Mosquitoes of the Northwestern States

UNITED STATES DEPARTMENT OF AGRICULTURE Agriculture Handbook No. 46

WASHINGTON, D. C ISSUED NOVEHBBB 1951

MOSQUITOES OF THE NORTHWESTERN STATES

By H. H. STAGE. C. M. GJULX.IN and W. W. YATES, Entomologists

Division of Insects Affecting Man and Animals Bureau of Entomology and Plant Quarantine Agricultural Research Administration

For «al« b7 tli« Snpcrintendmt of Docmneiita, Washiixton, D. C. - - Prie« 35 cents (Paper Corar) This handbook deals with the mosquitoes recorded from the three Northwestern States—Oregon, Washington, and Idaho. It brings together widely scattered information on 39 species and subspecies, including descriptions and keys for identifying the species and notes on the several associations of species and their biology, their economic importance, distribution, and methods of control. The handbook has been prepared as a companion to Miscellaneous Publi- cation 336, The Mosquitoes of the Southeastern States (83). The control methods recommended here differ considerably from those in that publication because many new insecticides have been developed since it was last revised. Culex tar salis y the most widely distributed mosquito in the Northwest. It breeds in the widest variety of waters and is one of the most potent transmitters of western equine encephalomyelitis and St. Louis encephalitis. UNITED STATES DEPARTMENT OF AGRICULTURE Agriculture Handbook 46

WASHINGTON, D. C. ISSUED NOVEMBER 1952 MOSQUITOES OF THE NORTHWESTERN STATES

H. H. STAGE, C. M. GJULLIN, and W. W. YATES, entomologists, Division of Insects Affecting Man and Animals Bureau of Entomology and Plant Quarantine Agricultural Research Administration i

CONTENTS Page Page Mosquito literature 2 Associations of species in the Northwest—continued Mosquito-control associations and Tidal water 23 abatement districts in the Log ponds and water in United States artificial containers 24 General characteristics and habits Mosquito control 24 of mosquitoes Surveys 24 Life History Hand collections 25 Eggs Trap collections 26 Larvae Collections of larvae ...... 28 Pupae Collections of eggs 29 Adults V Engineering surveys 30 Longevity Control of larvae 30 Flight Elimination of breeding places 30 Collection and preservation of Use of larvicides 37 specimens Materials for controlling Identification of species mosquito larvae 39 History of mosquito control in the Control of adults ;.. 39 Northwest Repellents 39 Space sprays 40 Genera and species found in the Residual sprays 42 Northwest 10 Control of resistant mosquitoes 43 Mosquitos and disease 12 Equipment for applying Malaria 12 insecticides 44 Natural enemies of mosquitoes 44 Encephalitides 14 Keys and notes for identifying Associations of species in the mosquitoes of the Northwest 45 Northwest . 15 Key to genera 45 Floodwater 18 Genus Anopheles Meigen .... 49 Rain pools 19 Genus Aedes Meigen 53 Snow water 20 Genus Mansonia Blanchard . . 75 Tree holes 22 Genus Culex Linnaeus 75 Irrigation water 22 Genus Culiseta Felt 79 Permanent ponds 23 Bibliography 87 1 Grateful acknowledgement is made of the aid given by E. F. Knipling, who was in charge of mosquito investigations in the Pacific Northwest from August 1, 1940, until April 1, 1942, and who later, as chief of the Division, gave invaluable council. Thanks are due also for data contributed by A. W. Lindquist, R. A. Hoff- man, and A. R. Roth, of the Corvallis, Greg., laboratory. HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE MOSQUITO LITERATURE ment districts. It gives information on laws and agencies for 'T^HE literature on mosquitoes mosquito abatement, education of A has become exceedingly large. the public, general principles of Each year about 1,000 references abatement methods and tech- to various phases of mosquito niques, abatement of disease vec- biology and the diseases they tors, and a host of related data. carry appear in widely scattered The Engineering News Record publications. Probably no other (25) has issued a series of short group of insects has received so papers on the engineering aspects much study throughout the world. of mosquito control. Some of the publications of espe- For those concerned with the cial interest to workers concerned manipulation of water levels in with mosquitoes in the Northwest the control of malaria and mos- are given at the end of this hand- quitoes, a publication by the book (p. 87). United States Public Health Serv- One of the earliest comprehen- ice and the Tennessee Valley Au- sive works on any group of in- thority (162) is indispensable. sects is a four-volume monograph Although the information is fo- by Howard, Dyar, and Knab cused on malaria control, the (68), issued in 1912-17. It in- possible field of application is far cludes descriptions, biology, dis- broader as it may be of great use tribution, and taxonomy of mos- in the development of water re- quitoes in the Western Hemis- sources, pow. r, and irrigations phere north of the equator. in the Northvest. Matheson's handbook (99), re- Several Strie bulletins and a vised in 1944, gives much infor- Canadian report will be found mation on the taxonomy and bi- particularly useful in a study of ology of the mosquitoes of North the mosquitoes in the North- America and includes a discus- west : California, by Freeborn and sion of their relation to human Bohart (SO) ; Montana, by Mail welfare and problems of control. (97) ; Utah, by Rees (111) ; Ore- More recently, in 1949, Car- gon, by Yates, Lindquist, and penter, Middlekauff, and Cham- Mote (17Í) ; the Lower Fraser berlin (13) published an authori- Valley of British Columbia, by tative book of nearly 300 pages Hearle (58). A guide for identi- covering the taxonomy and bi- fying mosquitoes of the Pacific ology of species found in the Coast States, by Freeborn and Southern States east of the Mis- Brookman (81), contains unique sissippi River. but valuable keys. In another book that appeared The following serial publica- in 1949, Marston Bates (17) has tions will be of interest to stu- compiled a voluminous array of dents of Culicidae: Mosquito facts on the biology and disease News, published quarterly by the relationships of mosquitoes, American Mosquito Control As- which will be very valuable to all sociation at Albany, N. Y., and students specializing in mosquito the proceedings published each research and control. year by the New Jersey Mosquito A textbook by Herms and Gray Extermination Association, the (62) is designed primarily for California Mosquito Control As- entomologists, engineers, and sociation, the Florida Anti-Mos- staff employees who are directing quito Association, and the Utah the activities of mosquito-abate- Mosquito Abatement Association. MOSQUITOES OF THE NORTHWESTERN STATES Articles on mosquitoes also ap- The California Mosquito Control As- sociation, organized in 1932. pear in bulletins and reports of The American Mosquito Control the United States Public Health Association, Inc., organized in 1936. Service and in various entomolog- The Virginia Mosquito Control Asso- ical, medical, and other scientific ciation, organized in 1947. The Utah Mosquito Abatement Asso- journals throughout the world. ciation, organized in 1947. For a number of years articles The Illinois Mosquito Control Asso- on various phases of the biology ciation, organized in 1948. and control of anopheline mos- Each of these associations quitoes appeared in the Journal holds annual meetings, and most of the National Malaria Society. of them publish their proceed- This society has now amalga- ings, which contain valuable con- mated with the American Society tributions on mosquito biology of Tropical Medicine to become and control. the American Society of Tropical The American Mosquito Con- Medicine and Hygiene, and its trol Association is international journal includes papers on rnos- in scope and has a membership quitoes and their disease relation- of about 1,000. It is a nonprofit ships. technical and educational associa- MOSQUITO-CONTROL ASSOCI- tion of mosquito workers, com- ATIONS AND ABATEMENT posed of entomologists, sanitary DISTRICTS IN THE UNITED engineers, control officials, med- STATES 'j ical personnel, and laymen who There are sevm mosquito- are charged with or are inter- control associations 4n the United ested in mosquito control and States (1.Í0), as follows: related work. Annual meetings The New Jersey Extermination Asso- are held in various parts of the ciation, organized in 1913. The Florida Anti-Mosquito Associa- United States, usually conjointly tion, organized in 1929. with the State associations.

MALARIA AND PEST MOSQUITO CONTROL OPERATIONS IN UNITED STATES

MALARIA MOSOUITO CONTROL (Public H«alth S*rvl«*) U&an« STATE MOSQUITO CONTROL DISTRICTS

M.SA. Wwt.H»0. U. i. DCMRTMCNr OF ACmCUkTURC FIGURE 1.—Map of the United States showing location of mosquito-control operations, 1950. HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE There are about 250 local mos- three States, whereas Aedes hexo- quito-control agencies in 39 dontus is found only in snow States, Hawaii, and Puerto Rico water in high mountainous areas (fig. 1). These agencies are com- {27). Some genera, such as monly called mosquito-abatement Aedes y lay their eggs on ground districts and are usually named that may later be flooded, where- after the counties in which they as others, such as Culex and Culi" are located. In 1951 Florida had seta, lay them directly on the 21 such districts, with a total water surface. budget of about $985,000; Cali- Temperatures of air and water, fornia 44, with over $1,700,000; alkalinity or acidity of the water, New Jersey 16, with $640,000; and associated shelter and vege- Utah 4, with $117,000; Virginia tation aiïect the abundance and 13, with $178,000; and Rhode presence of most species. The Island 18, with $76,000. A total species also differ in biting hab- of more than $6,000,000 is bud- its, longevity, and flight range. geted annually in the fight The mosquito is an insect hav- against pest mosquitoes and ma- ing a complete metamorphosis. laria. Over 26,000,000 people in There are four well-defined stages the United States live in areas —^the egg\ the larva, sometimes protected from mosquito annoy- called wiggler; the pupa or tum- ance. During the last few years bler; and the adult or imago. Federal and State health agencies have treated more than 800,000 LIFE HISTORY homes with residual sprays annually for the control of malaria EGGS mosquitoes. The eggs may be laid singly as with the anophelines, or in rafts GENERAL CHARACTERISTICS of about 150, as with the culi- AND HABITS OF MOSQUITOES cines. In very warm weather the The characteristics and habits eggs may hatch within 2 or 3 of mosquitoes in the Southeastern days after they are laid. In north- States as described by King and ern latitudes, however, eggs laid CO workers (8S) apply generally by Aedes in the late summer do to species found in the North- not hatch until flooded the fol- western States. lowing spring. If not flooded the Although mosquitoes have ex- first season they may remain tremely diverse breeding habits, viable for several years (^5). particularly the type of place There is still some question as to they select to lay their eggs, all whether northern Aedes eggs re- have one important characteristic quire a certain amount of drying in common—^they live part of and exposure to cold before they their life in water and in water hatch or, as we believe, a low only. It may be in a small tin can oxygen concentration (^0). A or in a vast tidal marsh. blood meal has been considered Some species are found through- necessary for the production of out the Northwest and in different viable eggs {70), although among types of water. Others are found some of the northern Aedes this only in restricted areas and in one has not been definitely established. kind of water. For example, Culex tarsalis has been collected LARVAE in almost every kind of water All mosquitoes spend their in nearly every county of the larval and pupal stages in water, MOSQUITOES OF THE NORTHWESTERN STATES and most of them move freely ADULTS about as aquatic insects. Without Only the female mosquito has water these stages cannot survive mouth parts adapted for blood- more than a few hours. The sucking. While the insect is bit- larvae of most species must come ing, it injects a secretion that is to the water surface for air, responsible for the itching that which they obtain through an air follows. Not all mosquitoes have tube or other appendage located bloodsucking females, but all at the end of the "tail.'' The those found in the Northwest do larvae shed their skins four have. times, and each instar is larger The mouth parts of male mos- than the last. The larval stage quitoes are not strong enough for usually lasts from 4 days to 2 biting. Their food consists of weeks; in icy-cold water some pollen and of fruit and other Aedes mosquitoes may remain as plant juices. In the laboratory we larvae for a month or more. The have kept alive both sexes of larvae of Aedes varipalpus occur- some species for long periods on ring in tree holes and those of raisins, fruit juices, and sugar Mansonia perturbans attached to the roots of aquatic plants over- solutions. winter, and hence may exist as larvae several months. LONGEVITY The food of mosquito larvae consists of tiny plants, animals, The length of life of adult mos- and organic debris. Some species quitoes under natural conditions prey on the larvae of other is difficult to determine, but for species and some are cannabilis- most of the northwestern species tic. Barber (6) has reared larvae it is probably only a few weeks on pure cultures of various or- in spring and early summer. ganisms, and Hinman (63) has We have studied the longevity suggested that materials in solu- of Aedes vexans and sticticus tion or colloidal suspension in the by staining swarms of newly breeding water form a part of emerged adults in their breeding the larval food. We have reared areas. One vexans female was large numbers of Aedes vexans, taken after 55 days and one sticticuSy and hexodontus in the >sücticus after 85 days. Six sticti- laboratory on ground dog food cus females were taken after 52 and blood albumin. We have also days and one Aedes male after reared Culex quinquefasciatus on 24 days {H7). From these studies yeast and powdered milk. it appeared that longevity may depend somewhat on the time of the flood crest. Individuals hatch- PUPAE ing after a May flood lived longer than those that hatched after a With the fourth larval molt the late-June flood. Conditions of pupal stage appears. They move climate in the breeding areas about by somersaulting. Except probably exert the greatest influ- for Mmvsoniay a mosquito pupa's ence on the life span. In one life is a short and active one. An locality, for example, a sticticus excellent account of the emer- male was captured 94 days and gence of an adult mosquito from females of both species were col- the pupal stage is given by lected 104 to (rarelv) 118 days Marshall {98). after emergence. The climatic 6 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE and geographic factors in that viduals of Aedes squamiger may locality were especially favorable travel 60 to 70 miles, and those —the humidity was high and the of Culex pipiens may remain temperature comparatively low. within a few hundred yards of The relative abundance of these the place where they emerged as species in the lower Columbia adults. River valley in the years of high Sample collections and obser- and low flood crest is given in vations were made over several figure 2. seasons. Some of our recorded data (1J^7) on flight range (fig. FLIGHT 3) were obtained by staining and recovering adults. It was de- The distance that mosquitoes termined that vexans and sticti- fly varies with the species and cus of both sexes were dispersed with the individual. Some indi- in all directions, both within and

AEDES VEXANS

2 O 15 31 15 30 15 31 15 31 15 30 15 31 MAY JUNE JULY AUGUST SEPTEMBER OCTOBER

15 31 15 30 15 31 15 31 15 30 15 31 MAY JUNE JULY AUGUST SEPTEMBER OCTOBER FIGURE 2.—Abundance of Aedes vexans and sticticus in Multnomah County, Oreg.: A, In the low-flood-crest years 1930 and 1931; B, in the high-flood-crest years 1932-1936. LEGEND BREEDINÖ AREA FLIGHT RANGE SCALE,! INCH-12MILES 30 HILES H H H H H t- =1

FIGURE 3.—Breeding areas and flight range of Aedes vexans and sticticus in the lower Columbia River Valley

-^1 8 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE against general wind currents, for Upon reaching a spot to be a distance of 2 miles. Within 24 sampled, especially if the water hours they traveled 5 miles, 1/2 is more than a few inches deep, mile of which was across the wait a full minute and then quick- Columbia River. These staining ly skim the surface without tests were supplemented by ob- allowing the water to flow over servations made along a canyon the edge of the dipper. Transfer road, through a heavily timbered the larvae from the dipper to a section for a distance of 30 miles. collecting jar with an eye drop- For 15 miles vexans and sticticus per, the tip of which has been were numerous, but 30 miles broken ofl" to make an enlarged away only one female was taken mouth. in 10 minutes. As soon as a collection is made, The size of the brood influences number the jar and record the the distance that mosquitoes date, locality, and other pertinent travel, but not their rate of conditions under which the lar- travel. The height of the flood vae were found. crest also affects the size of the For easier identification place broods. The greater the flood, the the larvae and pupae in shallow greater the radius of dispersion. pans for rearing to the fourth instar, and then either preserve COLLECTION AND PRESERVA- them in 70-percent alcohol or allow them to emerge as adults. TION OF SPECIMENS Frequently several species may A white-enamel dipper, the be taken in one dip. Therefore, handle of which is lengthened select a few larvae and place with a cane or smooth stick, is the them individually in small vials most convenient implement for until the adults emerge. These collecting larvae (fig. 4). A little adults can then be associated with their larval and pupal cast skins. To make permanent slide mounts of the larvae, place them in 70-percent alcohol for a few minutes; then, pierce the larvae with a needle, place them in Cellosolve for a few minutes, and finally place the tissue to be pre- served in balsam to harden. Mounts of the male genitalia can be made in a similar way. A pillbox is convenient for holding or shipping specimens of adult mosquitoes. Place two pieces of soft tissue paper between two layers of cotton and FIGURE 4.—Using a long-handled dipper to collect mosquito larvae. the mosquitoes between the layers of tissue. Without the tissue experience is necessary before paper the tarsal claws may cling one can dip successfully, because to the strands of cotton and be- the larvae are frightened easily come broken when removed. and may disappear below the sur- Damaged, moistened, or rubbed face of the water and out of specimens are usually unsatisfac- range of the dipper. tory for identification. MOSQUITOES OF THE NORTHWESTERN STATES 9 Specimens of adults that are to identify some of the species in a be retained in permanent collec- given locality with a hand lens, tions are best mounted on a or even with the naked eye. minuten-pin stuck into a small Misidentification of mosquitoes square piece of cork, through may cause serious confusion. In- which is passed a larger pin. experienced workers will find it Thrust the tip of the minuten-pin helpful to have on hand for com- through the underside of the parison a few specimens that thorax of the mosquito, but not have been correctly identified. protruding through the mesono- Send specimens to a specialist tum. The No. 3 entomological pin with the request that they be is generally the best size for hold- named and returned. Identifica- ing the cork. tions may be obtained through Label the mounted specimens the Bureau of Entomology and carefully and pin them in a Plant Quarantine and some of the Schmitt insect box. Take care to State universities and agricul- protect the stored specimens tural experiment stations. from insect pests and dampness. Flake naphthalene or paradi- HISTORY OF MOSQUITO chlorobenzene placed in a per- CONTROL IN THE NORTHWEST forated container and securely fastened in one corner of the The great numbers of mos- Schmitt box will prevent damage quitoes appearing in the lower from insect intruders. These in- Columbia River Valley each May sect repellents must be renewed and June have been a serious occasionally. problem ever since the first set- tlers reached there early in the nineteenth century. As the popu- IDENTIFICATION OF SPECIES lation increased there was much One must have a knowledge of discussion of the annoying prob- mosquito anatomy to identify the lem. It finally came to the atten- different genera and species of tion of Oregon State College, and mosquitoes. The principal dis- beginning about 1924, D. C. Mote, tinguishing characters are the head of the Department of En- shape, size, coloration, and scal- tomology, was frequently con- ing of the different body parts. sulted for advice and guidance. A binocular dissecting micro- After surveying the situation and scope providing magnifications up gathering the available informa- to about 85 X is necessary for sat- tion, in March 1926 he initiated isfactory examination of the the first effort at mosquito con- identifying characters. trol in the Portland area by in- For examining larval parts and troducing mosquito fish {Gam- slide mounts of male terminalia, husia affinis) from California. a compound microscope having a Mote's efforts led to organized magnification up to 400 X is action, and meetings were held in necessary. A bright spotlight is which leading citizens of Port- required when high magnifica- land and Multnomah County took tions are used. part. In the field a good hand lens Among the people who contrib- giving a magnification of 10 or uted to the movement was H. H. 15 X is satisfactory for provis- Riddell, an observing naturalist ional identifications. After some although not a trained scientist. experience one will be able to Riddell became interested in mos- 10 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE quito control in Skamania Coun- several counties along the Colum- ty, Wash., about 1926, and by- bia and Willamette Rivers and correspondence with H. G. Dyar, made hundreds of collections of of the Smithsonian Institution, these insects for identification. and others, discovered the breed- Aerial photographs of the over- ing areas of the local species. flow area in Multnomah County Dyar had visited Oregon in 1916 made under his direction were of and had made field observations great value in studies of the mos- of mosquito conditions which quito-breeding areas. The au- later were to have an important thors of this handbook conducted part in their control. In 1927 Rid- investigations from 1931 until dell started mosquito control in a 1940. Much of the information small way in Skamania County. contained in it was obtained dur- He also met with the people of ing those years, although addi- Portland and Multnomah County, tional data subsequently obtained and beginning in 1930 was in by the junior authors are in- charge of the field operations of eluded. the Portland Chamber of Com- In the winter of 1933-34 mos- merce Mosquito Control Commit- ouito control in both Oregon and tee. This committee was headed Washington was greatly accel- by Charles Stidd, and consisted of erated through an allotment of the entomologist of Oregon State funds by the Civil Works Admin- College, representatives of Mult- istration (129, 130, 132). This nomah County and the city of work was conducted in Multno- Portland, certain recreational or- mah, Columbia, and Tillamook ganizations-—especially Jantzen's Counties in Oregon and in Kit- Beach—and was responsible for sap, Skamania, and Clark Coun- raising funds for the control pro- ties in Washington. Practical gram for more than 10 years. mosquito-control measures are In 1929 G. H. Bradley, of the being continued in the vicinity of Federal Bureau of Entomology, Multnomah and Clark Counties, made a brief visit to the lower in which Dorothy McCollough Columbia River Valley, collected Lee, Mayor of Portland, has been some of the annoying mosquitoes, an active leader. and made general recommenda- An enabling act for the organi- tions which further stimulated zation of mosquito-abatement dis- interest in organized action. tricts in Oregon was passed by Because little was known about the State Legislature in 1940. the biology and habits of mosquitoes in this valley, the United GENERA AND SPECIES FOUND States Department of Agricul- IN THE NORTHWEST ture was asked to undertake a research program. In 1930 Con- The mosquitoes found in tiie gress appropriated funds for Northwestern States, their dis- these investigations. tribution and economic impor- W. V. King, of the Bureau of tance as recorded during the Entomology, opened a laboratory years 1930-51, are listed in table in Portland in 1930, and spent 2 1. Their distribution is shown in months surveying the lower Co- the maps at the back of this lumbia River area and south- handbook. In addition to the 39 eastern Oregon. He examined species listed, several more have numerous breeding areas of the been reported from the region, flood water Aedes mosquitoes in but the records are either obscure MOSQUITOES OF THE NORTHWESTERN STATES 11

TABLE 1.—Species of mosquitoes occurring in the Northwestern States and their relative importance^

Species

Aedes: aboriginis ... 4 2 campestris . 5 5 canodensis .. 5 4 cataphylla .. 5 5 cinereus .... 3 2 communis .. 2 2 dorsalis .... 1 1 excrucians .. 3 4 fitchii 2 2 flavescens .. 4 4 hexodontus . 2 2 idahoensis .. 5 5 impiger .... 0 5 increpitus .. 1 2 intrudens .. 5 4 nearcticus .. 4 4 nigromaculis 4 4 niphadopsis . 5 0 pionips 0 0 pullatus .... 5 4 sticticus .... 1 1 trichurus ... 0 5 varipalpus .. 4 4 ventrovittis . 0 5 vexans 1 1 Anopheles: freeborni occidentalis pseudopunctipennis franciscanus punctipennis Culex : pipiens stigmatosoma territans Culiseta: impatiens . .. incidens .... inornata .... maccrackenae morsitans ... Mansonia: perturbans

11, Most important because of abundance, wide distribution and economic significance; serious pests or disease carriers. 2, Abundant under restricted ecological conditions. 3, Widely distributed, but not in large numbers. 4, Abundant but important in only a few isolated areas. 5, Rare species. 12 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE

or the species were confused with Culex tarsalis (see frontispiece) is valid forms. Some of the informa- one of the most widely distributed mosquitoes in the region. The larvae have tion presented in this paper was been taken from rain barrels, log ponds, obtained from records in the lit- stagnant pools, sluggish streams, wood- erature, principally from the land ponds, and alkaline sumps. They comprehensive works of Dyar have not been found at high elevations or in salt marshes. Although they pre- {22, 28) and Howard, Dyar, and fer to feed on fowls and livestock, they Knab {68) \ also from collections will readily attack man. Viruses of both in the National Museum, Oregon western equine encephalomyelitis and State College, Washington State St. Louis encephalitis have been isolated from collections of this species in sev- College, Idaho State College, and eral States, and transmission of these the U. S. Public Health Service. viruses to chickens and ducks has been The Northwestern States do demonstrated. not have a large number of spe- Culiseta inomata, an important live- cies, but in certain localities the stock pest, annoys humans very little. prodigious numbers of some of the Aedes mosquitoes have seriously affected economic enter- MOSQUITOES AND DISEASE prises. The following species are MALARIA of greatest economic importance : Anopheles freeborni {2) occurs in We are not sure when malaria great numbers in the irrigated valleys of Washington and Oregon. It has been first appeared in the Northwest, the most important vector of malaria since our sources of information in the region. do not agree {21, 90, 125, 163), Aedes dor salis breeds in saline, alka- but it was probably about 1830. line, or fresh irrigation water. It is abundant in the salt marshes, and in However, they all show the im- certain areas is a great handicap to portant bearing of the disease on the dairy industry. The viruses of the early history of the region— western equine encephalomyelitis and its fatal character and that great St. Louis encephalitis have been isolated from it in nature. numbers of the native population Aedes increpitus is a severe biter, and died because of it. Neither do we in high elevations is one of the most know how it reached the North- annoying species to man and animals. west, but as one author {125) Aedes hexodontus is very numerous aptly describes it, it was most and annoying in restricted mountainous areas. likely "dragged across the plains'' Aedes sticticus breeds in large num- by parties from the East and bers in the willow flats along the lower South that assembled at Inde- Columbia River, and is a severe biter pendence, Mo., for their long of man and livestock. Aedes communis occurs in mountain- journey into the Oregon Terri- ous areas, and in some places is a very tory. It may also have been serious hazard to recreational interests, brought in by sailors and travel- lumbering, and road building. ers who had come from malaria Aedes vexans is one of the most troublesome pest species in both irri- belts in the United States or gated and floodwater areas, and is found who had touched at Central near sea level and also in mountain American ports before reaching meadows. The adults disperse for 10 to the Northwest. 20 miles from their breeding places and are severely annoying to man and live- Malaria was first required to stock for 8 or 4 months each year. be reported to the State health Culex pipiens occasionally is ex- officer of Washington in 1915, tremely numerous and annoying in com- and of Oregon in 1918. Figure 5 munities in the western portion of the Northwest. It seldom occurs in Idaho shows the cases of malaria re- or the eastern half of Oregon and ported in Oregon for the period Washington. 1920-44. During the years 1945- MOSQUITOES OF THE NORTHWESTERN STATES 13 47 a considerable increase in this out the Northwest (iS), but disease was reported, but most breeds most profusely in the up- of the cases originated outside per Willamette Valley of Oregon. the United States. Since then only The other species of Anopheles two cases have been reported as occurring there are probably of originating within the State, one little significance as transmitters in 1948 and one in 1950. Only of the disease. The winter climate rarely have any cases of malaria is similar to that of the northern emanated from the State of range limits of the disease in the Washington. Mississippi Valley, although the In Idaho it has been a report- mean winter temperature is able disease on a voluntary basis slightly higher for Eugene, Oreg., since 1936. Up until 1945 only 20 than for Cardwell, Mo., where cases had been reported. malaria has been very common. Anopheles freebomi, a vector of The summers, however, are much malaria, occurs widely through- cooler in Oregon.

1925 1930 1940 1945

160 140 f\ r20 / \ 100 / \ 80 / \ 60 J \

40 ß 20

0 _^ v_ JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT. OCT. NOV. DEC.

FIGURE 5.—Cases of malaria reported in Oregon, 1920-44: A, by years; B, by months. Total of 583 cases. 14 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE ENCEPHALITIDES as experimental vectors of western equine and St. Louis viruses Encephalitis in man and equine U9, 50, 51, 52, 55), and species encephalomyelitis, known collec- of the first three genera have tively as encephalitides, are com- been found naturally infected. paratively new recognizable dis- Culex tarsalis undoubtedly is eases. Little was known of the the primary vector of western causative agent, host range, and equine encephalomyelitis and St. methods of spread until 1941, Louis encephalitis in the North- when Hammon and coworkers western States. In one year Ham- (5S) published the results of mon and coworkers found 1 out their research in the Yakima of every 386 of these mosquitoes Valley, They isolated the virus of caught to be infected. This mos- St. Louis encephalitis and wes- quito feeds on man, horses, mules, tern equine encephalomyelitis, the cattle, sheep, pigs, dogs, ducks, principal types of encephalitis doves, pheasants, and chickens found in the Northwest, from (75). It breeds in permanent Culex tar salis. Never before had ponds, barnyard puddles, irriga- ^this virus been found in mosqui- tion seepage, and along the mar- toes collected in an epidemic area. gins of streams. The problem is Several new viruses have been complicated also because birds isolated from mosquitoes by vari- serve as reservoirs of the virus ous research workers, and it is (55). As many as 2400 cases of suspected that they might pro- equine encephalomyelitis have duce clinical encephalitis in man. been reported in 1 year in Ida- The epidemiology of the en- ho (1935), 726 in Washington cephalitides is the most compli- (1940), and 525 in Oregon cated of any of the insect-borne (1936). Figure 6 shows the num- diseases. However, it is known bers of cases reported in the that Culex, Aedes, Culiseta, and Northwest from 1935 through Mansonia mosquitoes can serve 1951.

1935 42 43 44 45 46 47 48 49 50 1951

FIGURE 6 .—Cases of infectious equine encephalomyelitis reported in Idaho, Washington, and Oregon, 1935-51. Total of 10,294 cases. MOSQUITOES OF THE NORTHWESTERN STATES 15 Until more is known as to the Temporary bodies of water One generation annually merits of mosquito control as a Floodwater means of reducing the encephali- Rain pools tides, in known endemic areas Snow water with epidemic potentialities mos- Tree holes Several generations annually quito-abatement personnel must Irrigation water assume responsibility for making Permanent bodies of water—sev- their control measures broad eral generations annually except enough to include all mosquito Manaonia Permanent ponds species. The likelihood of reduc- Tidal water ing the incidence of encephalitis Log ponds and water in may be considered an added bene- artificial containers fit in areas where mosquito con- Each association at different trol is justified on the basis of re- times and in different places may lief from irritating annoyance. include species typical in other associations. The species in some of these associations cause more serious annoyance than do those ASSOCIATIONS OF SPECIES IN in other associations. The fact that the species in the ñoodwater, THE NORTHWEST rain pool, and snow-water associations have only one brood a The mosquitoes occurring in year greatly simplifies control the Pacific Northwest may be operations. Frequently, however, grouped as follows according to they may be complicated by the their ecological habitat or associa- extent and inaccessibility of the tion {13Í) : areas requiring treatment (fig. 7).

FIGURE 7.—Floating debris makes it difficult to control floodwater mosquitoes. 16 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE The ecology of a few areas in entirely new association of mos- the Northwest has been so altered quito species has resulted. For by the construction of dikes, example, the Bonneville Dam has ditches, or dams in connection prevented the spring flooding of a with irrigation projects that an large acreage overgrown to wil-

FiGUBE 8.—A, A willow swale along the lower Columbia River where Aedes vexans and sticticus bred before it was permanently flooded by the Bonneville Dam. B, The same area after it was permanently flooded; Anopheles and Culex replaced Aedes mosquitoes. MOSQUITOES OF THE NORTHWESTERN STATES 17

FIGURE 9.—Diagrammatic sketch of willow flat in figure 8, showing extent of mosquito breeding under natural and controlled water levels. lows for 50 miles or more above others that were not present be- the dam {1S5). These willow flats, fore the area was irrigated. (figs. 8 and 9), now permanently- An association of species may covered with water, no longer pro- also change with the advancing duce hordes of Aedes vexans and season. In the irrigated sections of sñcticus mosquitoes, but do pro- the Yakima Valley practically all vide marginal areas in some of the first mosquitoes are Aedes, places suitable for the production whereas after the irrigation water of Anopheles, Culex tarsalis, and forms permanent ditches and Mansonia, Grand Coulee Dam has ponds the next outbreak will con- afforded vast breeding grounds tain numbers of Culex tarsalis and for Aedes dor salis, Anopheles, and Anopheles freeborni. 18 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE FLOODWATER tory for several miles. They become extremely annoying in AEDES VEXAISS and STICTICVS residential sections of Portland, Oreg., and Vancouver, Wash., Along the banks of the Colum- over agricultural lands, especially bia River from the Cascade dairy and small-fruit farms, and Mountains to the sea are many- also in amusement parks and on areas that overflow each year golf courses. (fig. 10). The annual freshet us- The larval season usually be- ually occurs in May or June; the gins in April, rarely late in earliest date recorded for the March, and is over shortly after flood crest is March 19 and the the flood crest is reached in May latest is July 4. These areas are or June. At most it lasts 3 months. heavily overgrown with willow For the remainder of the year, brush and, at slightly higher ele- these willow swales are compara- vations, with cottonwood, briars, tively dry. Oviposition begins and small shrubs ; still higher are within a week or two after emerg- the conifers. ence, and probably continues dur- The normal mean level of the ing July and August in willow river is 7.1 feet. The flood crest is flats adjacent to the receding rarely so low as 10 or 12 feet. In river. most years it reaches at least 16 feet and one year in five it goes as In some seasons there is a high as 24 feet. Once in several single gradual rise and fall of the decades it has reached disastrous river and, although breeding is heights—about 30 feet in 1894 heavy over the entire valley at and 1948. the same time, with proper or- During the annual spring ganization good control can be freshet swarms of vexans and established. More often the river sticticus {J/^7) hatch when stimu- rises and falls from two to four lated by the floodwater. Three or times, and with each new crest 4 days after emerging from their new hatching takes place on aquatic life, the adult mosquitoes ground that has previously been spread over the contiguous terri- flooded (fig. 11).

WILLOW WILLOW. COTTONWOOD. SNOWBERRY. BRIARS, ETC 1CONIFERS Ä- '^^Êk ?lm i'J^&StgWL*' "w l^m b^ v:j^||i-. pr^ -201 FT NORMAL FLOOD CREST ^ j^ ^è^i^àii ...^^¿! C MAY AND JUNE ) ^

Z-H-Z-Z-y ^NORMAL MEAN RIVE« LEVEL ^:>r—ii-"i-^-~—3 ■ ^SLOUGH OH LAKE r-_-_-_7 75 '■T ^^-^^^_^^-/ .^ ^ FIGURE 10.—Profile of Columbia River bank, showing breeding grounds of Aedes mosquitoes in willow brush and other vegetation. MOSQUITOES OF THE NORTHWESTERN STATES 19

Uj 14-

$ 13-

APRIL MAY JUNE JULY

FIGURE 11.—Profile of Columbia River at Portland, Oreg., during flood of 1932. Each of the four flood crests shown produced Aedes vexans and sticticus mosquitoes.

Brush clearing has become an filled above the normal flood important control measure in a crests. This kind of work is satis- few restricted areas. Because of factory and permanent, and their greatly changed ecology, greatly reduces the breeding of these areas become unsuitable for these mosquitoes. shelter and oviposition until A large mosquito-breeding heavily overgrown again. area between The Dalles and Little ditching has been done in Bonneville Dam has been per- controlling mosquitoes of this manently flooded. This flooding association, because most of the immediately reduced the breed- breeding areas are flooded directly ing of vexans and sticticus and, from the river, by water backing as the ecology of the area became up into swales and sloughs or a permanent-pond type, new mos- seeping through the sand into quitoes, such as Culex tarsalis and the swales. Where saucer-shaped Anopheles freeborni, increased in swales can be emptied of water, numbers, although not seriously. ditches can be dug at the lower end, so that water will drain out of them quickly when the flood RAIN POOLS subsides. If the flood crest is a AEDES ABORIGimS, EXCRUCIANS, short one, these swales will dry and mCREPITUS, and CULISETA before the larvae pupate, or INCIDEISS the larvae will be carried There are a great many tem- into deep water, where they will porary woodland pools of rain be destroyed. and seep water in the Coast Much of the land bordering the Range of Oregon and Washing- Columbia River is now protected ton, where the rainfall is espe- by dikes, and some of it has been cially high early in the spring. 20 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE These pools, most of which are aircraft cannot be justified at much less than an acre in size but present. However, until more eco- occur for miles along the coast, nomical means are found, some are breeding places for vicious relief can be obtained locally by ahoriginiSy excrucians, and in- treating brush and other mos- crepitus. These species may also quito-sheltering vegetation around be found in the snow-water as- camp and resort sites with DDT sociation. Most parts of this rug- sprays. Two of these treatments ged country are so thickly over- per season will greatly reduce grown as to be nearly impene- annoyance by these species. At trable (fig. 12). The ditching of times of greatest mosquito activ- the low spots reduces the mos- ity, as at dusk, space sprays may quito population immediately, be used. but ditching is expensive and con- Many of these areas are inac- siderable clearing is necessary to cessible until June because of reach these breeding spots. An- heavy snow, and, if larvicide ap- other kind of rain pool, un- plications are contemplated, the doubtedly containing some salt, materials and equipment must be occurs on the high rocks along taken into the area the preceding the ocean. Culiseta incidens breeds fall. After mid-June these mos- in these pools. quitoes are on the wing and are widely dispersed. These mosquito- SNOW WATER breeding areas can also be treated when dry, late in the fall, with AEDES COMMUNIS, HEXODONTUS, a residual spray or dust that will INCREPITUS, FlTCHIh and CllS- remain effective and kill the EREVS young larvae as they hatch from These Aedes species are found snow water the next spring. This widely scattered along the back- method cannot be depended on bone of the Cascade Range, in for complete relief, however, be- the mountains of eastern Oregon cause migrating mosquitoes may and Washington and in Idaho. fly into the treated area. The larvae appear in the innum- Some semipermanent work has erable pools and ponds formed by been done in this region by the melting snow in April, May, or Forest Service. Ditches have been June. These mosquitoes breed also dynamited in the heavy peat soil, at the margins of lakes, the levels not so much for draining pools of which are raised by melting of snow water as to maintain the snow and lowered again when the levels of lakes whose upper mar- excess water evaporates and seeps gins otherwise produced larvae into the soil. when temporarily flooded. The The mountainous areas of the snow water and seep water then Northwest are great recreational quickly drain into the lakes, the centers where visitors from every levels of which are fairly well part of the United States camp, maintained by dams at the out- fish, hike, or pick blueberries lets. This type of mosquito-con- from May through September. trol work is distinctly advantage- Visitors who have suffered from ous to wildlife. It creates addi- these mosquito hordes, which are tional marginal areas dry enough vicious biters, will not remain for upland birds early in spring, long and probably will not return. and at the same time increases Perhaps in some places control and maintains the extent of lakes by ditching or treatment from suitable for fish and waterfowl. MOSQUITOES OF THE NORTHWESTERN STATES 21

''m'- M M:^:^' '• aiï'J

FIGURE 12.—A, Temporary rain pool in the Coastal Range. B, The same area after it had been cleared and ditched. 22 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE TREE HOLES rid themselves of these tormen- ÀEDES VARIPÀLPUS tors. The pests cause beef cattle on summer pasture to lose weight Here and there along streets, in and reduce the milk now in dairy parks, or in the deep forest are herds. They also prevent the de- tree holes that contain water for velopment of otherwise desirable long or short periods (fig. 13). real property and hinder all kinds In these holes one can nearly al- of recreational activities. ways find varipalpus larvae (Hi), and west of the Cascade Range they can be found at almost any time of year. These mosquitoes overwinter as eggs and as larvae. They are severe biters close to their breeding place, but frequently the tree holes are difficult to discover. When found they can be treated with DDT or filled with sand.

IRRIGATION WATER AEDES DORSALIS, VEXAISS, and NIGROMACVLIS, ANOPHELES FREEBORNI and PUNCTIPENNIS, and CULEX TARSALIS In large areas in eastern Idaho, Oregon, and Washington irriga- í^ílSt^ tion is practiced. Some of these areas are flooded with a thin sheet of water from the sur- rounding mountains. They are generally used as hayfields, which FIGURE 13.—Tree hole where Aedes vari- either go dry naturally or are palpus larvae are found. made to go dry by diverting the water before haying time. Aedes dorsalis or vexans mosquitoes ap- The only means of control pear in May and June and are ex- would be to treat large areas ceedingly abundant in these so- from aircraft, but this measure is called marshes of 10,000 to 60,000 seldom economical because of the acres but the anophelines and great size of the infested areas culicines have scarcely time to and the sparse human population. propagate except where the water The problem is how to furnish an is turned into border ditches. At adequate supply of water to the haying time it is difficult to hold fields and then dry them up labor because of the mosquitoes. within a week. The border method Men wear head nets and heavy of irrigation partially meets this clothing for protection. Horses problem where it can be em- have been known to lie down ployed, but there is seldom an while harnessed to mowing ma- adequate supply of water that can chines, in their frantic efforts to be held for later release. MOSQUITOES OF THE NORTHWESTERN STATES 23 PERMANENT PONDS 30 miles along the Willamette ANOPHELES FREEBORM and PVISCT- River and in some places occur in IPElSmS, CVLEX TARSALIS, CVLI- an area 5 miles wide. SETA INCIDEISS and INORNATA, and in some areas MANSONIA PER- TURBANS TIDAL WATER Contrary to common belief, AEDES DORSALIS ponds of permanent water present the least mosquito nuisance Only one mosquito species in the Northwest. The anophelines breeds in salt marshes along the and Culex tarsalis that breed coast of Oregon and Washington. there do not become numerous Except for certain tidal flats ad- until late in the season and are jacent to Puget Sound, the coastal seldom very annoying. However, breeding areas are small and freeborni is a potential carrier of malaria and tarsalis of encephalo- more or less isolated. Aedes dor- myelitis and encephalitis. Mos- salis breeds abundantly in these quitoes that transmit the last two salt-marsh areas, as well as in diseases should be controlled the alkaline irrigation water to whenever practicable. The ano- the eastward. These mosquitoes phelines are widespread through- probably fly but short distances, out the Northwest late in the but can be a severe annoyance to summer, but malaria has been man. They are vicious biters by endemic only in the upper Wil- day and have caused a decrease in lamette Valley of Oregon. Oxbow the milk production of dairy ponds (fig. 14) are numerous for cattle pastured on the marshes.

FIGURE 14.—A typical oxbow pond along the Willamette River from which large numbers of Anopheles freeborni and punctipennis have been taken. 24 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE LOG PONDS AND WATER IN Mosquitoes, by constant annoy- ARTIFICIAL CONTAINERS ance, cause livestock to lose weight and reduce milk flow. They CULEX PIPIENS and TARSALIS, CULI- often drive livestock from lush SETA INCIDENS, and ANOPHELES pastures to barren hillsides and PUNCTIPElSmS thus further reduce flesh gains. Large numbers of these mos- Annoyance from mosquitoes is a quitos breed in log ponds, and severe trial to fruit pickers, and in many towns in western Oregon may cause them to refuse to work and Washington they are the only in the fields. source of mosquito annoyance. The use of recreational areas Culex pipiens is occasionally a at some beach and mountain re- serious pest near heavily polluted sorts is greatly restricted by mos- ground pools, and in drains of quito annoyance at the very time septic tanks, offal disposals, and of year when the most people are other sewage-polluted water. on vacation. The losses from re- Wooden, tin, and rubber recept- duction of property values and acles also harbor this species as attendance at amusement parks, well as CuUseta incidens, some- and from injury to livestock are times in numbers sufficient to an- frequently much greater than the noy the occupants of several cost of mosquito control. homes. Anopheles punctipennis Mosquito control is a special- larvae are sometimes found in ized subject and one that requires rain or water barrels in this re- sound judgment, a background of gion, if the water is fairly clean. entomology, some training in engineering and, because of the innumerable personal contacts, an MOSQUITO CONTROL understanding of human psychol- Mosquito control has become ogy. Above all one must know the increasingly important during the different species, their life his- last few years. In many parts of tories, and habits, in order to the country it has become an es- apply practical measures against sential part of good living. The them. In mosquito control one recent incrimination of Culex can do the right thing, but do it tarsalis as a vector of equine at the wrong time, and so meet encephalomyelitis and its relation with failure. to sleeping sickness in humans has stimulated interest in mos- SURVEYS quito control to reduce the incidence of this disease. Although Before an effective mosquito- malaria is of little importance in control program can be under- the Northwest, it has been en- taken, a survey must be made of demic in the upper Willamette the area. Such a survey must be Valley in Oregon for over 100 made by an entomologist or a spe- years (1^6). cialist having knowledge of the The mosquito problem of the biology and habits of mosquitoes, Pacific Northwest is largely agri- and of the diseases they carry. In cultural and recreational in char- addition to finding out where the acter (17i). Mosquitoes affect mosquitoes are and what species the farmer, his family, his em- are present, information must be ployees, and his livestock. They obtained on their breeding places, cause financial losses to stockmen, and such other data that entomol- dairymen, and general farmers. ogists, sanitary engineers, and MOSQUITOES OF THE NORTHWESTERN STATES 25 mosquito-abatement engineers quito breeding season is necessary will need in planning a control for such studies. Two or three program. seasons is even better. In the Fay- If the mosquito-control project ette Valley of Idaho dorsalis pre- is aimed at the reduction of ma- dominates in May and nigromac- laria or equine encephalomyelitis, ulis in July and August. Along the presence of the disease itself the Columbia River flood crests indicates in some measure the vary greatly from year to year, species involved. A study of the or they may occur two or distribution of the disease serves three times during one season. to point up the problem, and a Each flood stage produces its survey of mosquito species aids brood of mosquitoes and, because in developing the plan of pro- of their habit, the relative abund- cedure and estimating costs. ance of the species may vary with When relief from mosquito annoy- the height of the flood. Several ance is the main consideration, a years of study are required, survey is necessary to determine therefore, before reliable aver- the limits of the infestation and ages can be determined. Fairly the relative importance of each effective control operations can species, since more than one kind be started before such an exten- is usually present. Even in one sive survey is completed, but county of the lower Columbia without adequate information River Valley the problem is com- control may be highly wasteful plicated by mosquitoes that breed and may result in loss of public in snow-water, floodwater, arti- confidence. ficial containers, and permanent ponds. HATO) COLLECTIONS A mosquito survey is begun by collecting and identifying both Collecting mosquitoes while larvae and adults during a mos- they are biting is the simplest quito outbreak. Because the flight and most direct method of de- range may be unknown, this col- termining the proportions of the lection should extend for some different species. Such collections distance beyond the limits of mos- are usually made with a chloro- quito annoyance. Since mosquitoes form tube or other type of killing have no regard for municipal, bottle. One procedure is to stand county, or State boundaries, it is or sit at the selected place and, sometimes necessary to control after allowing a minute or two them in one State or county to for the mosquitoes to accumulate, protect the citizens of another. to collect them as they alight over Some mosquito-abatement dis- a 10-minute period. Three 10- tricts maintain collections of minute periods may be totaled identified species of mosquitoes and multiplied by 2 for the hourly found locally. These collections rate. One person working alone are of use in quickly identifying can collect the mosquitoes land- species brought in for determina- ing on the front of his trousers. tion and for educational purposes. If two are working together, one A survey of the breeding places can collect those alighting either should determine their extent and on the shirt or bare back of his nature, whether permanent or companion. temporary, as well as the topo- When mosquitoes are abundant, graphy and natural drainage of the numbers caught can be in- the area. At least one entire mos- creased by placing a short paper 26 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE funnel, or guard, in the mouth of We have compared hand col- the collecting tube. The collector lections with those made with a can then catch the next specimen New Jersey light trap in a total without waiting for the first one of 10 hours of hand collecting for to succumb to the chloroform 10 minutes at hourly intervals fumes. The guard also conserves (133). Approximately three- the strength of the chloroform fourths as many female mos- and prevents the loss of spscimens quitoes have been taken as with when the mouth of the tube is the light trap in 60 hours. In turned downward. In heavily in- hand collecting, however, one sel- fested areas 100 or more mos- dom obtains the rare species, and quitos have been taken in 10 practically no males, as are taken minutes with a tube of this sort. with the light traps. When two or more persons are to make collections at different TRAP COLLECTIONS places, they should make a preliminary collection at one place For most species the New Jer- to determine the relative attrac- sey light trap (lOi) (fig. 15) is tiveness and dexterity of the different collectors, since much var- iation has been found in these respects. Certain species, such as those of Anopheles and Culex, can be obtained by daytime collecting in dark corners and underneath buildings, where they spend the daylight hours. However, Aedes species in the Northwest may be taken best at dawn or dusk and on cloudy days, when the humidity is high, by going to their breeding areas or places where they are reported to be annoying. For making the collections a series of stations well distributed over the area under observation are selected. At each location the most favorable place should be selected after an examination of the entire area. Collections are FIGURE 15.—A New Jersey light trap in made daily, weekly, or biweekly. operation. For data on comparative abundance in different parts of the area, very useful for obtaining samples or at different times of the year, of mosquito populations. Th ? collections should be made under traps are placed at strategic conditions as nearly uniform as places throughout the area and possible. are usually operated on one or Collections made during tha more nights each week. They first flight period (just at dusk) should be hung in an open space, may average much higher than with the light itself 5 or 6 feet daylight collections. The numbers from the ground, and they should will vary with climatic conditions. not be placed near a street or MOSQUITOES OF THE NORTHWESTERN STATES 27 other competing light. These were taken in a trap in one night. traps are of no value in con- Of these, 945 were Aedes dor salis trolling mosquitoes in an area; and the rest Anopheles freeborni, they serve only as a sampling de- Culex tarsalis, and Culiseta in- vice as an aid in determining ornata. We have taken more than the effectiveness of a control 1,200 mosquitoes, mostly tarsalis program. from one trap in the Yakima The number of mosquitoes Valley. caught per night in a trap fre- Reeves and Hammon (117) quently runs into the hundreds have designed a large box trap, and, since many other kinds of in- mounted on a two-wheel automo- sects are also found in the killing bile trailer, for collecting live bottles, the task of separating and mosquitoes. This is a modifica- identifying the material is often tion of the New Jersey light trap difficult. Rare species and males in that the insects do not have to not taken while biting appear in pass between the blades of a fan the light-trap collections. and are kept alive instead of be- The different species are not ing killed in a cyanide jar. As equally attracted to the lights. many as 1,055 mosquitoes have They are comparatively ineffec- been collected in one of these tive in trapping Aedes in the traps in a single night. Northwest. Our highest record Animal-baited traps have been for vexans and sticticus was 444 used in the Tropics (95), but so individuals in one night, even far as we know they have not though they were very abundant been used in the Northwest. in the area. In southeastern Ore- A mechanical trap (fig. 16) has gon as many as 1,700 mosquitoes been used in the Arctics (1^5)

Jb'lGURE 1Ö.—A mosquito-collecting device operated by a gasoline motor. 28 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE with fair success and has some COLLECTIONS OF LARVAE advantages over the New Jersey light trap. The trap is operated The collecting of larvae in mos- by a gasoline motor and does not quito surveys is done mainly to depend on electricity or darkness locate breeding places and de- for effectiveness. This rotary termine their importance. Such trap catches all flying mosquitos collections also show the compar- that happen within its collecting ative abundance of the different range, and by this means an exact species. The presence or absence number of cubic feet of atmos- of larvae determines whether an phere per time unit can be sam- area should be treated with a lar- pled. A trap equipped with two vicide. If larvae cannot be found, nets and operated at 55 r.p.m. we recommend against treating a removes the insects from approx- "likely looking" area. Sometimes imately 500,000 cubic feet of air the productivity of a breeding per hour. By mounting a cone of area can be measured by placing this trap on the fender of an cloth nets or screen cages over automobile (fig. 17) (126), one the water. can take continuous samples of Breeding places are of two gen- mosquito populations while trav- eral classes, permanent and tem- eling at dusk. A serious disad- porary, but the status of a given vantage of this type of trap is area may change over a period of that it may injure the specimens time. Anopheles, Culex, Culiseta, when they are unattended for and Mansonia occur typically long periods. in permanent breeding places,

FIGURE 17.—A cone screen mounted on the fender of an automobile for sampling mosquito populations. MOSQUITOES OF THE NORTHWESTERN STATES 29 whereas the Aedes mosquitoes of utes, and after several hours the the Northwest breed in areas that small larvae can be seen readily are flooded only a few weeks in in strong light. Several factors the year. Because most of these little understood complicate this floods occur but once a year, Aedes technique. Apparently the ele- has only one brood a year, but ments of time, dryness of soil where floods are more frequent (166), species of mosquito, and a brood follows each flooding. temperature all influence the

FIGURE 18.—Diagram of a grain cleaner modified for separating mosquito eggs from soil.

Because of deep snow in the hatching of these Aedes mos- high mountains, it is often impos- quitoes. sible to get to those breeding areas in June before the mos- COLLECTIONS OF EGGS quitoes have emerged from the snow water. It is sometimes pos- In areas where mosquitoes lay sible to obtain data from these their eggs on the ground, the ex- areas by taking samples of soil tent of the breeding areas can be from dry depressions late in the determined by sampling the top summer and flooding them with layers of soil and debris (27). It water in the laboratory. Some ex- is impossible to recover many perience is required, however, be- eggs without examining and sep- fore one can become adept in arating a large volume of soil. choosing just the right sample The samples of soil and debris for flooding. If eggs are present, are dried until almost dusty, and if they have been laid several passed through a mesh sieve, and weeks before the sample is taken, then through a modified grain they will hatch within a few min- cleaner (fig. 18) (86) to concen- 30 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE trate the eggs in a very small To prevent the eggs from dry- quantity of soil. The eggs can be ing out, each 100 cubic centi- picked out of the infested soil meters of soil containing eggs under a microscope, with a moist- should be moistened with 8 to 15 ened camel's-hair brush. This is cubic centimeters of water, de- best done by spreading the soil pending on the type of soil. over a white background. Husbands (7) has used a vac- A grain cleaner 24 inches wide uum-cleaner suction device for is used as a basis for the separ- picking up eggs in pasture areas ator. It consists of four shaker and has developed technique for sieves, a roll screen, and an air separating them from the gath- blast. The sifted soil is placed in ered soil and debris. the hopper and, as it feeds down over the shaker sieves, the coarse material is removed by 14-, 30-, ENGINEERING SURVEYS and 40-mesh sieves. The eggs and the soil particles of the same size Surveys in connection with pass through these sieves, but the mosquito-control projects should 80-mesh sieve below separates the include an engineering survey to particles of material that are determine the possibility of elim- smaller than the eggs, which drop inating the breeding places. Re- down the opening into the roll clamation of land, diking against screen. On the way down some of floods, and maintaining water the light particles the same size levels are permanent solutions to as the eggs are blown out by a the problem. Such a survey will breeze from the fan. The turning determine whether such methods motion of the roll sieve causes the are feasible and the approximate eggs to pass endwise through the cost. Will the local budget justify 60-mesh roll screen. As they slide drainage or other construction, or down the chute to the catch pan, is the use of insecticides the only waste material passes out of the practicable measure? Will in- lower end of the roll. creased land values and recrea- The meshes used are suitable tional advantages offset the cost for concentrating eggs of sticticus of mosquito control? The legality and vexans. It has also been used of the proposed work and the for obtaining eggs of dorsalis, al- need for obtaining easements on though the mesh of the selecting private property must also be sieve is slightly large for them. considered. An engineering sur- To sieve out the eggs of other vey to answer such questions v^ill species sieves of larger or smaller provide a background upon which mesh can be used. The separator to base an effective control can be equipped with a 14-horse- program. power electric motor, or can be operated by hand with a crank. CONTROL OF LARVAE The separator recovers about 90 percent of the eggs from the ELIMINATION OF BREEDING PLACES soil, and the final product may Wherever possible and practic- contain from 10 to 200 eggs per able we recommend the control cubic centimeter of soil. In the of larvae by eliminating the lower Columbia River Valley the breeding places by draining, dik- average number of vexans and ing, and sanitation, or by main- sticticus eggs is about 85 per taining permanent water levels. cubic centimeter. In some places brush clearing is MOSQUITOES OF THE NORTHWESTERN STATES 31

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FIGURE 19.—^A, A tidal marsh at high tide; flooded pothole in center breeds Aedes dorsalis. B, Pot holes shown in A after being connected with the drainage channel by ditches. effective. Where water levels are tidal-marsh breeding areas along maintained, control workers must the seacoast can be freed of Aedes be on the lookout for Anopheles, dorsalis mosquitoes by digging Culex tarsalis, and Mansonia, ditches to connect the numerous which breed in permanent ponds. pot holes in the marshes with the Drainage undoubtedly is one of main channels of streams (fig. the quickest and best methods of 19). The pot holes are drained of controlling mosquito species in water as the tide ñows out, and the Northwest, but construction the mosquito larvae are carried and labor costs are usually pro- along to deeper water, where they hibitive. It is highly advantage- perish before becoming pupae or ous in several locations in the adults. Such ditches need clean- Pacific Northwest. Many of the ing every year. 32 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE Ditches have been highly effec- ditched at the lower end so that tive also in the Coast Range of the water quickly drains out of Oregon and Washington (131), them as soon as the flood sub- where the rainfall is abundant at sides. If the flood is of short dur- all seasons. Early in the spring ation, the mosquito larvae are innumerable temporary woodland carried out of the swale into nools of rain and seep water are deeper water, where they are de- heavily infested with Aedes ab- stroyed. These ditches also allow originis and fitchii. Most of this fish to enter the infested swale country is rugged and so thickly and devour the larvae. overgrown as to be nearly impen- Many acres of bottom lands etrable. If these areas can be along the lower Columbia River opened up with hand labor and have been diked against the an- connected by ditches to some nual floods of the river. The stream or other drainage, the financial justification of such mosquito pest can be greatly re- work lies in the increased value duced. This tyne of work is semi- of the land for agricultural pur- permanent and requires a certain poses; nevertheless, diking of amount of annual maintenance. this acreage has reduced mosquito Very little ditching has been breeding to a minimum. done along the Columbia River Sanitation as a mosquito-con- bottomlands, because most of the trol measure includes the destruc- breeding areas are flooded di- tion of tin cans and other artificial rectly from the river or by water containers in which Culex pipiens backing up into swales and and Culiseta breed. It also in- sloughs. However, a few isolated cludes the treatment of fire bar- saucer-shaped swales have been rels and log ponds (fig. 20) with

FIGURE 20.—Treating a log pond with a mosquito larvicide. MOSQUITOES OF THE NORTHWESTERN STATES 33 insecticides, and, in permanent larvae. Septic tanks must be in- ponds, the removal of aquatic veg- spected for leaks and unused etation and other shelter for the wells and cisterns for the pres-

FiGURE 21.—A, Depression in a mountainous area where mosquitoes breed in melting snow water. B, Same area in July. When area is completely dry mosquitoes lay their eggs on the ground. 34 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE ence of larvae. Culex tarsalis, ing practice than any other irri- stigmatosoma, and pipiens and gation method, because it pro- Culiseta incidens are usually vides an efficient and compara- abundant in log ponds late in the tively cheap means of controlling summer. mosquitoes. It also prevents the Thousands of acres of land in growth of such weeds as foxtail the Northwest which have be- barley and marsh grass, com- come valuable through irrigation monly found growing where irri- are now producing mosquitoes so gation has been excessive. abundantly as to present a seri- In mountainous areas there are ous menace to man and beast. In many small depressions that have these areas wise use of water and no natural drainage. Early in the an effective device for manipulat- spring they are flooded to a depth ing water levels are imperative. of several inches with icy water, Most of the irrigated hayfields which drains from the surround- in the valleys of eastern Wash- ing banks of snow. This water is ington, Oregon, and Idaho, which frequently teeming with mosquito produce myriads of mosquitoes, larvae, and in many inaccessible have an unlimited water supply areas adults may emerge even early in the spring. When water before roads and trails have been is applied in excessive amounts cleared of snow (fig. 21). Treat- without provision for adequate ment of these depressions with a drainage, optimum breeding con- larvicide, such as DDT wettable ditions exist for several species powder, in September and Oc- of Aedes and Anopheles, and for tober will control these larvae. Culex tarsalis. The manipulation of water The problem is to furnish an levels to reduce mosquito abund- adequate supply of water to the ance can be done in two ways. fields and dry them up within Small dams can be constructed a week's time to reduce the across the outlets of the lakes and mosquito nuisance. The border ponds to hold the water level method of irrigation (28) not constantly high and thereby pre- only meets this problem but is vent the deposition of eggs along also economical in water con- the upper margins (fig. 22). Sat- sumption. In this method the isfactory control can also be ef- fields are divided into a series of fected on the upper margins by strips by low levees, or dikes, digging ditches parallel to the running parallel to the general contours to collect the seepage, slope of the land. Water is turned and secondary ditches may be dug into the upper end of each strip to transport the seepage to the from a larger border ditch and main channels of streams, or to flows across the strip in a thin ponds. Mosquitoes may later ovi- sheet. When the strips have been posit at the upper margins, but flooded for a few days, the flow the eggs cannot hatch, since all of water is checked. The mos- free water quickly flows off. This quito larvae either die on the dry method of control, however, is surface or are carried into drain- limited to very special situations. age ditches, which may be stocked In some isolated areas where with mosquito-killing fishes or thickly matted jungles of willow treated with a larvicide. brush furnish maximum protec- The border method of irrigation for egg laying, vexuns and tion, which makes short-period sticticus have been controlled for flooding possible, is a better farm- a few years by clearing the areas MOSQUITOES OF THE NORTHWESTERN STATES 35

FIGURE 22.—A, Permanent pond surrounded by mountain meadows, which are covered with temporary water early in the spring. B, Same meadows, drained of surplus melting snow and seepage into large ponds and held by dams.

of all herbaceous growth (fig. tioned, we found it practical for 23). Although the effectiveness of short periods. We believe tem- this procedure has been ques- porary control was established by 36 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE a radical change of the micro- for maximum mosquito develop- climate of the breeding site, since ment. This type of control can be shade, humidity, and freedom considered no more than tempor- from strong winds are essential ary, however, because brush.

FIGURE 23.—A, Willow flat along the lower Columbia River offers shelter and breeding places for floodwater mosquitoes. B, Same willow flat cleared of shade and other protection and thus freed of mosquitoes. Regular maintenance is necessary to prevent their return. MOSQUITOES OF THE NORTHWESTERN STATES 37 grass, and herbaceous perennials containing 66 percent of kero- soon return. However, pasturing sene, 0.07 percent of pyrethrins, stock and some annual clearing in 0.5 percent of an emulsifier, and these areas will reduce their ca- 33.5 percent of water can be pur- pacity for producing mosquitoes. chased, and diluted with 9 parts of water. This larvicide is not USE OF LARVICIDES recommended for use in the extensive willow flats along the Where it is not feasible to elim- Columbia River. inate mosquito-breeding places, With the advent of DDT in control may be accomplished by 1942-43, the scope of chemical treating them with a larvicide. control of mosquito larvae was Before DDT and other recently greatly enlarged. Other materials, developed insecticides were avail- such as TDE, BHC, lindane, tox- able, petroleum oil was used aphene, aldrin, and dieldrin, de- against all species and paris veloped since that time have also green against Anopheles, A light been tested. distilled fuel oil (No. 2) was DDT in oil solution has been widely used, but it was not con- widely employed as a mosquito sistent in its effectiveness because larvicide (fig. 24). Concentrations it was made from different types of 1 to 5 percent in fuel oil No. of crude petroleum. 2, Diesel oil, or kerosene, with or Recently three spreading agents without auxiliary solvents and have been found particularly ef- spreaders, will control mosquito fective when added to No. 2 fuel larvae. Except where resistance oil (Knipling, Gjullin, and Yates has been developed, (18, ^1, 88, 87). They are sulfonated sperm 1U8,169), they are effective when oil (Nopco 1216), a phthalic gly- applied at the rate of 0.05 to 0.4 ceryl alkyd resin (Triton B- pound of DDT per acre, depend- 1956), and an 18-carbon-chain ing on the species, the type of complex amine (Amine 230X). water, the amount of vegetation, When 3 to 5 percent of one of and other factors. Emulsifiable these spreaders was added to this concentrates are also satisfactory oil, adequate coverage and satis- when diluted with water to give factory control were obtained the required dosage, although they with about 6 gallons, instead of are not recommended where fish the usual 20 to 50 gallons, of oil and wildlife are involved. A con- per acre on fresh water. centrate containing 25 percent of Pyrethrum larvicides, as de- DDT, 65 percent of xylene or veloped by workers in New Jer- other solvent, and 10 percent of sey (Ginsburg 38), are very ben- Triton X-100 or other emulsifier eficial under certain conditions. is satisfactory. The effectiveness They are soap emulsions of pyre- of DDT-oil solutions has been in- thrum extract in kerosene, and creased by the addition of 0.25 to are particularly adapted for use 0.5 percent of Triton B-1956. in garden pools containing val- Long-lastinir larvicidal action can uable aquatic plants and fish, be obtained, especiallv in local where other mosquito larvicides and restricted areas where annli- might be harmful. They are cations of 1 to 2 pounds of DDT sprayed over the surface of pools per acre does not present hazard at the rate of about 50 gallons to wildlife. per acre or 1 quart to 200 square TDE, also called DDD. is par- feet of surface. A concentrate ticularly useful where fish are 38 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE

FIGURE 24.-—Applying a mosquito larvicide with a compressed-air sprayer. present (157). Solutions and satisfactory. It is recommended emulsifiable concentrates may be for use by experienced operators, formulated the same way as those but not by the general public be- containing DDT, and can be ap- cause of its high toxicity to man, plied at the same dosages. animals, and wildlife. BHC and lindane compare fa- All these larvicides are effec- vorably with DDT and are su- tive, economical, and safe for use perior where mosquitoes have over large areas when applied by become resistant to DDT. Dos- aircraft if the operation is closely ages of 0.05 to 0.1 pound of the supervised by specialists and gamma isomer per acre are trained pilots. DDT is usually ap- recommended. plied at the rate of 0.1 to 0.2 Toxaphene has been found an pound per acre. A good solvent effective substitute for control of and carrying agent for 20 per- DDT-resistant mosquito larvae in cent of DDT is a methylated California and Florida. It is naphthalene such as Velsicol more toxic to fish than is DDT. NR70, Solvesso No. 3, or Shell and a dosage of 0.2 to 0.4 pound 42 (161). Lindane is used at the per acre is necessary for control. rate of 0.05 to 0.2 pound per acre, Investigations with chlordane technical BHC at the same rate in the Northwest are incomplete, of gamma isomer. but preliminary data indicat'e that EPN has recently given excel- 0.2 to 0.4 pou"d per acra will pro- lent control of larvae in Cali- vide satisfactory control. fornia, when applied as an emul- Dieldrin is one of the most ef- sion or wettable powder spray fective mosquito larvicides. A at tha rate of 0.075 pound of dosage of 0.1 pound per acre is EPN per acre (Gjullin AOa). Mos- MOSQUITOES OF THE NORTHWESTERN STATES 39 quito Abatement Districts in Cali- Ornamental pools and rain barrels,— 1-percent pyrethrum emulsifiable con- fornia uèed EPN successfuly dur- centrate, 1 tablespoonful to 50 gallon! ing the 1952 mosquito season. of water as needed. At the present time we have had very little experience with We have observed several allethrin, the new synthetic com- ground-inhabiting beetles that aie pound chemically related to the predaceous on Aedes eggs {150), pyrethrins (Gjullin iOa), the ac- The carabids Trechus chalybaeus tive constituent in pyrethrum. It Dej., Agonum pusillum (Lee), appears to be almost as effective Pterostichus algidus Lee, and as pyrethrins. Bembidion sp. destroyed the greatest number, 8 to 15 eggs per MATERIALS FOR CONTROLLING individual per week. MOSQUITO LARVAE CONTROL OF ADULTS Floodwater, irrigation water, tidal water, Before DDT and other new in- rain pools, and permanent ponds,— secticides became available, mosquito-control measures were No. 2 fuel oil, 25 to 50 gallons par usually directed against the lar- acre. vae, because the insects were most No. 2 fuel oil with 3 to 5 percent vulnerable in that stage. These of an emulsifier, 3 to 6 gallons per new materials, however, are acre. equally effective against the 5-percent DDT-oil solution. For use in adults. aircraft, 1 to 3 quarts per acre; for Screens (16-mesh), head nets, ground equipment dilute to 1 to 2 percent of DDT and apply 1 to 2 repellents, aerosols, and space and gallons per acre. residual sprays are all used for protection against mosquito an- 25-percent DDT emulsifiable concentrate. For application by airplane, noyance. dilute with 4 parts of water and use 1 to 3 quarts per acre; for ground REPELLENTS application dilute to strength recommended for the oil solution. During World War II several new mosquito repellents were de- Snow water.—Any of the treatments described above or a DDT solution, veloped (128, 158, 160), When emulsifiable concentrate, or wettable properly applied to exposed skin, powder applied to the breeding areas about 12 drops for the neck, face, late in the fall before the ground and both hands, they will prevent is covered with snow. Apply 0.5 to 1 mosquito bites for 2 hours to half pound of DDT per acre. a day, depending on the person, Log ponds,—DDT emulsion prepared as the species of mosquito present, described above, but applied about once a month as needed. A dosage of and mosquito abundance. The best 3 quarts per acre or about 0.2 part known of these repellents are of DDT to 1 million parts of water dimethyl phthalate, Rutgers 6-12, in the pond. and Indalone, and mixtures of Fire barrels,—25-percent DDT emulsi- them, usually 6 parts of dimethyl fiable concentrate, 1 cup to each bar- phthalate and 2 parts each of rel two or three times a year. Indalone and Rutgers 6-12. We Tree holes,—50-percent DDT wettable have tested a number of these re- powder, 1 or 2 tablespoonsful to each pellents against several species of cavity once or twice a year. Such cavi- mosquitoes in the Northwest and ties can also be filled with sand, or a hole can be bored at the bottom to believe a mixture is superior to allow drainage. the same materials used alone. 40 HANDBOOK 46. U. S. DEPARTMENT OF AGRICULTURE These materials can also be Practically all the commercial ñy sprayed lightly on field garments sprays containing pyrethrum, (fig. 25) to make them repellent DDT, methoxychlor, certain or- for several days {127). ganic thiocyanates, or lindane are safe and effective when used as directed on the label. Their proper application with a hand sprayer will quickly kill any mosquito indoors. A 1-pound aerosol bomb is a handy device for killing adult mosquitoes in homes (fig. 26) or

FIGURE 25.—Work clothing being sprayed with a repellent to keep mosquitoes from biting through.

Two repellents recently recommended for military use {159) are (1) 6 parts of dimethyl phthalate, 2 parts each of Indalone FIGURE 26.—Using an aerosol bomb to and Rutgers 6-12, and 4 parts of kill mosquitoes within a home. the n-propyl ester of N, N-diethyl- succinamic acid; and (2) 6 parts when on camping trips (fig. 27) of dimethyl phthalate, 2 parts and when traveling from place to each of dimethyl carbate and place during the mosquito season. Indalone. A few seconds' release of the Since the repellents are sol- aerosol will kill all mosquito spe- vents for paints, varnishes, and cies in an ordinary-sized room, plastics such as watch crystals, tent, or trailer. It is not hazardous nylon fabrics, and fountain pens, to humans if used as directed on they should be used with caution. the container. An aerosol formula Care should be taken not to apply much in use contains 0.4 percent them too liberally on the fore- of pyrethrins, 1.6 percent of re- head, as they will sting if they fined kerosene, 3 percent of DDT, get into the eyes. 5 percent of cyclohexanone, 5 percent of motor oil (A.A.E. 10), SPACE SPRAYS and 85 percent of Freon-12. Many Protection against mosquitoes modified formulas containing py- can be obtained with space sprays. rethrins, allethrin, DDT, meth- MOSQUITOES OF THE NORTHWESTERN STATES 41 oxychlor, and synergists are now Jersey mosquito larvicide (34-) available. A recently recommend- (see page 37) is also used as a ed aerosol formula contains 2 per- space spray against adult mos- cent of DDT, 0.6 percent of all- quitoes out of doors at the rate ethrin, 5 percent of alkylated of 15 to 25 gallons per acre. naphthalene, 7.4 percent of deod- Space sprays are effective for orized kerosene, and 42.5 percent only a few hours, but have been each of Freon-11 and Freon-12. used very successfully for outdoor

FIGURE 27.—Using an aerosol bomb to kill mosquitoes in a pup tent.

Mechanically generated aero- social functions and picnics, and sols, fogs, mists, sprays, and in and about amusement centers. smokes are now widely used out Where practical to treat late each of doors. Many home owners, afternoon, this is an excellent small-fruit farmers, and resort way of gaining relief from annoy- managers reduce mosquito annoyance, even though large numbers ance to a minimum with these of mosquitoes are in the neigh- new devices. The best results are borhood. Fruit pickers and lum- obtained when the work is done ber and road crews also benefit by experts such as mosquito- from their use. abatement superintendents or The new insecticides, such as licensed pest-control operators. BHC, lindane, chlordane, aldrin, DDT-oil solutions can be used for and dieldrin, are also effective as this purpose but some prefer a space sprays, but these materials pyrethrum-allethrin mixture be- are highly toxic and can harm cause of its rapid action against those using them, as well as those mosquitoes and low toxicity to living within the treated areas. warm-blooded animals. The New We must, therefore, caution 42 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE against their use by uninformed to 0.2 pound of DDT per acre. and untrained persons. For out- All applications from aircraft door space spraying in the North- should be directed by specialists west, a 5-percent DDT emulsion, and trained pilots. DDT concen- oil solution, or the New Jersey trates should not be used over larvicide is recommended until water where they would be haz- additional information is obtained ardous to fish. on the other materials. The use of aircraft is an eco- RESIDUAL SPRAYS nomical and safe way to disperse sprays over large areas to kill The stability, or long-time resid- adult mosquitoes (3). An oil solu- ual effectiveness, of DDT makes tion containing 5 to 20 percent it possible to apply a spray on of DDT and from 10 to 20 per- the interior surfaces of homes to cent of a heavy oil (S.A.E. 30 to kill mosquitoes that come in con- 50) in kerosene is an excellent tact with these surfaces for sev- formula for use by aircraft. eral months (fig. 28). This Larger pay loads may be ob- method is particularly adapted to tained by using a concentrate control of Anopheles mosquitoes, containing 25 percent of DDT, 10 because of their habit of entering percent of a wet±ing agent (such homes and other buildings, but it as Triton X-lOO-or equal parts of can also be used against Culex Span 20 and Tween 20), and 65 pipiens and tarsalis and some of percent of xylene. Both the oil the house-frequenting Aedes in solution and the concentrate are the Northwest. DDT residual applied at the same dosage of 0.1 sprays for use within buildings

1^ f-j'Ä S6?>i -Ä-ii*'j^ iEÍ»Í«l*.>É.

FIGURE 28.—Applying a DDT residual spray to the inside of a building to kill mosquitoes. MOSQUITOES OF THE NORTHWESTERN STATES 43

FIGURE 29.—Applying a DDT residual spray to vegetation to control mountain mosquitoes. should contain 5 percent of DDT. orchard sprayers. Water is added An oil solution or emulsion, ap- to give a 5- to 10-percent emulsion plied at the rate of about 1 gallon or a 2.5-percent wettable-powder per 1,000 square feet, is pre- suspension. ferred. A dosage of II/2 pounds of lin- The spraying of all vegetation dane per acre gives about the to a height of about 10 feet (fig. same control as 2 pounds of DDT. 29), as well as the surfaces of Space sprays containing 0.2 to the buildings and the screens, to 0.4 percent of pyrethrins or all- leave a residue of DDT where the ethrin applied at dusk will give mosquitoes rest will reduce mos- excellent control when used in quito annoyance in mountain conjunction with the heavier resi- camps (66). Applications of 2 to dual spray. 3 pounds of DDT per acre have given good control for 10 days and sometimes for as long as 45 CONTROL OF days. If the area to be protected RESISTANT MOSQUITOES is surrounded by extensive breeding areas, enough mosquitoes may The only known mosquito vec- fly into the treated areas to be tor of disease that appears to annoying for 2 hours at dusk, but have developed a high resistance they will be killed later as they to insecticides on the West Coast settle on the treated foliage. is Culex tarsalis in California. Emulsifiable concentrates are pre- Up to the end of 1951 no resist- ferred for use in mist blowers and ance by tarsalis had been ob- either emulsifiable concentrates served in the Northwest. While or wettable powders for use in no specific recommendations are 44 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE made for the Northwest, if resist- trucks or jeeps (^S, 108). ance develops toxaphene, lindane, Aircraft {3) is both effective aldrin, heptachlor, dieldrin, and economical for treating large chlordane, EPN, NPD, or mala- areas to kill both larvae and thon may be considered for use. adults (fig. 30). Excellent results have been obtained with small aircraft over extensive flood- EQUIPMENT FOR water lowlands along the Colum- APPLYING INSECTICIDES bia River and in large irrigated sections. Most commercial air- Hand sprayers of the flit-gun craft operators can be relied on type are satisfactory for spray- to do an effective and safe job. ing small puddles to kill larvae or for use indoors against adult NATURAL ENEMIES mosquitoes. Aerosol bombs are OF MOSQUITOES best for applying space sprays within enclosures. Areas of an Many insects, fishes, birds, and acre or more can be treated with other organisms prey upon mos- a 3- or 4-gallon compressed-air quito larvae {6Ip). However, the sprayer or knapsack sprayer only natural enemies of appre- {H-3). Paint-type sprayers, which ciable value in control programs produce an atomized spray, can are the minnows Gambusia affinis also be used in such places. and Fundulus (119). These fish Power equipment of various thrive best in warm parts of the types is used in extensive low- country, but may establish some lands and marshes. This equip- tolerance to freezing for short ment includes orchard-type spray- periods west of the Cascade ers, mist blowers, heat-generated Mountains. We have introduced aierosol and fog machines, and de- Gambtisia into the Northwest vices attached to the exhaust of from California, but since, except

FIGURE 30.—An airplane with a breaker-bar sprayer mounted under each wing strut for treating large areas against mosquitoes. MOSQUITOES OF THE NORTHWESTERN STATES 45 for dorsalis, most of the impor- tured the larvae by wavering tant Aedes breeding grounds in about the container. After a lar- this region are dry the greater va was captured it appeared un- part of the year, these fish are able to release itself, even with of little practical use here. How- some assistance from the ob- ever, they do keep Culex and server. In our limited observa- Culiseta larvae in check in log tions each worm devoured one ponds until the water becomes to two larvae per day. too polluted for the fish. They Adult mosquitoes have a num- can be used also in permanent ponds and ornamental pools in- ber of natural enemies, such as habited by Anopheles and Culex certain birds, bats, and preda- tarsalis. ceous insects (65). Undoubtedly Rarely we have observed Pia- swallows, some night-flying birds, naria maculata Lindy, a fiat worm bats, dragonflies, and damsel flies 15 mm. long, feeding on larvae eat large numbers, but they seem in the laboratory. In restricted to have little effect in reducing quarters these worms easily cap- mosquito populations.

KEYS AND NOTES FOR IDENTIFYING THE MOSQUITOES OF THE NORTHWEST The 39 species of mosquitoes found. Only the more important found in the Northwestern States characters for each species have belong to 5 genera. Keys for their been included in this section, and determination have been based on synonyms of recent date are given, those found in the literature (2, The taxonomic characters used 22, 2U, 35, 37, 63). In a number for identifying the Aedes mos- of species new characters which quitoes in the Northwest are facilitate determination have been shown in figures 31 to 35. KEY TO GENERA ADULTS 1. Scutellum trilobed with marginal setae on the lobes only; palpi (in females) much shorter than the proboscis 2 Scutellum crescent-shaped with marginal setae evenly distributed; palpi of males and females almost as long as proboscis Anopheles 2. Postspiracular bristles present Aedes Postspiracular bristles absent 3 3. Spiracular bristles present Culiseta Spiracular bristles absent 4 4. Wing scales broad, pale, and dark-mixed Mansonia Wing scales narrow or slightly broadened all dark Culex LARVAE 1. Eighth segment without a dorsal siphon or respiratory tube Anopheles Eighth segment with elongated siphon or respiratory tube 2 2. Distal half of tube attenuated with saw-tooth projection at tip for piercing purposes ; without pectén teeth Mansonia Air tube cylindrical and elongated 3 3. Air tube with siphonal tufts at base Culiseta Air tube with tufts within the pectén teeth or distal to them 4 4. Air tube with several pairs of tufts extending from pectén teeth to end of tube Culex Air tube with only one pair of tufts distal to pectén teeth^ Aedes 2 Aedes trichurus has a small tuft on the dorsal and one on the lateral surface of the air tube. 46 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE

FIGURE 31.—Taxonomic characters used in identifying adult mosquitoes in the Northwest. Aedes hexodontus. MOSQUITOES OF THE NORTHWESTERN STATES 47

Scutellum

FIGURE 32.—Lateral view of Aedes head and thorax, /is, Hypostigial spot of scales. Sclerites of the thorax: l,anterior pronotiim; 2, proepisternum; 3, postpron- otum; 4, mesanepisternum; 5, prealar, area; 6, sternopleuron; 7, mesepimeron; 8, metepisternum; 9, metasternum ; 10, metepimeron ; 11, postnotum; 12, meron. Setae: apn; anterior pronotal; ps, proepisternal; ppn, postpronotal; psp, postspiracular; pa, prealar; si, sternopleural; ume, upper mesepimeral; /me, lower mesepimeral.

FIGURE 33.—Wing of Aedes mosquito, illustrating venation (modified from Ross and Roberts 120), H-v, humeral cross-vein; C, costa; Se, subcosta; Pt, petiole of vein 2; 1, 2.1, 2.2, 3, 4.1, 4.2, 5.1, 5.2, and 6, numbered longitudinal veins and their branches. 48 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE

FIGURE 84.—Male genitalia of Aedes cataphylla, dorsal view, showing parts: SP, side piece; Sc, scale; BL, basal lobe; Mes, mesosome; L9, lobe of ninth tergite; 9T ninth tergite; S, spine of clasper; CL, clasper; AL, apical lobe; F, filament of claspette; Clsp, claspette; lOS, tenth sternite; P, paramere; BP, basal plate,

ANTENNA. HEAD HAIRS . ANTENNAL TUFT UPPER.tî'Tf^Z ANTEANTENNAL TUFT HEAD

THORAX

ABDOMEN

LATERAL COMB ^^OF 8TH SEGMENT

ANAL G/LLS. DORSAL TUFT. ^ ...,.,.. Ll^ENTRAL TUFT

FIGURE 35.—Larval characters used in identifying mosquito larvae ^f the Northwest. MOSQUITOES OF THE NORTHWESTERN STATES 49 Genus ANOPHELES Meigen

KEY TO SPECIES

Adults 1. Wings with yellowish-white spots on the costal margin 2 Wings without spots on the costal margin 3 2. Palpi white-banded; wings with pale spots on the forks and on the stem of vein 5 pseudopunctipennis franciscanus Palpi unhanded; wing scales on vein 5 dark punctipennis 3. Wings with patch of silvery or bronze-colored scales on the apex and heavy dark patches of scales on the veins occidentalis Wings dark scaled at the apex, the patches on the veins not very pronounced freeborni

Male Genitalia 1. Claspette with dorsal lobe bearing 2 or 3 broad leaflets; mesosome with very delicate leaflets psevdopunctipennis franciscanus Claspette with dorsal lobe bearing 2 or 3 sharp spines; mesosome with well-developed leaflets 2 2. Claspettes abruptly conical punctipennis Claspette lobe rounded 3 3. Claspers with dense patch of small hairs at the base; lobes of the ninth tergite short and broad occidentalis Claspers with patch of scattered hairs at the base; lobes of the ninth tergite long and slender freeborni

Larvae 1. Both inner and outer anterior clypeal hairs single pseudopunctipennis franciscanus Outer anterior clypeal hairs branched 2 2. Antepalmate hair of abdominal segments 4 and 5 one-branched; postclypeal hair multiple occidentalis Antepalmate hair of abdominal segments 4 and 5 usually two- branched; postclypeal hair bifurcate at middle to base; fronto- clypeus with a spotted pattern freeborni Antepalmate hairs of segments 4 and 5 usually three-branched ; postclypeal hairs bifurcated from insertion point and frontoclypeal banded punctipennis^

ANOPHELES FREEBORNI Aitken into spots at the junction of the Anovheles maculipennis freeborni fi^*st and second veins, the forks Aitken, Pan-Pacific Ent. 15: of the second and fourth, and at 192. 1939. the cross veinSo Legs black, the A^^^^-r 1^ X i^ ' Tr- j apices of the femora and tibia Anopheles /ree&orm King and with pale-yellowish scales. Bradley, Human Malaria, pp. ^ ^ .^ ,. .^ ^^ _. 65, 75. 1941. Claspettes^. ^«^t. ^^ u'fbilobed, u^ ^^?liwith ^^' 2 (some-.^"-^ Female.—Palpi as long as pro- times 3) spines on ventral lobe boscis, dark brown. Mesonotum and usually with 2 spines on dor- with a pruinose gray stripe sal lobe. Mesosome with four bordered by dark bands, the pairs of nonserrated leaflets. median stripe with hair-like yel- Ninth tergite with slightly short- lowish scales and a small tuft of ened, broadened lobes. Claspers whiter scales anteriorly. Wing with bases covered with a dense scales dark brown and aggregated patch of nonpapillated hairs. 3 These larvae are difficult to separate from those of freeborni. 50 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE Larva.—The larvae of this spe- Female.—Similar to freeborni, cies are very similar to those except for slightly more con- of punctipennis. Minor variations trasting stripes on the meso- are given in the key. notum, darker and more pro- Distribution^ biology^ and im- nounced wing spots, and the pres- portance,—Anopheles freeborni is ence of a spot of pale scales at widely distributed in open and the apex of the wing. wooded country throughout the Northwestern States (2), It oc- Male genitalia (fig. 36, F).— curs in clean, sunny water, Similar to genitalia of free- wherever suitable breeding places borni, except for the smaller num- are found. Comparatively large ber of hairs on the base of the populations develop in irrigated claspers and the slightly longer areas in the Yakima Valley in and more slender lobes of the Washington and in the vicinity of ninth tergite. Scappoose, Prineville, and Kla- math Agency, Oreg. It has been Larva.—Only minor characters found in abundance in the irri- are available for separating gated section of west-central the larvae of this species from Idaho. This species, the most im- freeborni and punctipennis. The portant malaria carrier in the postclypeal hairs have 2 to 3 Western States, is prevalent also stout branches near the middle. in the Willamette Valley in Ore- The frontoclypeal is banded and gon, where most of the malaria the antepalmate hairs on seg- cases in this region have occurred. ments 4 and 5 are usually single Western equine encephalomyelitis and unbranched. has been isolated from it in na- Rozeboom {12S), in recent ture. work in Montana on anophelines, The females hibernate in root claims that the mosquito east of cellars, barns, outbuildings, and the Rocky Mountains hitherto other sheltered locations. They called occidentalis is earlei. An emerge from these places by the additional character he has used latter part of February ^ in the to differentiate between the two warmer parts of this region, but species is that the egg of earlei few eggs are laid before April is barred whereas that of occi- or May. Larvae have been taken dentalis is plain. along the margins of rivers, creeks, and irrigation ditches and Distribution^ biology^ and im- in ponds, sloughs, and roadside portance.—This mosquito has been ditches from early in May until found in small numbers in south- frost. Apparently the females ern Oregon, in the mountains of mate before going into hiberna-» northern Washington and Idaho, tion, because the males do noti and near the southeastern border overwinter. The adults are some- of Idaho. The larvae have been times found in fairly large num- found alone and also associated bers early in September. It is fre- with the other three species of quently associated with Culex Anopheles in this region. They tarsalis. have also been taken with Culex ANOPHELES OCCIDEISTALIS (Dyaii tarsalis and Culiseta inornata. and Knab) Breeding places usually contain Anovheles oceidentalîi^ Dvar and moss and algae, but larvae have Knab, Biol. Soc. Wash. Proc. been observed in open grassy 19: 159. 1906. pools. MOSQUITOES OF THE NORTHWESTERN STATES 51

FIGURE 36.—Male genitalia: A, Culex stigmatosoma; B, C. tarsalis; C, C. pipiens; D, C. territans; E, Anopheles freeborni; F, A. occidentalis, lobes of ninth tergite; G, A, punctipennis. 52 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE ANOPHELES PSEUDOPUlSCTIPENmS Larva.—Both the inner and FRANCISCANVS McCracken outer clypeal hairs of the larvae Anopheles franciscanus McCrack- of this species are single and un- en, Ent. News 15: 12. 1904. branched, and the postclypeal hairs are also single and long. Anopheles pseudopunctipennis The abdominal palmate hairs on var. franciscanus King and segments 3 to 7 are well-developed Bradley, Human Malaria, 65 and serrate. In the race francisca- pp. 1941. nus the posterior spiracular plates Anopheles pseudopunctipennis are not developed into "tails," but franciscanus Aitken, Calif. are rounded. Univ. Pubs. Ent. 7 (11) : 327. Distribution^ biology^ and im- 1945. partance.—This species has been found rarely in the extreme south- Female.—Palpi as long as pro- western part of Oregon and in the boscis, black-scaled with white vicinity of Medford. The larvae rings at the joints of the apical are usually associated with free- end of the two preceding seg- borni along streams in sunny ments. Mesonotum with a median pools containing algae. Very little pruinose gray stripe bordered by information is available regard- dark bands; the median stripe ing its habits in the Northwest. with hairlike gray scales and a tuft of whiter ones anteriorly. ANOPHELES PUNCTIPENNIS (Say) Wing scales black, with yellowish- Culex punctipennis Say, Acad. white scales forming spots as Nat. Sei. Phila. Jour. 3: 9.1823. follows : Costa and subcosta with Anopheles perplexens Ludlow, two on the apical half, the sub- Canad. Ent. 39: 267. 1907. costa with two additional ones Female.—Palpi as long as the on the basal half; second vein proboscis, dark brown. Mesono- with a small one near the cross tum with pruinose gray stripe vein and a small one before the bordered by dark bands; the apex of the upper branch; third median stripe with hairlike gray vein with a small one at the base scales and a tuft of whiter ones and a large one in the middle; anteriorly. Wing scales black, fourth vein with a small one at with yellow ones forming spots the cross vein and a small one at as follows: A large one on the the apices of the forks ; fifth vein basal third of the costal margin, with a small one at the base and which involves the base of the a large one extending into the second vein before the fork; a lower fork, small ones at the smaller one on the apex of the apices of the forks and a small wing, which involves both forks one near the middle of the upper of the second vein; third vein fork ; sixth vein with a long spot with a spot at apex or near the at the base. Legs black, the tips middle or completely dark-scaled ; of the femora and tibia with pale- fourth vein with two spots on the yellowish scales. base and one spot on each fork; Male genitalia.—Claspette bi- sixth vein with one spot in the lobed with 2 slender spines on middle. Legs black, the tips of the the ventral lobe and 2 or 3 broad, femora and tibia with pale-yel- leañike spines on the dorsal lobe. lowish scales. Mesosome with very small non- Male genitalia (fig. 36, G).— serrated leaflets. Ninth tergite Claspettes bilobed, usually with with low conical processes. one large outer spine and an MOSQUITOES OF THE NORTHWESTERN STATES 53 inner more slender spine on the Either 2 or 3 antepalmate hairs ventral lobe, and 2 spines on the on segments 4 and 5. Anal seg- dorsal lobe. (The number of ment longer than wide, and dor- spines is highly variable.) Meso- sal plate with a long, single lateral some with well-developed non- hair. Anal gills as long as segment serrated leaflets. Ninth tergite and bluntly pointed, with broad, normal lobes. Distribution^ biology, and im- Larva.—Head longer than wide, portance.—This is a common Posterior clypeal hairs usually species throughout Washington, bifurcate to the base, inner the northern half of Idaho, and clypeal hairs sinlge, unbranched, west of the Cascade Mountains in and set close together. Fronto- Oregon. The larvae are usually clypeal sclerite pale-banded, associated with freeborni in clean Abdomen with palmate tufts shaded pools. A. punctipenms is on segments 3 to 7 and occasion- believed to be of little impor- ally a small one on segment 2. tance as a malaria carrier.

Genus AEDES Meigen KEY TO SPECIES Adults 1. Tarsal segments ringed with white 2 Tarsal segments not ringed with white ^^ 2. Tarsi with white rings at both ends of the segments ^ Tarsi with white rings at base of segments only o 5. Wing scales black and white intermingled ;••.•• ^ Wing scales uniformly dark or with some white scales on anterior vein ^ .' 4. Wing scales uniformly mottled black and white compestris Wing scales not uniformly mottled; third vein with more dark scales than second and fourth dorsahs 6. Mesonotum golden brown; base of costa dark scaled canadensis Mesonotum with variable pattern of pale yellowish and dark spots; base of costa with white scales varipalpus tí. Proboscis of female ringed with white mgromacuhs Proboscis of female not ringed with white ., • • < 7. Basal white rings of tarsal segments narrow (mesonotum uniformly brown; abdominal pale bands indented centrally) . ... vexans Basal white rings of tarsal segments broad, especially on the hind legs ° 8. Abdomen without bands and clothed with yellow scales; (mesonotum yellowish brown with darker median area) flavescens Abdomen dark-scaled with white or gray dorsal bands 9 9. Lower mesepimeral bristles absent (mesonotum with variable pattern of brown and white, on completely reddish-brown scale) excrucians fitchii (in part) Lower mesepimeral bristles present 10 10. Torus without scales on dorsal half; 1 to 5 lower mesepimeral bristles tncrepitus Torus with white scales on dorsal half; lower mesepimeral bristles 0 to 4 but rarely more than 2 fitchii (in part) 11. Wing scales distinctly bicolored 12 Wing scales uniformly dark or nearly so 13 12. Wing scales pale and dark intermixed, the dark predominating; lower mesepimeral bristles present niphadopsis Wing veins alternating black and white ; lower mesepimeral bristles absent • • idahoensis 13. Mesonotum without lines or stripes 14 Mesonotum with lines or stripes 18 14. Lower mesepimeral bristles absent 15 Lower mesepimeral bristles present 16 54 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE 15. Mesonotum uniformly brown; abdomen with continuous lateral white line cinereus Mesonotum brown with margin of yellowish scales; abdomen with continuous lateral white line ventrovittis 16. Torus with integument of outer side yellow to light brown or darker; mesonotum uniformly brown; or rarely with indications of median brown lines intrudens Torus with integument of outer side dark brown or black 17 17. Mesonotum gray around the sides with golden-brown scales in the middle, which sometimes show faint dark lines cataphylla Mesonotum with dark-brown or bronzy scales, sometimes with a pair of lighter spots centrally nearcticus 18. Lower mesepimeral bristles absent; mesonotum with two golden brown stripes, with or without a faint pale median line sticticus Lower mesepimeral bristles present 19 19. Hypostigial spot of few to many white scales 20 Hypostigial spot absent 21 20. Mesonotum with paired brown lines separated by a double line of yellowish scales with a narrow bare median line between them; torus with integument of outer side dark brown or black pullatus Mesonotum with a median brown stripe expanded in width behind the middle; torus with the integument of the outer side usually yellow to light brown trichurusy impiger (in part) 21. Mesonotum yellow or rarely gray, with paired dark-brown lines or variable pattern; integument of tori varying from yellow to t>lack communist Mesonotum yellow or rarely gray, with paired dark-brown stripes narrowed at the back and extending to the scutellum ...., pionips^ Mesonotum with median brown stripe, paired brown stripes or variable pattern ; margin grayish white impiger Mesonotum golden brown with paired dark-brown stripes which are sometimes joined; integument of tori black or dark brown hexodontuss Mesonotum yellowish to light golden brown with dark-brown stripes and posterior half lines aboriginis^

Male Genitalia

1. Clasper inserted before the apex of side piece; unequally bifurcate at the base cinereus Clasper not inserted before the apex of the side piece; not branched at the base 2 2. Clasper broad and flat throughout its length with subapical spine; claspette a setiferous knob without a filament vexans Clasper tapered to the apex with apical spine; claspette with a filament 3 3. Side pieces without distinct apical lobe 4 Side pieces with both apical and basal lobes 5 4. Side piece expanded at the base; the basal lobe narrowly elongate and clothed with long setae; a secondary area with short setae beside it varipalpus Side piece not expanded at the base ; the basal lobe a small elevated area with relatively short setae nigromaculis 5. Filament of claspette with transverse ridges; (small secondary lobe near basal lobe with two long spines) trichurus Filament of claspette without transverse ridges 6 6. Apical lobe with short appressed setae 7 Apical lobe with long hairs or nearly bare 8 7. Basal lobe with portion extending toward apex of side piece, semidetached sticticus, idahoensis, ventrovittis Basal lobe with portion extending toward apex of side piece, not semidetached hexodontus, aboriginis 4 Base of costa and sometimes vein 1 white-scaled in 75 to 95 percent of the specimens. 5 Base of costa white-scaled in about 95 percent of specimens. 6 Base of costa black-scaled in 90 to 100 percent of specimens. MOSQUITOES OF THE NORTHWESTERN STATES 55 8. Basal lobe without spines ^ Basal lobes with spines 11 9. Filament of claspette narrow and of approximately equal width... canadensis Filament of claspette expanding along one margin 10 10. Basal lobe flat, rugose, setose, and extending to apical lobe ... excrucians Basal lobe not extending beyond middle of side piece increpitus 11. Basal lobe with one spine 12 Basal lobe with two or more spines 17 12. Basal lobe extending almost to the apical lobe flavescens Basal lobe a small area at the base of the side piece 13 13. Apical lobe of the side piece nearly bare 14 Apical lobe distinctly setose 15 14. Filament of the claspette expanded into a sharp projection near the base impiger Filament of claspette expanded in a gradual curve near the base niphadopsisy cataphylla 15. Filament of the claspette sickle-shaped with a small notch at the base fitchii Filament of the claspette not notched at the base 16 16. Basal lobe quadrilateral in outline communis, pionips Basal lobe cone- or wedge-shaped nearcticus 17. Claspettes with sharp projections or right angle bends at the middle of the inner margin ^ 18 Claspettes without sharp projections or bends at the middle of the inner margin 19 18. Claspette with rounded angle at the middle pullatus Claspette with sharp projection ending in a stout setae at the middle intrudens 19. Filament of claspette gradually expanded in a circular shape from the base to the middle campestris Filament of claspette a narrow basal stem which expands broadly near the middle dorsalis

Larvae 1. Pectén on air tube with detached teeth outwardly 2 Pectén on air tube without detached teeth outwardly 11 2. Air tube with tufts within pectén « 3 Air tube with all tufts outside pectén and distal to it 4 3. Air tube with tuft within the pectén and several rows of tufts distal to pectén trichurus Air tube with tuft between evenly spaced pectén teeth and detached teeth ^ cataphylla 4. Anal segment completely ringed by plate nigromaculis Anal segment not completely ringed by plate 5 5. Both t>airs of head hairs usually single 6 Both pairs of head hairs multiple 8 6. Air tube about four times as long as wide; gills small or budlike.. .niphadopsis Air tube about 2^/^x1; gills pointed and as long or longer than segment 7 7. Comb on eighth segment 6 to 9 scales, with basal spinules ventrovittis Comb on eighth segment 9 to 20 scales, without basal spinules idahoensis 8. Both pairs of head hairs, 5 or more, tufts set close together; gills very long and pointed cinereus Upper head hairs 4, lower 2 or 3 (anal gills short and bluntly pointed) intrudens Lower hairs double, upper usually double or triple 9 9. Comb on eighth segment 10 to 25 scales in irregular row (tuft of small fine hairs on air tube set close to end of pectén teeth).... vexans Comb on eighth segment 40 or more scales in triangular patch ... 10 10. Air tube 4x1, pectén not reaching middle of tube; lateral abdominal hairs usually double on segments 1 and 2 and single on 3 to 6. .. excrucians Air tube 3x1, with pectén reaching the middle; lateral abdominal hairs double on segments 1 to 6 flavescens 11. Anal segment ringed by the plate hexodontus Anal segment not ringed by the plate 12 56 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE 12. Anal gills long, enlarged and spatulate (antennae slender, without spines, and with single hairs in middle) varipalpus Gills and antenna normal 13 13. Both pairs of head hairs single 14 Upper head hairs multiple, lower usually multiple 17 14. Comb on eighth segment has many scales in triangular patch 15 Comb on eighth segment has 10 to 25 scales in irregular rows 16 15. Anal gills pointed and two to three times length of segment; lateral abdominal hairs double on segments 1 and 5 and single on 6 communis Anal gills budlike or, if longer, bluntly pointed and not so long as segment; lateral abdominal hairs triple on segments 1 and 2, double on the rest dorsalis 16. Comb on eighth segment, 8 to 14 scales; anal gills three to four times length of segment nearcticus Comb on eighth segment, 15 to 25 scales; gills slender and about ^ as long as segment impiger 17. Air tube four or more times as long as wide fitchii Air tube never 4x1, usually 3 x 1 or less 18 18. Upper head hairs 5 to 8, lower 3 to 5 19 Upper head hairs not more than 4, lower 1 to 3 21 19. Air tube stout 2% x 1 with closely set pectén teeth to near middle; anal segment as long as wide pionips Air tube 3x1 with pectén teeth on basal one-third; anal segment longer than wide 20 20. Anal gills two or more times length of anal segment pullatus Anal gills only about as long as segment ccmadensis 21. Gills small and budlike; pectén on air tube extending two-thirds of its length, the last tooth sometimes slightly detached, a tuft near tip campestris Gills pointed, as long or longer than segment ; pectén not extending beyond middle of segment 22 22. Head hairs, upper 3 to 4, lower 2 to 4 (lateral abdominal hairs, 1 or 2 long stout hairs) aboriginipt Upper head hairs 2 to 3, lower 1 to 2 23 23. Anal segment broader than long; air tube stout 2i^ xl; anal gills considerably longer than segment sticticus Anal segment as long as broad ; air tube 3x1; anal gills about as long as segment increpitus

AEDES CAMPESTRIS Dyar and Knab Male genitalia (fig. 37, C).—

29QYN. Y. Ent. Soc. ^Jour. ux. 15:J.U. ^xo.213 lowf convex^^^^ ^^ With .,^^^1 rather ^?'''^^ long setae ^^^ ; basal lobe rounded, slightly Female. — Mesonotum yellow- raised, and covered with many ish-white with median brown setae, a large spine and several stripe, the sides with a narrow long spinelike setae at the basal brownish margin. Abdomen black margin. Claspette hirsute with with median white line, and apical two or three small setae just be- and basal white bands forming low the apex, the filament nar- small paired segmental dark rowly and roundly expanded in a areas. Wing scales pale and dark, sickle shape, evenly intermixed. Legs with dark Larva.—Antennae spinose. Up- and pale scales, tarsi dark with per head hairs multinle, lower basal and apical white bands, ex- 1 or 2. Comb on eighth segment cept on last two segments of mid- with many scales in a triangular tarsus and last three segments of patch. Air tube about 3x1, taper- fore tarsus. ing with pectén reaching two- MOSQUITOES OF THE NORTHWESTERN STATES 57

FIGURE 37.—Male genitalia: A, Aedes dor salis; B, canadensis; C, campestris; D, aboriginis; E, excrucians; F, nearcticus; G, increpitus; H, pullatiis; I, mtn¿c?e?2S. 58 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE thirds of the distance to apex and Male genitalia (fig. 37, A).— a small tuft near the tip, the last Side pieces about three times as tooth sometimes stouter and long as wide ; apical lobe rounded, slightly detached. Anal segment and somewhat shortened apically, as long as wide, anal plate reach- the surface clothed with rather ing nearly to ventral line; gills long setae; basal lobe prominent, small and budlike. slightly constricted at the base, Distribution^ biology, and im- and covered with short setae, a portance.—This species has been stout spine on the margin and a found in only a few small areas smaller adjacent spine. Claspette in Oregon and Washington. The straight, hirsute, and constricted larvae develop in open, unshaded just before the apex, with 2 long water and are sometimes associ- and 1 short setae at the constric- ated with dorsalis. Correspon- tion, the filament broadly expand- dents report the eggs as very re- ed in a rounded rectangular shape sistant to adverse conditions. It at the middle. is an early-season species, the Larva.—Antennae spinose. adults appearing in June. They Both pair of head hairs single. will bite during the day, as well Abdomen stout with few hairs; as during the hours of darkness. lateral tufts triple on segments Rees (109) reports it flying 10 1 and 2 and double on the rest. miles from its breeding place in Comb on eighth segment with Utah. It is of little importance in many scales in a triangular patch. the region. Air tube tapering, about 3x1; pectén evenly spaced to near middle of the tube, with a multiple AEDES DORSALIS (Meigen) tuft set close to end of pectén. Anal segment slightly longer Culex dorsalis Meigen, Syst. Bes. than wide; anal gills either bud- Bek. Eur. Zwei, Ins. 6: 242. like or, if longer, bluntly pointed 1830. and seldom as long as the Aedes melanimon Dyar, Ins. segment. Ins. Mens. 12: 126. 1924. Distribution, biology, and ¿m- portance.—This is one of the most Female.—Mesonotum yellowish important and widely scattered white with a median brown pest mosquitoes in the Northwest- stripe, or with only a few brown ern States. We have not found scales medianly; posterior brown it in the northern half of Idaho. half lines and side lines may or The larvae develop in open, sunny may not be present. Abdomen areas that are flooded by saline, with apical and basal white bands alkaline, or fresh water. They and complete or partial median thrive in water of high alkalinity. white line; the last onç or two It is the only species that breeds segments may be entirely white- in the salt marshes in this region scaled. Wing scales black and and is one of the most abundant white; the costa first, third, and and troublesome species in irri- fifth veins with more black scales gated meadows and in grasslands than the others. Legs with dark that are inundated by floodwater. and pale scales ; tarsi dark with A. dorsalis larvae are sometimes apical and basal white bands on associated with those of nigro- all but last two segments of mid- maculis and campestris in the tarsus and last three segments of more alkaline waters and with fore tarsus. vexans in fresh water. Rees {111) MOSQUITOES OF THE NORTHWESTERN STATES 59 reports that seven successive Larva.—Antennae spinose. Up- broods have been taken from the per head hairs 6 to 7, lower 4 to same locality during a single sea- 5; lateral abdomen hairs usually son, and that the eggs may re- double on segments 1 to 5 and main viable for 2 or 3 years. The single on 6. Comb on eighth seg- high temperatures in midsummer ment with 25 to 40 scales in an in the inland valleys cause the irregular patch. Air tube 3x1; adults to emerge in about 5 days pectén even, reaching beyond one- after the land has been flooded. third of tube, followed closely by It is a persistent biter, even in tuft of 4 to 6 medium hairs. Anal midday and will enter houses to segment longer than wide; anal obtain blood meals. It is very an- gills pointed and about as long as noying to livestock. Adults are the segment. readily attracted to light traps Distribution^, biology^ and im- and are strong fliers. Rees (109) portance.—This species breeds in has observed them 22 miles from woodland pools. It has not been their breeding grounds. Western taken in Oregon, but has been equine encephalomyelitis and St. collected in large numbers in Louis encephalitis viruses have northern Idaho and has also been been isolated from this species in taken in Ferry, Okanogan, and nature, and it has been demon- Grant Counties, in Washington. strated as an experimental vector It is the predominating species for Japanese B and California around Payette Lake in Idaho. encephalitis viruses. The larvae can be found in temporary forest pools which are flooded by melting snow. They AEDES CANADENSIS (Theobald) seem to prefer laying their eggs in depressions containing decay- Culex canadewsis Theo., Mon. Cu- ing leaves and other debris. We lic. 2: 3. 1901. have also found a few at high Female. — Mesonotum reddish elevations in open meadows. The brown with pale-yellow scales species bites severely and is a con- around the margins. Abdomen siderable pest, especially in late black without basal white bands afternoon in large wooded areas. or with narrow indistinct ones; the sides with triangular white AEDES MGROMACULIS (Ludlow) spots. Wing scales all dark. Legs black; hind and midtarsal seg- Grabhamia nig7^omaculis Lud., ments apically and basally white- Geo. Wash. Univ. Bui. 5: 85. banded; fore tarsus banded on 1907. segments 1 and 2 ; last segment of Female.—Proboscis of female hind leg entirely white-scaled. ringed with white. Mesonotum Male genitalia (fig. 37, B).— with varying shades of yellowish Side pieces slightly more than scales, a broad median bronzy- twice as long as wide ; apical lobe brown stripe, and brown sides. large, low, and broadly rounded Abdomen black with basal seg- with short bladelike setae; basal mental bands and median stripe lobe long, with many short setae. of yellowish scales; the lateral Claspette cylindrical and setose, a spots usually concolorous with the larger seta before the apex; the median stripe. Wing scales pale filament narrow, linear, pointed, and dark, the dark predominat- and slightly shorter than the ing. Femora and tibiae partially stem. pale-scaled ; tarsi black with basal 60 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE

FIGURE 38.—Male genitalia: A, Aedes nigromaculis; B, hexodontus; C, sticticus; D, varipalpus; E, einereics; F, vexans. MOSQUITOES OF THE NORTHWESTERN STATES 61 white bands ; the last segment of to brown with a broad median the hind tarsus rarely all white, stripe of slightly darker brown the white band on the first seg- scales. Abdomen covered with ment broadly extended by scat- dull-yellow scales or with a dark tered white scales. median line and sides partially Male genitalia (fig. 38, A).— black-scaled anteriorly. Wing with Side pieces twice as long as wide ; a mixture of black and yellow apical lobe absent; basal lobe a scales. Legs brown with a mix- small elevated area with many ture of yellow scales; tarsi with rather short setae. Claspette with broad basal white band. a cylindrical stem and a short Male genitalia (fig. 39, D).— setae near the outer end ; the fila- Side pieces more than twice as ment narrow and as long as the long as wide; apical lobe promi- stem. nent rounded with many setae; Larva.—Both pairs of head basal lobe a rugose, slightly ele- hairs single and antennal tuft vated area with many setae, a small. Comb on eighth segment stout spine and several long setae with about 9 thornlike scales. Air near the base, the lobe extending tube 2 X 1 ; pectén extending well nearly to the base of the apical past the middle, with 3 stout de- lobe. Claspette lightly hirsute tached teeth; a small tuft near with three stout setae on the in- the tip. Anal segment longer than ner margin of the base; the fila- wide and ringed by the plate. ment angularly expanded to a Anal gills pointed and longer rounded point near the base. than the segment. Larva.—^Upper head hairs usu- Distribution, biology^ and im- ally 3 to 4, lower usually double. portance.—This species is found Lateral abdominal hairs double associated with dorsalis, idaho- on segments 6 to 8. Comb on ensis, and vexans in open irri- eighth segment with many long gated or flooded meadows in spinelike scales in a triangular prairie or open country. It has patch. Air tube tapering, about been found in only south-central 3x1; pectén reaching middle, Washington, but is more common with 2 detached teeth followed by in the semiarid plains of Oregon a tuft of 4 to 6 hairs. Anal seg- and Idaho. It is most numerous in ment slightly longer than wide. the lower Payette River district Anal gills about as long as the of western Idaho. It is also an segment. important pest in some other irri- Distribution, biology, and im- gated sections. It is a persistent portance.—This is a typical plains daytime biter. Apparently it species, and has been taken in breeds continuously throughout limited numbers in widely sep- the season and is associated fre- arated places east of the Cascade quently with dorsalis. This spe- Mountains, but it rarely occurs in cies is a strong flier. Experimen- sufficient numbers to be a serious tally it has transmitted western pest. Larvae have been found in equine encephalomyelitis and St. meadow pools and marshes in the Louis and Japanese B encepha- vicinity of alkaline flats. It is a litis viruses. fierce day-time biter and attacks both man and beast. We have ob- AEDES FLAVESCENS (Müller) served it biting in full sun and Culex flavescens Müller, Faun. during a breeze of about 7 miles Ins. Fried, p. 87. 1764. per hour. Hearle (59) has report- Female.—Mesonotum yellowish ed its life history. 62 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE

FIGURE 39.—Male genitalia: A, Aedes communis; B, A. fitchii; C, A. niphadopsis; D, A. flavescens; E, Culiseta impatiens; F, C incidens; G, C. inornata; H, C morsitans. MOSQUITOES OF THE NORTHWESTERN STATES 63

AEDES EXCRUCIAISS (Walker) Distribution, biology, and importance.—This species is widely Culex excrucians Wlkr., Ins. distributed at low elevations in Saund., p. 429. 1856. mountainous areas in the North- Aedes aloponotum Dvar, Ins. western States and is found in Ins. Mens. 5: 98. 1917. both open and semiwooded areas. Female.—Tori with inner sur- We found it in the Cascade Moun- faces predominately white-scaled. tains and in Lake and Klamath Mesonotum yellowish white with Counties of Oregon, as well as a median brown stripe, varied through the wooded section of pattern of brown and white scales southern Idaho, but it is more or completely reddish-brown abundant in northern Idaho and scales. Mesepimeral bristles ab- in Washington. The larvae have sent or rarely there may be one. been taken also in roadside Abdomen black with basal seg- ditches bordered by brush, in pot- mental white bands and frequent- holes in open meadows, and in ly with scattered white scales. other temporary pools. It is some- Wings predominantly dark- times as^ociatf^d with Mchn and scaled with pale scales inter- hexodontus. The adults appear mixed. Legs black with tarsal later than do those of many of white bands broad on hind legs the Aedes, sometimes not until and usually absent on last seg- July. The species is important ment of mid tarsus and last two only in local areas and then only segments of fore tarsus. for a short time. Male genitalia (fig. 37, E).— Side pieces about three times as AEDES FITCHII (Felt and Yovmg) long as wide; apical lobe prominent with small setae; basal lobe Cidex fitchii Felt and Young, Sci- slightly raised, rugose, and ex- ence (n.s.) 20: 312. 1904. tending to the base of the apical Female.—Torus with white lobe, the surface covered with scales on dorsal half. Mesonotum short setae. Claspette hirsute ex- yellowish white to light brown, cept at the apex; the filament with a broad median brown stripe angularly expanded to a sharp or variable pattern of brown and point near the base. light scales. Wings dark-scaled, Larva.—Upper head hairs mul- usually with an admixture of tiple, lower usually double. Lat- white scales along the costa. Mes- eral abdominal hairs long and epimeral bristles none to two, stout, usually double on segments rarely three or four. Abdomen 1 and 2 and single on the rest. black with basal white bands, and Comb on eighth segment with sometimes with apical white many scales in a triangular patch. scales which may extend into a Air tube slender, about 4x1; median white line. Legs black, pectén not reaching the middle, tarsi with basal white bands on with 2 to 3 large detached teeth; all except the last two segments tuft with 4 to 6 large hairs. Anal of fore tarsus and first segment seermei^t lonorer than wide: r)late of mid tarsus, the white bands extending about three-fourths of broader on the hind legs. the distance down the side, and Male genitalia (fig. 39, B).— with a single long hair on the Side pieces about three times as posterior angle. Anal gills point- long as wide; apical lobe promi- ed and slightly longer than the nent and slightly elongated, the segment. surface clothed with long setae 64 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE bordered by a number of shorter bands on all except the last two ones; basal lobe triangular, segments of fore tarsus and first densely tubercular with many segment of midtarsus, the white setae, those at the margin of the bands broader on the hind legs. base longer and preceded by a The absence of white scales on spine. Claspette lightly hirsute the dorsal surface of the torus except at the apex, the filament easily distinguishes this species short and sickle-shaped with a from fitchiL notch at the base. Male genitalia (fig. 37, G).— Larva.—Upper head hairs 3 to Side pieces more than three times 4, lower 2 to 3. Lateral abdominal as long as wide; apical lobe hairs usually double. Comb on prominent and bluntly pointed eighth segment with many scales with a few small inwardly direct- in a triangular patch. Air tube ed setae ; basal lobe a small rugose slender and tapering, four or elevated area with short setae, more times longer than wide with which extends halfway to the closely set pectén teeth to middle apical lobe. Claspette lightly hir- of tube and tuft of 3 to 5 long sute except at the apex; the fila- hairs set close to end of pectén, ment angularly expanded to a occasionally one or more teeth sharp point near the middle. may be slightly detached. Anal Larva.—Antennae well spined segment longer than wide; plate all over. Upper head hairs usually extending nearly to ventral line 2, occasionally 3; lower 1 or 2. and with a pair of long hairs near Lateral abdominal hairs 1 or 2 posterior angle. Anal gills long long hairs on each segment. Comb and pointed. on eighth segment with 25 or Distribution^ biology^ and im- more scales in a triangular patch. portance.—Aed&s fitchii is most Air tube about 21/2 x 1, pectén prevalent in mountainous regions, not reaching the middle of tube but has also been taken near sea with a tuft of 4 to 6 hairs. Anal level. The larvae usually appear segment as long as wide; plate early in spring in flooded meadows extending only about two-thirds or potholes in semi wooded areas. down the sides with lateral edges It is present over most of Oregon, uneven. Anal gills pointed and Washington, and Idaho, wherever only about as long as the segment. suitable breeding situations are Distribution^ biology^ and im- found. We have found it associ- portance.—This is a common spe- ated with increpitits, excrucianSy cies that is generally distributed and pullatus, over the plains areas of Oregon, Washington, and Idaho. The lar- AEDES INCREPITUS Dyar vae have been taken also in open meadows and small pools in seni- Aedes increpitus Dyar, Ins. Ins. wooded country fro:T\ sea level to Mens. 4: 87. 1916. an elevation of about 6,000 feet. Female.—Torus without white Near Portland the larvae have scales on dorsal half. Mesonotum been found developing in pools yellowish white to light brown, filled by rain in March. The lar- with a broad median brown stripe vae may be associated with fitchii, or variable pattern of brown and but sometimes they occur alone. light scales. Mesepimeral bristles This species is one of several one to five. Wing dark with white found at higher and wooded ele- scales along the costal area. Legs vations that contribute to the black, tarsi with basal white serious discomfort of m.an and MOSQUITOES OF THE NORTHWESTERN STATES 65 animals. It is a persistent biter, March by Elwood Seaman and by but prefers shaded situations. Don Rees in shallow, alkaline pools in valleys of south-central AEDES MPHADOPSIS Dyar and Knab and southeastern parts of Idaho. Aedes niphadopsisDysiYSLndKnah, We have not found it abundant Ins. Ins. Mens. 5: 166. 1918. enough to constitute a pest, al- Female.—Mesonotum with a though it readily bites both man median brown stripe and usually and animals. It has been reported with posterior half-lines; the as able to fly several miles. margins, sides, and antescutellar space with white scales. Lower AEDES IDAHOENSIS (Theobald) mesepimeral bristles two or three, Grabhamia spencerii var. idaho- or rarely none. Abdomen black ensis Theob., Mon. Culic. 3 : with basal white bands with or 250. 1903. without a median line of white Aedes idahoensis Howard, Dyar, scales. Wings with a mixture of and Knab, Mosq. N. and Cent. pale and dark scales, the dark Amer, and W. I. 4: 727. 1917. predominating. Legs with a mixture of pale and dark scales. Female.—Mesonotum with a Male genitalia (fig. 39, C).— broad reddish-brown stripe, usu- Side pieces about three times as ally separated by a fine line of long as wide, apical lobe small, grayish scales ; faint posterior elongate, narrowly attached, bare half-lines present or absent ; sides or with a few small setae; basal and antescutellar space with gray- lobe small, elevated into a trans- ish-white scales. Lower mesepi- verse ridge at the base with a meral bristles absent. Abdomen row^ of 3 or 4 stout hairs preced- black with broad basal white ed oy a short spine at the margin. bands. Wing with costa, first, Claspette lightly hirsute on the third, and fifth veins dark-scaled, basal half, the filament expanded the other veins with pale scales. in a gradual curve near the middle. Legs mostly pale-scaled; femora, Larva.-—Both pairs of head tibiae, and some of apical tarsi hairs usually single, occasionally partially dark-scaled outwardly. double. Comb on eighth segment Male genitalia.—The characters with 10 to 12 scales in an irregu- of the male genitalia of this spe- lar double row. Air tube nearly cies are the same as those of 4x1; pectén teeth not extending stictictos. to the middle with the last 2 or 3 Larva.—Both pairs of head teeth detached and followed by a hairs single. Comb on eighth seg- large tuft. Anal segment longer ment with 9 to 20 scales in a very than wide; plate not reaching irregular patch. Air tube stout, middle of side. Anal gills short or about 21/2 X 1 ; pectén closely set budlike. teeth to middle or slightly beyond, Distribution^ biology^ and im- the last two teeth detached and portance.—This species has been followed by a small tuft. Anal found in Klamath County in Ore- segment longer than wide; plate gon and in Fremont, Custer, and nearly reaching ventral line. Anal Jefferson Counties in Idaho. The gills pointed and as long or longer adults were present in large num- than the segment. bers in Custer County. Larvae Distribution^ biology^ and im^ were collected at the edge of portance.—This species is present drainage ditch in the open coun- in a few places in Washington try below Klamath Falls in and along the eastern border of 66 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE Oregon on the treeless plains or southeastern Idaho. The larvae in low mountain areas. It has develop in pools in mountain been found in largest numbers in meadows at high elevations. Bannock and Bear Lake Counties, Little is known about its habits in southern Idaho, where it is an and distribution. important daytime pest. The larvae usually develop in irrigated AEDES IISTRUDENS Dyar areas, but have been taken in Aedes intrudens Dyar, Ins. Ins. pools of high alkalinity. We have Mens. 7: 23. 1919. found it associated with dorsalis and increpitus in spring and early Female.—Torus with integu- in summer. It is important locally ment of outer side yellow or light and for a short period late in brown. Mesonotum uniformly spring. bronzy brown or occasionally with indications of median brown AEDES VENTROVITTIS Dyar stripes. Lower mesepimeral bristles one to five. Hypostigial Aedes ventrovittis Dyar, Ins. Ins. spot of scales present or absent. Mens. 4: 48. 1916. Abdomen black with broad basal Female.—Torus with integu- white bands; venter completely ment of outer side yellow to black. white-scaled. Wing scales dark, Mesonotum brown, darker cen- with or without a small patch of trally, a fringe of yellowish scales pale scales at base of costa. Legs around the margin. Lower mes- black with a mixture of pale epimeral bristles absent. Abdo- scales ; the tarsi mostly black. men black with basal white bands, Male genitalia (fig. 37, I).— which may be narrow or absent Side pieces about three times as medianly. Wing scales dark, with long as wide; apical lobe promi- or without a mixture of white nent rounded with numerous scales extending outwardly from rather long setae ; basal lobe rep- the bases of the veins. Legs black resented by a large spine at the with a mixture of pale scales ; the base of one side and two spines tarsi mostly black. on a raised projection on the Male genitalia.—The characters other. Claspette with basal half of the male genitalia of this spe- hirsute and forming a sharp pro- cies are the same as those of jection ending in stout setae at sticticus. middle. The apical half slender; Larva.—Both pairs of head the filament angularly expanded hairs single. Comb on eighth seg- to a sharp point at the middle. ment with 6 to 9 thornlike scales Larva.—Upper head hairs usu- with basal spinules in an irregu- ally 4, lower 2 or 3. Lateral ab- lar row. Air tube tapering, about dominal hairs double on first seg- 21/2 X 1; pectén reaching nearly ment and single on second to to middle of tube with two de- sixth. Comb on eighth segment tached teeth and with the tuft of with 10 to 15 scales in an irregu- 5 to 6 hairs near middle of tube. lar double row. Air tube 21/2x1; Anal segment longer than wide, pectén reaching the middle with with plate nearly reaching ven- 2 to 3 detached teeth followed by tral line. Anal gills long and large multiple tuft. Anal segment pointed. longer than wide ; plate extending Distribution^ biology^ and int' to near ventral line and ventral parlance.—This species has been margin deeply incised. Anal gills taken in central Washington and short and bluntly pointed. MOSQUITOES OF THE NORTHWESTERN STATES 67 Distribution, biology, and int' longer than wide and ringed by portance.—Aedes intrudens lar- the plate. Anal gills pointed and vae have been found in small longer than the segment. numbers in snow-water pools in Distribution, biology, and int' low mountainous areas of south- portance.—Aedes hexodontus is a eastern Idaho and in northern mountain species usually associ- Oregon. It is typically a forest ated with communis and fitchii. species and usually survives there It is not so widely distributed as as adults from May until mid- these species in the Northwest August. It is rarely abundant but in some areas it is very abun- enough to be of much importance. dant and an important pest. Large It is a vicious biter day and night. numbers of the larvae develop in meadows in the Cascade Moun- AEDES HEXODONTUS Dyar tains in the vicinity of Mount Aedes hexodontus Dyar, Ins. Ins. Adams and Rainier National Mens. 4: 83. 1916. Park in Washington and in the Aedes cyclocerculus Dyar, Ins. Mount Hood and Diamond Lake Ins. Mens. 8: 23, 1920. areas in Oregon. This species has Aed0s leuconotips Dyar, Ins. Ins. also been taken in various places Mens. 8: 24. 1920. in Idaho. In shaded areas it is a vicious biter during the day. Female.—Mesonotum yellowish to light golden brown, with paired AEDES CATAPHYLLA Dyar dark-brown lines and posterior half-lines. Lower mesepimeral Aedes cataphylla Dyar, Ins. Ins. bristles, 2 or 3. Abdomen black Mens. 4: 86. 1916. with basal segmental white bands. Aedes pearyi Dyar and Shannon, Wings dark-scaled with patch of Wash. Acad. Sei. Jour. 15: 78. 2 or 3 to many pale scales at base 1925. of costa in about 95 percent of Female.—Torus with integu- specimens. Legs black with fe- ment of outer side dark brown or mora partially pale-scaled. black. Mesonotum gray around Male genitalia (fig. 38, B).— the sides with golden-brown Side pieces three times as long as scales in the middle, which some- broad; apical lobe long and times show faint dark lines. Scu- rounded with short curved setae ; tellum with pale-yellowish scales. the basal lobe flatly conical with Lower mesepimeral bristles 2 to numerous setae and a long curv- 7. Hypostigial spot of scales usu- ing spine near the base. Claspette ally present. Abdomen black with pilose, slightly curved and ex- basal segmental white bands. panded near the middle; the fila- Legs black with a mixture of pale ment shorter than the stem, scales; the tarsi mostly black. slightly expanded at the middle Wing scales dark with pale scales and terminating in a blunt curved at base of costa and first vein. point. Male genitalia. — Side pieces Larva.—Antenna sparsely about three times as long as wide. spined. Both pairs of head hairs The filament of the claspette ex- usually in multiples of 2 or 3. panded in a gradual curve near Comb on eighth segment with 5 the middle. The other characters to 9 scales in a row. Air tube as in impiger. 3x1; pectén fine and even and Larva.—Both pairs of head not quite reaching the middle of hairs single. Comb on the eighth the tube. Anal segment slightly segment in two irregular rows. 68 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE Air tube about 3x1, taperiner, Larva.—Antennae sparsely with evenly spaced pectén teeth spined.—Both pairs of head hairs to the hair tuft, and beyond the single. Lateral abdominal hairs tuft there are 3 to 5 widely spaced multiple on first segment and teeth. Anal segment longer than double on second to fifth. Comb wide; plate small, only reaching on eighth segment 8 to 14 scales about two-thirds of the distance in two irregular rows. Air tube down the. sides. Anal gills as long about 214 X 1 ; pectén on basal or longer than the segment. third followed by multiple tuft. Distribution^ biolof(y^ and im- Anal segment as long as wide. portance.—This species is found Anal gills stout and several times only in a few places in mountain the length of the segment. areas of Oregon, Washington, and Distribution^ biolos(y^ and im- Idaho. The eggs hatch very early portance.—This species occurs in when first covered with melting a few places in the high moun- snow. The adults have been taken tainous areas of Oreeron, Wash- as early as May and are usually ington, and Idaho. The largest abroad before associated species. numbers have been found in It is a vicious biter, and will bite Mount Rainier National Park in in bright sunshine. Washington and near Diamond Lake in Oregon. The larvae hatch AEDES ISEARCTICVS Dyar with the first melting snow. The Aedes nearcticus Dyar, Canad. species is too rare to be of much Arct. Exp. Rept. 3 (C) : 32. importance. 1919. AEDES STICTICVS (Meîgen) Female. — Mesonotum bronzy Floodwater Mosquito brown with or without a mixture Culex sticticws Meigen, Svst. of yellowish-white scales around Beschr. Zweifl. Ins. 7: 1. 1«38. the sides and two lighter colored Culex hirsuteron Theob. Mon. patches of scales centrally, the Culic. 2: 98. 1901. entire surface with many black Aedes aow'y^ns Dvar and Knab bristles. Scutellum with pale yel- Ins. Ins. Mens. 5: 165. 1918. lowivsh scales. Lower mesepimeral Aef^^'' f^^p/vnlis ^Meio*.). T^^^warrls bristles 3 to 8. Abdomen black in Wytsman, Gen. Ins. 194:144. with basal segmental white bands. 1932. Wing scales dark with a patch of Aedes aldrirhn Dyar and Knab, pale scales on the base of the U. S. Nati. Mus. Proc. 25: 57. co^ta. Leor« black with fe^iora and 1908. tibiae partially pale-scaled. Female.—Mesonotum yellowish Male genitalia (fig. 37, F).— white, with two golden-brown Side pieces about three and one- stripes and posterior half-lines; half times as long as wide ; apical the anterior stripes separated bv lobe roimded. the surface with a a narrow median line of pale few small setae; basal lobe coni- scales, which is sometimes indis- cally sloped to the basal edge, with tinct or absent. Lower mesepi- long setae and a spine at the meral bristles absent. Abdomen margin, the rest of the surface black with basal white bands. bare or with a few small setae. Winer scales dark with or without Claspette hirsute on basal half, a patch of pale scales on the base the filament angularly expanded of the co^ta. Legs black with fe- to its maximum width near the mora and tibiae partially pale- base. scaled. MOSQUITOES OF THE NORTHWESTERN STATES 69 Male genitalia (fig. 38, C).— mitting western equine and St. Side pieces nearly three times as Louis encephalitis viruses. long as wide ; the apical lobe large and rounded with short, curved AEDES PULLATUS (CoquiUett) setae; the basal lobe expanded, semidetached apically; the outer Culex pullatus Coq., Ent. Soc. surface with short setae, a large Wash. Proc. 6: 168. 1904. spine at the base and an adjoining Female.—Torus with integu- tuft of long setae. Claspette cylin- ment of outer side black to dark drical and slightly tapered at the brown. Mesonotum with yellow- apex with one or two spines at the ish-brown scales; a narrow bare midpoint of the inner side; the median line with parallel stripes filament short, broad, expanded at of brown scales, each stripe the middle, and terminating in a bordered by a broader stripe with blunt, curved point a few dark scales ; with or without Larva.—Upper head hairs 2 or narrow, bare, curved posterior 3, lower 1 or 2. Lateral abdominal half-lines. Lower mesepimeral hairs variable, usually multiple on bristles 1 to 5. Hypostigial spot of first segment and double on many white scales. Abdomen black second to sixth. Comb on eighth with basal white bands. Wings segment with many scales in a dark-scaled with patch of pale triangular patch. Air tube stout, scales at base of costa. Legs black 21/^x1; closely set, even pectén with femora and tibiae partially teeth to near middle of tube, with pale-scaled. a multiple tuft set close to pectén. Male genitalia (fig. 37, H).— Anal segment broader than long; Side pieces about three and one- plate extending nearly to ventral half times as long as wide ; apical line. Anal gills long and pointed. lobe prominent and somewhat elongated, by ventral surface cov- Distribution^, biology^ and im- ered with numerous setae; basal portance.—This is one of the most lobe represented by a large spine important pest mosquitoes in the at the margin and two adjacent Northwestern States. It breeds in smaller spines. Claspette with large numbers in the brushy bot- basal half large, hirsute, and tom lands along the Columbia forming a rounded projection at River. It is also found along some the middle, the apical half slender ; other rivers in northwestern the filament angularly expanded to Washington and northern Idaho. a rounded point near the middle. The larvae, which are almost in- Larva.—Upper head hairs 5 to variably associated with those of 7, lower usually 4; hairs short vexans, are found in large num- and tufts set close together. bers for about 100 miles below Lateral abdominal hairs long, and Bonneville Dam, when the annual double or triple on first to fifth spring flood of the Columbia in- segment and single on sixth. undates the bottom lands. The Comb on eighth segment with adults disperse for a distance of many scales in a triangular patch. 15 to 20 miles or more and re- Air tube 3x1, pectén teeth closely main a serious pest to man and set, not reaching the middle, livestock throughout the summer. closely followed by large 6- to 7- The eggs may remain viable for haired tuft. Anal segment longer at least 3 or 4 years if not reached than wide, not ringed by the plate. by normal floods. This species Anal gills saclike and two or three has been found capable of trans- times longer than the segment. 70 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE Distribution, biology, and im^ Air tube stout and about 3x1; portance.—This species has been pectén reaching basal fourth of taken in a number of places in tube with 4 to 5 widely separated the high forested mountainous detached teeth, and multiple hair areas of the Northwest. The lar- tuft within the pectén, and an ad- vae are usually found in melting ditional small tuft on dorsal and snow pools, most frequently asso- lateral surfaces of siphon. Anal ciated with communis but also segment as long as wide, with with punctor and fitchii. The plate nearly reaching ventral adults emerge rather late and line. Anal gills ensiform and are severely annoying for only a slightly longer than segment. short time after emergence. They Distribution, biology, and ¿m- will bite during the daylight portance.—This mosquito occurs hours in shade. in timbered areas at high elevations in Idaho and near Mount AEDES TRICHURUS (Dyar) Adams in Washington. The larvae have been found associated Culex trichurus Dyar, N. Y. Ent. with those of fitchii, increpitus, Soc. Jour. 12: 170, 244. 1904. cinereus, and communis in pools Female.—Torus with integu- formed by melting snow. Al- ment of outer side yellow to light though a severe biter, this species brown. Mesonotum with a median does not occur in large enough brown stripe expanded to width numbers to be of much impor- behind the middle; sides and mar- tance. gins with grayish-white scales. Lower mesepimeral bristles 3 to AEDES COMMVmS (DeGeer) 6. Hypostigial spot of few to Culex communis DeG., Mem. des. many white scales. Abdomen Ins. 6, pi. 17, figs. 2 and 5. 1776. black with basal segmental white Female.—Mesonotum dull-yel- bands. Wing scales dark, with low or gray-scaled with a narrow patch of 2 or 3 to many pale pale median line separating paired scales at base of costa. Legs black dark-brown lines, and with pos- with femora pale-scaled beneath. terior brown half-lines. The colo- Male genitalia. — Side pieces ration is variable and may be three times as long as wide; brown-scaled centrally with a mix- apical lobe prominent and angu- ture of pale scales and a border larly rounded with a few setae; of grayish-yellow scales. Lower ' basal lobe small with conical cen- mesepimeral bristles 2 to 5. Abdo- ter portion covered with setae men dark brown with basal white and an adjacent elevated portion bands. Wings dark-scaled, with a bearing two long spines. Clasp- patch of 2 or 3 to many pale scales ette with long, cylindrical, curved at base of costa in about 85 per- stem slightly expanded before the cent of specimens. Legs dark with apex; the filament short and femora partially pale. conical, with a series of trans- Male genitalia (fig. 39, A).— verse ridges. Side pieces about three times as Larva.—Upper head hairs us- long as wide; apical lobe large ually double, lower single. Lateral rounded with many long spinelike abdominal hairs triple on first seg- setae; basal lobe small, quadri- ment, double on second and third, lateral in outline, partially de- and single on fourth to sixth; tached at base, the surface with other hairs few and small. Comb some small setae, several larger on eighth segment in double row. curved ones and a stout spine on MOSQUITOES OF THE NORTHWESTERN STATES 71 the margin. Claspette lightly hir- well-defined, dark-brown stripes sute on the basal half, the apical and posterior half-lines, the me- half more slender; the filament dian stripes separated by a line angularly expanded to its maxi- of pale scales. Lower mesepimeral mum width near the base. bristles 1 to 4, or rarely none. Larva.—Both pairs of head Abdomen with or without narrow hairs single. Lateral abdominal basal white bands. Wing scales hairs double on first to fifth seg- dark with small patch of pale ment and single on the sixth. scales at base of costa in about Comb on eighth segment with 85 percent of specimens. Legs many scales in a triangular patch. black with femora partially pale- Air tube stout and about 21/2 x 1 ; scaled. pectén evenly spaced to near mid- Male genitalia.—The side piezas dle of tube; tuft of 4 to 6 hairs. are slightly longer than those of Anal segment longer than wide; Aedes communis. There are no plate extending only about two- other taxonomic differences in thirds the distance down the sides. the genitalia of these two species. Anal gills lanceolate and consider- Larva.—Antennae long and ably longer than the segment. well spined. Upper head hairs Distribution^, biology^ and im- usually 5, lower 4. Comb on eighth portance.—This is one of the most segment arranged in a large tri- widely distributed species in high angular patch. Air tube about mountain areas of the Northwest. 21/^ x 1; pectén not reaching the In many localities it is present in middle and followed by large mul- large numbers and is a serious tiple tuft. Anal segment about as pest. It breeds in flooded moun- long as wide, with the plate reach- tain meadows and woodland pools ing only about half the distance left by melting snow, and around down the sides, and with notched the margins of mountain lakes. lateral edges. Anal gills long and The larvae may occur along or pointed. associated with pullatus, cata- Distribution^ biology^ and im- phylla, intrudervs, fitchii, and hex- portance.—This is a rare species odontus. In Oregon it is numerous in the Northwestern States. The throughout the Cascade and Blue larvae have been found only in Mountains. It is abundant in the small pools in high mountain Cascade and other mountain meadows of south-central Idaho ranges in Washington and north- at an elevation of over 7,000 feet. ern Idaho, and is present in Very little is known about it, and smaller numbers in central and because of its rarity it is of no southern Idaho. The adults are economic importance. sometimes seen late in May and may occur until mid-August. They AEDES IMPIGER (Walker) are vicious biters and, although Culex impiger Wlkr., Brit. Mus. they will attack during the day, List Dept. 1: 6. 1848. are generally more active at dusk. Female.—Tori with integument AEDES PIONIPS Dyar varying from black to yellow. Mesonotum with a median oblong Aedes pionips Dyar, Ins. Ins. area of brown scales, usually in Mens. 7: 19. 1919. the form of a broad stripe or FemaZe.—Tori with white paired stripes; margins grayish scales. Mesonotum with dull-yel- white. Lower mesepimeral bristles low or white scales, two broad, 1 to 3, or rarely none. Wing 72 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE scales dark with patch of 2 or 3 Male genitalia (fig. 37, D).— to many pale scales at base of Side pieces three times as long as costa. Legs black with femora broad; apical lobe long and pale-scaled beneath. rounded with short curved setae ; Male genitalia.—Side pieces the basal lobe flatly conical with about four times as long as wide, numerous setae and a long curv- apical lobe small elongated and ing spine near the base. Claspette narrowly attached with a few pilose, slightly curved, and ex- short spines; basal lobe small, panded near the middle; the fila- elevated into a transverse ridge ment shorter than the stem, at the base with a row of long slightly expanded at the middle setae and a slender spine at the and terminating in a blunt curved margin; claspette lightly hirsute point. except at the apex, the filament Larva.—Antennae sparsely angularly expanded to a sharp spined. Head hairs, upper usually point near the base. 3 to 4 and lower 2 to 4. Lateral Larva.—Antennae short and abdominal hairs 1 to 2 long hairs. spined. Upper and lower hairs Comb on eighth segment with single. Lateral abdominal hairs about 30 scales in a patch. Air double on first to fourth segments tube around 3x1; pectén fine and and single on fifth and sixth. even and not reaching the middle, Comb on eighth segment with 15 the tuft consists of 4 to 6 large to 25 scales. Air tube about 21^ hairs. Anal segment about as long X 1; closely set pectén teeth not as wide; anal plate extending to reaching the middle, followed by near ventral line; anal gills tuft of 3 or 4 hairs. Anal segment pointed and longer than the longer than wide ; plate extending segment. about halfway down the sides and Distribution, biology, and int' covered with minute spines. Anal portance.—^Large numbers of this gills pointed and only about as species are found in the dense long as the segment. timbered coastal areas of Oregon Distribution^ biology, and iiw- and Washington, where the win- portance.—This species occurs in ter precipitation is very high. It small numbers in Washington and is also common at moderate ele- Idaho. The larvae are usually as- vations in the Cascade Mountains sociated with other Aedes larvae and in other mountain areas in in pools in semiwooded areas at Washington and northern Idaho. the higher elevations. It is too The larvae are found associated rare to be of any importance. with communis, cineretos, and fitchii in small temporary rain AEDES ABORIGimS Dyar pools. It is of economic im- Northwest Coast Mosquito portance only in a few restricted Aedes aboriginis Dyar, Ins. Ins. situations in the Olympic Penin- Mens. 5: 99. 1917. sula of Washington. Female.—Mesonotum yellowish AEDES CINEREUS (Meigen) to light golden brown, with paired dark brown stripes and posterior Aedes einer ens M e i g. Syst. half-lines. Lower mesepimeral Beschr. Eur. Zweif. Ins. 1: 13. bristles 1 or 2. Abdomen black 1818. with basal white bands widening Female.—Mesonotum clothed at the sides. Wings dark-scaled in with reddish-brown scales. Lower about 95 percent of specimens. mesepimeral bristles absent. Ab- Legs black. domen black without white bands MOSQUITOES OF THE NORTHWESTERN STATES 73 or with narrow partial or com- species is a severe biter but im- plete ones ; the lateral spots usu- portant only in local areas. ally joined to form a line. Wing scales dark. Legs dark brown. AEDES VEXAISS (Meigen) Coxa of front leg with white scales and a central patch of Culvex vexans Meig. Syst. Beschr. brown scales on the anterior Eur. Zweif. Ins. 6: 241. 1830. surface. Female.—Occiput with patch Male genitalia (fig. 38, E).— of flat black scales bordering top Side piece twice as long as wide, edge of flat white lateral patch. broad, and sharply tapered to the Mesonotum clothed with bronzy- densely spined apex. Clasper sub- brown scales, paler at the base of apically inserted, with forked the wings and around antescutel- arms of unequal length. Claspette lar space. Lower mesepimeral two-branched with 3 spines at bristles absent. Abdomen black apex of each branch. with centrallv indented basal Larva.—Both pairs of head white bands. Wing scales brown. hairs in tufts of 5 or more, the Legs black ; all the segments of tufts set close together. Lateral the hind tarsus, the first four seg- abdominal hairs double on first ments of the mid-tarsus, and the and second segments, single and first three segments of the fore long on the third to sixth. Comb tarsus narrowlv white-banded. on eighth segment in a double Male genitalia (fig. 38, F).— row. Air tube slender, about 4 x Side pieces twice as long as wide, 1; pectén extending past middle clasper long, broad, and divided of tube with about 3 detached near the apex, the short arm with teeth; tuft small. Anal segment a stout spine. Claspette short and longer than wide, gills very long capitate with dense crown of and lanceolate. spines. Filament absent. Distribution^ biology, and im- Larva.—Upner head hair usu- portance.—This mosquito is found ally 2 or 3 and lower double. Lat- throughout the partially wooded eral abdominal hairs 2 to 3 on areas of the Northwestern States. first to third segment; 2 on It breeds in shaded pools, and the fourth and fifth and single on the larvae are usually found associ- sixth. Comb on eighth seorment ated with other species of Aedes with 10 to 25 or more scales in in March and early in April; it an irregular double row. Air tube appears a little later than its as- 3x1; pectén reaching past the sociates. In some mountain areas middle with 1 to 3 detached teeth it is the predominating species and a small multiple-haired tuft and is a serious pest; it is found near end of pectén. Anal segment in smaller numbers at lower ele- longer than wide. Anal gills vations. The females attack both pointed and longer than segment. during the day and at dusk, but Distribution^ biology, and im- they stay close to the ground in portance.—This species is found the grass or underbrush. The over the greater portion of the adults are not found very far Northwestern States. It is one of from their breeding places. Ap- the most important pest snecies parently their flight range is very in both irrigated and flood-water limited, since Freeborn (30) area8, and occurs near sea level, states that they prefer to walk as well as in mountain meadows. rather than fly, and when flying It is present in overflow areas remain close to the ground. This along many rivers, but is most 74 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE abundant on the bottom lands scales dark with a patch of white along the Columbia River and its scales at the base of the costa. tributaries for about 100 miles Legs black, with white bands in- below Bonneville Dam. In this volving both ends of all but the region the larvae are found asso- last two joints of the fore and mid ciated with those of sticticus in tarsi, which are black, and the last the partially open, brushy, or joint of the hind tarsus, which is wooded areas that are flooded by white. the annual spring rise of these Male genitalia (fig. 38, D).— rivers. The adults sometimes dis- Side pieces three times as long as perse for distances of 15 to 20 wide; the apical lobe absent; the miles or more from their breed- basal lobe narrow with long ing places and are a serious pest spines basally and short setae ex- to man and livestock for 3 to 4 tending to apical fourth of side months during the summer. Along piece. ClasDette with cylindrical the Columbia River several hatch- stem, the filament narrow, ligu- ings may occur, depending on the late and as long as the stem. number of floods, since all eggs Larva.—Antennae slender with- do not necessarily hatch with the out spines and with a single hair first flooding. More than one gen- on the middle. Both pairs of head eration may occur in the irri- hairs small and either single or gated sections and there the double. Comb on eighth segment larvae are associated with nigro- with about 12 scales in an irregu- maculiSy dorsaliSy and idahoensis. lar double row. Air tube about In mountain areas they are usu- 3x1; pectén evenly spaced on ally found with increpitus and basal third and with tuft near the cinereus. The females enter middle. Anal segment about as houses and will feed there during long as wide. Anal gills enlarged, the hours of darkness. They also spatulate, and about four times bite at mid-day in shaded areas. as long as segment. This species has been found nat- Distribution^ biology^ and im- urally infected with western portance.—This small mosquito equine encephalomyelitis and has breeds in water-filled holes in been experimentallv infected with practically any kind of tree. St. Louis encephalitis virus. Reeves {IH) reports finding it also in rock pools and wooden re- AEDES VARIPALPUS (Coquille«) ceptacles under trees. The larvae "Western Tree-hole Mosquito may be found in midwinter in this region if temperatures be- Culex varipalpus Coq., Cañad. low freezing do not prevail for Ent. 34: 292. 1902. long periods. In summer the Female.—Palpus black-scaled aquatic stage is completed in with the tip broadly white-scaled about 3 weeks. The species occurs and a few white scales at apex of in the western half of Oregon and second segment. Mesonotum Washington, but is seldom very brown with a median anterior abundant. The largest numbers patch, and narrow posterior are found in the foothills of the curved lines of yellow scales ; the Coast Range and the Olympic margins with a mixture of pale Mountains in Washington, li is a scales and scutellum with broad vicious biter but has a restricted white scales. Abdomen black with flight range. It has been found an median triangular dorsal and lat- experimental vector of western eral patches of white scales. Wing equine encephalomyelitis. MOSQUITOES OF THE NORTHWESTERN STATES 75 Genus MANSONIA Blanchard fitted for piercing, a pair of hair MANSONIA PERTVRBAm (Walker) tufts near the middle. Anal segment much longer than wide, Culex perturbans Wlkr., Ins. ringed by the plate, the dorsal Saund., 428. 1856. tufts of two unequal groups of Female.—Mesonotum with nar- hairs on each side. Anal gills row, curved, pale-yellow scales, slender and shorter than segment. with or without two faint silvery- Distribution^ biology^ and im- longitudinal lines. Abdomen black portance.—Many adults of this with narrow basal segmental species are present near Scap- white band, sometimes lacking poose, Oreg., in some years. Lar- medianly or consisting of scat- vae probably occur in cattail tered black and white scales on swamps in the area but none have the last few segments. Wing been taken. They are difficult to scales broad, black and white in- find, because, unlike other mos- termixed. Legs black with a mix- quito larvae, they attach to the ture of white scales; the hind succulent roots of aquatic plants tibiae with a white ring on the by their siphons and come to the outer third; the first joints of all water surface only for emergence tarsi with a narrow basal white as adults. The winter is passed in ring and a broad median white the larval stage. The pupae also ring; all other tarsal joints with attach to roots. The adults emerge the basal half white-scaled. for several weeks in the summer Larva.—Antennae long and and are extremely vicious biters. slender with large tuft beyond the Adults have also been taken in middle and short pair of hairs not small numbers in Washington and far beyond the tuft. Dorsal head Idaho. Fortunately, they are so hairs in multiple groups. Lateral rare that they are of little impor- comb of the eighth segment of 10 tance. Howitt et al. (69) has to 12 spines in a single irregular shown this species may transmit row. Air tube short, broad at the eastern equine encephalomyelitis base. Attenuated apically and in nature.

Genus CULEX Linnaeus KEY TO SPECIES Adults 1. Tarsi and proboscis ringed with white 2 Tarsi and proboscis not ringed with white 3 2. Femora and tibia with a line of white scales on the outer surfaces; the inner surfaces of the tori and the ventral surface of the first segment of the flagellum with white scales tarsalis Femora and tibia without a line of white scales on the outer surfaces; the inner surfaces of the tori and the first segment of the flagellum without white scales stigmatosoma 3. Abdominal segments with dorsal, basal white bands pipiens Abdominal segments with dorsal, apical white bands territans Male Genitalia 1. Mesosome with the halves connected by a narrow sclerotized band before the apex territans Mesosome without connecting band before the apex 2 2. Apical lobe with eight or more appendages pipiens Apical lobe with six or less appendages 3 3. Tenth sternite with spines forming a flattened outline at the apex; the outer spines bluntly rounded tarsalis Tenth sternite with spines forming a circular outline at the apex; the spines all pointed stigmatosoma 76 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE

Larvae 1. Both pairs of head hairs usually single and long, occasionally double territans Both pairs of head hairs multiple 2 2. Air tube with four pairs of tufts, the next to last out of line; lateral abdominal hairs multiple on first and second segments, double on third and sixth pipiens Air tube with four to five pairs of tufts all in line or nearly so; lateral abdominal hairs triple on third to sixth segments 3 3. Subapical tuft on air tube sometimes smaller and slightly out of line ; plate on anal segment indented with row of short bristles near ^P^x stigmatosoma Tufts on air tube uniform and all in line; plate on anal segment with smooth edges and no bristles tarsalis

CVLEX TERRITAISS (Walker) segment twice as long as wide Culex territans Wlkr, 1856. In- and anal gills about as long as the sects Saundersiana, Dipt., 1: segment. Air tube long and taper- 428. ing, about 7 X 1 ; pectén of 12 to Culex apicalis Adams, of Dyar 14 teeth on basal third of tube and other authors, not of with four pairs of prominent Adams. tufts beyond pectén, and also sometimes a small fifth pair near Female. — Mesonotum brown- the apex. scaled with median indistinct Bohart (10) found that C. nearly bare lines and usually with apicalis consisted of two species. two median spots of yellowish He used this name for the species scales. Abdomen black-scaled found in California and Arizona, with apical segmental white but applied the name ''territans'' bands. Wing scales all black. Legs to the more widespread species black, the undersurface partially which occurs in other parts of white-scaled. North America. Male genitalia (fig. 36, D).— Distribution^ biology^ and iwi- Side piece more than twice as portance.—This species is well long as wide ; subapical lobe with distributed in the Northwestern two large rods, a spine and five States. The larvae have been col- hooked filaments. The first three lected in semishaded and in open partially serrated. Tenth sternite grassy pools. They are never prominent, the apex broad, ex- found in large numbers. The fe- tending beyond the mesosome and males feed on cold-blooded ani- terminating in a row of short mals, such as frogs, and are not setae. Mesosome halves with re- known to attack man or other latively even, oblong outlines ter- warm-blooded animals. minating apically in a rounded, serrated margin, the halves CULEX PIPIENS (Linneaus) joined by a sclerotized band near Northern House Mosquito the apex. Larva.—Head hairs single or Culex pipiens L., Syst. Nat., ed. double. Antennae large, cylindri- 10: 602. 1758. cal, and spined. Lateral abdomi- Female.—Mesonotum brown- nal hairs multiple on first and sec- scaled. Abdomen black with basal ond segments and double on third segmental white bands, which are to sixth; secondary hairs numer- widest at the middle and at the ous and well-developed. Comb on sides. Wing scales all brown. eighth segment with numerous Legs brown-scaled. scales in a triangular patch. Anal Male genitalia (fig. 36, C).— MOSQUITOES OF THE NORTHWESTERN STATES 77 Side pieces more than twice as encephalomyelitis and St. Louis long as wide, subapical lobe with encephalitis viruses have been re- 8 appendages, beginning at the covered from this species in na- apical end ; a seta, a leaf, 3 setae, ture and experimentally it has and 3 rods. Tenth sternite promi- been shown to be a vector of nent and extending beyond the Japanese B encephalitis virus. mesosome, and the apex semi- CVLEX TARSALIS Coquille« circular and densely crowned with stout spines. Mesosome Culex tarsalis Coq., Cañad. Ent. halves each with ends of 3 proc- 28: 43. 1896. esses projecting outwardly past Female.—Proboscis ringed the outer edges of the tenth ster- with white. Tori with inner sur- nite. faces, and basal segment of fla- Larva.—Both pairs of head gellum with ventral surface bear- hairs multiple. Antennae large, ing many white scales. Mesono- spinose, cylindrical, and con- tum dark brown with white stricted beyond the tuft. Lateral scales around the margins and 2 abdominal hairs multiple on first narrow white lines extending and second segments and double posteriorly from median white on third to sixth ; subdorsal hairs spots. Abdomen black with basal of segments 3 and 4, single or segmental white bands; venter double. Comb on eighth segment with pale scales, each segment with numerous scales in a tri- marked with a dark-scaled V- the angular patch. Anal segment apex anteriorly directed. Wing longer than wide and gills slightly scales dark with some white longer than the segment. Air tube scales on the costal veins. Legs gradually tapering, about 5x1; black, the femora and tibia with pectén about 12 teeth on basal a line of white scales on the sides, fourth followed by 4 pairs of hair the tarsi with a ring of white tufts, the subapical pair more scales at both ends of all joints dorsal and out of line than the except the first 1 or 2 on the front others. and middle legs. Distribution^ biology^ and im- Male genitalia (fig. 36, B).— partance,—This species is occa- Side pieces more than twice as sionally present in large numbers long as wide ; subapical lobe usu- in some communities in the west- ally with five appendages, begin- ern parts of Oregon and Wash- ning at the apical end; a seta, a ington. It seldom occurs in the narrow leaf, a seta, and two rods. eastern half of these States. The Tenth sternite prominent, well larvae breed in temporary and chitinized, and extending beyond permanent pools and in artificial the mesosome, the broad apex containers. Because of its habit crowned with short pointed spines of developing in any polluted medianly and short, broad, blunt place provided by man, it is often ones outwardly. Mesosome halves abundant and annoying around each consisting of inner sword- homes and industrial plants. It like blade and an outer 4-pronged enters houses freely and over- process. winters in basements, root cel- Larva.—Both pair of head lars, and other shelters. The flight hairs multiple. Antennae long range is short and, if breeding and curved, basal two-thirds places are not great in number spinose and enlarged. Lateral ab- and widely scattered, the area af- dominal hairs triple on third to fected is small. Western equine sixth segments. Comb on eighth 78 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE segment with numerous scales in definite pattern. Abdomen black a triangular patch. Anal segment with basal segmental white slightly longer than wide ; gills as bands; venter pale-scaled, each long as segment and bluntly- segment marked with a median pointed. Anal plate without bris- oval dark-scaled spot. Wing scales tles. Air tube slender and about all dark. Legs black, the tarsi 5x1; pectén on basal third fol- with a ring of white scales on lowed by 5 pairs of tufts, none both ends of all joints except the displaced or out of line. first one or two of the front and Distribution^ biology^ and im^ middle legs. portance.—This (fig. 2) is one of Male genitalia (fig. 36, A).— the most abundant and widely Side pieces more than twice as distributed mosquitoes in the wide as long; subapical lobe usu- Northwestern States. It has been ally with 6 appendages, beginning collected in every county in Ore- at the apical end—a seta, a leaf, gon and from all but a few coun- a seta, and 3 rods. Tenth sternite ties in Washington and Idaho. It prominent, well sclerotized, and occurs in largest numbers in extending beyond the mesosome, poorly drained irrigated areas the apex semicircular and densely where water accumulates. It is crowned with slender spines, with readily found around Klamath a few slightly heavier ones on the Lake, along the John Day River, outer margin. Mesosome similar and elsewhere in eastern Oregon. to mesosome of tarsalis. In Washington it is common in Larva.—Both pairs of head Yakima and Okanogan Valleys, hairs multiple. Lateral abdominal and in western Idaho it is very hairs triple third to sixth seg- numerous in the lower Boise and ments and subdorsal hairs, 3- Payette River Valleys. It is also branched, on segments 3 and 4. abundant around American and Comb on eighth segment with Bear Lakes, in Idaho. The larvae many scales in a patch. Anal seg- are associated with anophelines, ment about as long as wide ; anal Aedes dorsalis, and Culiseta inor- plate indented and with row of nata. The females pass the winter short bristles near apex ; anal gills in hibernation. Culex tarsalis has broad and as long as segment. Air been shown to be infected in na- tube about four to five times as ture with both St. Louis encephal- long as wide; pectén on basal itis and western equine encephal- third followed by five pairs of omyelitis in several areas and is hair tufts, but apical one usually capable of transmitting these dis- very small; subapical one some- eases to chickens. It has been ex- times out of line. perimentally infected with Japan- Distribution^ biology^ and im^ ese B and California encephalitis portance.—In western Oregon viruses. and Washington the larvae of this species are usually associated CULEX STIGMATOSOMA Dyar with tarsalis or other species of Culex stigmatosoma Dyar, U. S. Culex and Culiseta. It has not Nati. Mus. Proc. 32: 123. 1907. been taken in the pastern half of Female,—Proboscis ringed these States or in Idaho. Western with white. Tori without scales equine encephalomyelitis has been and basal segment of flagellum isolated in nature from this spe- brown-scaled. Mesonotum with cies, but it is probably of little im- bronzy-brown scales intermingled portance as a vecto?:* because of its with paler ones and forming no limited numbers aijd distribution. MOSQUITOES OF THE NORTHWESTERN STATES 79 Genus CULISETA Felt KEY TO SPECIES Adults 1. Tarsi with white bands on some of the segments 2 Tarsi without white bands 4 2. Femora with subapical white rings maccrackenae Femora without subapical white rings ^ , 3 3 Wing scales black and clustered into spots incidens Wing scales brown and evenly distributed morsttans 4. Wing scales brown with an admixture of white scales on the anterior veins inornata Wing scales all brown impatiens Male Genitalia 1„ Apical lobe absent 2 Apical lobe present ^ 2. Lobes of the ninth tergite with short broad spines inornata Lobes of the ninth tergite with rather long setae morsitans 3. Eighth segment with row of 20 to 40 short spines on basal margin; basal lobe large with single spinelike sets • impatiens Eighth segment with less than 12 spines on the basal margin; the basal lobe with 2 or 3 spines 4 4. Eighth segment without spines or with a single short spine at the center of the basal margin: (the basal lobe with 3 stout spines) maccrackenae Eighth segment with 5 to 10 spines at the center of the basal margin incidents Larvae 1. Pectén on air tube not produced into long hairs on outer half morsitans Pectén teeth normal near base and becoming long hairs near apex of tube 2 2. Upper and lower head hairs multiple and similar; a tuft of small hairs on posterior margin of anal plate impatiens Upper and lower head hairs multiple, the lower hairs longer 3 3. Basal pectén on air tube with 3 or more outstanding denticles; a tuft of 1 to 3 long stout hairs on posterior margin of anal plate.. inornata Basal pectén on air tube with minute denticles; a tuft of small hairs on posterior margin of anal plate ^ 4 4. Anterior tufts of ventral brush puncturing anal plate incidens Anterior tufts of ventral brush in a cleft in anal plate, a tuft of small bristles near its apex maccrackenae

CULISETA MACCRACKENAE Dyar and dark scales forming spots at the Knab base of the second, the forks of its second and fourth, the upper Culiseta maccrackenae y Dyar and fork of the fifth and on the cross Knab. Biol. Soc. Wash. Proc. veins. Legs black with portion of 19: 133. 1906. inner side white-scaled, femora with subapical white ring fol- Female.—Mesonotum dark lowed by a black ring, apical seg- brown with a light-brown median ments of tarsi without rings and stripe and narrow white posterior succeeding tarsi with gradually half-lines ; the sides, anterior broadening white rings, margin, and margins of ante- Male genitalia.—Side piece scutellar space with a mixture of about three times as long as white scales. Abdomen black with wide ; apical lobe a small elevated basal segmental white bands and area with a number of long a few scattered white scales, setae ; basal lobe small and conical Wing scales black with a few pale with many small setae, the apex scales on the costal veins, the with two or three stout spines. 80 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE Lobes of the ninth tergite not Male genitalia (fig. 39, F).— separated but indicated by two Side piece more than twice as large groups of small spines. long as wide, apical lobe a small Eighth segment without spines or elevated area with a number of with one spine at center of basal small setae and a long spine; margin. basal lobe small and conical with Larva.—Both pairs of head small setae, the apex with 2 stout hairs multiple, the lower with spines. Lobes of ninth tergite about three long hairs, the upper slightly separated, and each bear- more numerous and shorter. Air ing 5 to 8 rather long setae. tube stout, about 2x1; pectén Eighth segment with 5 to 8 with a few basal teeth followed spines on basal margin. by long hairs that extend nearly Larva.—Both pairs of head to apex of tube; a paired tuft hairs multiple, lower tufts longer near base of tube between rows of than the upper. Lateral abdom- pectén. Anal segment ringed by inal hairs multiple on first and the plate with 2 anterior tufts of second segments and double on ventral brush arising from a cleft third to sixth. Air tube stout in the plate and a small patch of about 2x1; pectén with a few short bristles near apex of the basal teeth that have 1 or 2 min- plate. Anal gills slightly longer ute denticles, teeth followed by than segment. long hairs to apical third of tube ; Distribution^ biology^ and im- and a multiple tuft near base be- portance.—This species is rare in tween rows of pectén. Anal seg- the Northwest; it has been taken ment ringed by the plate with only in a few places in south- several tufts of ventral brush western Oregon. The larvae were puncturing the plate and a small found associated with larvae of 1- to 3-haired tuft on lateral incidens and territans in pools posterior margin. Anal gills overgrown with vegetation. slightly longer than segment. Distribution^ biology^ and im- CULISETA INCIDENS (Thompson) portance.—This species is widely distributed at lower elevations in CuUseta incidens Thompson, the Northwestern States. The Kongl. Sven. Eng. Resa. 6, largest numbers occur in Oregon Dipt.: 433. 1868. and Washington west of the Cas- Female.—M esonotum with cade Mountains, but it is common dark-brown scales and a mixture also in southern Idaho. The larvae of yellowish scales some of which breed in both permanent and form partial longitudinal lines or semipermanent pools and in ar- spots. Abdomen black with basal tificial containers. They are asso- segmental white bands. Wing ciated with inornata and tarsalis. scales dark, aggregated into Only the females hibernate. They patches on the fork and base of occasionally attack man, but they the second vein, the fork of the are of little importance as a pest. second and fourth vein, the upper The species has been reported as fork of the fifth and the middle of favoring animals for blood meals, the sixth veins. Legs dark brown although it is seldom abundant with narrow faint white rings on enough to be a pest of livestock. the bases of some of the tarsal It has been infected experiment- joints, the femora and tibia with ally with western equine ence- narrow white rings at their phalomyelitis and St. Louis and apices. Japanese B encephalitis viruses. MOSQUITOES OF THE NORTHWESTERN STATES 81 CVLISETA mORlSATA (Williston) distributed in the Northwestern States. It occurs in largest num- Culex inornatus Williston, U. S. bers in poorly drained irrigated Dept. Agr., Div. Ornith. and areas. Under such conditions the Mam., N. Amer. Fauna 7: 253. larvae are usually found with 1893. those of freeborni and tarsalvs. It Female.—Mesonotum with is also found in shaded pools in mixture of brown and yellowish forests at elevations up to 6,000 scales, usually with 2 fine, pale, feet. It seldom bites man, but can median posterior half lines and become a pest of livestock because pale obscure longitudinal stripes. of its long breeding season and Abdomen black with broad basal wide distribution in irrigated segmental bands widening at the areas. The females hibernate, and sides, the last segment entirely Rees {111) believes that some pale scaled. Wing scales dark larvae may overwinter, since they brown with mixture of pale scales are very resistant to low temper- on the anterior veins. Legs with a atures. Western equine encephal- mixture of brown and pale scales. omyelitis has been isolated from Male genitalia (fig. 39, G).— this species in nature. Experi- Side pieces stout conical, less mentally, it has been shown to than twice as long as wide ; apical transmit St. Louis and Japanese lobe absent or faintly indicated; B encephalitis viruses. basal lobe conical and prominent, with 2 or 3 spines on the apex and CVLISETA MORSITANS (Theobald) small setae on the sides. Lobes of the ninth tergite broad, rounded Culex morsitans Theob., Mon. projections with 10 to 14 short, Culic. 2: 8. 1901. thick spines. Eighth segment Female.—Mesonotum brown without row of spines on basal with a mixture of yellowish scales margin. around the margins, a pair of Larva.—Both pairs of head faint nearly bare median stripes, hairs multiple, the lower with 3 and posterior yellowish white or 4 long hairs, and upper multi- half-lines. Abdomen brown-scaled ple and shorter. Lateral abdom- with scattered yellowish-white inal hairs multiple on first and scales, most heavily concentrated second segments and double on along the apices and bases of seg- third to sixth. Air tube stout, 3 ments, or these may occasionally X 1 ; pectén of 10 to 12 stout teeth form basal pale bands only. Wing followed by long hairs that ex- scales dark with pale scales at the tend nearly to apex of tube, the base of the costa. Legs dark with teeth with 3 to 4 outstanding faint white rings at both ends of denticles; paired tuft large and the tarsal joints. arising from base of tube be- Male genitalia (fig. 39, H).— tween the rows of pectén. Anal Side pieces conical, more than segment ringed by the plate with twice as long as wide ; apical lobe 2 to 3 anterior tufts of ventral absent; basal lobe prominent and brush piercing the plate and a conical, with 3 to 5 spines on the tuft of 1 to 2 long hairs on its apex and small setae on the sides. lateral posterior margin. Anal Lobes of the ninth tergite with gills longer than segment with broad projections each with 6 to tips rounded. 12 slender setae. Eighth segment Distributionj, biology^ and im- with a group of small spines cen- portance.—This species is widely trally on basal margin. 82 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE Larva.—^Upper head hairs mul- Male genitalia (fig. 39, E).— tiple, lower double. Lateral ab- Side pieces stout conical, about dominal hairs multiple on first twice as long as wide ; apical lobe and second segments, single and a small slightly elevated chitin- long on third to sixth. Air tube ized area with long setae; basal about 6x1; pectén 6 to 9 teeth lobe large and conical in outline, on basal fourth; a small paired the apex rounded with 1 large tuft at base between the rows of spine-like seta and several smaller pectén. Anal segment longer than ones. Lobes of the ninth tergite wide and ringed by plate. Anal only slightly separated and each gills slender and longer than the bearing about 10 long setae. segment. Eighth segment with a row of 20 Distribution^, hiologyj, and ¿m- to 40 short stout spines on basal portance.—This rare species has margin. been found in small numbers in Larva.—Both pairs of head Kittitas and Yakima Counties in hairs multiple and long. Lateral Washington and in Columbia, abdominal hairs multiple on first Clatsop, and Klamath Counties in to fifth segment and double on the Oregon. It has been reported sixth. Air tube stout, 2x1; from Franklin County, Idaho. pectén of 8 to 9 teeth on basal The larvae have been collected fourth, followed by long hairs from unshaded pools grown up that nearly reach apex of tube; with rank grass and fed by fresh paired tufts large and arising water. This mosquito is not close to base between rows of known to bite man, and very little pectén. Anal segment wider than is known about it. long, ringed by the plate with 2 to 3 of the anterior tufts of ventral brush puncturing the plate, CVLISETA IMPATIENS (Walker) and with a tuft of small hairs Culex impatiens Wlkr. Brit. Mus. near posterior margin. Anal gills Dipt. List 1: 5.1848. bluntly pointed and longer than the segment. Female.—Mes on o turn with Distribution^ biology^ and im* brown and yellowish scales, two portance.—This species has been fine pale lines extending posteri- found in small numbers in a few orly from median pale patches timbered sections of Oregon and and a variable pattern of other Washington and in Fremont pale scales. Abdomen black with County, Idaho. The larvae usually basal segmental white bands. develop in shaded spring- or Wing scales brown and aggre- snow-fed pools. The overwintered gated to form faint spots at the females can usualy be found in forks of second and fourth veins, the woods very early in spring on and the bases of the second and warm days. They are said to pre- third veins. Legs black, the fe- fer animals for food, but will bite mora white tipped. man at times. MOSQUITOES OF THE NORTHWESTERN STATES 83

A*^ • ANOPHELES FREEBORNI

À ANOPHELES PUNCTIPENNIS

»SHOSHONTV ©ANOPHELES OCCIDENTALIS

D A.PSEUDOPUNCTIPENNIS FRANCISCANUS

MAP 1.—Distribution of Anopheles freeborni, punctipennis, occidentalism and psevdopnnctipennis franciscamis in the Northwest.

• AEOES CINEREUS

A AEDES FITCHII

^ D\^ ® AEDES COMMUNIS D D AEDES PULLATUS

HAEDES CAMPESTRIS

MAP 2.—Distribution of Aedes cinereus, fitchii, communis, pullatus, and campestris in the Northwest. 84 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE

• AEOES VEXANS

▲ AEDES STICTICUS

sHosHONE^ 0 AEDES NI6R0MACULIS

a AEDES NEARCTICUS

MAP 3.—Distribution of Aedes vexans^ sticticus, nigromaculis, and nearcticus in the Northwest.

• AEDES DOR SALI s

A AEDES EXCRUCIANS

O AEDES IDAHOENSIS

D AEDES VARIPALPUS

0 AEDES CANADENSIS

MAP 4.—Distribution of Aedes dorsalis, excrucians, idahoensisy varipalpus, and canadensis in the Northwest. MOSQUITOES OF THE NORTHWESTERN STATES 85

• AEDES INCREPITUS ▲ AEDES HEXOOONTUS

4^\^ 0 AEDES AB0RI6INIS

D AEDES FLAVESCENS

MAP 5.—Distribution of Aedes increpitus, hexodontus, aboriginis, and fla'^vescens in the Northwest.

• MANSONIA PERTURBANS A AEDES VENTROVITTIS 0 AEDES INTRUDENS □ AEDES CATAPHYLLA

■ AEDES TRICHURUS ^A AEDES NIPHADOPSIS

■e- AEDES IMPI6ER

+ AEDES PIONIPS

MAP 6.—Distribution of Aedes ventrovittis, intrudens, cataphylla, trichurus, niphadopsis, impiger, pionips, and Mansonia perturbans in the Northwest. 86 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE

• CULEX TARSALIS

A CULEX PIPIENS

sHosH!^V O CULEX TERRITANS

fa CULEX STIGMATOSOMA

MAP 7.—Distribution of Culex tarsalis, pipiens, territans, and stigmatosoma in the Northwest.

CULISETA INCIDENS

▲ CULISETA i NOR NATA

O CULISETA IMPATIENS

D CULISETA MORSITANS

B CULISETA MACCRACKENAE

MAP 8.—Distribution of Culiseta incidenSy inornatay impatiens, morsitans, and maccrackenae in the Northwest. MOSQUITOES OF THE NORTHWESTERN STATES 87 BIBLIOGRAPHY

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1952. PRESENT STATUS OF MOSQUITO RESISTANCE TO INSECTICIDES. Amer. X Jour. Trop. Med. and Hyg. 1: 389-394. (89) GJULLIN, C. M., and YATES, W. W. 1943. A NEW OIL EMULSION MOSQUITO LARVICIDE. U. S. Bur. Ent. and Plant Quar. E-587, 4 pp. [Processed.] (90) LEE, J., and LEE, D. 1834-37. MISSION RECORD BOOK, Methodist Episcopal Church, Willamette Station, Oregon Territory, N. A. [Manuscript.] (91) LiNDQUIST, A. W. 1951. RADIOACTIVE ISOTOPES IN STUDIES OF MOSQUITOES AND FLIES. Calif. Mosquito Control Assoc. Ann. Conf. Proc. and Papers 19: 82-83. (92) ROTH, A. R., and YATES, W. W. 1949. GROUND PREHATCHING TREATMENT FOR MOSQUITO CONTROL. Calif. Mosquito Control Assoc, Ann. Conf. Proc. and Papers 17; 42-44. (93) LiNDUSKA, J. p., and MORTON, F. A. 1948. TESTS ON PERMEABILITY OF FABRICS TO BITING BY MOSQUITOES. Jour. Econ. Ent. 41: 788-794. (94) MACCREARY, D. 1939. COMPARATIVE RESULTS OBTAINED BY THE USE OF SEVERAL MOSQUITO TR4PS IN A LIMITED AREA. Jour. Econ. Ent. 32: 216-219. ^(95) MAGOON, E. H. 1935. A PORTABLE STABLE TRAP FOR CAPTURING MOSQUITOES. Bul. Ent. Res. 26: 363-369. (96) MAIL, G. A. ^ 1930. VIABILITY OF EGGS OF AEDES CAMPESTRIS D. & K. Science 72: 170. /<97) ^^ 1934. THE MOSQUITOES OF MONTANA. Mont. Agr. Expt. Sta. Bul. 288, 72 pp. (98) MARSHALL, J. F. 1938. THE BRITISH MOSQUITOES. 341 pp. London. (99) MATHESON, R. 1944. A HANDBOOK OF THE MOSQUITOES OP NORTH AMERICA. Rev. Ed. 314 pp. New York. UOO) MATTINGLY, P. F. 1946. TECHNIQUE FOR FEEDING ADULT MOSQUITOES. Nature [London.] 158: 751. (101) MCDUFFIE, W. C, CROSS, H. F., TWINN, C. R., BROWN, A. W. A., and HUSMAN, C. N. 1949. THE EFFECTIVENESS OF DDT AND OTHER INSECTICIDES AS LARVICIDES AGAINST ARCTIC SPECIES OF AEDES. Mosquito News 9: 145-149. 92 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE

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UNITED STATES PUBLIC HEALTH SERVICE AND TENNESSEE VALLEY AUTHORITY. 1947. MALARIA CONTROL ON IMPOUNDED WATER. 422 pp. Washington, D. C. WILKES, C. 1845. NARRATIVE OF THE UNITED STATES EXPLORING EXPEDITION. Num- ber Five, 218 pp. YAMAGUSHI, T. 1952. SAMPLING METHODS FOR MOSQUITO LARVAE IN IRRIGATED PASTURES. Mosquito News. [In press.] YATES, W. W. 1943. VARIATIONS NOTED IN THE ANATOMICAL STRUCTURES OF CULEX TAR- SALis LARVAE. Ent. Soc. Wash. Proc. 45: 180-181.

1945. THE EFFECT OF DRYING ON THE VIABILITY OF AEDES MOSQUITO EGGS. Mosquito News 5: 98-99.

1947. A COMPARISON OF THE TOXICITY OF DDT, TDE, AND THE METHOXY ANALOG TO SEVERAL SPECIES OF MOSQUITOES. Calif. Mosquito Con- trol Assoc. Ann. Conf. Proc. and Papers 16: 49-51.

1947. TIME REQUIRED FOR AEDES VEXANS AND A. LATERALIS LARVAE TO OBTAIN A LETHAL DOSE OF SEVERAL LARVICIDES. Jour. Econ. Ent. 39: 468-471.

1950. COMPARATIVE RESISTANCE OF DIFFERENT INSTARS OF AEDES MOS- QUITOES TO CHLORINATED HYDROCARBON INSECTICIDES. Jour. Econ. Ent. 43: 944-945. (170) 1950. EFFECT OF TEMPERATURE ON THE INSECTICIDAL ACTION OF MOSQUITO LARVICIDES. Mosquito News 10: 202-204. (171) 1950. THE TOXICITY OF SEVERAL INSECTICIDE RESIDUES TO MOSQUITOES COM- MON IN THE PACIFIC NORTHWEST. Mosquito News 10: 132-134. (172) and GJULLIN, C. M. 1946. PREHATCHING APPLICATIONS OF DDT LARVICIDES ON FLOODWATER AEDES MOSQUITOES. Mosquito News 7: 4-6. '(173) GJULLIN, C. M., LINDQUIST, A. W., and BUTTS, J. S. 1950. TREATMENT OF MOSQUITO LARVAE AND ADULTS WITH RADIOACTIVE PHOSPHORUS. Jour. Econ. Ent. 44: 34-36. 7(174) LINDQUIST, A. W., and MOTE, D. C. 1951. SUGGESTIONS FOR MOSQUITO CONTROL IN OREGON. Oreg. Expt. Sta. Bui. 507, 12 pp. (175) and STAGE, H. H. 1941. T'ACTORS THAT MAY AFFECT THE TOXICITY OF PYRETHRUM-OIL EMUL- SIONS AS MOSQUITO LARVICIDES. N. J. Mosquito Extermin. Assoc. Proc. 28: 127-135.

i^ U. S. GOVERNMENT PRINTING OFFICE: 1952—213336