which proved so successful, making notes on the methods used against the yellow-fever mosquito and taking photographs.
During 1906 Dr. Dyar made extensive observations upon the Pacific coast of the United States, stopping first at Bright Angel Camp in Arizona, and then proceeding gradually from San Diego northward through California, Oregon, and Washington into British Columbia, stopping a sufficient length of time at favorable localities to make the requisite observations and rearings. The trip was begun in April and the final observations were made August 26.
Considerable additional material was received from volunteer assistants dur- ing the year, and especially from Mr. F. W. Urich, of Trinidad, British West Indies. The main portion of the year was devoted to preparation of descrip- tions and illustrations and general work on the monograph. The intended ex- pedition for the study of the mosquitoes of Alaska was, however, not made.
In 1907 the paucity of material from the Panama Canal Zone was very obvious as contrasted with the abundant material from other Tegions, and,
INTRODUCTION 4)
although liberal promises had been made by persons stationed in the Zone, practically no material had been received during the four years already spent upon the monograph. An arrangement, therefore, was made with the Isthmian Canal Commission by which the expenses of a trained observer were met by the Commission during a period covering the end of the dry season and practically all of the rainy season, the time occupied in a visit to the Zone and a careful study of its mosquito fauna. Mr. August Busck was selected for the purpose. He left New York April 12, arrived at Colon April 19, and from April 19 to July 30 worked the Zone from Panama to Colon, though mainly the region around Tabernilla, and also made two trips into Panama, on the Upper Chagres River, from May 18 to 28, and to Taboga Island, from June 30 to July 7. The amount of information gained by this expedition was extraordinary. Previously only 7 species of mosquitoes were known from the Canal Zone, but Mr. Busck returned with more than 90 species, of which 30 were new to science. His visit also interested certain persons, resident there, in the more careful study and rearing of mosquitoes, and a great deal of additional valuable material has been received since his return, especially from Mr. A. H. Jennings of the Sanitary Department. The expedition resulted in benefit to the Sanitary Department of the Isthmian Canal Commission, since Mr. Busck was able to give some im- portant points on the habits of certain species concerned in the transmission of disease. At the same time he learned much concerning the practical work carried on under the Sanitary Department and returned filled with admiration for the enlightened efforts which had accomplished such admirable results in the prac- tical elimination of the disease-carrying mosquitoes from the Zone.
Mr. Knab undertook an expedition to Saskatchewan to work out the life histories of the mosquitoes of the northern prairies, until then unknown. He left Washington early in April and returned the latter part of June. Dr. Dyar later visited a new locality in Maine.
The work during 1908 was mainly devoted to the continuance of the prepara- tion of the monograph. Dr. Dyar did some field work in Maine and New Hamp- shire in midsummer. Mr. Knab in the winter of 1907-1908 visited Mexico, remaining during the early months of 1908 in the vicinity of Vera Cruz, Cér- doba, Orizaba and Omealca, engaged partly upon another investigation, but also collecting and rearing mosquito material.
During the entire period of the preparation of the monograph the grantee and his fellow authors have met with the heartiest cooperation on all sides. While it is true that many promises have been made which have not been fulfilled, and while it is true that the completion of the work has been delayed through a too great reliance upon certain of these promises, and while through such a reliance the mosquitoes of certain regions have not been studied with the necessary care to properly round out the work, it is well understood by the authors that by no means all of the good intentions of a busy man can be fulfilled, and they are grateful for the intention itself and for the cordial promises. They realize also that while it seems easy to collect and rear mosquitoes, it is really a rather diffi- cult thing to do properly, and only when properly done are the results of value.
6 MOSQUITOES OF NORTH AMERICA
It has been found necessary to omit the group Corethrine, which should be included to properly round out the family Culicide, and restrict ourselves to the Culicine—the forms with the long proboscis.
It seems advisable to call attention at the outset to changes in the scientific names of those species which are most important from the economic standpoint. These changes have become necessary, partly through the strict application of the laws of priority, partly through generic revision, and also from a more exact knowledge of the specific limitations of the species concerned. The reasons for these changes will appear in the systematic part of the work.
Most important is the change in the name of the yellow-fever mosquito from the generally adopted Stegomyia fasciata and Stegomyia calopus to Aédes calo- pus as a result of the untenability of the generic concept “ Stegomyia.” What was known in this country as Anopheles maculipennis is now Anopheles quad- rimaculatus and A. occidentalis, the first-named species being distinct and con- fined to the Old World. Through priority Culex fatigans or Culex cubensis be- comes Culex quinquefasciatus. Culex pungens appears to have been used in the earlier writings on North American mosquitoes as a concept to include Culex pipiens, Culex restuans, and Culex quinquefasciatus (and perhaps others) before these species had been differentiated.
While it is expected that this work will be of assistance to medical and sani- tary men, as well to others, it must be distinctly understood that it is an ento- mological monograph and not a medical monograph. The writers are ento- mologists and not physicians or medical investigators. Thus, while necessarily in the first volume some space is given to the history of the discoveries of the relation of mosquitoes to disease, and to the diseases themselves in a broad way, as well as some consideration of the life histories of their causative organisms, these portions are not the result of original investigation, but have been com- piled from reliable sources.
We are under great obligations to Dr. Arthur Neiva, of the Instituto Oswaldo Cruz in Rio de Janeiro, who, during a visit in Washington, gave us liberal help and advice in the preparation of the parts on mosquito-borne diseases. The part on the malarial organisms is from his pen and presents the modern views in succinct form.
Especial thanks are also due to Mr. Louis H. Aymé, United States Consul- General at Lisbon, Portugal, who, while in the States on a vacation from his former Brazilian post, spent many hours of his leisure time in translating for the writers, from the Portuguese into English, the more important portions of Goeldi’s large work on the mosquitoes of Para. To the following the hearty thanks of the authors are due for material or for assistance in one way or an- other. In this list are not mentioned the writers’ colleagues in the Division of Insects, U. 8. National Museum, or in the Bureau of Entomology of the U. 8. Department of Agriculture, although many of them have been of assistance. Individual species or small lots of mosquitoes have been received from many
correspondents, but these are mentioned in the text in the consideration of the individual species.
INTRODUCTION 7
Rev. J. Aiken, St. Catherines, Berbice, British Guiana.
Prof. J. M. Aldrich, University of Idaho, Moscow.
Mr. E. E. Austen, British Museum of Natural History, South Kensington, London, England.
Dr. George E. Beyer, Tulane University, New Orleans, Louisiana.
Prof. Raphael Blanchard, University of Paris.
Mr. J. Turner Brakeley, Hornerstown, New Jersey.
Dr. Hiram Byrd, Sanitary Department, Jacksonville, Florida.
Dr. F. E. Campbell, Surgeon, U. S. Navy.
Prof. T. D. A. Cockerell, University of Colorado, Boulder, Colorado.
Mr. O. F. Cook, Washington, D. C.
Prof. R. A. Cooley, Entomologist, Bozeman, Montana.
Dr. C. C. Craft, Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, D.C.
Dr. Oswaldo Goncalves Cruz, Instituto Oswaldo Cruz, Rio de Janeiro.
Dr. George Dimmock, Springfield, Massachusetts.
Dr. A. Dugés, Guanajuato, Mexico.
Mr. F. W. Edwards, British Museum of Natural History, South Kensington, London, England.
Dr. J. Hobart Egbert, Willimantic, Connecticut.
Dr. E. P. Felt, Entomologist, Albany, N. Y.
Dr. J. Fletcher, Ottawa, Canada.
Mr. Arthur Gibson, Ottawa, Canada.
Dr. E. A. Goeldi, Berne, Switzerland (formerly Parad, Brazil).
Col. W. C. Gorgas, U. S. Army, Chief Sanitary Officer, Isthmian Canal Com- mission.
Dr. M. Grabham, Kingston, Jamaica.
Prof. Dr. Anton Handlirsch, k. k. Zool. Museum, Vienna.
Prof. A. L. Herrera, Mexico City.
Prof. Glenn W. Herrick, Agricultural College, Mississippi.
Mr. A. H. Jennings, formerly Entomologist to the Isthmian Canal Commission, Ancon, Canal Zone, Panama.
Prof. C. W. Johnson, Boston Society of Natural History.
Prof. K. Kertész, Hungarian National Museum, Budapest.
Dr. Eduardo Liceaga, Mexico City.
Dr. C. S. Ludlow, Washington, D. C.
Dr. Adolpho Lutz, Instituto Oswaldo Cruz, Rio de Janeiro.
Sir Patrick Manson, London School of Tropical Medicine.
Prof. Frederick Meinert, Zoological Museum, Copenhagen.
Mr. H. W. B. Moore, Georgetown, British Guiana.
Dr. G. H. F. Nuttall, Cambridge, England.
Dr. P. Osterhout, Bocas del Toro, Panama.
Dr. José H. Pazos, San Antonio de los Bafios, Cuba.
Dr. H. Polak, Paramaribo, Surinam.
Sir Ronald Ross, Liverpool School of Tropical Medicine.
Dr. A. H. S. Russell, Surgeon, U. S. Navy.
Dr. A. E. Shipley, Cambridge, England.
Mr. W. H. Sligh, Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, D. C.
Dr. John B. Smith, Entomologist, New Brunswick, New Jersey.
Prof. E. P. Taylor, Entomologist, Mo. State Fruit Experiment Station, Moun- tain Grove, Missouri.
Mr. J. R. Taylor, Las Animas Hospital, Havana, Cuba.
Prof. F. V. Theobald, Wye (Kent), England.
Mr. J. K. Thibault, jr., Scott, Arkansas.
Dr. W. F. Thornton, Bluefields, Nicaragua.
Prof. E. S. G. Titus, Entomologist, Logan, Utah.
Prof. W. V. Tower, Entomologist, San Juan, Porto Rico.
Mr. F. W. Urich, Entomologist, Port of Spain, Trinidad.
Mr. J. B. Vanduzee, Estero, Florida.
Dr. H. A. Veazie, New Orleans, Louisiana.
Mr. H. C. Weeks, Bayside, Long Island, New York.
Mr. T. N. Willing, Regina, Saskatchewan.
Dr. K. S. Wise, Public Hospital, Georgetown, British Guiana.
EARLY ACCOUNTS OF MOSQUITOES. MOSQUITOES AS PESTS.
The old writer, Thomas Moufet, collected from early writings accounts of mosquito abundance, from which it appears that Herodotus noted that these insects swarmed in prodigious numbers in old Egypt and that the natives of marshy regions built towers on which to sleep, since the mosquitoes did not fly high. Mosquito nets and canopies were in use in those early days. The army of Julian the Apostate on one occasion was so fiercely attacked by mosquitoes as to be driven back. In ancient Greece, according to Pausanias, the inhabitants of cities were sometimes forced to abandon their homes on account of mosquitoes making it impossible for them to remain. Mionte, a rich city of Ionia, was abandoned by its inhabitants on account of mosquitoes which forced them to flee to Mileta. The same thing happened with Pergamo, a beautiful city in Asia. Sapor, King of Persia, according to Theodoritus, was compelled to raise the siege of Nisibis by a plague of gnats which attacked his elephants and beasts of burden and so caused the rout of his army.
Ammianus Marcellinus, in his Roman History, in discussing the wild beasts of Mesopotamia, gives the following paragraph on lions versus mosquitoes (quoted from Cowan) :
“ The lions wander in countless droves among the beds of rushes on the banks of the rivers of Mesopotamia and in the jungles, and lie quiet all the winter, which is very mild in that country. But when the warm weather returns, as these regions are exposed to great heat, they are forced out by the vapours, and by the size of the Gnats, with swarms of which every part of that country is filled. And these winged insects attack the eyes, as being both moist and sparkling, sitting on and biting the eyelids ; the lions, unable to bear the torture, are either drowned in the rivers, to which they flee for refuge, or else, by frequent scratch- ings, tear their eyes out themselves with their claws, and then become mad. And if this did not happen, the whole of the East would be overrun with beasts of this
kind.”
Pliny, in his natural history, speaks of mosquitoes and in referring to their humming noise says (freely translated) : “ Who gave the mosquito so terrifying a voice, infinitely greater than it should be in comparison to the size of its body?” He distinguished the Hymenoptera from the Diptera by stating that the former have the sting in the tail and the latter in the mouth, and that to the one it is given as an instrument of vengeance and to the other of avidity.
About 1736 Culex pipiens became so numerous in England that, as described by John Swinton, vast columns of them were seen to rise in the air from the steeple of the cathedral at Salisbury, which, at a little distance, resembled columns of smoke and caused many people to think that the cathedral was on fire. In the same account it is stated that in the year 1766, in the month of August, they appeared in such incredible numbers at Oxford as to resemble a black cloud darkening the air and almost intercepting the rays of the sun. On
8
MOSQUITOES IN THE CRIMEA 9
the evening of August 20, Sir John Swinton, in the garden of Wadham College, about half an hour before sunset, saw six columns of these insects ascending from the tops of six boughs of an apple tree—two in a perpendicular, three in an oblique direction, and one in a pyramidal form—to the height of 50 or 60 feet. During that season mosquitoes were particularly troublesome by their bites.
Such swarms as these were evidently rather commonly seen in the marshy parts of old England, as indicated by the following lines from Spenser’s Faerie Queene:
As when a swarme of gnats at eventide
Out of the fennes of Allan doe arise,
Their murmuring small trumpets sownden wide, Whiles in the air their clust’ring army flies,
That as a cloud doth seem to dim the skies;
Ne man nor beast may rest or take repast,
For their sharp wounds and noyous injuries,
Till the fierce northern wind with blust’ring blast Doth blow them quite away, and in the ocean cast.
Spenser, in his “ View of Ireland ” (1633), has the following on the subject of the Irish mosquitoes :
“They goe all naked except a mantle, which is a fit house for an outlaw—a meet bed for a rebel—and an apt cloak for a thiefe. It coucheth him strongly against the Gnats, which, in that country, doe more to annoy the naked rebels, and doe more sharply wound them, than all their enemies’ swords and speares, which can seldom come nigh them.”
Kirby and Spence have brought together several instances of remarkable stories from the older travels, such as the following:
“In the neighborhood of the Crimea the Russian soldiers are obliged to sleep in sacks to defend themselves from the mosquitos; and even this is not a suffi- cient security, for several of them die in consequence of mortification produced by the bites of these furious blood-suckers. This fact is related by Dr. Clarke, and to its probability his own painful experience enabled him to speak. He informs us that the bodies of himself and his companions, in spite of gloves, clothes, and handkerchiefs, were rendered one entire wound, and the consequent excessive irritation and swelling excited a considerable degree of fever. In a most sultry night, when not a breath of air was stirring, exhausted by fatigue, pain and heat, he sought shelter in his carriage; and, though almost suffocated, could not venture to open a window for fear of the mosquitoes. Swarms never- theless found their way into his hiding-place ; and, in spite of the handkerchiefs with which he had bound up his head, filled his mouth, nostrils, and ears. In the midst of his torment he succeeded in lighting a lamp, which was ex- tinguished in a moment by such a prodigious number of these insects, that their carcasses actually filled the glass chimney, and formed a large conical heap over the burner. The noise they make in flying can not be conceived by persons who have only heard gnats in England. It is to all that hear it a most fearful sound. Travellers and mariners who have visited warmer climates give a similar account of the torments there inflicted by these little demons. One traveller in Africa complains that after a fifty miles journey they would not suffer him to rest, and that his face and hands appeared, from their bites, as if he was infected with the small-pox in its worst stage. In the Hast, at Batavia, Dr. Arnold, a most attentive and accurate observer, relates that their bite is the most. venomous he ever felt, occasioning a most intolerable itching, which lasts several days. The sight or sound of a single one either prevented him from going to bed for a
2
10 MOSQUITOES OF NORTH AMERICA
whole night, or obliged him to rise many times. The species, which I have ex- amined, is distinct from the common gnat, and appears to be nondescript. It approaches nearest to C. annulatus, but the wings are black and not spotted. And Captain Stedman in America, as a proof of the dreadful state to which he and his soldiers were reduced by them, mentions that they were forced to sleep with their heads thrust into holes made in the earth with their bayonets, and their necks wrapped round with their hammocks.”
Quite the most interesting and really important of the observations upon mosquitoes by the older travellers, however, are those of Humboldt. The account is of general interest as indicating the conditions of life in the regions of the upper Orinoco and Magdalena rivers, and the hardships endured by the mission- aries who early visited those regions and who passed their lives there. It is also of special interest as a record of the observations of a very acute observer and reasoner. The observations were all original, and most of them were in direct contradiction to the views of former travellers and of the writers on natural history. The differentiation between the different species of biting flies, includ- ing mosquitoes, the discovery that different species inhabit different regions and bite at different times of the day and of the night, the fact that with certain of the residents of the upper Orinoco the existing fevers and other maladies were attributed to mosquitoes, the curious reasoning of the author on the possible carriage of disease by blood-sucking insects and the origin of fevers, and many other points in this chapter combine to make it one of very great interest in thé light of present knowledge of the Culicide of tropical regions. Parts of it, therefore, in free translation, are here presented. It must be kept in mind that Humboldt’s account deals with biting flies belonging to different families, and, in speaking of the separate forms, he uses the terminology customary in the Spanish-American countries. By the term “ mosquitos” he does not mean Culicide, but Simuliide; the mosquitoes in our sense are called “ zancudos” and “ tempraneros” ; the “ jéjen ” are minute Chironomid, now assigned to the genus Culicoides. In speaking of these forms collectively, Humboldt uses the term “ tipulaires,” which roughly corresponds to the group Nemocera, as now understood. In order to avoid confusion we have translated the French word “cousin,” which corresponds to our word “ mosquito,” by the word “ gnat.”
“ After having spent two days at the cataract of Atures we were glad to be able to leave a place where the temperature of the air was generally 29° C. in the day and 26° C. at night. This temperature seemed still warmer than it really was. The lack of concurrence between the thermometer and our feelings should be attributed to the continuous irritation of the skin by the mosquitoes. An atmosphere filled with venomous insects always appears hotter than it really is. A Saussure hygrometer indicated in the shade (as usual) at the minimum in the day time (3 hours after noon) 78° 2”, at night at the maximum 81° 5”. .. » We were horribly tormented by the mosquitos and by the jéjen, venomous little flies or simuliums; at night by the zancudos, a species of large gnat or mosquito which is feared even by the natives. We began to have badly swollen hands and faces, and the inflammation increased from day to day until our arrival on the banks of the Temi. The means by which they try to escape from
these little animals are very extraordinary. The good missionary, Bernardo Zea, who passes his life under the torments of mosquitoes, has constructed himself,
HUMBOLDT’S OBSERVATIONS 11
near his church, upon a scaffolding of palm trunks, a little room in which he can breathe more freely. We mounted there in the evening by the help of a ladder, to dry our plants and to write up our journey. The missionary had noticed with exactness that the insects abound most in the lower layer of the atmosphere, that which is near the soil, up to 12 to 15 feet in height. At Maypures the indians leave their village in the night in order to go to sleep on the little islands in the middle of the cataract. They get some sleep there; the mosquitoes appear to avoid the air surcharged with vapors. Everywhere we found them less abundant in the middle of the river than on the banks; in descending the Orinoco one suffers only when getting into the boat.
“ Persons who have not sailed upon the great rivers of equinoctial America, the Orinoco for example, or the Magdalena, can not conceive that at every mo- ment, without interruption, one can be tormented by the insects swarming in the air, and how the number of these little animals can render vast regions almost uninhabitable. One can never become accustomed there to stand the bites with- out complaint. However lively may be one’s interest in the objects of his search, it is impossible that one should not be constantly distracted by the mosquitos, the zancudos, the jéjen, and tempraneros, which cover the hands and face, which pierce the clothing with their spear-like suckers, and which, getting into the nostrils and into the mouth, make you cough and sneeze. Thus... in the missions of the Orinoco, in these villages placed on the banks of the river, sur- rounded by immense forests, the plague of flies affords a constant topic for con- versation. When two persons meet in the morning the first question asked is, “ How have you found the zancudos during the night?’
“This is the place to mention the geographic distribution of these insects which shows quite remarkable phenomena. It does not appear to depend solely upon the heat of the climate, upon the excess of humidity, or the thickness of the forests, but upon the local conditions difficult to characterize. It can be said, for example, that the torment of mosquitos and zancudos, is not as general in the torrid zone as is commonly believed. Upon plateaux more than 400 fathoms higher than the ocean level, on very dry plains distant from the banks of great rivers, for example at Cumana and at Calabozo, there are not obviously more mosquitos than in the most civilized part of Europe. Their number becomes enormously increased in Neuva Barcelona, and, more to the west, upon the coast which extends towards Cape Codera. Between the little port of Higuerote and to the mouth of the River Unare the unfortunate inhabitants have the custom of stretching themselves upon the ground and passing the night covered with earth 3 or 4 inches thick, leaving out only the head, which they cover with a handkerchief. One still suffers from the bite of the insects, but in so much less degree that it can be easily borne, in descending the Orinoco from Cabruta towards Angostura, and in going up from Cabruta towards Uruana, between the %th and 8th degree of latitude. But beyond the mouth of the Arauca River, after the Straight of Baraguan is passed, the scene changes constantly. Beyond this point there is no longer any repose for the traveller. If one remembers his Dante he believes that he has entered the citta dolente, and he will believe he can read upon the granite rocks of Baraguan the memorable lines of the third canto:
Noi sem venuti al luogo, ov’i’ t’ho detto Che tu vedrai le genti dolorose.
“ The lower layers of the air, from the earth up to 15 to 20 feet in height, are filled with venomous insects like a condensed vapor. If one places himself in an obscure place, as, for example,'in the grottos of the cataracts formed by blocks of granite, and directs his eyes towards the opening, one sees clouds of mosquitos which are thicker or thinner according as these little animals in their movements come together or disperse. At the mission of San Borja they
12 MOSQUITOES OF NORTH AMERICA
suffer even more from mosquitos than at Carichana, but at Aturés, and above all at Maypurés, this suffering reaches its maximum. I doubt whether there is any part of the earth where man can be exposed to more cruel torments during the rainy season. In passing the fifth degree of latitude one is somewhat less bitten, but on the upper Orinoco the bites are more painful because of the heat and the absolute lack of wind. }
“One should be in the moon,’ said a Saliva indian to Father Gumilla, ‘ for in its beautiful and clear light one would be free from mosquitoes.’ These words coming from a savage are very remarkable. Everywhere this satellite of the earth is for the American savage the habitation of happiness, the country of abundance. The Eskimo who counts among his riches a plank or tree trunk thrown by the waves upon a coast deprived of vegetation, sees in the moon plains covered with forests. The indians of the forests of the Orinoco see bare fields in which the inhabitants are never bitten by mosquitoes.
“ Going further towards the South where the system of brownish yellow river waters begins, which are generally called black waters, upon the banks of the Atabapo, of the Temi, of the Tuamini, and of the Rio Negro, we enjoyed a repose, I had almost said an unexpected happiness. These rivers run through thick forests like the Orinoco, but the Nemocera and gnats, and the crocodiles as well, avoid the neighborhood of the black waters. Are these waters, a little colder and chemically different from the white, unsuitable for the larve and nymphs of the Nemocera which must be considered as true aquatic animals? Some small rivers, which are dark blue or yellowish brown, like the Toparo, the Mateveni, and the Zama, are exceptions to the general rule of the absence of mosquitos near black waters. These three rivers swarm with them, and even the indians discuss the problematical causes of this phenomenon. In descending the Rio Negro we breathed freely at Maroa, at Vavipe, and at San Carlos, villages situated on the borders of Brazil. But this amelioration of our condition was very short, for our sufferings recommenced when we entered the Cassiquiare. At Esmeralda, at the eastern extremity of the upper Orinoco, where the country known to the Spaniards ends, the clouds of mosquitos are almost as thick as in the Grand Cataracts. At Mandavaca we found an old missionary who told us with an air of sadness that he had passed his twenty years of mosquitos in America. He told us to look at his legs in order that we might be able to tell the people some day across the sea what the poor monks suffer in the forests of the Cassiquiare. As each bite leaves a little brownish black spot, his legs were so speckled that one could with difficulty see the whiteness of his skin between the spots of coagulated blood. While the insects of the genus Simulium abound on the Cassiquiare, which has white waters, the Culex or zancudos are proportionately rare; one hardly encounters them, whereas on the rivers which have black waters, on the eel and the Rio Negro, there are generally many zancudos and no mos- quitos....
“JT have just shown according to my own observations that the geographic distribution of venomous insects varies according to whether the water is white or black, and it is much to be desired that a learned entomologist should study upon the spot the specific differences between these criminal insects which play in the torrid zone, in spite of their minute size, a very important part in the economy of nature. What appears to us very remarkable, and it is a fact known to all the missionaries, is that the different species do not associate, and that at different hours of the day one is bitten by distinct species. Each time the scene changes, and when, according to the naive expression of the missionaries, other insects mount guard, one has some moments, even a quarter of an hour, of rest. The insects which disappear are not immediately replaced in the same number by those that succeed them. From half past six in the morning until five o’clock
HUMBOLDT ON BITING DIPTERA 13
in the evening the air is filled with mosquitos, which are not, as has been stated in some travellers’ stories, of the shape of our European gnats, but of that of a little fly. These are the Simuliums. . . . Their bite is as painful as that of Stomozys. It leaves a little reddish brown spot which is very excruciating and is the extravasated and coagulated blood where the beak has pierced the skin. An hour before the sun sets these creatures are replaced by a species of small gnat called tempraneros (one which shows itself early) because they appear also at sunrise ; their presence lasts one hour and a half; they disappear between six and seven o’clock, or, as they say here, after the Angelus. After some minutes of sleep one is bitten by the zancudos, another species of gnat with very long legs. The zancudos, whose beak forms a piercing sucker, causes the sharpest pain and an inflammation which lasts several weeks. Its song is like that of our European gnat, but it is stronger and more prolonged. The indians claim to recognize the zancudos and the tempraneros by their song; these latter are true twilight insects, while the zancudos are nocturnal and disappear towards sunrise.
“In the journey from Carthagena to Santa Fé de Bogota we have observed between Mompox and Honda, in the valley of the Rio Grande de la Magdalena, zancudos filling the air from eight o’clock in the evening until midnight, dimin- ishing about midnight and hiding themselves three or four hours, and return- ing in clouds with a devouring appetite about four o’clock in the morning. What is the cause of these alternations of movement and repose? Are these animals tired by a long flight? On the Orinoco it is very rare to see true day gnats, while on the Magdalena one is bitten day and night except for about two hours at midday. The zancudos of the two rivers are without doubt of dif- ferent species. Are the eyes of one of these species affected by the light of the sun more than the eyes of the other species? . . .
“ At a time when they had not yet studied the geography of animals and plants they often confounded the analogous species of different climates. They thought that in Japan, in the Andes and at the Strait of Magellan the pines, the Ranunculus, the deers, rats, and the Nemocera were the same as those of Europe. Celebrated naturalists have thought that the gnat of the torrid zone was the same as the gnat of the European marshes, only more vigorous, more ferocious, and more dangerous under the influence of a burning climate. This opinion is very erroneous. I have examined and described with care upon the spot the zancudos with which one is most tormented. On the rivers of Magdalena and Guayaquil there are five very distinct species. Latreille, the foremost entomologist of the century, has been good enough to revise the detailed description of these little animals, which I will give in a note.
[Here follow the Latin descriptions of the following new species: Culex cyanopen- nis, C. lineatus, C. ferox, C. chloropterus, and C. maculatus.]
“The species of Culex of South America generally have the wings, the thorax and the feet bluish and striped, giving a metallic effect from the mingling of spots. Here, as in Europe, the males, which are distinguished by their plu- mose antenne, are extremely rare, and one is never pierced except by the females. The preponderance of this sex explains the immense increase in numbers of in- dividuals, each female laying several hundred eggs. In traveling up one of the great rivers of America, one notices that the appearance of a new species of Culex announces the proximity of a new tributary. To cite an example of this curious phenomenon, Culex lineatus, which belongs to the Cafion of Tamalamé- que, is noticed in the valley of the Rio Grande de la Magdalena only at a spot north of the juncture of the two rivers. It extends up but not down the Rio Grande. Itis in the same way that upon a principal vein the appearance of a new substance in the vein rock indicates to the miner the neighborhood of a secondary vein joining the first.
14 MOSQUITOES OF NORTH AMERICA
“In recapitulating the observations just indicated, we see that in the tropics these insects do not extend upon the slope of the Cordilleras toward the tem- perate region where the mean heat is below 19 to 20 degrees C.; that with only a few exceptions they avoid rivers with black waters, and dry and deforested localities. On the upper Orinoco the atmosphere swarms with them much more than on the lower Orinoco, because in the first region the river is bordered by thick forests and because the borders of the forest are not separated from the river by extensive arid plains. With the diminution of water and the de- struction of the woods the mosquitos will diminish in the new world; but the effects of these changes are as slow as the progress of agriculture. The towns of Angostura, of Nueva Barcelona, and of Mompox, where, by a lack of police supervision, the streets, the squares, and the interior of the courts are covered with brush, are sadly celebrated for their abundance of zancudos.
“ The people born in the country, whether they are whites, mulattoes, negroes, or indians, all suffer from the bite of these insects ; but, just as the extreme cold does not render the north of Europe uninhabitable, the mosquitos do not deter men from establishing themselves in countries where they abound if these countries, by their situation and their government, offer resources to agriculture and to industry. The inhabitants pass their lives complaining of the plague, of the insufferable torment of flies ; but, in spite of these continual complaints, they none the less seek by preference the commercial cities of Mompox, of Santa Marta, and of Rio la Hacha. Such is the power of adaptation to evils con- tinually suffered, that the three missions of San Borja, of Aturés, and of Es- meralda, where, to use the hyperbolical expression of the friars, there is less air than mosquitoes, would become, without doubt, flourishing cities if the Orinoco offered to the colonists the same advantages for exchange of productions as the Ohio and the lower Mississippi. The abundance of venomous insects retards but does not entirely stop the progress of population ; it does not prevent the whites from establishing themselves there where the commercial and politi- cal condition of the country promises real advantage. . . .”
[Here follows an account of the chigoe (Sarcopsylla penetrans) |:
“One of the most barbarous of the tribes of the Orinoco, the Otomaques, know the use of mosquito bars made of palm fibers. We have seen that at Higuerote the people of color sleep covered with earth. In the villages of the River Magdalena the indians often invited us to lie down with them under the skins of cattle, near the church, in the middle of the plaza, where they brought together all the cows of the vicinity. The proximity of the cattle gave some repose to the men. The indians of the upper Orinoco and of the Cassiquiare, seeing that Monsieur Bonpland could not prepare his plants on account of the continual torment of mosquitos, made him enter their ovens or hornitos. Thus they call their little rooms without doors or windows, which they enter on their bellies through a very low opening ; then by a fire of damp brush which produces much smoke they succeed in driving out the insects through the opening. The absence of mosquitos is purchased very dearly by the excessive heat of the stagnant air and by the smoke of the torch of copal which lights the oven while one remains in it. Monsieur Bonpland dried, with a courage and a patience eee of eulogy, hundreds of plants, shut up in these bake-houses of the indians.
“ The pains which the natives take in order to lessen the annoyance by insects sufficiently proves that, in spite of the different organization of the dermal system, the copper-colored man is as susceptible to the bites of mosquitoes as the white man, but, as we have elsewhere stated, the pain appears less great and the bite is not followed by the swelling which follows without interruption
MOSQUITO LOCALITIES 15
for several weeks, and which increases the irritability of the skin, and which throws persons with delicate complexion into that feverish condition which always accompanies irruptive maladies. Whites born in equinoctial America, and Europeans who have lived a long time in the missions on the borders of the forests and of the great rivers, suffer much more than indians, but infinitely less than Europeans recently landed. It is not, then, as some travelers say, the thick- ness of the skin which renders the bite more or less painful at the moment it is experienced ; it is not on account of the particular character of the skin that the swellings and the inflammatory symptoms are less with the indians; it is upon the nervous irritability of the dermal system that the degree and the duration of the trouble depends. This irritability is increased by very warm clothes, by the use of alcoholic liquors, and by the habit of scratching the wound; finally, and this physiological observation is the result of my own experience, by baths taken at too short intervals. In places where the absence of crocodiles allows one to enter the river we have observed that the immoderate use of baths, while allaying the pain of old zancudo bites, rendered us much more sensitive to new bites. If one bathes more than twice a day one gets his skin into a state of nervous irritability of which no one in Europe can form any idea. One would say that all of his sensitiveness was in his skin.
“ As the gnats pass two-thirds of their life in the water, it is not surprising that in forests traversed by great rivers these injurious insects become more rare in proportion as one leaves the river. They seem to prefer to remain near places where they have bred and where they are to lay their eggs. As a matter of fact the savage indians become accustomed to mission life with greater difficulty since in the Christian villages they find a torment which they did not know in their own homes in the interior. We have seen at Maypurés, at Aturés, and at Esmeralda that the indians fled to the forests solely from fear of mosquitoes. Unfortunately all the missions of the Orinoco, from their very beginning, have been too near the banks of the river. At Esmeralda the inhabitants assured us that if the village had been placed in one of the beautiful plains which sur- round the high mountains of Duida and of Maraguaca, they would have breathed freely and would have enjoyed some sleep. The ‘great cloud of mosquitos’ (this is the expression of the friars) is found only upon the Orinoco and its tributaries. This cloud grows less in proportion as one leaves the rivers. . . .
“T have learned that these little insects make migrations from time to time, like the monkeys that live gregariously. At the beginning of the rainy season certain species, by which we have not yet been bitten, are found in certain places. We have been informed that on the Rio de la Magdalena, at Simiti, they know no other Culex than the jejen. One can pass the night there peacefully, for the jejen is not a nocturnal insect. Since 1801 the large gnat with blue wings (Culex cyanopterus) has become so abundant that the poor inhabitants of Simiti do not know how to obtain a peaceable nap. On the swampy canals of the island of Baru, near Carthagéna des Indes, there is a little whitish fly known as the cafafi.* It is scarcely visible to the naked eye, and causes very painful swellings. It is necessary to wet the mosquito bars in order to prevent the cafaft from working through them. This insect, fortunately rare elsewhere, comes up in January by the canal to Morales. When we were in this village in the month of May we found Simulwum and zancudos, but more of the jejen.
“ Slight changes in nourishment and in climate appear to change the activity of the poison in the same species of gnats or mosquitoes. On the Orinoco the most voracious insects are those of the Grand Cataracts, of Esmeralda and of Mandavaca. On the Rio de la Magdalena Culex cyanopterus is the one feared
*“ Perhaps a Culicid.” [This is very probably a Culicoides, H., D. & K.]
16 MOSQUITOES OF NORTH AMERICA
above all at Mompox, at Chilloa, and at Tamalaméque. It is here that it is the largest and strongest, and here its legs are blacker. One can hardly help laugh- ing when one hears the missionaries dispute about the size and ferocity of the mosquitos on different parts of the same river. In the midst of a country where they are ignorant of what is going on in the rest of the world this is the favorite subject for conversation. ‘How sorry I am for you!’ the missionary of the Raudales on our departure said to the missionary of the Cassiquiare. ‘ You are alone just as I am in this country of tigers and of apes; fishes where I live are rarer than here; the heat there is greater, but as to the flies, I can boast that with one of mine I can beat three of yours.’ : :
“ This voracity of insects in certain places, this avidity with which they attack man,* this activity of the venom, variable in the same species, are remarkable facts, but they find their analogy with some of the larger animals. The croco- dile of Angostura pursues man, while one can bathe peacefully at Nueva Barce- lona in the Nevari River in the midst of these carnivorous reptiles. The jaguars of Maturin, of Cumanacoa, and of the Isthmus of Panama are cowardly com- pared with those of the upper Orinoco. The indians know very well that the monkeys of such and such a valley are easily domesticated, while others of the same species, caught elsewhere, will die of hunger rather than submit to slavery.
“The people in America form ideas concerning the health of climates and concerning pathological phenomena, just as the savants of Europe do, and these ideas, just as with us, are diametrically opposed to one another according to the provinces into which the new continent is divided. On the Rio de la Magda- lena the abundance of mosquitos is regarded as a nuisance, but very healthy. ‘These animals,’ say the inhabitants, ‘ bleed us slightly, and in an excessively warm country, preserve us from the tabardillo, from scarlet fever, and other in- flammatory maladies.” On the Orinoco, the banks of which are very dangerous to health, the sick people accuse the mosquitos of all the diseases that they have. ‘ These insects are born in corruption and increase it; they inflame the blood.’ It is useless to deny this poe belief which considers mosquitos as acting in a salutary way by local bleeding. Even in Europe the inhabitants of swampy countries do not ignore the fact that insects irritate the dermal system. Far from diminishing the inflammatory condition of the skin, the bites increase it.
“The abundance of gnats and mosquitos characterizes unhealthy countries only when the development and multiplication of these insects depends upon the same causes which give birth to miasmas. These injurious animals love a fertile soil covered with vegetation, with stagnant pools, and moist air which is never agitated by the wind. They prefer, in place of bare spots, shade, that degree of light, of heat, and of humidity, which all favor the action of chemical affinities and accelerate the putrefaction of organic substances. Do the mos- quitos themselves add to the unhealthiness of the atmosphere? When one thinks that, at an elevation of three or four fathoms, a cubic foot of air is often peopled by a million winged insects and that these have within them a caustic and poisonous liquid—when one remembers that several species of Culex are from the head to the end of the body (without counting the legs) 1-4/5 lines long—when one considers finally that in this swarm of gnats and mosquitoes, spread like a cloud in the air, there are a great number of dead insects carried by the force of the ascending current and by the side currents which are caused by the unequal heat of the soil—one asks if the presence of so much animal matter in the air does not give birth to certain miasmas. I think that these substances
* “ How surprising is this voracity, this appetite for blood on the part of littl h teed Donnas ge ae ge Pacturs five Yn oe pimost ‘uninhabited country ! ‘ what baa ou; ere,’ the creo there are only crocodiles covered with scaly skin and hairy cionkeyin im: paralng ‘planes: waere
INSECT TORMENTS 17
act differently upon the atmosphere than soil and dust; but it will be prudent to make no definite assertions upon this subject. Chemistry has not yet solved any of the numerous mysteries of the unhealthiness of the air. It has taught us only that we are ignorant of many things which we thought we knew fifteen years ago, thanks to the ingenious dreams of the ancient eudiometry.
“What is less uncertain, and confirmed, so to speak, by daily experiences, is that on the Orinoco, the Cassiquiare, the Rio Caura, and everywhere where the air is very unhealthy, the bite of the mosquitos increases the disposition of the organs to receive miasmatic impression. When during whole months one is ex- posed night and day to the torment of insects, the continual irritation of the skin causes febrile movements and depresses the functions of the stomach by the effect of the antagonism, so long known, between the dermal system and the gastric system. One begins to digest with difficulty; the inflammation of the skin brings about abundant perspiration ; one can not quench his thirst; and to his always increasing impatience follows, with persons of weak constitution, a condition of low spirits during which all the pathogenic causes act with force. Today it is not the dangers of navigation in little canoes, it is not the savage indians, or the serpents, the crocodiles, or the jaguars, which makes Spaniards fear the voyage up the Orinoco; it is, as they say naively, ‘the sweats and the flies’ Let us hope that man, in changing the surface of the earth, will little by little bring about a change in the constitution of the atmosphere. The insects will diminish when the old trees of the forest will have disappeared, and one will see in these desert countries the rivers bordered with villages, the plains covered with pastures and cultivated fields.
“ Whoever has lived a long time in countries infested by mosquitos will have proven, as we have, that there is no radical remedy against the torment of insects. Indians covered with onoto, with bolary earth, or with turtle oil, are every instant slapping their shoulders, their sides, their legs, almost as though the body had not been painted. It is doubtful in general whether paint- ing is a relief—certainly no great relief. Europeans recently arrived on the Orinoco, on the Rio de la Magdalena, on the Guayaquil or the Chagres rivers (I mention the four rivers where the insects are the most numerous) at first cover the face and the hands. They soon find the heat too great, and they are tired of being completely inactive, and end by uncovering. Persons who do not wish to do any kind of work during the navigation of the rivers can bring from Europe an especial kind of clothing in the form of a sack under which they can rest hidden, opening it only every half hour. This sack should be held open by whalebone hoops, for a simple mask and gloves would be hardly bearable. Sleep- ing upon the earth, upon skins or in hammocks, we have not been able in the Orinoco region to use mosquito bars. A mosquito bar is useful only when it forms about the bed a tent so well closed that there is not the least opening by which a mosquito can enter. This condition is very difficult to bring about, and often one is forced (for example when going up the Rio de la Magdalena, where they travel with these mosquito bars), in order not to suffocate with heat, to get out from under his bar and to walk in the open air. A mild wind, smoke, and strong odors afford almost no relief in the places where these insects are very numerous and very voracious. It is wrongly stated that these little insects avoid the odor of the crocodile. We were horribly bitten at Bataillez on the road from Carthagéna des Indes to Honda, while we were dissecting a crocodile eleven feet long and which infected the whole atmosphere of the neighborhood. The indians recommend the exhalation of burnt cowdung. When the wind is very strong and accompanied by rain the mosquttos disappear for some time. They bite the most cruelly on the approach of a storm, and especially when the thunder is not followed by showers.
18 MOSQUITOES OF NORTH AMERICA
“ Bverything which moves about the head or the hands helps to chase the insects away. ‘The more you move, the less you are bitten, say the mission- aries. The zancudo buzzes a long time before alighting, but when it has gained confidence and has once commenced to insert its sucker and to suck blood one can touch its wings without frightening it. At this time it holds its two hind legs in the air, and if, without bothering it, one lets it suck its fill there is no swelling and no pain. We have often tried this experiment upon ourselves in the valley of the Rio de la Magdalena on the advice of the natives. One asks oneself whether the insect only injects the poison at the moment when it is frightened away, or if it sucks back the poison when it is allowed to suck as much as it will. I am inclined to the latter opinion, for, in allowing Culex cyanopterus to peace- ably bite the back of my hand, I noticed that the pain, very strong in the begin- ning, diminished as the insect continued to pump up the blood. It ceased absolutely at the moment when the sucking was finished. I tried also the experi- ment of wounding my skin with a pin and of rubbing the puncture with crushed gnats, but no inflammation followed. The irritating liquid of the nemocerous insects, in which chemists have not yet recognized any acid property, is con- tained, as with the ants and other hymenopterous insects, in special glands, and it is probably too dilute and in consequence too weak if one rubs the skin with all of the crushed insect.”
If, in the above account, one has kept in mind that by the word “ mosquito” Humboldt designated Simulium, it will be seen that he clearly distinguished between the blood-sucking flies belonging to different families.
In the account which follows, of the abundance of mosquitoes in southern Russia, by Jaeger, the Culicide and Simuliide were evidently not differen- tiated. Thus the statement of the mosquitoes entering the noses, mouths and ears of cattle and of causing the death of many of these animals, clearly applies to the Simuliide, the ravages of which, in that country, are well known. The account is nevertheless of interest.
“ When traveling some years ago in the country of the Czernomorzi, or Cos- sacks of the Black Sea, we observed before each house of the different slanilzas or villages, of the Cossacks, large heaps of half dried manure ignited and smok- ing, which our driver informed us was for the purpose of keeping off the mos- quitoes. Toward evening, on a very hot June day, we ascended the right bank of the muddy and slowly-running River Kuban, on the left bank of which the independent Circassia stretched out before us, when suddenly swarms of small mosquitoes covered us, our servant, and driver, and horses, lighting upon us in lumps an inch thick, and, in spite of all the covering we could hastily throw over us, tormenting us excessively with their bites.
“On the road, at a distance of every four or five versts (three or four English miles), we found a military post of about a dozen Cossacks, keeping themselves and their horses under ground, except one sentinel, who was standing upon a scaffold twelve feet high, in order to watch any inimical movements of the Circassians, to repulse their attacks, and, in case of one, to give notice of it to the two nearest posts by means of the ancient Persian telegraph, viz. : by igniting a bundle of straw, which was then fastened to the top of a high pole and elevated. At midnight our misery reached its climax. Though covered with a wide cloak, the mosquitoes entered every opening, and inflicted upon us such painful wounds that our faces were so swollen we could scarcely recognize one another. To our joy a large camp-fire was seen at some distance, which, according to the driver’s assurance, was the post-station, where fresh horses could be had. We arrived at
BITING GNATS OF SOUTHERN RUSSIA 19
the spot, and with great precipitation left the carriage, running in haste to the fire, near which a large dog was howling and running as if mad; the horses, as soon as they were unharnessed, sprang into the fire to get rid of the mosquitoes, and only with difficulty could they be removed to the subterranean stable, where the postmaster, a half-invalid officer of the army, with some men and a number of imperial horses, resided. The officer immediately ordered fresh horses for us, and, looking from under a very heavy covering at our pitiful condition, told us to hurry on, and by daybreak we should arrive at the next station, where we could find comfortable houses and be relieved from the attacks of mosquitoes. In less than five minutes the horses were harnessed, and the Russian word Boshoal, ‘ Go on,’ from the commander to the new driver, was music to our ears. When we arrived at the next station we stopped at the first house, the owner of which was a captain of the Cossacks, who received us with the usual hospitality, inborn in the Russians of all grades, and entirely unknown in any part of Europe or America, Poland and Hungary excepted. The captain conducted us into a well-furnished, comfortable room, assisted us to undress and get to bed, and from time to time applied wet cloths to our swollen face and body, until a pro- found sleep temporarily relieved our excruciating pains. The same care was taken of our servant, who, in the madness caused by his sufferings, attempted to shoot himself that he might be out of misery, but was prevented by two athletic Cossacks, and watched and nursed until he, too, was relieved by sleep. It was not until after a week of suffering that the fever and inflammation sub- sided so that we could open our eyes. .
“ As the Cossacks of the Black Sea are no agriculturists, but derive their sub- sistence from their numerous herds of horses, oxen, sheep, goats, and hogs, they suffer immensely at times from the ravages of the mosquitoes. Although they are fortunately not seen every year, these blood-suckers may be considered a real Egyptian plague among the herds of these Cossacks ; for they soon transform the most delightful plains into a mournful, solitary desert, killing all the beasts, and completely stripping the fields of every animated creature. One can not look upon the spectacle without pity when he sees the poor cattle exhibiting so much terror at the approach of these innumerable swarms of mosquitoes, whole herds hurrying home for shelter, running as if mad, and often, in their fright, plunging into the river and being drowned. Thousands of these insatiate tor- mentors enter the nostrils, ears, eyes, and mouth of the cattle, who shortly after die in convulsions, or from secondary inflammation, or from absolute suffoca- tion. In the small town of Elizabethpol alone, during the month of June, thirty horses, forty foals, seventy oxen, ninety calves, a hundred and fifty hogs, and four hundred sheep, were killed by these flies.”
20 MOSQUITOES OF NORTH AMERICA
EARLY ACCOUNTS OF THE BIOLOGY AND STRUCTURE OF MOSQUITOES.
Although simple lenses were known in very ancient times, and although many interesting and important observations were made with these simple lenses, it was not until the invention of the compound microscope, at the end of the six- teenth century and its development during the seventeenth century, that com- petent observations began to be made upon the very small animals. In that century, and especially towards its close, a number of patient workers examined with these new instruments the small, common forms of life about them and discovered many most interesting and, to them, almost miraculous facts con- cerning their microscopic appearance and concerning their habits and methods of life.
The organization of the proboscis of the mosquito and its manner of function- ing were the objects of especial interest to the early investigators with lens and microscope. The work of some of these anatomists, when we consider the in- struments at their command, was most remarkable, and while faulty in the light of our present knowledge, gives testimony to the enthusiasm and devotion of these men. It would lead too far to enter into a discussion of the early investi- gators. A brief account of them, and their relation, to the facts as found by modern workers, is given by Dimmock, while Meinert, in his “ Fluernes Mund- dele,” gives a very complete account of these early researches on the composition of the mosquito’s proboscis. There were naturally enough discrepancies as to the component parts of the proboscis, but Swammerdamm, in his work of 1669, had already determined them correctly.
Many of the earlier works, like Barth’s “ De Culice dissertatio,” contain little that is original, but quote, as was then the fashion, at great length from the writings of ancient authors.
Robert Hooke, in his “ Micrographia, or Some Physiological Descriptions of Minute Bodies made by Magnifying Glasses, with Observations and Inquiries thereupon,” published in 1665, treats so interestingly of the life-history of the mosquito that we quote from it at some length. He calls the larva “. . . a small scaled or crusted animal which I have often observed to be gen- erated in Rain water. . . . It is supposed by some, to deduce its first original from the putrifaction of Rain-water, in which, if it have stood any time open to
the air you shall seldom miss, all the Summer long, of store of them striking to and fro.”
its body, and a little lighter then the water it swims in, presently boys it up to the top 2 . . where it hangs suspended with the head swage dee a . the hanging of these in this posture, put me in mind of a certain creature I have seen in London that was brought out of America, which would very firmly sus-
TRANSFORMATION OF MOSQUITO 21
pend it self by the tail . . . and was said to sleep in that posture, with her young ones in her false belly. . . .” He kept some in a glass of rain-water and observed their transformation to
pupa and adult and described the pupa, and also, very accurately, the emergence of the adult. He philosophizes:
_ “Thave been the more particular, and large in the relation of the transforma- tion of divers of these little Animals which I observed, because I have not found that any Authour has observ’d the like; and because the thing it self is so strange and heterogeneous from the usual progress of other Animals, that I judge it may not onely be pleasant, but very usefull and necessary toward the completing of
Natural History.”
He speculates upon what he has seen, and wonders if, after all, the varied organisms supposed to come from putrefaction may not develop from eggs dropped in the water by the parent. He had an idea that the gnat’s eggs might possibly be ejected in the air—*. . . for it seems not very improbable, but that those small seeds of Gnats may (being, perhaps, of so light a nature and having so great a proportion of surface to so small a bulk of body) be ejected into the Air, and so, perhaps, carried for a good while too and fro in it, till by the drops of Rain it be washed out of it.” He believes, speaking of metamorphoses of insects, that were men “ diligent observers, they might meet with multitudes ” of instances.
He describes, in another place, a female mosquito, and speaks of letting it bite
his hand, and of watching its body swell with the blood, “ making it appear very red and transparent, and this without further pain than whilst it was sinking in its proboscis . . . a good argument that these creatures do not wound the skin and suck the blood out of enmity and revenge, but for meer necessity and to satisfy their hunger.”
The copper plates of Hooke’s work were republished with new text by an anonymous writer in 1745, under the title “ Micrographia Restaurata.” The self-satisfied complacency of this edition is in sharp contrast to the intimate style of the original work. It alternately apologizes for Hooke’s short-comings and exalts the present-day perfection of scientific knowledge, brevity and direct- ness of speech. Under our treatment of the mosquito larva the accounts of Swammerdamm, Réaumur and Hooke are mentioned. The unknown com- mentator, however, draws upon the paper by J. J. Wagner, “ De Generatione Culicum ” (Ephem. Acad. Nat. Curios., 1684), for his description of the life- history. This account, which in reality treats of one of the Chironomide, states that the female gnat dips its tail into the water and lays a gelatinous mass of eggs attached to a water weed—that they hatch into small reddish maggots which sink to the bottom of the water, where they form cases in which they live for a time and later come forth and become pup and mosquitoes.
John Swammerdamm, in his Historia Insectorum Generalis, Utrecht, 1669 (in English in Book of Nature, London, 1758, pp. 153-159), shows plainly that he had carefully studied mosquitoes with the microscope, and describes the larva very carefully (complimenting Robert Hooke’s admirable figures in his Micro-
22 MOSQUITOES OF NORTH AMERICA
graphia) and stating that the mosquito larva holds its position at the surface of the water because its tail never becomes wet, supposing it to be oily. He de- scribes the transformation to the pupa stage, carefully describes the pupa stage and the transformation to adult, and gives a long description of the adult, in- cluding the mouthparts, determining correctly the number of sete in the proboscis. He thought, however, erroneously, that in biting the mosquito was able to protrude the sete: from the end of the sheath, without flexion of the latter.
P. Bonanni, in a curious work entitled “ Observationes Circa Viventia,” etc., Rome, 1691, in which he considers the methods of reproduction of many dif- ferent kinds of lower animals with especial reference to spontaneous generation, gives very good figures of the larva, pupa, and adult, and of the wing-scales, of a Culex. The drawing of the adult is obviously traced from Swammerdam and printed reversed. The larva and the pupa are different from the Swammerdam drawings, and may have been drawn originally from specimens under obser- vation.
P. P. San Gallo, “ Esperienze intorno alla generazione dele zanzare” (Ephem. Acad. nat. Curios., 1712, cent. 1 and 2, pp. 220-223, Tab. 1), gives some atten- tion to the writings of earlier authors, and quotes Pliny, Ammianus Marcellinus, the Arabian doctor Zacharias Ben Muahammed Ibn Mahmud, and Francisco Redi. He gives an account of observations made by himself in June, 1679, upon mosquitoes in breeding-jars. He describes the larva, figures the male and female adults, and also a larva which is very poorly done.
D. Reviglias, in an article entitled “ De Culicum Generatione,” in the Acta Acad. Nat. Curios., 1737, T, 4, Obs. 3, p. 420, gives a study of the mosquito’s beak, and figures very poorly the adults. He gives an illustration of a larva which is obviously not a mosquito larva, but that of a dermestid beetle which had found its way under the glass in which the female mosquito had been confined.
In 1734 Réaumur began the publication of his “Mémoires pour servir 4 VY Histoire des Insectes,” and in his fourth volume (1738), has, as his thirteenth memoir (pp. 573-636), his famous “ Histoire des Cousins ” in which he describes the entire life-history and structure of Culex pipiens with a wealth of detail that is almost the despair of modern naturalists—in fact, few modern works even approach it, if we except Lownes’s classical study of the anatomy of the blow-fly. The observations of Réaumur were so full, and his authority was ac- cepted as so all-satisfying, that the publication of this memoir practically put a stop, for a hundred and fifty years, to all further studies of the aspects of mos- quito life. The general works published in that period derived their informa- tion concerning mosquitoes from the standard observations of Réaumur, and this, it may parenthetically be stated, holds for a number of the other studies made of common species of insects by the famous French author. And this confidence in him has in the main been fully justified, although here and there a different interpretation is possible in the light of later knowledge, especially in physics and in microscopic interpretation. While it is not strange that his accurate observations on the transformations and structure should have been
REMARKABLE EARLY WORK 23
followed by later writers, frequently without credit, it is a curious fact that the duration of the different stages as ascertained by him in Paris prior to 1738 should have been slavishly quoted in standard works as the duration of the stages of practically all mosquitoes. Down to the publication of the life-history of Culex pipiens in America by one of us in 1896, the data established by Réaumur in a different part of the world have been considered as applicable to all mos- quitoes. The frequent references to Réaumur by Miall in his admirable book entitled “The Natural History of Aquatic Insects,” published in London in 1895, shows that even at the present time, and with the latest instruments and methods of research, the French author practically remains standard.
Most of the accounts of the early writers are based on material obtained from tain-water barrels or like receptacles and consequently treat of the same species of mosquito, the common Culex pipiens, or at most closely related forms. As we have already mentioned, the transformation so faithfully described by Wagner was not that of a mosquito but a Chironomus, a midge quite similar in general appearance. A Parisian naturalist, Joblot, in 1754, was the first to describe the larva of Anopheles in “Observations d’histoire naturelle, faites avec le microscope, sur un grand nombre d’Insectes.” We have not seen this work.
The Swedish naturalist, De Geer, in the sixth volume of his “ Mémoires,” published in 1776, gives a chapter on mosquitoes with many interesting original observations. He had already determined that the adults are by no means restricted to a blood diet. He states that they visit various flowers to suck honey and that he had found them particularly abundant on the blooms or catkins of the willow. He gives an excellent description of the mating habits and of the swarms of dancing males. He appears to have been the first to observe the larvee of the species of Aédes which develop in the snow-water of early spring and which are the predominating mosquitoes in northern countries. “It is in the stagnant waters of ponds and swamps that the larve of mosquitoes live, and which swarm with them in the spring and summer; but it is principally during the first season, and in those in which the ice has melted, that one finds them in abundance.” Very naturally De Geer confused the species of Culex and Aédes, and io complete his description of the life-history he drew upon Réaumur, re- peating his statements for Culex pipiens regarding the eggs, the succession of generations and the mode of hibernation. The Aédes he appears principally to have had under observation have but one brood and lay their eggs singly, facts which have only been determined within the present century and which will be found discussed in our general account of the habits of mosquitoes.
The German miniature painter Kleemann published, in continuation of Rosel’s “ Insecten-Belustigungen ” a remarkable work under the title “ Beytrage zur Natur- und Insecten-Geschichte.” The work in some respects even exceeds that of the famous Réaumur. Thus we find in the chapter on mosquitoes (vol. 1, 1792, pp. 125-148, plates 15 and 16) that, while he gives the observations of Réaumur and others, he has verified them by observation, adding to them, and in some cases criticizing them. His plates, particularly the one illustrating the
24 MOSQUITOES OF NORTH AMERICA
life-history of Culex pipiens, are wonderfully characteristic, exquisite in execu- tion, and stand unsurpassed to this day. Like De Geer, he found the Aédes larve which appear in the early spring in snow-water, although, like that author, he failed to realize that they were different from the rain-barrel mos- quitoes, assuming that they were the first of a series of generations produced through the warmer months. He is quite pardonable in this, as the error per- sists with many even to this day.
Kleemann calculated that there could be three generations of mosquitoes during a season. After speaking of the retarded development of the larvee, when confined in a small receptacle, he says (free translation) :
“ However, in this year 1762, with long-continued warm spring weather, I found this out in the following manner: I had already found these worms, full grown, in a wooden vat in which rain-water had been caught, at the beginning of June, and soon brought some of them to transformation. On this account I emptied it out and left it standing for some days without water. Towards the end of the month, however, I had it again filled with clean water and at the be- ginning of July found very many mosquito eggs therein, which brood then came to completion at the beginning of August. Thereupon I emptied the vat once more and again filled it with clean water, and also found in this, after some days, mosquito eggs which hatched in the middle of September. Even in October of this year I have still found mosquito eggs, the worms of which, however, at present (towards the end of this month) do not incline to transform: therefore I believe that they will hibernate without food and only transform in the spring ; as I have also found the like full-grown worms already in April and May in the swamps of the forests; yes, even in March of this year, on a bright day, I have caught a male mosquito which I could not take for a hibernated one but for one freshly issued.”
As above stated, the other general accounts of the last century followed Réaumur, and the life-history of Culex pipiens was not restudied until 1896, and of other mosquitoes not until several years after this. Since 1900 the whole civilized world has been turning out mosquito literature, good, bad, and in- different ; papers descriptive of new species have multiplied, many accounts of habits have been published, and much space has been devoted to the subject of internal anatomy, so that since that date the bibliography of mosquito literature has run into many thousands of titles.
STRUCTURE OF THE ADULT MOSQUITO. THE HEAD.
The head is more or less globose, inserted upon a slender, flexible neck, a large part of its surface occupied by the eyes; there is a prominent clypeus, the an- tenne are long, and the mouthparts consist of a long sucking proboscis and a pair of palpi, usually considered maxillary, inserted at its base. There are no ocelli,
THE EYES.
The many-faceted compound eyes are large, in most species almost or quite contiguous above and beneath. In front the eyes are deeply emarginate to make place for the insertions of the antennz and the depth of the emarginations varies with the size and place of insertion of these organs according to the species or the sex. As the basal joint of the antenne is often much larger in the male than in the female, in accordance with this the emargination of the eyes is deeper in that sex.
Aside from the emargination the eyes of the two sexes usually differ somewhat in shape and those of the female may be somewhat larger than those of the male. In the culicine tribe the eyes are markedly broadest at the sides and are much narrowed above the antenne, particularly in the male; beneath they are broad and may be contiguous in’ their whole width. In the Sabethini the eyes are nearly as broad behind the antenne as at the sides and the sexual differences are less marked. In certain genera of this tribe the eyes are broadly contiguous be- hind the antennz ; in other forms a chitinous wedge is inserted between the eyes in such a manner that the eyes touch at their hindermost angles and diverge towards the front. In a curious sabethid from the Philippine Islands, Heiz- mannia scintillans, the eyes are separated above by a broad strip of chitin, almost a third the entire width of the head. In the Culicini the eyes, when contiguous above, are never contiguous along the entire margin. The chitin of the occipital region is produced wedge-shaped between the eyes ; when this wedge is small the eyes are contiguous, when large they are separated, the separation being usually greatest at the broadly rounded hind angles. In this tribe the median suture of the occiput may be seen continuing forward between the eyes thus clearly indicating that the intra-ocular wedge belongs to the occiput. In the Sabethini, as already mentioned, a wedge is inserted anteriorly and the eyes are approximated at their hind angles.
In addition to the compound eyes there are present a pair of rudimentary or vestigial eyes. These are situated laterally, close to the hind margin of the compound eyes. They are covered by the scale vestiture of the cheeks and are therefore not visible; however, they become plainly visible in a balsam prep- aration in which the pigment of the eyes has not been destroyed. These vestigial eyes consist, in fact, wholly of groups of pigment cells; there does not appear to
3 25
26 MOSQUITOES OF NORTH AMERICA
be any modification of the chitin overlying them, and of course there is no trace of the “rod and cone” structure of the compound eyes. We shall revert to these vestigial eyes again in our discussion of the eyes of the larva.
THE ANTENN-.
The antenne are composed of fifteen segments. The basal segment is greatly reduced and not distinctly visible, and therefore in descriptive work the antennx are considered as fourteen-jointed.
Child, who demonstrated the presence of the basal rudimentary segment, states that the antenna is made up of sixteen elements, but he was in error with the number of joints in the shaft. In all Culicide examined by us the number of antennal joints, both in the male and female, have been found the same, fifteen, if one counts the basal reduced joint. The second joint differs from all the others; it is large, globose, with a cup-shaped hollow on top, and upon the floor of this hollow the third joint is inserted. In descriptive work this joint is usually termed the torus. This joint constitutes a highly specialized sense- organ, generally accepted to be an organ for the perception of sound waves. Farther on we will give the details of structure of this organ and a discussion of its functions. The joint differs considerably in size in different species and in the two sexes. The torus is largest in the male and this sexual difference is most marked in those species in which the male antenne are strongly plumose. The tori are usually naked and smooth; often they are pruinose and sometimes more or less densely clothed with scales; there may be small scattered hairs present upon the surface.
The outer thirteen joints constitute the shaft and are slender, more or less elongate, and cylindrical ; they are more or less pubescent and each bears a whorl of hairs. The appearance of the shaft, and the details of structure of the com- ponent joints, differ considerably with the species and groups of species and particularly in the two sexes.
The simplest form, perhaps, is that which obtains in the females of Culez, Aédes, Anopheles, and related forms. In these the joints are elongate, cylindri- cal, subequal, with a whorl of long hairs at the base; the fourth joint (the second of the shaft) is the shortest, each succeeding joint progressively longer. The first and the last joints of the shaft differ most from the others. The first joint of the shaft is longer than the succeeding ones and usually more or less swollen; it also differs from the others in lacking the basal whorl of hairs and bears in- stead some irregularly inserted hairs near its middle. The terminal joint is the longest of the series and has a pointed apex; besides the basal whorl it has a whorl of sparse hairs just below the tip.
In some forms there is an apical whorl of smaller hairs upon all the joints of the shaft, but these do not show the regularity of insertion of the basal whorl of hairs. Besides these coarse hairs of the whorls there are many fine hairs, in- serted in sensory pits, scattered irregularly over the surface of the joints; they vary in coarseness and abundance with the species. In addition scales may be present on some of the joints—particularly the first joint of the shaft is some-
ANTENNZ OF IMAGO 27
times densely clothed with scales, as in Megarhinus and Aédeomyia. The shape and proportion of the joints differs considerably in different genera. Thus in Aédeomyia the joints are very short and stout, the second joint of the shaft hardly longer than broad; the succeeding ten joints are subequal, hardly twice as long as thick. The opposite extreme is reached in Deinocerites, where the joints of the shaft are slender and very long.
In a majority of the species the antennx of the male are plumose; that is, the joints of the shaft are shortened, bringing the whorls of hairs close together, and the whorls themselves are composed of longer and much more numerous hairs. The torus, as already mentioned, is larger in the male, and this contrast is greatest in the forms in which the male antennz are differentiated most. In the typical plumose antenna the whorls of the first eleven segments of the shaft are subapical, the basal one bearing a whorl as well as the others. The last two joints are very long and slender and bear basal whorls of hairs. On all but the last the slender segment is greatly expanded at the insertion of the whorl in order to accommodate the numerous, closely crowded hairs; the whorl does not form a complete circle, but there is a very slight interruption on the outer side. The first joint of the shaft is much longer than the succeeding ones and it bears coarse hairs upon the part below the whorl. The short segments, aside from the whorl, are smooth or nearly so; sometimes very small hairs are present upon the very short chitinous ring just above the whorl. The two last very long joints are densely hairy beyond the whorl, the hairs of the penultimate joint are particu- larly long and thus complete the plumose effect. The last joint is pointed at the tip, its whorl contains fewer hairs and they are inserted as in the female.
Raphaél Blanchard, in Les Moustiques, pages 45 and 47, states that the antenna of the female has fourteen joints, that of the male fifteen, following Ficalbi in this respect. In fact, the number of segments is the same in both sexes. Ficalbi’s error occurs, as one can readily see by his figure, with the first joint of the shaft of the male antenna; the parts above and below the whorl are regarded as separate segments. This was done, apparently, in the attempt to homologize the antennz of the two sexes and, as the third antennal joint of the female bears no whorl, it was natural to consider the basal part of the same seg- ment of the male as a unit, and the part beyond, with the whorl at its base, as a separate segment.
Many modifications occur in the different genera and species. In the male of Megarhinus the antenna is remarkably stout and rigid; the first joint of the shaft is unusually long and very stout, clothed with numerous coarse hairs and a dense covering of scales; the whorl is apical. In the succeeding ten joints the whorls are much nearer base than apex, and the apical part of the joints is dis- tinctly hairy.
In Culex latisquama the antenne of the male are remarkably long, nearly equaling the considerably lengthened antennex of the female. They are of the usual plumose plan but there is a lengthening of all the joints; even the two terminal joints are longer than in the ordinary type and the last joint is the longest ; the ten shorter subequal joints are from three to four times as long as
28 MOSQUITOES OF NORTH AMERICA
broad and bear the whorl slightly below the middle, the part above the whorl being pubescent. The hairs of the whorls are unusually long.
In Culiseta the antenne of the males are usually as in the typical Culex males ; in Culiseta inornatus, however, the male antenne approach in character those of Culex latisquama, just described. The subequal joints of the shaft have the part above the whorls lengthened and the hairs of the whorls are less numerous, so the antenne do not present the usual plumose appearance. Thus it will be seen that considerable differences in the character of the male antenne may occur within a genus.
Another striking example of such difference occurs in the genus Uranotenia, where they are usually distinctly plumose in the male. In U. lowi, however, the male antennz closely resemble those of the female. In the males of U. sap- phirina and U. geometrica, with distinctly plumose antennz, the joints of the shaft are long and slender; the whorls are basal and consist of numerous very long hairs and the part beyond the whorl bears many, irregularly inserted, long hairs which give the effect of a secondary whorl; the last two joints are lengthened, but not to the same degree as in the forms first described; these joints are coarsely hairy and the whorl on the last one is represented by a few hairs, inconspicuous among the general pubescence. Thus, in these forms, the antenne, while distinctly plumose, approach in structure those of the female. In U. lowti the male antennz are like those of the female. The joints of the shaft are long, cylindrical, and very coarsely hairy; the whorls are basal and consist of a few coarse, moderately long bristles; the two last joints are not modified in the manner of the plumose type and only the last joint is somewhat lengthened.
The mosquitoes of the genera Deinocerites and Dinomimetes are remarkable for the very great length of their antenne, those of the male even exceeding those of the female. The joints of the shaft are cylindrical, long and slender, coarsely hairy, with a basal whorl of but few hairs. The first joint of the shaft is always very long and differs from the other joints by lacking the whorl-hairs. In the female of Deinocerites the first joint is three or three and a half times as long as the one following it and at least fourteen times as long as its own diam- eter. The other joints are subequal, each successive one becoming slightly shorter. The antenna of the male Deinocerites closely resembles in character that of the female but is still longer and more slender. The second joint of the shaft is nearly as long as the first and the joints beyond shorter slightly in suc- cession ; the last five to seven joints, however, are about equal. The relative proportions of the joints differ with the species. There may be a slight thicken- ing of these last joints, most pronounced in the terminal one, the species differ- ing in this respect. Thus in Deinocerites troglodytus the last seven joints show a thickening, while in D. cancer the last joint only is distinctly swollen.
In Dinomimetes the female antenna approaches very closely in character that of the male Deinocerites. The first four joints of the shaft are greatly elongated, the second nearly as long as the first, the next two somewhat shorter. The an- tenn of the male Dinomimetes are very similar but lengthened still more. In both these genera the whorls are inconspicuous and consist of few and rather
ANTENNAL SENSE-ORGAN 29
short hairs and they are further obscured by the presence of scattered equally coarse hairs among the general pubescence of the shaft.
The antennx of Dinanamesus are intermediate in character between the forms just discussed and the ordinary culicine type, both as regards length and the nature of the hairs.
In the Sabethini the antenne of the two sexes are usually similar and those of the female may in many cases be characterized as sparsely plumose. In the genus Joblotia, however, the antennx approach closely the culicine type. In the female the hairs of the whorls are longer than in the culicines and there is a crowding of cilia towards the tip of the joints, giving the effect of a small apical whorl. In the male Joblotia the antenne are densely plumose but differ from the common type by having the whorls basal and by having the penultimate joint densely clothed with long hairs. In the common type of sabethine antenna the joints of the shaft are slender, cylindrical, with a basal whorl of long hairs and an apical whorl of short hairs. The apical whorl is a modification of the general pubescence of the joint and is variously developed according to the species. The shaft of the male antenna is often longer and more slender than in the female. When the hairs of the whorls are sufficiently abundant the female antenne appear sparsely plumose, like those of the male. The last two joints of the male antenna are somewhat longer than the preceding ones, but these differences are less marked than in the culicine forms. This lengthening of the last two joints also occurs in the females of some species, but usually it is only the last joint that is longer in this sex.
The globose second antennal segment, as we have already mentioned, is a highly developed organ of sense. Child has investigated this organ anatomically and histologically in the most careful manner, not only in a number of Nemocera, including Culex, but in insects of other orders. He succeeded in tracing the organ, variously modified, in nine different orders of insects. The organ reaches its highest development in the Nemocera, and, as it was first recognized as a sense-organ by Johnston, Child has named it Johnston’s organ. The function of this organ has been frequently discussed. As our present knowledge of mos- quito habits tends to modify the generally accepted ideas regarding its function, a description of the organ itself is essential. We translate this, as far as seems necessary, from Child’s classic paper, and adhere to his procedure in first de- scribing the organ in Corethra (Mochlonyzx auct.), a non-biting culicid, and following with a comparative description in Culex. The conditions in the male of Corethra culiciformis are as follows:
“The cup-shaped second segment is 0.15 mm. in length and 0.25 mm. broad. The hollow of the cup, in which the shaft is attached, measures 0.08 mm. in diameter and is 0.05 mm. in depth. The outer surface of the segment is densely clothed with very small sete and in addition with a few larger ones. This seg-
ment rests upon the annulate segment which is hidden in the anterior surface of the head, so that the movement of the entire antenna is brought about by the
muscles attached here. “ Tt is this second segment which contains the sense-organ in question, Johns- ton’s organ, an organ of great development and very complicated structure (pl. I,
EXPLANATION oF Prats I.
ANTENNAL SENSE-ORGAN OF CULICIDA.
Figs. 1-6. Corethra
1. First and second antennal segments of mature male; longitudinal section. N, main antennal nerve. , antennal muscles within first segment. O, anterior head-integument. C, chitinous covering of first segment. @, posterior portion of layer of ganglion cells. N’, nervecord which passes through layer of ganglion cells. W, transition stages between rods and hypo- dermal cells. 8t, layer of rods. K, basal nuclei of the rods. fibrous layer. layer of ganglion cells. single layer of hypodermis. echitinous covering of the second segment. chitinous process of plate. the plate. , Inass of hypodermis behind plate. oO”, chitinous covering of first segment of shaft (third antennal segment). N”, nervecords of antennal shaft. M’, muscles of head. T, trachea. 2. Part of plate with processes drawn in perspective. A, chitinous processes. P, plate with radial thickenings. c”, chitinous covering of first segment of shaft.
A H, O, A, a
First and second antennal
main antennal nerve. muscles of first segment. chitinous covering of first segment. , nervecord which supplies second segment. Ca outer and inner layers of ganglion cells. ? Cc’,
Hepoeer ee ¢e St, rods.
Fig. 7. Culex. N, M, NW (ea
itinous covering of second segment.
culiciformis Degeer.
3. Section through periphery of plate showing bases of processes.
A, transverse section of a process.
c’, chitinous covering of second antennal seg- ment.
P, peripheral part of plate.
Sector at about point A of fig. 1 of transverse section of second antennal! segment of male.
A, chitinous process seen in transverse section.
0’, chitinous covering of second segment.
V, radiate spaces between groups of rods.
St, rods,
K, basal nuclei of rods.
F, fibrous layer.
G, layer of ganglion cells.
, hypodermis of second segment. Rods. G, ganglion cells of rods. fiber.
F er. K, basal nucleus. St, body of rod. . Transverse sections of rods; a, through base of a rod; b, through upper nucleus. St, body of rod. K, nucleus of rod.
4
segments of female; longitudinal section.
L, K, V, thickened parts of chitinous covering of second segment.
P, plate. :
B, base of shaft.
o”, chitinous covering of first segment of shaft.
WN”, nervecords of shaft.
T, trachea.
29a
SVwUIVALIVIN 109
PLATE |
After C, M. Child.
Antennal sense-organ of Culicide.
30 MOSQUITOES OF NORTH AMERICA
fig. 1), especially in the male. As mentioned above, the shaft of the antenna (pl. I, fig. 1, C”) is inserted in the center of a plate which is striped with radial thickenings of the cuticula (fig. 1, P; fig. 2, P) and which forms the floor of the cup-shaped depression upon the distal surface of the segment. Through an opening in its center the tracheal trunk and the nerves (fig. 1, V”, T’) penetrate into the shaft of the antenna. Around the base of the shaft the plate is 0.01 mm. in thickness, however, towards the periphery it becomes somewhat thinner, then again thicker. At the same time it bends forward and joins the chitin covering the sides of the cup-shaped depression. This plate therefore, when seen from in front, has the form of a radially striped saucer with an opening in the center. From the periphery of this plate, in its entire circumference, there arise in a lateral direction 70 to 90 fine chitinous processes, 0.03-0.05 mm. in length, which gradually bend forward (fig. 1, A, 2, 4) and which serve as points of at- tachment to the nervous end-organs in the manner to be described later. The processes do not take their origin from the surface of the plate but from deep within its substance. This is proved by the fact that in a section through this part of the plate from front to back the transverse sections of the processes can be recognized as small, more strongly light difracting circles (fig. 3, 4) within the surrounding mass of the plate substance. The plate is composed of cuticular substance and its posterior surface is covered by a layer of hypodermal cells (fig. 1, H'). The plate is affected by different coloring substances in entirely the same manner as the connecting membrane between the antennal segments ; for this reason and others to be mentioned below, it is not to be looked upon as a separate segment of the antenna but simply as connecting membrane.
The outer surface of the segment, as well as the sides of the cup-shaped de- pression up to the margin of the plate, which also belong to the surface, is formed by a layer of chitin, 0.005—0.008 mm. in thickness (fig. 1, C’). At the anterior margin of the cup its hollow is somewhat narrowed by the thickening of the chitin (fig. 1). At the base also, which serves as point of insertion for the muscles moving the antenna, the chitin is somewhat thickened. Under the chitinous layer there lies the hypodermal layer which in the imago generally consists of very small cells (fig. 1, H).
“ Separated from the chitinous covering by a narrow space there is a layer of ganglion cells, 0.02—0.04 mm. in thickness (fig. 1, @),* consisting of nearly round, indistinctly defined ganglion cells of about 0.005 mm., which possess comparatively large nuclei. In preparations by maceration one sees that from the cells fine protoplasmic processes proceed (fig. 5, G). Owing to these fine threads, which are probably connected with each other, this layer has the ap- pearance, under low magnification, of a nearly homogeneous mass densely filled with nuclei.
“ Still farther inward, between the ganglion cells and the end-organs, there lies a layer, 0.005-0.007 mm. in thickness, of fibres running in two directions (fig. 1, F; 4, F). One set of these connects the ganglion cells, with the end organs, the others cross these at right angles from behind forward; these are fibres originating from the large antennal nerve and which connect with the ganglion cells. On the posterior portion of the ganglion layer the place can be detected where this nerve fiber passes through the cell layer (fig. 1, N’). It is noteworthy in this connection that the nerve fibres, which supply the larger part of the cell layer, lie between these and the end-organs instead of on the outer side of the layer, as in the posterior section. The smaller portion of the ganglion cells lying within the posterior half of the organ (fig. 1, G’) connect mostly with fibres emanating directly from the nerve.
*“ With reference to the cells my drawings are diagrammatic. I have not attempted to draw in the fine processes.”
JOHNSTON’S ORGAN 31
_ “This part of the organ contains only such cells and nerve-fibers as are found in the ganglion of every sense-organ composed of several elements, and in this case they are, moreover, very similar to the elements of the optic ganglion of the same animal. Its cells show the same size and also appear to stand in connection with each other by a net-work of protoplasmic fibers.
“ More differentiated are the end-organs proper which form the remainder of the nerve-elements filling the interior of the chitinous capsule (fig. 1, St; 4, St). These lie inward from the layer of fibers and consist of a great number of small, thin, rod-like structures which can only be distinguished clearly in an isolated state, after maceration. Such a rod (fig. 5) is 0.04 to 0.05 mm. long, 0.002 to 0.003 mm. in diameter at its base, and represents a very pointed cone on the sides of which are generally found two oval nuclei, 0.005 to 0.008 mm. long and rich in chromatin, of which one is situated basally and the other towards the apex. In transverse section (fig. 6) the nucleus lies, perhaps covered by a thin layer of protoplasm, upon the surface of the rod, which is clasped more or less by it. At its base the rod gradually passes over into a fiber which proceeds through the fibrous layer to the ganglion cells (fig. 5, F). The body of the rod itself behaves towards stains like a cell-body but appears to be of more solid consistence and in preparations by maceration often shows an inclination to split from the apex into two or three fibres. Ontogeny proves that the rods are formed from the cell bodies. The rods are attached or hang by their apices from the chitinous processes of the above described central plate (fig. 1, 4), and mostly upon their posterior surface. Asis proved by maceration, this connection is a very firm one, for sometimes the apices of the rods may still be seen upon the processes while the larger part of them is already torn away. Through their slender form and close disposition the radiate arrangement is brought about. In longitudinal section (fig. 1, St) they correspond approximately with the radii of a circle the center of which is situated somewhat before the chitinous process. In a trans- verse section through the anterior end of the processes one sees that the rods (fig. 4, St) are divided into groups corresponding with them ; between these groups there are narrow spaces, through about half their length (fig. 4, V), which are probably filled with blood during life. In each group the rods lie close together, and each, in transverse section, possesses several rods. Upon the rods lying next to the interspaces the nuclei are nearer to the apices of the rods than in the others ; these nuclei lie upon the surface of the group and bound the interspaces, so, that, in a transverse section through the groups striking the rods at about their middle, one sees the rods and their nuclei as alternating layers; a double layer of nuclei separated by a narrow interspace and a multiple layer of rod- bodies, ete. In their basal portion the groups can no longer be distinguished
fig. 4).
a. antennal nerve arises on both sides from the anterior ventral part of the cerebral ganglion as a large nerve trunk containing ganglion cells. At the point of entrance into the antenna the nerve is nearly 0.1 mm. in diameter (fig. 1, V). After its entrance into the second segment the nerve spreads out in all directions and gives off fibers (fig. 1, N’) to the ganglion layer in the entire circumference of the organ, and these form a funnel, as it were, upon which the nervous parts of the sense organ are attached. These fibers pass through the layer of ganglion cells and continue into the fibrous layer (fig. 1, F), which in the anterior part of the organ separates the ganglion cells from the rods. This funnel is incompletely separated into bundles of fibres by interspersed ganglion cells. Other fibers go directly towards the posterior part of the layer of ganglion cells and from the center of the funnel there arise two thin threads of fibers which pass anteriorly through the opening in the central plate into the shaft of the antenna (fig. 1, NV”).
32 MOSQUITOES OF NORTH AMERICA
“The tracheal system is somewhat complicated and very variable. In general the antenna is supplied by a large tracheal trunk which is present upon both sides of the head. This generally throws off a branch, which, passing towards the median side of the antennal nerve, enters the antenna and in its course sends out a number of branches to the large nerve. Another somewhat larger trunk passes along the lateral side of the nerve-trunk as continuation of the main trunk, probably also throws off branches to the antennal nerve and can also be traced into the antenna. At the base of the second segment both trunks divide into several branches; some of them pass between the ganglionic layer and the hypodermis and divide further, while others penetrate the ‘ nerve-funnel’ and supply the central parts of the organ. At least one of these continues through the opening in the central plate into the shaft of the antenna.
“ Beneath the central plate there is a space through which the trachee and the nerve cords pass. This space is enclosed at the sides by the ‘ nerve-funnel,’ the layer of ganglion cells and the rods, as well as by some less differentiated cells (fig. 1, W) which represent transition states between the rod-cells and hypo- dermis (H’) lying beneath the plate; anteriorly the hollow space is limited by the plate and the hypodermal layer pertaining to it. It is connected, through the opening in the plate, with the interior space of the shaft as well as with the radial spaces between the groups of rods and in consequence it is also connected with the outer space between the hypodermis and the layer of ganglionic cells; during life it is filled with blood fluid.
“The essential among the elements of this highly developed sense-organ are then the rods, which are, as will be shown in the following, modified hypodermal cells. The remarkable size of the organ and the great number of sensory termi- nal elements, as well as the large nerve-trunk in immediate connection with the cerebral ganglion, point to a function of great importance in the life of the insect or the preservation of the species.”
In the female the antenna is more simple and the sensory organ is much smaller and less complicated.
“ The part corresponding to the plate of the male consists of a circular plate of cuticular substance surrounding the base of the shaft. Here it is clearly apparent that the plate is nothing but the connecting membrane, and the plate of the male is without doubt homologous with that of the female, only developed to a much higher degree. . . . The rods are in every respect similar to those of the male, of the same size, and also connected with the ganglion cells by fine fibers. Their mode of termination is, however, a different one than in the male. The plate in this case does not possess any processes but the rods terminate with their apices in the substance of the plate itself, and, to be more exact, between the chitinous ring and the base of the shaft. Upon the median and lateral surfaces of the rod-layer lie elongate, less differentiated cells representing intermediate stages between the rods and the ordinary hypodermal cells.”
Child gives the following comparison of Culex pipiens with Corethra: 1. Male:
“The antenna of the Culex male shows great similarity with that of Moch- lonyz. . . . The basal segment is here also rudimentary, somewhat sunken into the head and serves as point of attachment for the antennal muscles.
“The second segment is a comparatively large, cup-shaped organ, the relation of which to the other segments, and its structure, are in general the same as in Mochlonyz, so that I do not need to give a separate figure; I only wish to men- tion a few points in which the two forms differ from each other. The entire segment measures 0.17 mm. in length and 0.12 mm. in breadth, therefore is
ANTENNAL NERVE-STRUCTURES 33
smaller than in Mochlonyx. The hollow of the cup is proportionally somewhat deeper and larger. The ganglion cells, instead of lying in one, lie in two layers separated from each other by nerve-fibres. Accordingly the nerve, which corre- sponds to the nerve N’ (fig. 1), divides into two parts, of which one passes be- tween the two layers of ganglion cells, and the other between the inner layer and the rods.* The rods are somewhat shorter and more slender than in Mochlonyz. Their length fluctuates from 0.02 to 0.025 mm. They appear shorter in the anterior part of the organ than in the posterior. Their nuclei are richer in chromatin than the ganglion cells.”
2. Female: The following gives the essential parts relating to the organ:
“Tt departs in its structure from that of the female Mochlonyx and forms, to a degree, a transition between this and that of the male.
“The form of the entire segment is that of a very thick-walled cup provided with a very shallow hollow (pl. I, fig. 7); in this hollow the shaft is placed, the base of which is formed by a disk perforated by a central opening (fig. 7, B). In connection with this disk and covering its peripheral part, is the con- necting membrane (P), which, as in the male, is furnished with radial thicken- ings and corresponds to the plate. The noteworthy thing is that here the base of the shaft forms a part of the floor of the depression. I consider this part B as belonging to the shaft because it is in direct connection without interruption with the lower part of the shaft and no difference can be detected from the chitinous covering of this. At the same time the demarkation between it and the connecting membrane or plate (P) is very distinct. The latter is nearly transparent, like the plate of the male, and appears to possess a consistency dif- ferent from that of the common chitin. The outer wall of the depression is formed by a thickened portion (fig. 7, K) of the chitinous covering of the second segment with an annulate projecting margin (fig. 7, V) which projects towards the shaft and reduces the opening of the hollow. Outwardly from this excrescence the chitinous covering forms a zone covered with blunt elevations which carry fine bristles (fig. 7, L). The remainder of the surface of the seg- ment is also covered with short, fine bristles.
“Close below the chitinous covering lies, as usual, the hypodermis of one layer ; these are succeeded inwardly by the ganglion cells, which here, as in the male, are arranged in two layers, incompletely divided by nerve fibres. Sepa- rated from the inner layer of ganglion cells by a layer of fibres lie the rods, which are directly connected at least with the inner layer of cells by fine fibres. The rods are somewhat longer than in the Culex male, about 0.03 mm., but agreeing with them in form. In longitudinal section they lie in radiate arrangement, radiating from the connecting membrane or plate. In transverse section it is seen that, similarly to the male of Mochlonyz, the rods form groups (compare pl. I, fig. 4), separated by very narrow interspaces, throughout the circumfer- ence of the organ and corresponding to the thickenings of the connecting mem- brane. On the median and lateral margins of the rod-layer more or less modi- fied hypodermal cells represent the transition stage between rods and ordinary hypodermal cells. Two nerve cords and a tracheal trunk pass through the cen- tral hollow space into the shaft of the antenna.”
This organ, in conjunction with the antennal shaft and its whorls of hairs, has been generally looked upon as an organ of hearing. The long hairs of the whorls vibrate in response to sound waves of a certain pitch and react upon the sensory organ of the globose second segment. Johnston, in a paper published in 1855, was the first to describe the antenna as a complex sense-organ, and he
* In fig. 7, plate I, belonging to the female of Ouleg, this arrangement is likewise present.
34 MOSQUITOES OF NORTH AMERICA
confidently termed the second joint the “auditory capsule.” His studies were evidently influenced by his knowledge of the structure of the vertebrate ear, not only in the interpretation of the anatomical structure of the organ, but, in con- sequence, also of its functions. Probably inadequate microscopes and methods contributed in large part to his errors. He described what he found as follows:
“The auditory capsule is filled with a fluid of moderate consistency, opales- cent, and containing minute spherical corpuscles, and which probably bears the same relation to the nerve as does the lymph in the scale of the cochlea of higher animals. The nerve itself of the antenna proceeds from the first or cerebral ganglion, advances towards the pedicle of the capsule in company with the large trachea which sends its ramifications throughout the entire apparatus, and, penetrating the pedicle its filaments divide into two portions. The central threads continue forward into the antenna and are lost there; the peripheral ones, on the contrary, radiate outwards in every direction, enter the capsule space, and are lodged for more than half their length in sulci wrought in the inner wall or cup of capsule.
“In the female the disposition of the parts is observed to be nearly the same, excepting that the capsule is smaller.”
Assuming the conditions to be such as described it was very natural to at- tribute to the organ complex functions. Johnston sums up his reasons for be- lieving the antenna an auditory organ of high perfection as follows:
“The position of the capsules strikes us as extremely favourable for the per- formance of the function which we assign to them; besides which there present themselves in the same light the anatomical arrangement of the capsules, the disposition and lodgment of the nerves, the fitness of the expanded whorls for receiving, and of the jointed antenne fixed by the immovable basal joint for transmitting vibrations created by the sonorous modulations. The intra-cap- sular fluid is impressed by the shock, the expanded nerve appreciates the effect of the sound, and the animal may judge of the intensity, or distance, of the source of the sound, by the quantity of the impression: of the pitch, or quality, by the consonance of particular whorls of the stiff hairs, according to their lengths ; and of the direction in which the undulations travel, by the manner in which they strike upon the antenna, or may be made to meet either antenna, in consequence of an opposite movement of that part.”
A. M. Mayer, in the course of his researches in acoustics, made most interest- ing experiments with the supposed auditory function of the antennal hairs of the male mosquito. With tuning-forks, he showed that some of the hairs are of such a structure that they vibrate in response to sound-waves numbering 512 per second. Other hairs vibrated to other notes, showing altogether a considerable range. He says:
“T infer from my experiments on about a dozen mosquitoes that their fibrils
are tuned to sounds extending through the middle and next higher octave of the piano.”
Mayer carried his experiments farther, and, taking accurate measurements of the thickness and length of two hairs which vibrated in response to the tuning- forks Ut 3 and Ut 4, made large wooden models of them. The model of the hair vibrating to the Ut 3 tuning-fork was a meter in length. These models responded to vibrations of approximately the same number as the hairs them- selves.
HEARING IN MOSQUITOES 35
Perhaps the most interesting result of his experiments was the discovery of the fact that the antennal hairs enable the mosquito to determine the direction from which the sound-waves proceed. He experimented with the song of the female and found that the hairs of the male antenne vibrate when the song of the female comes more or less at right angles to them, while those which point to or from the source of sound are not affected. If the song is directly in front of the head it will be most fully received by the antennal hairs. If the song of the female affects one antenna more than the other, the male, by turning until both antenne are equally affected, could thus determine the direction of the female.
“The song of the female vibrates the fibrille of one of the antenne more forcibly than those of the other. The insect spreads the angle between his an- tenne, and thus, as I have observed, brings the fibrille, situate within the angle formed by the antenne, in a direction approximately parallel to the axis of the body. The mosquito now turns his body in the direction of that antenna whose fibrils are most affected, and thus gives greater intensity to the vibrations of the fibrils of the other antenna. When he has thus brought the vibrations of the antenne to equality of intensity, he has placed his body in the direction of the radiation of the sound, and he directs his flight accordingly ; and from my ex- periments it would appear that he can thus guide himself to within 5° of the direction of the female.”
While Mayer accepted the function of the antenne as auditory, he clearly perceived that no comparison could be made with the sense of hearing in the higher vertebrates, and expresses his conclusions in these terms:
“ Some may assume from the fact of the co-vibration of these fibrils to sounds of different pitch, that the mosquito has the power of decomposing the sensation of a composite sound into its simple components, as is done by the higher verte- brates ; but I do not hold this view, but believe that the range of co-vibration of the fibrils of the mosquito is to enable it to apprehend the varying pitch of the sounds of the female. In other words, the want of definite and fixed pitch to the female’s song demands for the receiving apparatus of her sounds a corre- sponding range of the co-vibration, so that instead of indicating a high order of auditory development it is really the lowest, except in its power of determining the direction of a sonorous centre, in which respect it surpasses by far our own ear.”
Our own observations of the habits of mosquitoes lead us to doubt that the antenne, if auditory at all, are so in their primary function. The foregoing hypotheses are founded upon the assumption that the male seeks the female and is attracted by her song. In fact such is not the case. At least in those forms in which the antenne of the male are most highly specialized the males “swarm ” and the female seeks the male. In our experience the song of the female does not attract the male. Mayer appears to have come very near the truth when he found that the antennex served for orientation. One of us (Knab) has observed that the males in a swarm always dance facing the breeze or air- current, no matter how slight this may be, and adjust themselves instantly to any shifting of the breeze. Why this is done would be difficult to explain, but that the antennz make this possible is clearly apparent from Mayer’s observa- tions. Of course it can not be denied that the antenne are perhaps also, in a
36 MOSQUITOES OF NORTH AMERICA
very rudimentary way, auditory in function. Child already observed the great sensitiveness of the swarms of dancing males to sound vibrations,
“ moreover not alone to the higher, but also to deeper tones. If one sings a deep note in the vicinity of a swarm, the entire swarm is immediately thrown into confusion which lasts several seconds. . . . Faint noises have the same effect, naturally in a lesser degree. I have observed the same from the whistle of a loco- motive, even when this was one or two kilometers away. If one approaches a swarm of gnats in a boat, upon some sudden noise, such as a stroke of the oars, the entire swarm is thrown into a wild dance and frequently flies away or dis- solves. As, however, with great care, even with fairly rapid movements, one can get close to the swarm without the gnats reacting in any way, it follows that the disturbance is caused by the sound and not by a visual impression. From these observations of course nothing can be concluded regarding the location of the organs of hearing; it is only proved thereby that the gnats are very sensitive to sound. But because it is in these insects that an organ occurs which appears especially equipped for the reception of air-vibrations, the probability of a con- nection with that behavior is very great.”
While it is evident from the foregoing that mosquitoes react to sound-waves, it is by no means clear that they can perceive them as such. If the sound-im- pressions are received through the antenne, as the organization of these ap- pendages seems to indicate, it is still to be doubted that there is a differentiation of the impressions produced by sound-waves and other stimuli, such as a current of air, or between sounds of different pitch. Child’s conclusion was that the function of Johnston’s organ was originally the perception of tactile stimuli, and that when it became more highly developed it also served for the perception of sound-waves. “The resulting ‘auditory impression’ is a modified tactile impression.” It is worthy of note, in this connection, that the male mosquitoes emit a very high-keyed song while swarming ; in fact, this sound is so high that it is probably beyond the range of many human ears.
The part of the head inclosed by the eyes and bearing the antenne shows little specialization, is partly membranous, and in large part hidden by the globose second antennal joints. Medianly, above the antenna, and resting against the front margin of the eyes, is a small chitinous piece. In the Culicini this is usually rather poorly defined, subquadrate or more or less triangular, with its base resting against the margin of the eyes and the apex projecting forward be- tween the antennz. In the Sabethini it is conspicuous, although small, in those forms in which the eyes are separated above by a narrow wedge. This wedge, in fact, is a backward extension of the chitinous piece in question ; the portion pro- jecting forward beyond the margin of the eyes is prominent and may be either pointed or truncate in front. That part of the front below the antenne and above the clypeus usually shows no structural peculiarities. In one sabethid genus, Rhunchomyia, however, this portion is produced into a tubercle which projects just above the clypeus.
CLYPEUS.
The clypeus is large and prominent, chitinous, and projects above the inser- tion of the proboscis. Its development is unusual, and this is to furnish a place of attachment, on its inner walls, for the powerful muscles of the epipharynx. It is strongly chitinized above and its shape is roughly globose, or roundedly
SO WAM Rob E
_
11,
12. 13. 14, 15.
EXPLANATION OF Puate II.
. Side view of head of Culex, with extended mouth-parts; @, antenne.
Same from above with mouth-parts partly cut away.
Tip of labium of female Culex.
Tip of labium of male Cuwlez.
Tips of separated sete of mouth-parts of Culez.
Tip of labrum-epipharynx seen from beneath and in section.
. Cross-section through labelle and tip of labium of female Culez.
Cross-section near middle of the proboscis of female Culez. Cross-section through pharyngeal region of forward part of head of female Culez.
. Cross-section through posterior part of head of female Culez, to show the sucking
bulb of the esophagus. 0b, lumen of esophageal bulb; bm and bm’, muscles to dilate the bulb; 7, chitinous rods which support the wsophageal bulb; rm, retractor muscles of maxille, at their point of origin; t, elastic plates of sides of bulb.
Longitudinal section of head of a female Culex. b, esophageal bulb; g, point where the clypeus appears cut off from rest of head; v, valve between pharynx and esophagus.
Cross-section near middle of the proboscis of a male Culez.
Cross-section at base of the proboscis of a male Culez.
Cross-section further into the base of the proboscis of a male Culez.
Cross-section through pharyngeal region of head of a male Culez.
The following letters have the same signification throughout :
ce, clypeus. Ir, labrum. p, pharynx.
e, epipharynx. Ire, labrum-epipharynx. pm, pm’, pharyngeal muscles. h, hypopharynx. , mandibles. &, supracesophageal ganglion. i, infrewsopiagedl ganglion. wh maxillary palpi. tr, tracheal stem.
i, labium, me, maxille.
1b, labelle. oe, cesophagus.
36b
FUBLICATION 159
PLATE (i
After Dimmock.
Mouth-parts of Culex.
MOUTHPARTS OF MOSQUITO 37
conical more or less constricted at base. It presents no noteworthy modifica- tions. Its surface is usually naked and smooth, or, due to the presence of very fine hairs, pruinose. In some cases it is densely clothed with scales, and in one genus, Joblotia, it bears many scattered coarse hairs, particularly towards the margin. THE PROBOSCIS.
All true mosquitoes have a long proboscis of complex structure; it is used as a sucking-organ, and in the females of many species as a piercing organ as well. It is most highly organized in the females with blood-sucking habits. The organ was already carefully studied by the early workers with the microscope, among whom may be particularly mentioned Leeuwenhoek, Swammerdamm, Barth, and Réaumur. These early investigators only studied the mouthparts per se, without thought of their relations to the mouthparts of other insects, It was not until after the study of entomology had been put on a firm footing by systematists, and the significance of the mouth-parts of insects in classification had been pointed out by Fabricius, that attempts were made to homologize the mouthparts of the different orders of insects. Savigny, in 1816, already developed the idea that the mouthparts of all insects were reducible to the same general plan of those of the chewing insects, and that these mouthparts were the serial homo- logues of locomotory appendages. The belief that the mouthparts of the mosquito (and of the Diptera in general) are homologous with those of mandibulate insects has been very generally accepted by modern entomologists. It was not, however, until about 30 years ago that any exact knowledge of the organization of the proboscis of the mosquito was reached, the previous analyses having been unsatisfactory from the scientific point of view, and conflicting. In 1880 two careful studies of the mouthparts of the mosquito and of other Diptera, carried out independently with strictly modern methods, were published by Dimmock and by Meinert. Both these works describe very completely the anatomy of the proboscis and related parts; the interpretation of the mouthparts by the two authors, however, is quite different. Dimmock followed the generally accepted idea and homologized the components of the proboscis with the mouth-organs of mandibulate insects. Meinert, on the other hand, concluded that no such homology exists and presented an entirely different interpretation. The studies of Kellogg, of the development of the mouthparts of the dipterous imago within the larva, show conclusively that the generally accepted view is correct and essen- tially as presented by Dimmock. It seems desirable, however, to present briefly Meinert’s views, and also those of other authors when at variance with the ac- cepted interpretation of the facts. Additions to our knowledge of the mouth- parts made since by different workers will be also considered. Dimmock’s de- scription of the mouthparts of the female and male Culez is so clear and full that we reproduce it herewith, together with the excellent plate elucidating the structures (pl. II, opposite page 36).
In the female:
“The mouth-parts which form the proboscis of the female Culez, as I have found them by study of C. rufus, C. ciliatus, and C. pipiens, consist of a labrum 4
38 MOSQUITOES OF NORTH AMERICA
(pl. II, fig. 1, Ir), an epipharynx (e), a hypopharynx (1), two mandibles (m), and two maxille (mz), all sheathed, when in repose, in the labium (7), which receives them into a groove on its upper side. Hach maxilla has a maxillary palpus (mp), which lies outside the labium ; the latter has no palpi. The labium and maxillary palpi are covered with hair and scales ; the other mouth-parts are naked, light brown, setiform, and transparent ; they all originate at the anterior basal portion of the head, and are, with the exception of the maxillary palpi, of about equal length, that is, about three to four times the length of the head. The maxillary palpi, in the females of Culex proper, are about the length of the head. The scaleless mouth-parts are not jointed, and are the ones which pene- trate the skin in biting. The labrum and epipharynx are united in their whole length, forming a piece which is shown in section in fig. 6, d. The other mouth- parts are free to the base. A pumping organ, trianguloid in cross-section (fig. 10, b), is formed by a dilation of the esophagus behind the cesophageal nerve- ring. Each of the above-mentioned parts will be described more in detail later. In comparative size and strength the mouth-parts would be arranged as follows, the largest and stoutest first: labium, labrum-epipharynx (the name by which I designated this compound piece in diptera), hypopharynx, maxille, and mandibles.
“ The general arrangement of the mouth-parts, relative to each other, is shown best in fig. 8, which is a figure of a cross-section through the middle of the pro- boscis of a female Culex rufus, while in repose, with the sete sheathed in the labium. The labium (J), clothed on the outer side with its scales and hairs, is wrapped nearly around the other mouth-parts. In it lie the two maxille (mz), partly enclosing the parts above them, and thus helping to bind the parts to- gether; above the maxille are the two mandibles (m), and immediately above the mandibles, in the median line, is the hypopharynx (h), with a thickened middle portion. Resting on the hypopharynx is the labrum-epipharynx; the epipharynx (¢) is omega-form in section, and above it, delicately attached, is the labrum (Ir). The changes in relative position which the mouth-parts of Culex undergo as they approach the head can be best described in the subsequent description, in detail, of each separate part.
“ The labrum-epipharynx (fig. 1, 5, 6, 7-8; Ir and e) of Culex consists of the thin labrum resting upon and fastened to the epipharynx; it tapers gradually from base to apex. The epipharynx is omega-form in cross-section, being a chan- nel rather than a tube, a tube being formed by the pressing of the hypopharynx upon its under side. The tube thus formed is the channel through which the blood, which Culex sucks, passes into the pharynx. At its base or proximal end the epipharynx is supported and moved by strong muscles having their inser- tions on the upper side of its wings or lateral portions, and upon the upper side of its tube. These muscles extend upward and posteriorly, and have their origin on the inner surface of the clypeus. (See figs. 9 and 11.) These muscles (pm), by their contraction, elevate, and perhaps slightly retract, the epipharynx and the labrum to which they are attached. These muscles probably atd in suction for when the sete are all stuck firmly in the skin, the contraction of these muscles would only serve to raise the base of the epipharynx from that of the hypo- pharynx; this action would tend to produce a vacuum between the two (see fig. 9), and thus cause the blood to be drawn up in the tube of the epipharynx. The probability that these muscles aid in suction is augmented by the fact, the ex- planation of which I have more fully developed in the part of my dissertation devoted to a comparison of the mouth-parts and suctorial apparatus in the dif- ferent families of diptera upon which I have worked, that the corresponding muscles are devoted to suction in other flies, which cannot raise their epi- pharynx from their other mouth-parts so freely as is seen in fig. 1, and further,
LABRUM ; HYPOPHARYNX 39
that in the male Culex, which does not possess—as does the female— a pumping apparatus behind the oesophageal nerve-ring, these muscles are the ones that must serve for suction. The section represented in fig. 9 was taken near the base of the clypeus ; a few sections further on, posteriorly, the channel for the passage of food turns upward and then backward again, passing in its course a place (fig. 11, v) where its walls approximate dorsally and ventrally. This narrowing of the walls is probably a valve to prevent the return of fluids to the mouth dur- ing the pumping process. The pharynx with its surrounding muscles in Culex is the equivalent of what has been termed the fulcrum in Musca. Macloskie * writes of the fulcrum, ‘It seems to be general in diptera; even the mosquito possesses it,’ but he does not further describe it, in other diptera than Musca.
“The tip of the labrum-epipharynx seems to turn upward (fig. 1, Ir-e), al- though the opening is upon the ventral surface, as may be seen in fig. 6, b, which represents the ventral view of the tip of this part. The tip of the labrum-epi- pharynx is comparable to a quill-pen with three tips near each other, the middle one of these three tips being slightly shorter than the other two. The two lateral portions of the epipharynx, as seen in section, when they near the tip, lay them- selves closely upon the sides of the tubular portion, passing upward upon it, as seen in fig. 5, lv-e; they thus serve to strengthen the two outer points of the tip of the epipharynx, while the labrum continues to a sharp point at the tip, and, united with the upper surface of the epipharynx tube, forms the middle point of the tip. The channel, or slit, along the under side of the epipharynx, widens toward the tip (fig. 6, b), leaving thus an opening for the passage of fluids into the tube of the epipharynx.
“The labrum itself is a thin lanceolate lamella of chitin, concave along the under side from the basal portion to the tip, and its concavity rests upon and fits to the convexity of the tubular part of the epipharynx, to which it is so lightly attached that they readily separate by application of caustic potash. The outer edges of the labrum roll slightly inward toward the epipharynx along most of its length. (See fig. 6, d.) Atits base the labrum sends a chitinous support beneath the clypeus, where it separates more from the epipharynx and has its own muscles, indicating that the labrum has a degree of motion independent of the epipharynx, a motion allowed, perhaps, by the elasticity of the connection between the labrum and epipharynx. The muscles of the labrum (fig. 9, pm’) are inserted upon the upper side of its base and have their origin on the inner surface of the roof of the clypeus. These muscles are, at least in the females of Culex rufus, divided into three portions in their upper part, as shown in fig. 9.
“The hypopharynx of the female of Culez is a linear, lanceolate, transparent lamella of chitin, with a longitiudinal rod through the middle, the nature of which will be discussed later. At its base the hypopharynx forms the continua- tion of the under wall of the pharynx. (See fig. 11,4.) The hypopharynx is closely pressed upon the under side of the epipharynx, completing the tube nearly formed by the epipharynx. No muscles have their insertion on the base of the hypopharynx. Its tip is simply lanceolate (fig. 5, h). In Culex pipiens and C. rufus nothing further is visible (with a magnifying power of five hundred diameters), in sections of the thicker middle portion of the hypopharynx, than a simple rod of chitin ; but, in C. ciliatus, a North American species of which the mouth-parts are larger, this rod appeared to be tubular. Is it a rod or is it a tube? Menzbier + writes (p. 25) that in diptera ‘neither the labrum nor the hypopharynx possesses a completed tube, but only a channel’ which leads into
* Macloskie, G.: The proboscis of the house-fly. (Amer. Naturalist, March, 1880, v. 14, pp. 153-161, figs. 1-3. a
+ Menzbier, M. A. Ueber das Kopfskelet und die Mundwerkzeuge der Zweifliigler. (Bull, Soc. impér. natur. de Moscou, 1880, t. 55, no. 1, pp. 8-71, tabs. 2-3.)
40 MOSQUITOES OF NORTH AMERICA
the salivary duct. That Menzbier is incorrect in affirming that the hypopharynx has no complete tube I have clearly proved in my observations on Bombylius and #ristalis; but the question still remains unsettled whether Culex has any passage, either tube or groove, through the hypopharynx. Réaumur * (tome 4, part 2, p. 396) discusses the probability of a poisonous fluid being secreted by Culez, to cause the blood to flow more readily when it bites, and since his time writers have, on the one hand, accepted this statement, without proving the presence of such a fluid or of the glands to secrete it, or they have, on the other hand, denied the existence of such a fluid and affirmed, as Leeuwenhoek did, that the swelling subsequent to the bite of Culex was due to the irritation produced by the tearing of the mouth-parts in the skin, without the aid of a poisonous secretion. After having experimented a large number of times with the living mosquito, I am convinced that there is use made of a poisonous saliva; for, when biting, if the mosquito fails to strike blood, which it often does on parts of the back of my hand, it may have inserted its proboscis (labium of course excepted) nearly full length, in from one to six directions, in the same place, and with- drawn its proboscis; indeed it may have inserted its proboscis, as often occurs, in extremely sensitive parts; yet in such cases, if no blood be drawn, no more effect is produced upon my skin than is produced by the prick of a sharp needle; a red point appears only to disappear in a few hours. Certainly there has been as much tearing of tissues in such a case as the above-mentioned, as there is when Culex settles on a place richer in blood, and, with a single probing, draws its fill. When the insect is allowed to draw its fill on the back of my hand, the subsequent swelling lasts from forty to forty-eight hours, and the amount of poisonous effect upon me, as proved by numerous experiments, is in direct pro- portion to the length of time which the Culex has occupied in actually drawing blood. The above-mentioned facts would indicate a constant outpouring of some sort of poisonous fluid during the blood-sucking process, and would neces- sitate a tube or channel for its conduction. Now, no other channel exists through which saliva could pass from the base to the tip in the mouth-parts which Culex inserts in the skin, and this, together with the position occupied by the salivary duct in other diptera, leads me to believe, without as yet being able to give anatomical proof for it, that the hypopharynx of Culex contains a duct that pours out its poisonous saliva. Having no fresh specimens of Culez ciliatus, and the extreme minuteness of the hypopharynx in the species of Culex available, has precluded my determination of the actual presence of glands in connection with this mouth-part.
“The mandibles (figs. 1 and 8, m), the most delicate of the mouth-parts of Culex are two very thin linear-lanceolate lamelle of transparent chitin, which rest with their inner edges beneath each half of the hypopharynx, their outer edges projecting beyond its outer edge, on each side. At the base of the proboscis they appear to have no muscular attachments. They are slightly tapering from the base to the tip, but are of equal thickness throughout their breadth; at the tip they have a slight thickening, in form of a letter V, with its opening turned toward their very delicate, almost invisible tip. (See fig. 5, m.)
“The maxille (mistaken by Gerstfeldt + for the mandibles, but correctly figured by Muhr { on his diagram as maxille) are tapering lamellx of chitin, apparently serrate at the tips. Hach maxilla is thicker near the inner edge, the thickening being formed by a solid chitinous shaft, which is fixed longitudinally upon the upper side. (See figs. 5 and 8, mz.) The bases of the maxille join
im Re A. F. Mémoires pour servir & I’histoire des Insectes. ... . {Edition 17387- . 4, part 2. Gerstfeldt, G. Ueber die Mundtheile der saugenden Insecten .... 1858.
Muhr, J. Die Mundtheile der Insekten dargestellt auf 5 Wandtafeln....1878.
MAXILLARY PALPI; LABIUM 41
the stouter maxillary palpi just before passing under the clypeus, and immedi- ately afterwards they join the labium, and become imbedded, with the man- dibles, in connective tissue. (See fig. 9, ma.) Their continuations in the head are two delicate chitin-supports, each of which ends in a strong muscle; this muscle, the retractor maxille (fig. 10, rm), passes backward and downward through the head, beneath the infracesophageal ganglion, and has its origin in the posterior basal part of the head. The maxille probably have no protractor muscle, their forward motion being due to the elasticity of the chitin frame-work of the head. The shaft of the maxille is very transparent, except near the inner side where the chitin-rod runs; here it is brownish and more opaque. Out from the above-mentioned chitin-rod extends a very delicate feathering, or corruga- tion, of chitin to the edge of the most transparent portion of each maxilla, as seen upon the basal portion of fig. 5, mz. The tip of the maxille (fig. 5, mz) is very acute, has none of the before-mentioned chitinous corrugations, but, in their place, near the outer edge, is a row of papille, which have their tips slightly recurved toward the head, and consequently appear serrate. These papille are upon the upper surface of the maxille, as can be readily seen, by preparing the mouth-parts by lateral pressure, as in fig. 1.
“The maxillary palpi (figs. 1, 2, and 9, mp) are four-jointed in some species of Culex, five-jointed in others. At first sight they appear to be three-jointed, but more careful examination serves to show that the apparent basal joint is made up of two joints, and oftentimes to reveal a very short, knob-like joint at the extremity of what appears to be, at first, the apical joint. At their base the maxillary palpi join the maxilla just before the latter pass beneath the clypeus, and, with the maxille, join the other mouth-parts, as shown, in section, by fig. 9.
“The function of the maxille is, probably, to draw the other mouth-parts into the skin, when Culez bites, for if one watches the maxillary palpi of Culex, while the sete are entering the skin, the sete seem to pierce the skin, and enter it with a slow gliding motion, as if drawn from below, instead of pressed from above ; meanwhile, if one observes carefully, with a lens, the maxillary palpi can be seen to be in an alternating motion, as if the maxille to which they are attached, pressed, first one then the other, into the skin, and then pulled the other parts after them. The muscles, retractores maxillarum, already described, lend weight to this view of the functions of the barbed maxille.
“The labium (figs. 1, 2, and 3, 1), the largest of the mouth-parts of Culez, and the only one of them, helping form the proboscis, which contains muscles, forms a sheath opening along the upper side, and receiving in its channel the other mouth-parts (excepting the maxillary palpi), as seen in cross-section in fig. 8; it tapers from base to tip, is flexible, has a delicately annulated structure, and is clothed with hair and scales. At its base it unites with the maxille, man- dibles, and hypopharynx, and continues into the under surface of the head. Throughout its length it contains, on each side, muscles, which have their origin in the base of the head and serve to control the motions of the labium. (See figs. 8 and 9, ml.) At the sides of the tip of the labium are attached two lobi- form appendages, the labelle, which are seen at Ib in fig. 3 with the true tip of the labium proper between them. These terminal lobes are jointed to the labium, a little distance behind its tip, as can be seen in fig. 7, which is a cross- section of the labium a trifle anterior to the actual centre of motion of these joints. The section of that portion of the labium which extends forward to form its tip is seen in the middle of the figure, just below the section of the maxille (mx). Outside the section of each lobe is seen the section of a portion of the exterior edge of the labium itself, which here forms a double socket, or pair of acetabula, into which the heads of the two labelle are set. Each of the lobes of the labium,—the labella,—is provided with an extensor and flexor muscle (fig. 7, me, and mf), and is attached to the labium by a true joint.
42 MOSQUITOES OF NORTH AMERICA
“The labium has for function, for the most part, the protection of the fine setee which form the true piercing organ of Culex. In the females of Culex proper, the protective sheath is formed by the labium alone. When the mosquito has found a place which suits its taste for piercing, it plants its labelle firmly upon the spot, and a moment later the labium flexes backward in its middle, the sete, firmly grouped together, remain straight and enter the skin, while the two labellee guide them, much as a carpenter guides his bit with his fingers while boring a piece of plank. When the sete of Culex have entered the skin to nearly their full length the labium is bent double beneath the body of the insect, the labellee still holding the base of the sete at the point where they enter the skin. When the mosquito wishes to withdraw the sete it probably first withdraws the two barbed maxille beyond the other sete, that is, so that their barbs, or papille, will be kept out of action by the mandibles and hypopharynx; then it readily withdraws the sete, perhaps aiding their withdrawal by the muscles of the labium, for, during the process of extracting the sete from the skin, while they are slowly sinking back into the groove upon the upper side of the straightening labium, the mosquito keeps the labelle pressed firmly upon the skin.
“The mouth-parts of Culex, as above described, are suspended under a clypeus, or epistom, which is figured from the side in fig. 1, c; from above in fig. 2, c; in length-section in fig. 11, c; and in cross-section in fig. 9, ¢. This clypeus is the hood-shaped forward continuation of the lower part of a A-shaped piece of chitin which forms the framework of what may be termed the ‘ face’ of Culex; right and left of the upper portion of this framework pass out the an- tennal nerves, the antenne being supported by the framework itself.
“ The pharynx (fig. 11, p), the tubular continuation of the epipharynx above and the hypopharynx below, as it passes backward, beneath the centre of the A-shaped framework, turns somewhat upward, is narrowed to the valve pre- viously described, then widens slightly again, and, as cesophagus (fig. 11, oe) passes through the cesophageal nerve-ring, in which it is supported by three delicate chitinous rods, which lie, one longitudinally on its ventral surface, and two to the right and left on its dorsal surface. Just posterior to the cesophageal nerve-ring, directly above the nerve-commissure which connects the infra- cesophageal ganglion with the first thoracic ganglion, the cesophagus suddenly expands into an cesophageal pump, or bulb, the longitudinal section of which is shown in fig. 11, 6 ; the cross-section in fig. 10, 6. This bulb, which is the chief sucking organ in the female Culex, and which I have found in no other dipteron, is supported by three longitudinal chitinous rods, which are stouter continua- tions of the three rods supporting the cesophagus through the nerve-ring. These rods (fig. 10,7) have between them chitin-plates (fig. 10, +) which are suspended from the rods by elastic membranes. On the dorsal plate is inserted a double muscle, or a pair of muscles (bm), the origin of which is in the dorsal part of the chitinous shell of the head. Each of the lateral plates has inserted on it a muscle (bm’), the origin of which is in the chitin of the lower lateral regions of the head. The origin of each of these muscles is in the so-called occipital region of the head, that is, behind the eyes. By the simultaneous contraction of these muscles (bm and bm’), the lumen of the esophageal bulb is enlarged, and the blood flows into the bulb from the pharynx, and, upon their relaxation, the elasticity of the chitinous walls of the bulb, drives the blood, which can not return to the pharynx because of the closing of the valve at v (fig. 11), into the stomach.
In the male.
“ The mouth-parts of the male of Culex have not been described, as far as I know, with any degree of accuracy, although, since Swammerdamm’s time, the
PROBOSCIS OF MALE 43
males have been distinguished from the females, by all scientific entomological ue on the subject, by means of their feather-like antenne and maxillary palpi.
“The proboscis of the male of Culex pipiens, the only species the male of which I have studied, is slightly longer and slenderer than the corresponding organ inthe female. The sete are fewer in number and less completely sheathed by the labium than in the female; they consist of a well-developed labrum-epi- pharynx and two slightly developed maxilla. The mandibles are absent, and the hypopharynx coalesces with the labium (fig. 12 h and /). The labium and maxillary palpi are more densely covered with hair and scales than they are in the females, and they contain muscles; the other mouth-parts, the sete proper, are naked, chitinous, and contain no muscles. In comparative length the mouth- parts may be arranged, longest first: maxillary palpi, labium and labrum-epi- pharynx, maxilla ;—in comparative size they may be arranged, largest first : labium, maxillary palpi, labrum-epipharynx, maxille. The relative position of the mouth-parts of the male is different from that in the female (compare figs. 8-9 with 13-15) in that the short, rudimentary maxille are pushed out sidewise to allow the hypopharynx to coalesce with the labium. In the male the cesoph- ageal pump, or bulb behind the nerve-ring, fails, and the sucking of fluids must be done by the pharynx alone, as it is done in most diptera.
“ The labrum-epipharynx is nearly the same in general form and structure in the male Culez as it is in the female, it is a trifle longer and slenderer, but the same figures (5, Ir-e, and 6) will serve for the tips of both. In section (fig. 12, lr-e), the labrum shows a groove on its upper surface, which deepens as it nears the base (fig. 13, Ir-e). The apical four-fifths of the labium contains no other seta than the labrum-epipharynx, as seen in fig. 12, which is a section at about the middle of the proboscis. At the base of the labrum-epipharynx are pharyn- geal muscles similar to those found in the female, and with similar insertions and origins, except that the median muscle (fig. 15, pm’) is not divided into three parts as in the female (fig. 9, pm’).
“ The hypopharynx is, throughout its whole length, joined to the labium, and thus necessarily pushes the maxille, which would normally lie between it and the labium, to one side. (See fig. 13, 4 and mz.) The hypopharynx shows, in section (fig. 18-15, h), the same chitinous rod through the middle as in the females, but I was unable to detect any channel for saliva through this rod.
“The maxille are very thin lamelle of transparent chitin, about one-fifth as long as the labium, and so delicate as to be easily overlooked. Although as broad at the base as is the tube of the epipharynx, they taper regularly from their base to their fine tips.
“The maxillary palpi are five-jointed, very hairy toward the tip, much longer than they are in the female, and when at rest their basal portions cover the labrum-epipharynx and maxilla in the sheath of the labium.
“The labium of the male Culex is similar in general structure to that of the female, if one considers it together with the hypopharynx. It is, however, slenderer, more densely covered with scales, has a shallower groove for the recep- tion of the labrum-epipharynx, and has a joint near the middle. The slender- ness of the labium in the male extends itself to the labelle. (Compare fig. 4, 1b, with fig. 3,7b). The groove of the labium of the male increases in shallowness from tip to base; at the middle of the proboscis (fig. 12) it is so shallow that it fails to fully protect the labrum-epipharynx, and at its base (fig. 13) it is so shallow that the other mouth-parts rest only on top of the labium. To make up for this deficiency of protection by the labium, the maxillary palpi, as was pre- viously mentioned, cover over the upper side of the enclosed parts (see fig. 13), and thus, although free from the labium, form a part of the protective sheath,
44 MOSQUITOES OF NORTH AMERICA
which, in the female, is formed by the labium alone. Whether the joint near the middle of the labium of the male Culex is true or false I cannot say, since I have never seen it bent by the insect itself ; its appearance is that of a true joint. Like the labium of the female, that of the male has two longitudinal main tracheal stems (figs. 12-14, tr), and two rows of longitudinal muscles.”
Kraepelin expressed the opinion that the labrum is not formed by the union of two pieces, the labrum and epipharynx, but that it is an evagination of the head and in consequence necessarily hollow. “It can therefore, as all body- appendages are evaginations and consequently hollow, impossibly be interpreted as the fusion of an upper and lower lamina.”
Becher was of the same opinion and states that the so-called epipharynx of the Diptera is never found as a free part; he calls the part the lower lamella of the labrum.
Meinert has traced the course of the salivary duct and found that it differs in the two sexes. His interpretation of the hypopharynx does not agree with that of Dimmock. In the female Meinert found that the salivary duct penetrates the posterior part of the hypopharynx; before entering it forms a large receptacle from the upper part of which a strong muscle extends to the under side of the pharynx. “In the male the hypopharynx does not protrude but is very short and rounded anteriorly and the salivary duct runs through the entire sheath [labium] along the under side of its floor until it terminates in the tongue.”
Wesché considers the hypopharynx of the male as long, like that of the fe- male, and the “ tongue” of Meinert, protruding between the labelle, as its apex. He speaks of the ciliation of the free apex, which he states to be present in all males, as “ a surprising reversion ”; perhaps it can be explained as readily as an adaptation to the feeding habits of the male. One gets the impression from Wesché’s paper that he believed that the hypopharynx is free in the male throughout its entire length ; such does not, however, appear to be the case. He figures the abnormal mouthparts of a male Anopheles maculipennis which ap- proach those of the female. Not only the mandibles and maxille are present, but also a free hypopharynx which extends to the tip of the proboscis.
The mandibles of Diptera are present only in the females of the blood-sucking orthorrhaphous forms. Becher, whose work has been criticized for its inexact- ness, states that two parts can usually be clearly distinguished in these organs: “a basal piece, which lies in the interior of the head, and the mandible proper, which can be moved upon this base by means of a joint.” None of the students who have followed exhaustive methods appear to have detected any such joint. Becher’s interpretation of the mouthparts is at variance with the commonly accepted homologies in various details but his paper is neither clear nor con- vincing. Furthermore, he commits the error of basing his views on studies of the mouthparts of the higher Diptera and interpreting the lower forms from this standpoint ; thus we can, with the more propriety, pass over a detailed considera- tion of his work. It may, however, be pointed out in passing, that while Becher Tightly, we believe, rejects the idea, held by some of the earlier authors, that the maxille and even the mandibles may enter into the composition of the labium
MEINERT ON MOUTH-PARTS 45
of the Diptera, he adopts Burmeister’s view that the labelle are homologous with labial palpi. None of the recent authors have concurred in this view. The three terminal lobes of the labium have been designated by Kellogg, who has given a very clear exposition of the mouthparts of the Nemocera, as, medianly the fused glosse, and, outwardly the paraglosse. This interpretation has been followed by Wesché and others. Other details, such as the attempts to find homologues of the components of the maxille and labium of mandibulate in- sects, can be passed over as purely hypothetical.
All the authors who have endeavored to homologize the mouthparts of the Diptera with those of the mandibulate insects have, with one exception, agreed » as to the fundamental parts, the labrum, hypopharynx, mandibles, maxille, and labium.
John B. Smith, in a paper published in 1890, took an entirely different view and defended this in a further paper which appeared in 1896. This interpreta- tion has been adopted in a recent popular book on mosquitoes. He used the mouthparts of certain highly specialized Hymenoptera and Coleoptera as a basis for his homologies. Smith found in Simulium, apically in the labrum, a pair of small dentate chitinous structures which he considered rudimentary mandibles ; these structures appear to be absent in all other nemocerous Diptera. He sup- posed, not only that the parts usually considered mandibles are maxillary, call- ing them lacinie, but that maxillary structures entered largely into the composi- tion of the labial sheath. The parts supporting the labelle are said to be part of the maxille, the subgalex, the labellee themselves the gale. The labium is rep- resented as a free piece, enclosed by the galeal structures, and the hypopharynx united with it. Smith’s work has been adversely criticized by the students of dipterous mouthparts and moreover bears clear evidence that it was based merely on rough dissections; only recently Leon, in a paper on Stimulium, discusses Smith’s homologies and points out the relationships of the parts in accordance with modern studies.
Meinert developed views at variance with all the other students and did not believe that the mouthparts of the Diptera are homologous with those of man- dibulate insects. While his interpretation is in the main controverted by the histological work of Kellogg, it still seems of sufficient interest for a brief notice, all the more as it has been generally ignored.
Like all other modern investigators Meinert recognized that generally the mouthparts of insects are homologous with the legs of the body and that, there- fore, they are the exponents of distinct metameres. He demanded, however, that to identify them with these, and those of the different orders of insects with each other, something sufficiently characteristic should be in evidence and he says:
“I find this in the presence of a metamere and in the free jointing of the ex- ponents to the under side of such a metamere, and according to this criterion I test, whether the mouth-parts (that is the mouth-parts proper, the paired ones) are homologous with appendages of the body on the one side, or among them- selves on the other.”
DEVELOPMENT OF MOUTH PARTS 47
adult insects of incomplete metamorphosis. There remains to determine the relations of the larval mouth parts of Simulium with its very different imaginal mouth parts.
“In selecting flies for the study of the postembryonic development of the mouth parts I have chosen two which in the imaginal condition possess all the parts possessed by any fly, and these parts in as generalized condition as is to be found in the order, and which also possess in the larval stage a similarly full complement of mouth parts. Such larvee as those of the Muscide, with their problematical hooks and lack of other parts, and such imagines as the muscid flies, with no parts left except proboscis and maxillary palpi, are impossible for the determination of the relation between larval and imaginal parts. From the mouth parts of the imaginal Simulium and of other nematocerous forms it is
Fic. 1.—Sagittal section through head of old larva of Simulium sp., showing forming imaginal head parts within.
i.¢., larval head wall; i.d., imaginal derm; l@., larval antenna; i.a., imaginal antenna ; 7.¢., imaginal eye; i.md., larval mandible; peer eae mandible ; l.ma., larval maxilla ; i.ma., imaginal maxilla ; 1.1i., larval labium; 4. ,» imaginal labium,
not difficult to trace the evolution to the specialized muscid conditions, and if the mouth parts of Simulium and similarly equipped flies can be interpreted, the various members of the dipterous series culminating in the muscids can. So in Simulium and Blepharocera I have found suitable forms for study ; both with females possessing the so-called mandibles, both with maxille and labium well developed in both sexes, and both with larve equipped with biting mouths with unmistakable mandibles, maxille, and.labia, and in one case, that of Simulium,. with the embryonic development of the larval mouth parts fully traced and the homologies certainly * determined.
’“ Simulium sp.—tn the female imago ¢ the mouth parts consist of a short liplike labium composed of a short basal sclerite and three terminal lobes, being the two large paraglosse and a median short membranous lobe, the fused gloss ; a pair of maxille, each consisting of a basal sclerite, a long five-segmented palpus, and a single pointed, bladelike terminal lobe reaching nearly to the end
* Metschnikov, E. Embryologische Studien an Insekten. Zeitschr. f. wiss. Zool., vol. xvi. 1866; embryonic development of mouth parts of Simulium described on pe. 392-421.
+ ‘In describing the adult mouth I shall assign to the various parts those names which, from my earlier study of the comparative anatomy, seem correctly used, and the use of which is confirmed by the results of this ontogenic study.”
48 MOSQUITOES OF NORTH AMERICA
of the third palpar segment, serrate on its inner margin at the tip and better developed than in most Nematocera; and a pair of short mandibles, broad, thin, and weakly chitinized. As in other nematocerous flies, there is a well-developed labrum-epipharynx and an elongate flattened hypopharynx. In the males the mandibles are wanting.
“Tn the larva the mouth is of the biting type, with short-toothed and heavy mandibles, short, jawlike maxilla with distinct one-segmented palpus, and a small, strongly chitinized labium or labial plate. In addition, labrum, epi- pharynx, and hypopharynx are all well developed. : :
“The head of the larva having a thoroughly opaque, strongly chitinized cuticle,
A
e \ § ae 7 il : % { id Lama.
Fic, 2.—Frontal section through the head of old larva of Simulium sp., show- ing forming imaginal parts.
lc., larval cuticle; ¢.d., {maginal derm; I.md., larval mandible; ¢.md., imaginal mandible ; Lme., larval maxilla; t.ma., imaginal maxilla; l.ma.p., larval maxillary
palpus; Lhyp., hypopharynx.
it was impossible to clear whole heads sufficiently to make visible the develop- ing imaginal head and its parts, so that the method of sections had to be relied on to reveal the internal conditions. These sections of heads of larve of various ages show plainly that the general method of development of the imaginal parts within the larval head, and the correspondence between forming imaginal parts and the corresponding larval parts already noted in the other orders of holo- metabolous insects, hold good in the Diptera. Fig. 1 shows in sagittal longitud- inal section the forming imaginal head parts within the larval head. This sec- tion shows particularly well the relation of the forming imaginal antenna to the larval antenna. In the larva the antenne are very small compared with their size in the imago, and the imaginal antenna is thus forced, in its development, to occupy a region in the larval head not included in the larval antenna. But the tip of the imaginal organ lies fairly within the larval organ, thus indicating by correspondence in position, what is plainly obvious from anatomical considera- tion, the homology between the larval and imaginal organs. Similarly the forming imaginal mouth parts are to be found in unmistakable correspondence or homologous relation with the larval parts. By tracing the development of the parts, marked in fig. 1 as the forming imaginal mouth parts, through larve
MODIFICATIONS OF MOUTH-PARTS 49
of successively older ages to pupation and the achievement of the definitive imaginal condition of these parts, it is certain that the parts marked respect- ively imaginal mandible, imaginal maxillx, and imaginal labium, lying respect- ively in the larval mandibles, maxille, and labium (with homologies firmly based on ontogenic basis) , do develop into those definitive imaginal parts named mandibles, maxille, and labium. ... Fig. 2, a horizontal, frontal section through the head of a Simulium larva, shows also the forming imaginal maxilla and mandibles within corresponding larval parts.”
Wesché has found that abnormal male Culicids occur with all the trophi present, as in the females, although in these cases the maxille and mandibles did not extend to the tip of the proboscis. Such males, to conclude from Wesché’s work, appear to be not uncommon. Examining a number of males of different species, he found an abnormal Anopheles and also a male Culex pipiens with all the parts present.
It would seem that the mandibles and maxille may be absent in the female of certain species which do not suck blood. Such appears to be the case with the female of Harpagomyia splendens, recently described by De Meijere. This curious Javan species feeds upon honey which it obliges the ant, Cremastogaster difformis, to disgorge. In this mosquito the hypopharynx is free, as usual, but appears to lack the salivary duct. It is interesting to note that early in the pupal stage both mandibles and maxille can be readily seen in the developing imago. These gradually retrograde, until, by the end of the pupal period, they have become wholly atrophied, just as has been shown to occur in the develop- ment of the males of the blood-sucking forms.
While the external appearance of the proboscis is frequently described, we know practically nothing of the modifications of structure in the different species or genera—Wesché states that in Anopheles the mandibles are serrated at the tip. The sheath of the proboscis shows much variation in length and diameter in the different species and it is frequently expanded towards the apex. The labellz also show much difference in shape and in details of structure but these need not be described. In Megarhinus the sheath is unusually rigid, tapering, becoming very slender at the tip, and the labelle are narrow and much elongated. In this genus, in which both sexes feed wholly upon the honey of flowers, the labium can not be bent as it can in the forms which suck blood.
In the males of many species the sheath of the proboscis shows a suture out- wardly from the middle. Usually it is indistinct, but in the male of Deinocerites there are chitinous margins connected by a membranous strip as in a true joint. Its significance is not clear; perhaps it indicates the limits of the true labial structures. It may be mentioned in this connection that Meinert considered the sheath of the proboscis as of composite origin and formed mainly by the greatly produced portion of that part of the head which he considers the ventral plate of the first metamere.
It has already been shown that there is a salivary duct in connection with the hypopharynx. Macloskie found that there were two sets of salivary and poison glands in connection with this duct. The glands are situated in the anterior ventral part of the thorax and each set consists of three glands, two of which
50 MOSQUITOES OF NORTH AMERICA
are ordinary salivary glands and the third, between the other two, differs in ap- pearance and structure and secretes the poison. Each set of glands discharges into a very fine duct and these ducts unite in the back of the head and continue forward as a single duct through the ventral region of the head. Macloskie’s studies were made with Aédes teniorhynchus and a species of Anopheles.
At the base of the hypopharynx is the salivary pump into which the salivary duct empties, to be continued beyond it into the hypopharynx. Macloskie failed to recognize its true character and called it the salivary “ reservoir.” Its true character appears to have been first recognized by Annett, Dutton, and Elliott. The organ is fully described by Nuttall and Shipley, from whom we quote. As yet the organ has only been demonstrated in Anopheles.
“. .. The structure is more than a receptacle, it constitutes a pump, the mechanism of which corresponds to that of the pharyngeal pump in a sense, that is, it depends upon the action of powerful voluntary muscles which overcome the elasticity of a chitinous membrane which, when released by the muscles becom- ing relaxed, rebounds or returns to its original form, as a bow does when the pull on the bow-string is released. . . . It will be seen then that the common salivary duct ends (lumen 5) in the centre of the chitinous membrane, the junction be- ing strengthened by a chitinous thickening of annular form. The membrane is continuous with a highly chitinized cup, which tapers anteriorly, and is continu- ous with the hypopharynx, an opening therein connecting it with the groove described above. . . . Spicules of chitin occur about the duct on the pump- membrane, these serving for the attachment of the powerful muscles presently to be described. The thickened chitin surrounding the membrane is flattened on its dorsal surface which is applied to the floor of the buccal cavity. The pump-membrane is covered in the centre by the insertion of two stout bundles of muscle-fibres which pass backwards, parallel with one another, to their origin on the anterior surface of the chitinous flange which projects ventrally from the floor of the buccal cavity. When the muscles contract a partial vacuum is produced within the cup, saliva flows in from the glands, and when they relax the membrane rebounds forward, driving the saliva out of the cup into the salivary channel along the hypopharynx.”
Leon, who investigated this organ independently, gives a description at vari- ance with that of Nuttall and Shipley. He found that the salivary duct empties, not into the center of the posterior membrane of the cup, as described by Nuttall and Shipley, but into the side of the chitinous cup. The pumping device Leon describes as follows:
“The mouth of the cup, which is directed posteriorly and ventrally, is covered by an elastic chitinous membrane which is pushed back into the interior of the cup like the bottom of a champagne-bottle. Outside, in the middle of this mem- brane, a chitinous piston-rod is attached. This has the form of a round concave- convex disc and is more darkly colored ; the convex side of the disc is attached to the elastic membrane, while in the middle of the concave side the rod is fixed. . . . The posterior end of the rod is thickened and muscles are attached to it.”
THE PALPI.
The palpi, as they appear in both sexes of Culea, have been described in the foregoing in connection with the other mouthparts. Great diversities of opinion have been expressed by the different students as to their structure and
MAXILLARY PALPI 51
the number of the joints. They show great diversity in the different genera and in the species. They differ greatly in length, in shape, and in the number of joints. The relative length of the palpi, without reference to the number of joints, has been generally considered as a character of primary importance in classification. Beyond that there has been general disagreement as to the number of component joints. Dimmock, whom we have quoted, considered the palpi of Culex pipiens as four-jointed in the female, five-jointed in the male. Meinert states for the same species, three-jointed in the female, four-jointed in the male. Both these authors found that in other species a small additional joint was present in the females. Ficalbi considered that in Culex the palpi of the female are three to four-jointed, those of the male three-jointed. Wesché considered the palpi four-jointed in both sexes. Felt states that in most Culicide the palpi are five-jointed in both sexes, except in certain females “ when the rudimentary fifth appears to be wanting.” Theobald, in Genera Insectorum, states that the palpi of the Culicide have from one to six joints.
The idea that the number of joints in the palpi is constant within groups and of great classificatory importance has been very generally accepted. The state- ment that the palpi of the Nemocera are four or five-jointed, which originated with Latreille (1809), has been widely followed with but little modification. Becher considered the palpi of the Nemocera four-jointed and called the basal part “ Tasterschuppe,” the equivalent of the palpifer, or, in its absence, of the maxillary stipes. Williston, in the introduction to his Manual of North Ameri- can Diptera (third edition, 1908, page 26), states of the palpi of the Diptera:
“ Perhaps the most important of all the mouth-parts, from the systematic standpoint, are the maxillary palpi. . . . They are variously described as being composed of from one to five joints. There are never more than four articulated joints, the basal joint being merely a process of the plate bearing the maxille. The tendency in diptera is toward their entire loss, and in the more highly specialized families there is never more than one joint.”
Farther on (p. 65) he says of the Nemocera: “ Palpi usually more or less elongate, composed of from one to five, usually four, joints, rarely absent.” While there is undoubtedly a reduction in the palpi parallel with specialization, this reduction has taken place independently at different points, and, except in a very broad way, the palpi can not in themselves be considered as a safe index of relationships. The ideas of systematists have been based largely upon the study of a few typical forms, and no attempt appears to have been made to test their constancy within a family. In fact, within the Culicide the palpi may be said to be remarkably unstable in character. They range all the way from forms with several well-defined joints, as Anopheles, to forms in which they are re- duced to a small club-shaped organ without trace of jointing. In fact, the homologizing of the palpal joints of the different forms, which Felt attempted to carry out, assuming five joints for the more generalized forms, is beset with pe- culiar difficulties. The conditions in the basal portion of the organ, which have generally been considered as true joints, are not clearly defined or sufficiently. uniform within the group to be so interpreted. We have not found any mos-
52 MOSQUITOES OF NORTH AMERICA
quitoes in which either one or both of the two supposed basal joints are differ- entiated in such a manner that they may be called true joints. We doubt that these correspond to the two basal joints of the four-jointed palpus of the more primitive Chaoborus; the integument is of the same character throughout, simply that there is less chitinization at the “ joints.” Furthermore, it does not seem plausible that joints would tend to disappear at the very point where they would be most in use and most needed.
Should we accept the two basal modifications as true joints, we would then have, in the female Anopheles, which has in addition three well-defined joints, mosquitoes with six-jointed palpi. If, on the other hand, we carry out strictly the idea that these basal joints are secondary modifications, we must consider all that part of the palpus below the first true joint as a prolongation of the basal structure and a part of the maxilla itself. Thus we would have to con- sider the first “ long joint ” of Anopheles, there being no jointing apparent at the base of the palpus, as belonging to the basal structure. The palpi of Anopheles would then be three-jointed in the female, two-jointed in the male. In the normal Culex pipiens there would be but a single true palpal joint in the female, two in the male. In the higher forms, where there has been a reduction to a club-shaped organ, this appears to have been produced, not by fusion of the joints, but by their loss. This unjointed club would then represent the basal structure.
This process of reduction, first in the length of the joints, then in their num- ber, can in fact be traced progressively through the genera and species of mos- quitoes. The arrangement we have adopted in our classification, although it was founded upon other characters without reference to the palpi, follows very closely this process in the two tribes. It is interesting to note that this reduction has been the most rapid in the female, where the functions of the mouth-organs are of the most importance, and that in the majority of species the palpi of the male show the more primitive condition. Thus Anopheles, in which the palpi are long in both sexes and show several joints, is to be regarded as the most primitive mosquito, while such forms as Uranotenia and Sabethes, with greatly reduced and unjointed palpi, must be considered highly specialized.
We have already, on a previous page, called attention to the view of Meinert, apparently supported by Kellogg’s histological work, that the palpi of the Diptera are not homologous with the maxillary palpi of other insects but are rather modifications of the maxille themselves. As this view has some bearing on the interpretation of these organs and the number of joints, we quote Meinert in part:
“.. . The palpi are regarded by everybody as corresponding to the maxillary palpi of the other insects; but I shall here make some comments on this. The maxillary palpi always originate from a maxillary trunk, which, through an intermediate joint, the cardo, springs from the metamere. They are, in other words, only the outer joints (corresponding to the foot of the exponent. In the Diptera, on the other hand, the palpi originate directly from the metamere;
and while in the several-jointed palpi the first joint might be regarded as a modified cardo, and consequently the outer joints of the palpi as homologous
REDUCTION OF PALPI 53
with the maxillary palpi, it is different when the palpi consist of only two, or even of a single joint, as is the rule in the Diptera, for there will then be no joint left to explain as maxillary palpus. I therefore prefer to regard the palpi of the Diptera as homologous with the entire maxille of other insects, only that they are oftenest unjointed and not divided into different components. Only in Simulium, Tipula, and Limmobia I have thought to find an indication, in the before mentioned appendix at the base of the palpi, of the different working divisions of the exponents of the second metamere of other insects.”
The palpi are variously modified in the different forms. In Anopheles and in the males of a great many other forms the palpi about equal the proboscis in length, or even exceed it. In most of these forms the palpi are slender, particu- larly in their proximal halves, and furnished with false joints to increase their flexibility so that they can be folded back when the insects are feeding.
In Megarhinus, however, where the palpi are less in the way, on account of the downward-curved proboscis, they are stout and quite rigid, without basal false joints, and the joints are armed near their apices with heavy spines. In the males of Anopheles and of most species of Culiseta the palpi are enlarged apically into a distinct club. In Anopheles the club is composed of the outer two joints, while in Culiseta it may be composed of these same two joints or of the last joint alone.
In the males with long palpi of many species of Culex and Aédes the outer half of the palpi is more or less thickened and densely hairy, the last joint, how- ever, generally tapering to a point; the last two joints are usually curved upward.
In Megarhinus and Bancroftia we begin to get a reduction in the female palpi, and this occurs principally in the terminal joint. In the American species of Megarhinus the palpi of the female are about two-thirds the length of the pro- boscis, while in the Old World species of this genus the reduction has gone still farther and they are sometimes less than one-fourth the length of the proboscis. In the females of both the New and the Old World species of Megarhinus there is a minute terminal joint, and the number of joints is the same.
In Bancroftia the palpi of the female are about two-fifths the length of the proboscis, the terminal joint small; in the case of one species (B. fascipes) the terminal joint is about three times as long as wide, in another (B. signifer) it is nearly globose. In the male of this last-named species, although the palpi are as long as the proboscis, the last joint is similar in character to that of the female.
In the males of most species of Aédes and of Culex the palpi are longer than the proboscis, curved upward, their outer halves densely hairy, the last joint long and tapering. In certain species of Aédes the palpi of the male are slightly shorter than the proboscis, straight, less hairy, the last joint long but blunt at the tip. In Aédes fuscus the palpi of the male are very short, in fact shorter than those of the female, and the terminal joint is indicated by a flattened tubercle. In the related genus Stegoconops the reduction of the male palpi has. become more general. In S. equinus the palpi of the male are about three- fourths the length of the proboscis ; in S. albomaculatus the palpi are practically alike in the two sexes, short and with a minute terminal joint.
5
54 MOSQUITOES OF NORTH AMERICA
In certain species of the genus Culea a similar reduction of the male palpi is found. In Culex latisquama the palpi of the male are about half as long as the proboscis. The reduction is in the apical portion; the apical joint is sub- globose, the one supporting it is less than three times its own diameter in length. In the female of this species the palpi are about one-fourth the length of the proboscis, but, as in the male, have a minute terminal joint. In Culex bisul- catus the palpi are slightly less than half the length of the proboscis in both sexes. In the female there is a single true joint, which makes up more than half the length of the entire palpus. In the male we have been unable to dis- cover any differentiated joint except the minute terminal one.
In Uranotenia reduction has gone to the extreme. In both sexes of U. sap- phirinus the palpi are very small, projecting but slightly beyond the clypeus, club-shaped and unjointed.
In the females of most Culicini the palpi are short, although differing much in length and configuration in the different species. They consist of a basal portion, which in most cases shows a triple false-jointing ; beyond this there is a stout joint and in many species this bears at its apex another minute joint. Sometimes there is even what appears to be a second minute joint, inserted upon the other, but this is with little doubt produced by constriction of a single joint. Such a condition exists in Mansonia fasciolatus, as has already been indicated by Neveu-Lemaire, It may also occur as an abnormality, as in the case of a female Culiseta annulata figured by Dyé and Neveu-Lemaire. In the species in which the minute terminal joint is usually absent specimens may occur with this joint present. Dyé and Neveu-Lemaire describe such palpi in a female Oulex pipiens. We have a Culex tarsalis with the same abnormality.
In Deinocerites and Dinomimetes the palpi are short in both sexes, but show considerable diversity of structure in the different species. In Deinocerites pseudes female there is a distinct terminal joint, more than half the length of the entire palpus. In the male of this species there is in addition a minute apical joint. The palpi of the male D. troglodytus are similar but the apical joint is still more minute, while in the female there is no distinct jointing. The palpi of D. cancer are unjointed in both sexes. In Dinomimetes epitedeus there is a single joint in both sexes.
In the group of Sabethini the reduction of the palpi is far more general and in most species these organs are short and unjointed in both sexes. In the forms examined the female palpi always proved unjointed, and although only a few forms have been studied it is evident that such is the rule in this group. In Joblotia digitatus the palpi are long and slender in the male, distinctly jointed ; in the female the palpi are short and unjointed. In Lesticocampa the palpi are very slender. They may be long or short in the male, according to the species, but they are jointed like those of the male Joblotia. The palpi of the female, as in other sabethids, are unjointed.
STRUCTURE OF THE THORAX +599)
THE THORAX,
The terminology of the parts of the thorax of mosquitoes is very confused and shows that its structure has not been generally understood. We, on this account, requested Mr. R. E. Snodgrass, formerly of the Bureau of Entomology, U. 8. Department of Agriculture, who has made a study of the homologies of the thorax of insects of different orders, to prepare the following study, with figure, of the thorax of a mosquito, Psorophora ciliata (see plate IIT).
The thorax of the mosquito is conspicuously wedge-shaped, the base being uppermost and forming the large rounded dorsum of the thorax. The triangular sides form the pleura, while the apex is ventral and carries the legs. The wings (w,) are inserted on the upper parts of the sides much behind the middle, so that the greater part of the thorax is in front of them, but the balance of the entire body is preserved by the long, slender abdomen extending posteriorly. The second wings are represented by the halteres (w,) which, of course, take no part in the mechanism of flight. Consequently the great muscles of the meso- thorax alone afford the motive power of flying. The active function of the pro- thorax and the metathorax is the support of the front and hind legs. Hence, both of these segments consist of little more than anterior and posterior collars against the great mesothoracic mass. The consolidation of the three segments is so complete that many entomologists find it difficult to define their limits with certainty.
Two conspicuous points on each side of the thorax are the spiracles (1Sp and 2Sp). Hach is a large black-rimmed aperture situated in a membranous area, one near the middle of the anterior half of the side, the other somewhat behind the middle of the posterior half. Since, in most adult insects, these thoracic spiracles are situated in the intersegmental membranes, it is a difficult matter to decide to which segment each belongs. The second is nearly always regarded as metathoracic, but entomologists are divided in opinion as to whether the first is mesothoracic or prothoracic. Amongst morphologists, however, the first view seems to have the greater support. However, this question is of little importance for the more practical needs of the systematist, who may avoid the difficulty by referring to them simply as the first and second thoracic spiracles.
The Prothorax.—tThe lateral walls of this segment consist of three plates (T,, Eps,, and Epm,). Closely associated with them is a large cervical sclerite (mt) lying on each side of the neck and forming a support for the head an- teriorly. The most conspicuous of the prothoracic plates is the prominent oval lobe (T,) beneath the projecting anterior end of the mesotergum. This very probably is a lateral part of the protergum, for it is connected by a median narrow transverse bridge in front of the mesotergum with the corresponding part of the opposite side. These two lobes are called “ patagia” by Christophers, a name properly belonging to the prothoracic tergal appendages of Lepidoptera, but of doubtful propriety when applied to similar parts in the mosquito, because there can be no homology between them. Connected with the lower end of the protergal lobe is a stalk-like piece which expands ventrally into a larger plate
EXPLANATION OF Puiate III.
The individual segment of the thorax to which any part belongs is indicated by the
small figure placed behind and below its symbol.
The abdominal segments are
distinguished by Roman numerals placed before the symbols of the parts. Arabic numerals placed before symbols signify numerical order of repetition. r
Ant, antenna.
Ax, axillary cord of wing base.
Clp, clypeus.
Cx, coxa.
CzP, pleural coxal process.
E, compound eye.
Epm, epimerum.
Eps, episternum.
eps,, detached part of episternum of mesothorax.
Lb, labium.
mi, cervical sclerite.
MzPlp, maxillary palpus.
P, parapterum.
PN, postnotum (postscutellum).
Prb, proboscis.
PS, pleural suture.
psc, prescutum.
8, sternum.
scl, scutellum.
sect, scutum.
Sp, spiracle.
T, tergum.
W., wing.
W,, halter.
WP, pleural wing process.
a, small plate of mesopleurum bearing articulation of coxa.
b, accessory plate of mesoepimerum.
c, lower part of metapleurum.
56
PLATE Ill
PUBLICATION 159
- 4 ep
Ulcer,
fi 1 Le
hi fi Lit
Seen
Drawn by R:
E, Snodgrass. Thorax of Psorophora.
MESOTHORACIC STRUCTURES 57
(Eps,) above the base of the front coxa (Oz,), and which is connected by a transverse arm with the prosternum. (The last is not visible in side view.) The third prothoracic plate (Hpm,) lies behind and above the other two and is much larger than either of them. It extends posteriorly almost to the first spiracle (1Sp) and sends a narrow strip downward to the precoxal membrane. It might be questioned whether this plate does not really belong to the meso- thorax, but a little comparative study of other flies will make its morphological relations clear. It will be observed that in Psorophora the anterior coxa is not directly articulated to the side of the prothorax, being connected with it only by a wide membrane. In most other flies, however, it is articulated in normal fashion to the propleurum, at the ventral end of the pleural suture. In the lower flies this suture separates two distinct pleural plates—the episternum and the epimerum. In Tipula the first spiracle is much farther forward than in the mosquito and lies on a line which is clearly the boundary between the prothorax and the mesothorax, the epimerum of the prothorax being in no way expanded or specially developed. In Bibdio the first spiracle is farther back than in Tipula and the epimerum is much extended posteriorly. In Psorophora, finally, this character is still more exaggerated, the first spiracle being halfway between the base of the wing and the front of the mesotergum, while the epimerum of the prothorax forms a large lobe reaching posteriorly to the spiracle, though its ventral extremity is reduced to a narrow band close to the posterior edge of the plate in front. The latter (H#ps,) we can, therefore, identify as the episternum, and the line (PS,) between the two plates as the pleural suture. The only dis- tinctive character in the prothorax is, therefore, the separation of the coxa from its pleural articulation.
The plate (eps,) lying below and behind the spiracle is separated only by a weak line from the proepimerum, but for reasons to be given later it is regarded as belonging to the mesopleurum.
The prosternum consists of a transverse plate lying in front of the bases of the coxe, connected laterally with the episterna, and having a median posterior in- tercoxal extension fused with the anterior sternal part of the mesothorax.
The cervicum or “ microthorax” is represented by the two lateral cervical plates (mi) already mentioned. The two are connected with each other ven- trally by uniting transverse arms.
The Mesothorax.—This segment, in the mosquito, forms the great bulk of the entire thoracic mass. The anterior end of its tergum projects over the top of the head and the posterior end is separated from the abdomen only by the narrow metatergal bridge (7',). As in nearly all insects the mesotergum consists of two principal plates, a large anterior one (psc,, sct,, and scl.) constituting the true notum and carrying the wings, and of a smaller posterior postnotal plate (PN,) lying between the first and the metatergum and connected laterally with the epimera of the mesopleura. The first plate is indistinctly divided into a prescutum (psc,), a scutum (sct,) and a scutellum (scl,). The second plate constitutes the postnotum, usually termed postscutellum in the higher orders. On account of the posterior location of the wings and the narrowness of their
58 MOSQUITOES OF NORTH AMERICA
bases, both of the notal wing processes, 7. ¢., the lateral lobes of the notum to which the wings are articulated, arise near the posterior end of this plate. The first belongs to the scutum, the second to the scutellum. The scutum bears also a small lateral lobe (w) between the front spiracle and the base of the wing. The axillary cords (AxC), which form the corrugated cord-like thickenings of the posterior margins of the basal or axillary membranes of the wings, arise from the posterior margin of the scutellum. They thus mark the posterior limit of the true notum as distinguished from the postnotum, though the two plates are separated from each other by a membranous