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 Publication 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 tarsalisy 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

BY

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

Mosquito literature

Mosquito-control associations and

abatement districts in the

United States

General characteristics and habits

of mosquitoes

Life History

Eggs

Larvae

Pupae

Adults V

Longevity

Flight

Collection and preservation of

specimens

Identification of species

History of mosquito control in the

Northwest

Genera and species found in the

Northwest

Mosquitos and disease

Malaria

Encephalitides

Associations of species in the

Northwest .

Floodwater

Rain pools

Snow water

Tree holes

Irrigation water

Permanent ponds

Page

2

10

12

12

14

15

18

19

20

22

22

23

Associations of species in the

Northwest—continued

Tidal water

Log ponds and water in

artificial containers

Mosquito control

Surveys

Hand collections

Trap collections

Collections of larvae ......

Collections of eggs

Engineering surveys

Control of larvae

Elimination of breeding

places

Use of larvicides

Materials for controlling

mosquito larvae

Control of adults ;..

Repellents

Space sprays

Residual sprays

Control of resistant mosquitoes

Equipment for applying

insecticides

Natural enemies of mosquitoes

Keys and notes for identifying

mosquitoes of the Northwest

Key to genera

Genus Anopheles Meigen ....

Genus Aedes Meigen

Genus Mansonia Blanchard . .

Genus Culex Linnaeus

Genus Culiseta Felt

Bibliography

Page

23

24

24

24

25

26

28

29

30

30

30

37

39

39

39

40

42

43

44

44

45

45

49

53

75

75

79

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. Hoffman, and A. R. Roth, of the Corvallis, Greg., laboratory.
HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE

MOSQUITO LITERATURE

'T^HE literature on mosquitoes

A has become exceedingly large.

Each year about 1,000 references

to various phases of mosquito

biology and the diseases they

carry appear in widely scattered

publications. Probably no other

group of insects has received so

much study throughout the world.

Some of the publications of especial interest to workers concerned

with mosquitoes in the Northwest

are given at the end of this handbook (p. 87).

One of the earliest comprehensive works on any group of insects is a four-volume monograph

by Howard, Dyar, and Knab

(68), issued in 1912-17. It includes descriptions, biology, distribution, and taxonomy of mosquitoes in the Western Hemisphere north of the equator.

Matheson's handbook (99), revised in 1944, gives much information on the taxonomy and biology of the mosquitoes of North

America and includes a discussion of their relation to human

welfare and problems of control.

More recently, in 1949, Carpenter, Middlekauff, and Chamberlin (13) published an authoritative book of nearly 300 pages

covering the taxonomy and biology of species found in the

Southern States east of the Mississippi River.

In another book that appeared

in 1949, Marston Bates (17) has

compiled a voluminous array of

facts on the biology and disease

relationships of mosquitoes,

which will be very valuable to all

students specializing in mosquito

research and control.

A textbook by Herms and Gray

(62) is designed primarily for

entomologists, engineers, and

staff employees who are directing

the activities of mosquito-abatement districts. It gives information on laws and agencies for

mosquito abatement, education of

the public, general principles of

abatement methods and techniques, abatement of disease vectors, and a host of related data.

The Engineering News Record

(25) has issued a series of short

papers on the engineering aspects

of mosquito control.

For those concerned with the

manipulation of water levels in

the control of malaria and mosquitoes, a publication by the

United States Public Health Service and the Tennessee Valley Authority (162) is indispensable.

Although the information is focused on malaria control, the

possible field of application is far

broader as it may be of great use

in the development of water resources, pow. r, and irrigations

in the Northvest.

Several Strie bulletins and a

Canadian report will be found

particularly useful in a study of

the mosquitoes in the Northwest : California, by Freeborn and

Bohart (SO) ; Montana, by Mail

(97) ; Utah, by Rees (111) ; Oregon, by Yates, Lindquist, and

Mote (17Í) ; the Lower Fraser

Valley of British Columbia, by

Hearle (58). A guide for identifying mosquitoes of the Pacific

Coast States, by Freeborn and

Brookman (81), contains unique

but valuable keys.

The following serial publications will be of interest to students of Culicidae: Mosquito

News, published quarterly by the

American Mosquito Control Association at Albany, N. Y., and

the proceedings published each

year by the New Jersey Mosquito

Extermination Association, the

California Mosquito Control Association, the Florida Anti-Mosquito Association, and the Utah

Mosquito Abatement Association.
MOSQUITOES OF THE NORTHWESTERN STATES

Articles on mosquitoes also appear in bulletins and reports of

the United States Public Health

Service and in various entomological, medical, and other scientific

journals throughout the world.

For a number of years articles

on various phases of the biology

and control of anopheline mosquitoes appeared in the Journal

of the National Malaria Society.

This society has now amalgamated with the American Society

of Tropical Medicine to become

the American Society of Tropical

Medicine and Hygiene, and its

journal includes papers on rnosquitoes and their disease relationships.

MOSQUITO-CONTROL ASSOCIATIONS AND ABATEMENT

DISTRICTS IN THE UNITED

STATES

'j

There are sevm mosquitocontrol associations 4n the United

States (1.Í0), as follows:

The New Jersey Extermination Association, organized in 1913.

The Florida Anti-Mosquito Association, organized in 1929.

The California Mosquito Control Association, organized in 1932.

The American Mosquito Control

Association, Inc., organized in 1936.

The Virginia Mosquito Control Association, organized in 1947.

The Utah Mosquito Abatement Association, organized in 1947.

The Illinois Mosquito Control Association, organized in 1948.

Each of these associations

holds annual meetings, and most

of them publish their proceedings, which contain valuable contributions on mosquito biology

and control.

The American Mosquito Control Association is international

in scope and has a membership

of about 1,000. It is a nonprofit

technical and educational association of mosquito workers, composed of entomologists, sanitary

engineers, control officials, medical personnel, and laymen who

are charged with or are interested in mosquito control and

related work. Annual meetings

are held in various parts of the

United States, usually conjointly

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 mosquito-control agencies in 39

States, Hawaii, and Puerto Rico

(fig. 1). These agencies are commonly called mosquito-abatement

districts and are usually named

after the counties in which they

are located. In 1951 Florida had

21 such districts, with a total

budget of about $985,000; California 44, with over $1,700,000;

New Jersey 16, with $640,000;

Utah 4, with $117,000; Virginia

13, with $178,000; and Rhode

Island 18, with $76,000. A total

of more than $6,000,000 is budgeted annually in the fight

against pest mosquitoes and malaria. Over 26,000,000 people in

the United States live in areas

protected from mosquito annoyance. During the last few years

Federal and State health agencies

have treated more than 800,000

homes with residual sprays annually for the control of malaria

mosquitoes.

GENERAL CHARACTERISTICS

AND HABITS OF MOSQUITOES

The characteristics and habits

of mosquitoes in the Southeastern

States as described by King and

COworkers (8S) apply generally

to species found in the Northwestern States.

Although mosquitoes have extremely diverse breeding habits,

particularly the type of place

they select to lay their eggs, all

have one important characteristic

in common—^they live part of

their life in water and in water

only. It may be in a small tin can

or in a vast tidal marsh.

Some species are found throughout the Northwest and in different

types of water. Others are found

only in restricted areas and in one

kind of water. For example,

Culex tarsalis has been collected

in almost every kind of water

in nearly every county of the

three States, whereas Aedes hexodontus is found only in snow

water in high mountainous areas

{27). Some genera, such as

Aedesy lay their eggs on ground

that may later be flooded, whereas others, such as Culex and Culi"

seta, lay them directly on the

water surface.

Temperatures of air and water,

alkalinity or acidity of the water,

and associated shelter and vegetation aiïect the abundance and

presence of most species. The

species also differ in biting habits, longevity, and flight range.

The mosquito is an insect having a complete metamorphosis.

There are four well-defined stages

—^the egg\ the larva, sometimes

called wiggler; the pupa or tumbler; and the adult or imago.

LIFE HISTORY

EGGS

The eggs may be laid singly as

with the anophelines, or in rafts

of about 150, as with the culicines. In very warm weather the

eggs may hatch within 2 or 3

days after they are laid. In northern latitudes, however, eggs laid

by Aedes in the late summer do

not hatch until flooded the following spring. If not flooded the

first season they may remain

viable for several years (^5).

There is still some question as to

whether northern Aedes eggs require a certain amount of drying

and exposure to cold before they

hatch or, as we believe, a low

oxygen concentration (^0). A

blood meal has been considered

necessary for the production of

viable eggs {70), although among

some of the northern Aedes this

has not been definitely established.

LARVAE

All mosquitoes spend their

larval and pupal stages in water,
MOSQUITOES OF THE NORTHWESTERN STATES

and most of them move freely

about as aquatic insects. Without

water these stages cannot survive

more than a few hours. The

larvae of most species must come

to the water surface for air,

which they obtain through an air

tube or other appendage located

at the end of the "tail.'' The

larvae shed their skins four

times, and each instar is larger

than the last. The larval stage

usually lasts from 4 days to 2

weeks; in icy-cold water some

Aedes mosquitoes may remain as

larvae for a month or more. The

larvae of Aedes varipalpus occurring in tree holes and those of

Mansonia perturbans attached to

the roots of aquatic plants overwinter, and hence may exist as

larvae several months.

The food of mosquito larvae

consists of tiny plants, animals,

and organic debris. Some species

prey on the larvae of other

species and some are cannabilistic. Barber (6) has reared larvae

on pure cultures of various organisms, and Hinman (63) has

suggested that materials in solution or colloidal suspension in the

breeding water form a part of

the larval food. We have reared

large numbers of Aedes vexans,

sticticuSy and hexodontus in the

laboratory on ground dog food

and blood albumin. We have also

reared Culex quinquefasciatus on

yeast and powdered milk.

PUPAE

With the fourth larval molt the

pupal stage appears. They move

about by somersaulting. Except

for Mmvsoniay a mosquito pupa's

life is a short and active one. An

excellent account of the emergence of an adult mosquito from

the pupal stage is given by

Marshall {98).

ADULTS

Only the female mosquito has

mouth parts adapted for bloodsucking. While the insect is biting, it injects a secretion that is

responsible for the itching that

follows. Not all mosquitoes have

bloodsucking females, but all

those found in the Northwest do

have.

The mouth parts of male mosquitoes are not strong enough for

biting. Their food consists of

pollen and of fruit and other

plant juices. In the laboratory we

have kept alive both sexes of

some species for long periods on

raisins, fruit juices, and sugar

solutions.

LONGEVITY

The length of life of adult mosquitoes under natural conditions

is difficult to determine, but for

most of the northwestern species

it is probably only a few weeks

in spring and early summer.

We have studied the longevity

of Aedes vexans and sticticus

by staining swarms of newly

emerged adults in their breeding

areas. One vexans female was

taken after 55 days and one

>sücticus after 85 days. Six sticticus females were taken after 52

days and one Aedes male after

24 days {H7). From these studies

it appeared that longevity may

depend somewhat on the time of

the flood crest. Individuals hatching after a May flood lived longer

than those that hatched after a

late-June flood. Conditions of

climate in the breeding areas

probably exert the greatest influence on the life span. In one

locality, for example, a sticticus

male was captured 94 days and

females of both species were collected 104 to (rarelv) 118 days

after emergence. The climatic
6 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE

and geographic factors in that

locality were especially favorable

—the humidity was high and the

temperature comparatively low.

The relative abundance of these

species in the lower Columbia

River valley in the years of high

and low flood crest is given in

figure 2.

FLIGHT

The distance that mosquitoes

fly varies with the species and

with the individual. Some individuals of Aedes squamiger may

travel 60 to 70 miles, and those

of Culex pipiens may remain

within a few hundred yards of

the place where they emerged as

adults.

Sample collections and observations were made over several

seasons. Some of our recorded

data (1J^7) on flight range (fig.

3) were obtained by staining and

recovering adults. It was determined that vexans and sticticus of both sexes were dispersed

in all directions, both within and

13

2

O

AEDES VEXANS

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

MAY JUNE JULY AUGUST SEPTEMBER OCTOBER

31

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

H H H H H t30 HILES

=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

a distance of 2 miles. Within 24

hours they traveled 5 miles, 1/2

mile of which was across the

Columbia River. These staining

tests were supplemented by observations made along a canyon

road, through a heavily timbered

section for a distance of 30 miles.

For 15 miles vexans and sticticus

were numerous, but 30 miles

away only one female was taken

in 10 minutes.

The size of the brood influences

the distance that mosquitoes

travel, but not their rate of

travel. The height of the flood

crest also affects the size of the

broods. The greater the flood, the

greater the radius of dispersion.

COLLECTION AND PRESERVATION OF SPECIMENS

A white-enamel dipper, the

handle of which is lengthened

with a cane or smooth stick, is the

most convenient implement for

collecting larvae (fig. 4). A little

FIGURE 4.—Using a long-handled dipper

to collect mosquito larvae.

experience is necessary before

one can dip successfully, because

the larvae are frightened easily

and may disappear below the surface of the water and out of

range of the dipper.

Upon reaching a spot to be

sampled, especially if the water

is more than a few inches deep,

wait a full minute and then quickly skim the surface without

allowing the water to flow over

the edge of the dipper. Transfer

the larvae from the dipper to a

collecting jar with an eye dropper, the tip of which has been

broken ofl" to make an enlarged

mouth.

As soon as a collection is made,

number the jar and record the

date, locality, and other pertinent

conditions under which the larvae were found.

For easier identification place

the larvae and pupae in shallow

pans for rearing to the fourth

instar, and then either preserve

them in 70-percent alcohol or

allow them to emerge as adults.

Frequently several species may

be taken in one dip. Therefore,

select a few larvae and place

them individually in small vials

until the adults emerge. These

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 preserved 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

the mosquitoes between the layers of tissue. Without the tissue

paper the tarsal claws may cling

to the strands of cotton and become broken when removed.

Damaged, moistened, or rubbed

specimens are usually unsatisfactory for identification.
MOSQUITOES OF THE NORTHWESTERN STATES 9

Specimens of adults that are to

be retained in permanent collections are best mounted on a

minuten-pin stuck into a small

square piece of cork, through

which is passed a larger pin.

Thrust the tip of the minuten-pin

through the underside of the

thorax of the mosquito, but not

protruding through the mesonotum. The No. 3 entomological pin

is generally the best size for holding the cork.

Label the mounted specimens

carefully and pin them in a

Schmitt insect box. Take care to

protect the stored specimens

from insect pests and dampness.

Flake naphthalene or paradichlorobenzene placed in a perforated container and securely

fastened in one corner of the

Schmitt box will prevent damage

from insect intruders. These insect repellents must be renewed

occasionally.

IDENTIFICATION OF SPECIES

One must have a knowledge of

mosquito anatomy to identify the

different genera and species of

mosquitoes. The principal distinguishing characters are the

shape, size, coloration, and scaling of the different body parts.

A binocular dissecting microscope providing magnifications up

to about 85X is necessary for satisfactory examination of the

identifying characters.

For examining larval parts and

slide mounts of male terminalia,

a compound microscope having a

magnification up to 400X is

necessary. A bright spotlight is

required when high magnifications are used.

In the field a good hand lens

giving a magnification of 10 or

15X is satisfactory for provisional identifications. After some

experience one will be able to

identify some of the species in a

given locality with a hand lens,

or even with the naked eye.

Misidentification of mosquitoes

may cause serious confusion. Inexperienced workers will find it

helpful to have on hand for comparison a few specimens that

have been correctly identified.

Send specimens to a specialist

with the request that they be

named and returned. Identifications may be obtained through

the Bureau of Entomology and

Plant Quarantine and some of the

State universities and agricultural experiment stations.

HISTORY OF MOSQUITO

CONTROL IN THE NORTHWEST

The great numbers of mosquitoes appearing in the lower

Columbia River Valley each May

and June have been a serious

problem ever since the first settlers reached there early in the

nineteenth century. As the population increased there was much

discussion of the annoying problem. It finally came to the attention of Oregon State College, and

beginning about 1924, D. C. Mote,

head of the Department of Entomology, was frequently consulted for advice and guidance.

After surveying the situation and

gathering the available information, in March 1926 he initiated

the first effort at mosquito control in the Portland area by introducing mosquito fish {Gamhusia affinis) from California.

Mote's efforts led to organized

action, and meetings were held in

which leading citizens of Portland and Multnomah County took

part.

Among the people who contributed to the movement was H. H.

Riddell, an observing naturalist

although not a trained scientist.

Riddell became interested in mos-
10 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE

quito control in Skamania County, Wash., about 1926, and bycorrespondence with H. G. Dyar,

of the Smithsonian Institution,

and others, discovered the breeding areas of the local species.

Dyar had visited Oregon in 1916

and had made field observations

of mosquito conditions which

later were to have an important

part in their control. In 1927 Riddell started mosquito control in a

small way in Skamania County.

He also met with the people of

Portland and Multnomah County,

and beginning in 1930 was in

charge of the field operations of

the Portland Chamber of Commerce Mosquito Control Committee. This committee was headed

by Charles Stidd, and consisted of

the entomologist of Oregon State

College, representatives of Multnomah County and the city of

Portland, certain recreational organizations-—especially Jantzen's

Beach—and was responsible for

raising funds for the control program for more than 10 years.

In 1929 G. H. Bradley, of the

Federal Bureau of Entomology,

made a brief visit to the lower

Columbia River Valley, collected

some of the annoying mosquitoes,

and made general recommendations which further stimulated

interest in organized action.

Because little was known about

the biology and habits of mosquitoes in this valley, the United

States Department of Agriculture was asked to undertake a

research program. In 1930 Congress appropriated funds for

these investigations.

W. V. King, of the Bureau of

Entomology, opened a laboratory

in Portland in 1930, and spent 2

months surveying the lower Columbia River area and southeastern Oregon. He examined

numerous breeding areas of the

floodwater Aedes mosquitoes in

several counties along the Columbia and Willamette Rivers and

made hundreds of collections of

these insects for identification.

Aerial photographs of the overflow area in Multnomah County

made under his direction were of

great value in studies of the mosquito-breeding areas. The authors of this handbook conducted

investigations from 1931 until

1940. Much of the information

contained in it was obtained during those years, although additional data subsequently obtained

by the junior authors are ineluded.

In the winter of 1933-34 mosouito control in both Oregon and

Washington was greatly accelerated through an allotment of

funds by the Civil Works Administration (129, 130, 132). This

work was conducted in Multnomah, Columbia, and Tillamook

Counties in Oregon and in Kitsap, Skamania, and Clark Counties in Washington. Practical

mosquito-control measures are

being continued in the vicinity of

Multnomah and Clark Counties,

in which Dorothy McCollough

Lee, Mayor of Portland, has been

an active leader.

An enabling act for the organization of mosquito-abatement districts in Oregon was passed by

the State Legislature in 1940.

GENERA AND SPECIES FOUND

IN THE NORTHWEST

The mosquitoes found in tiie

Northwestern States, their distribution and economic importance as recorded during the

years 1930-51, are listed in table

1. Their distribution is shown in

the maps at the back of this

handbook. In addition to the 39

species listed, several more have

been reported from the region,

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 ...

campestris .

canodensis ..

cataphylla ..

cinereus ....

communis ..

dorsalis ....

excrucians ..

fitchii

flavescens ..

hexodontus .

idahoensis ..

impiger ....

increpitus ..

intrudens ..

nearcticus ..

nigromaculis

niphadopsis .

pionips

pullatus ....

sticticus ....

trichurus ...

varipalpus ..

ventrovittis .

vexans

Anopheles:

freeborni

occidentalis

pseudopunctipennis franciscanus

punctipennis

Culex :

pipiens

stigmatosoma

territans

Culiseta:

impatiens . ..

incidens ....

inornata ....

maccrackenae

morsitans ...

Mansonia:

perturbans

4

5

5

5

3

2

1

3

2

4

2

5

0

1

5

4

4

5

0

5

1

0

4

0

1

2

5

4

5

2

2

1

4

2

4

2

5

5

2

4

4

4

0

0

4

1

5

4

5

1

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

valid forms. Some of the information presented in this paper was

obtained from records in the literature, principally from the

comprehensive works of Dyar

{22, 28) and Howard, Dyar, and

Knab {68) \ also from collections

in the National Museum, Oregon

State College, Washington State

College, Idaho State College, and

the U. S. Public Health Service.

The Northwestern States do

not have a large number of species, but in certain localities the

prodigious numbers of some of

the Aedes mosquitoes have seriously affected economic enterprises. The following species are

of greatest economic importance :

Anopheles freeborni {2) occurs in

great numbers in the irrigated valleys

of Washington and Oregon. It has been

the most important vector of malaria

in the region.

Aedes dorsalis breeds in saline, alkaline, or fresh irrigation water. It is

abundant in the salt marshes, and in

certain areas is a great handicap to

the dairy industry. The viruses of

western equine encephalomyelitis and

St. Louis encephalitis have been isolated

from it in nature.

Aedes increpitus is a severe biter, and

in high elevations is one of the most

annoying species to man and animals.

Aedes hexodontus is very numerous

and annoying in restricted mountainous

areas.

Aedes sticticus breeds in large numbers in the willow flats along the lower

Columbia River, and is a severe biter

of man and livestock.

Aedes communis occurs in mountainous areas, and in some places is a very

serious hazard to recreational interests,

lumbering, and road building.

Aedes vexans is one of the most

troublesome pest species in both irrigated and floodwater areas, and is found

near sea level and also in mountain

meadows. The adults disperse for 10 to

20 miles from their breeding places and

are severely annoying to man and livestock for 8 or 4 months each year.

Culex pipiens occasionally is extremely numerous and annoying in communities in the western portion of the

Northwest. It seldom occurs in Idaho

or the eastern half of Oregon and

Washington.

Culex tarsalis (see frontispiece) is

one of the most widely distributed mosquitoes in the region. The larvae have

been taken from rain barrels, log ponds,

stagnant pools, sluggish streams, woodland ponds, and alkaline sumps. They

have not been found at high elevations

or in salt marshes. Although they prefer to feed on fowls and livestock, they

will readily attack man. Viruses of both

western equine encephalomyelitis and

St. Louis encephalitis have been isolated

from collections of this species in several States, and transmission of these

viruses to chickens and ducks has been

demonstrated.

Culiseta inomata, an important livestock pest, annoys humans very little.

MOSQUITOES AND DISEASE

MALARIA

We are not sure when malaria

first appeared in the Northwest,

since our sources of information

do not agree {21, 90, 125, 163),

but it was probably about 1830.

However, they all show the important bearing of the disease on

the early history of the region—

its fatal character and that great

numbers of the native population

died because of it. Neither do we

know how it reached the Northwest, but as one author {125)

aptly describes it, it was most

likely "dragged across the plains''

by parties from the East and

South that assembled at Independence, Mo., for their long

journey into the Oregon Territory. It may also have been

brought in by sailors and travelers who had come from malaria

belts in the United States or

who had touched at Central

American ports before reaching

the Northwest.

Malaria was first required to

be reported to the State health

officer of Washington in 1915,

and of Oregon in 1918. Figure 5

shows the cases of malaria reported in Oregon for the period

1920-44. During the years 1945-
MOSQUITOES OF THE NORTHWESTERN STATES 13

47 a considerable increase in this

disease was reported, but most

of the cases originated outside

the United States. Since then only

two cases have been reported as

originating within the State, one

in 1948 and one in 1950. Only

rarely have any cases of malaria

emanated from the State of

Washington.

In Idaho it has been a reportable disease on a voluntary basis

since 1936. Up until 1945 only 20

cases had been reported.

Anopheles freebomi, a vector of

malaria, occurs widely throughout the Northwest (iS), but

breeds most profusely in the upper Willamette Valley of Oregon.

The other species of Anopheles

occurring there are probably of

little significance as transmitters

of the disease. The winter climate

is similar to that of the northern

range limits of the disease in the

Mississippi Valley, although the

mean winter temperature is

slightly higher for Eugene, Oreg.,

than for Cardwell, Mo., where

malaria has been very common.

The summers, however, are much

cooler in Oregon.

1925 1930 1940 1945

160

140 f\

r20

/ \

100

/ \

80 / \

60 J \

40

20

0

ß _^ 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

Encephalitis in man and equine

encephalomyelitis, known collectively as encephalitides, are comparatively new recognizable diseases. Little was known of the

causative agent, host range, and

methods of spread until 1941,

when Hammon and coworkers

(5S) published the results of

their research in the Yakima

Valley, They isolated the virus of

St. Louis encephalitis and western equine encephalomyelitis, the

principal types of encephalitis

found in the Northwest, from

Culex tar salis. Never before had

^this virus been found in mosquitoes collected in an epidemic area.

Several new viruses have been

isolated from mosquitoes by various research workers, and it is

suspected that they might produce clinical encephalitis in man.

The epidemiology of the encephalitides is the most complicated of any of the insect-borne

diseases. However, it is known

that Culex, Aedes, Culiseta, and

Mansonia mosquitoes can serve

as experimental vectors of western equine and St. Louis viruses

U9, 50, 51, 52, 55), and species

of the first three genera have

been found naturally infected.

Culex tarsalis undoubtedly is

the primary vector of western

equine encephalomyelitis and St.

Louis encephalitis in the Northwestern States. In one year Hammon and coworkers found 1 out

of every 386 of these mosquitoes

caught to be infected. This mosquito feeds on man, horses, mules,

cattle, sheep, pigs, dogs, ducks,

doves, pheasants, and chickens

(75). It breeds in permanent

ponds, barnyard puddles, irrigation seepage, and along the margins of streams. The problem is

complicated also because birds

serve as reservoirs of the virus

(55). As many as 2400 cases of

equine encephalomyelitis have

been reported in 1 year in Idaho (1935), 726 in Washington

(1940), and 525 in Oregon

(1936). Figure 6 shows the numbers of cases reported in the

Northwest from 1935 through

1951.

1935

FIGURE 6

42 43 44 45 46 47 48 49 50 1951

.—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

merits of mosquito control as a

means of reducing the encephalitides, in known endemic areas

with epidemic potentialities mosquito-abatement personnel must

assume responsibility for making

their control measures broad

enough to include all mosquito

species. The likelihood of reducing the incidence of encephalitis

may be considered an added benefit in areas where mosquito control is justified on the basis of relief from irritating annoyance.

ASSOCIATIONS OF SPECIES IN

THE NORTHWEST

The mosquitoes occurring in

the Pacific Northwest may be

grouped as follows according to

their ecological habitat or association {13Í) :

Temporary bodies of water

One generation annually

Floodwater

Rain pools

Snow water

Tree holes

Several generations annually

Irrigation water

Permanent bodies of water—several generations annually except

Manaonia

Permanent ponds

Tidal water

Log ponds and water in

artificial containers

Each association at different

times and in different places may

include species typical in other associations. The species in some

of these associations cause more

serious annoyance than do those

in other associations. The fact

that the species in the ñoodwater,

rain pool, and snow-water associations have only one brood a

year greatly simplifies control

operations. Frequently, however,

they may be complicated by the

extent and inaccessibility of the

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

the Northwest has been so altered

by the construction of dikes,

ditches, or dams in connection

with irrigation projects that an

entirely new association of mosquito species has resulted. For

example, the Bonneville Dam has

prevented the spring flooding of a

large acreage overgrown to wilFiGUBE 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

the dam {1S5). These willow flats,

(figs. 8 and 9), now permanentlycovered with water, no longer produce hordes of Aedes vexans and

sñcticus mosquitoes, but do provide marginal areas in some

places suitable for the production

of Anopheles, Culex tarsalis, and

Mansonia, Grand Coulee Dam has

afforded vast breeding grounds

for Aedes dorsalis, Anopheles, and

others that were not present before the area was irrigated.

An association of species may

also change with the advancing

season. In the irrigated sections of

the Yakima Valley practically all

of the first mosquitoes are Aedes,

whereas after the irrigation water

forms permanent ditches and

ponds the next outbreak will contain numbers of Culex tarsalis and

Anopheles freeborni.
18 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE

FLOODWATER

AEDES VEXAISS and STICTICVS

Along the banks of the Columbia River from the Cascade

Mountains to the sea are manyareas that overflow each year

(fig. 10). The annual freshet usually occurs in May or June; the

earliest date recorded for the

flood crest is March 19 and the

latest is July 4. These areas are

heavily overgrown with willow

brush and, at slightly higher elevations, with cottonwood, briars,

and small shrubs ; still higher are

the conifers.

The normal mean level of the

river is 7.1 feet. The flood crest is

rarely so low as 10 or 12 feet. In

most years it reaches at least 16

feet and one year in five it goes as

high as 24 feet. Once in several

decades it has reached disastrous

heights—about 30 feet in 1894

and 1948.

During the annual spring

freshet swarms of vexans and

sticticus {J/^7) hatch when stimulated by the floodwater. Three or

4 days after emerging from their

aquatic life, the adult mosquitoes

spread over the contiguous territory for several miles. They become extremely annoying in

residential sections of Portland,

Oreg., and Vancouver, Wash.,

over agricultural lands, especially

dairy and small-fruit farms, and

also in amusement parks and on

golf courses.

The larval season usually begins in April, rarely late in

March, and is over shortly after

the flood crest is reached in May

or June. At most it lasts 3 months.

For the remainder of the year,

these willow swales are comparatively dry. Oviposition begins

within a week or two after emergence, and probably continues during July and August in willow

flats adjacent to the receding

river.

In some seasons there is a

single gradual rise and fall of the

river and, although breeding is

heavy over the entire valley at

the same time, with proper organization good control can be

established. More often the river

rises and falls from two to four

times, and with each new crest

new hatching takes place on

ground that has previously been

flooded (fig. 11).

WILLOW WILLOW. COTTONWOOD. SNOWBERRY. BRIARS, ETC CONIFERS 1

i'J^&StgWL*'

Ä- '^^Êk?lm

"w l^mb^

v:j^||i-.

-201 FT NORMAL FLOOD CREST ^ j^

C MAY AND JUNE ) ^<ii\^y^

- ISO FT JWi£il4U ^IMf7-S^

^^^m^è^i^àii ...^^¿!pr^

"^iaj,

- I05FT ^^UM^)Aiß'^^****^ffj^>

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

important control measure in a

few restricted areas. Because of

their greatly changed ecology,

these areas become unsuitable for

shelter and oviposition until

heavily overgrown again.

Little ditching has been done in

controlling mosquitoes of this

association, because most of the

breeding areas are flooded directly

from the river, by water backing

up into swales and sloughs or

seeping through the sand into

the swales. Where saucer-shaped

swales can be emptied of water,

ditches can be dug at the lower

end, so that water will drain out

of them quickly when the flood

subsides. If the flood crest is a

short one, these swales will dry

before the larvae pupate, or

the larvae will be carried

into deep water, where they will

be destroyed.

Much of the land bordering the

Columbia River is now protected

by dikes, and some of it has been

filled above the normal flood

crests. This kind of work is satisfactory and permanent, and

greatly reduces the breeding of

these mosquitoes.

A large mosquito-breeding

area between The Dalles and

Bonneville Dam has been permanently flooded. This flooding

immediately reduced the breeding of vexans and sticticus and,

as the ecology of the area became

a permanent-pond type, new mosquitoes, such as Culex tarsalis and

Anopheles freeborni, increased in

numbers, although not seriously.

RAIN POOLS

AEDES ABORIGimS, EXCRUCIANS,

and mCREPITUS, and CULISETA

INCIDEISS

There are a great many temporary woodland pools of rain

and seep water in the Coast

Range of Oregon and Washington, where the rainfall is especially high early in the spring.
20 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE

These pools, most of which are

much less than an acre in size but

occur for miles along the coast,

are breeding places for vicious

ahoriginiSy excrucians, and increpitus. These species may also

be found in the snow-water association. Most parts of this rugged country are so thickly overgrown as to be nearly impenetrable (fig. 12). The ditching of

the low spots reduces the mosquito population immediately,

but ditching is expensive and considerable clearing is necessary to

reach these breeding spots. Another kind of rain pool, undoubtedly containing some salt,

occurs on the high rocks along

the ocean. Culiseta incidens breeds

in these pools.

SNOW WATER

AEDES COMMUNIS, HEXODONTUS,

INCREPITUS, FlTCHIh and CllSEREVS

These Aedes species are found

widely scattered along the backbone of the Cascade Range, in

the mountains of eastern Oregon

and Washington and in Idaho.

The larvae appear in the innumerable pools and ponds formed by

melting snow in April, May, or

June. These mosquitoes breed also

at the margins of lakes, the levels

of which are raised by melting

snow and lowered again when the

excess water evaporates and seeps

into the soil.

The mountainous areas of the

Northwest are great recreational

centers where visitors from every

part of the United States camp,

fish, hike, or pick blueberries

from May through September.

Visitors who have suffered from

these mosquito hordes, which are

vicious biters, will not remain

long and probably will not return.

Perhaps in some places control

by ditching or treatment from

aircraft cannot be justified at

present. However, until more economical means are found, some

relief can be obtained locally by

treating brush and other mosquito-sheltering vegetation around

camp and resort sites with DDT

sprays. Two of these treatments

per season will greatly reduce

annoyance by these species. At

times of greatest mosquito activity, as at dusk, space sprays may

be used.

Many of these areas are inaccessible until June because of

heavy snow, and, if larvicide applications are contemplated, the

materials and equipment must be

taken into the area the preceding

fall. After mid-June these mosquitoes are on the wing and are

widely dispersed. These mosquitobreeding areas can also be treated

when dry, late in the fall, with

a residual spray or dust that will

remain effective and kill the

young larvae as they hatch from

snow water the next spring. This

method cannot be depended on

for complete relief, however, because migrating mosquitoes may

fly into the treated area.

Some semipermanent work has

been done in this region by the

Forest Service. Ditches have been

dynamited in the heavy peat soil,

not so much for draining pools

of snow water as to maintain the

levels of lakes whose upper margins otherwise produced larvae

when temporarily flooded. The

snow water and seep water then

quickly drain into the lakes, the

levels of which are fairly well

maintained by dams at the outlets. This type of mosquito-control work is distinctly advantageous to wildlife. It creates additional marginal areas dry enough

for upland birds early in spring,

and at the same time increases

and maintains the extent of lakes

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

ÀEDES VARIPÀLPUS

Here and there along streets, in

parks, or in the deep forest are

tree holes that contain water for

long or short periods (fig. 13).

In these holes one can nearly always 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 irrigation is practiced. Some of these

areas are flooded with a thin

sheet of water from the surrounding mountains. They are

generally used as hayfields, which

either go dry naturally or are

made to go dry by diverting the

water before haying time. Aedes

dorsalis or vexans mosquitoes appear in May and June and are exceedingly abundant in these socalled marshes of 10,000 to 60,000

acres but the anophelines and

culicines have scarcely time to

propagate except where the water

is turned into border ditches. At

haying time it is difficult to hold

labor because of the mosquitoes.

Men wear head nets and heavy

clothing for protection. Horses

have been known to lie down

while harnessed to mowing machines, in their frantic efforts to

rid themselves of these tormentors. The pests cause beef cattle

on summer pasture to lose weight

and reduce the milk now in dairy

herds. They also prevent the development of otherwise desirable

real property and hinder all kinds

of recreational activities.

í^ílSt^

FIGURE 13.—Tree hole where Aedes varipalpus larvae are found.

The only means of control

would be to treat large areas

from aircraft, but this measure is

seldom economical because of the

great size of the infested areas

and the sparse human population.

The problem is how to furnish an

adequate supply of water to the

fields and then dry them up

within a week. The border method

of irrigation partially meets this

problem where it can be employed, but there is seldom an

adequate supply of water that can

be held for later release.
MOSQUITOES OF THE NORTHWESTERN STATES 23

PERMANENT PONDS

ANOPHELES FREEBORM and PVISCTIPElSmS, CVLEX TARSALIS, CVLISETA INCIDEISS and INORNATA,

and in some areas MANSONIA PERTURBANS

Contrary to common belief,

ponds of permanent water present the least mosquito nuisance

in the Northwest. The anophelines

and Culex tarsalis that breed

there do not become numerous

until late in the season and are

seldom very annoying. However,

freeborni is a potential carrier of

malaria and tarsalis of encephalomyelitis and encephalitis. Mosquitoes that transmit the last two

diseases should be controlled

whenever practicable. The anophelines are widespread throughout the Northwest late in the

summer, but malaria has been

endemic only in the upper Willamette Valley of Oregon. Oxbow

ponds (fig. 14) are numerous for

30 miles along the Willamette

River and in some places occur in

an area 5 miles wide.

TIDAL WATER

AEDES DORSALIS

Only one mosquito species

breeds in salt marshes along the

coast of Oregon and Washington.

Except for certain tidal flats adjacent to Puget Sound, the coastal

breeding areas are small and

more or less isolated. Aedes dorsalis breeds abundantly in these

salt-marsh areas, as well as in

the alkaline irrigation water to

the eastward. These mosquitoes

probably fly but short distances,

but can be a severe annoyance to

man. They are vicious biters by

day and have caused a decrease in

the milk production of dairy

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

ARTIFICIAL CONTAINERS

CULEX PIPIENS and TARSALIS, CULISETA INCIDENS, and ANOPHELES

PUNCTIPElSmS

Large numbers of these mosquitos breed in log ponds, and

in many towns in western Oregon

and Washington they are the only

source of mosquito annoyance.

Culex pipiens is occasionally a

serious pest near heavily polluted

ground pools, and in drains of

septic tanks, offal disposals, and

other sewage-polluted water.

Wooden, tin, and rubber receptacles also harbor this species as

well as CuUseta incidens, sometimes in numbers sufficient to annoy the occupants of several

homes. Anopheles punctipennis

larvae are sometimes found in

rain or water barrels in this region, if the water is fairly clean.

MOSQUITO CONTROL

Mosquito control has become

increasingly important during the

last few years. In many parts of

the country it has become an essential part of good living. The

recent incrimination of Culex

tarsalis as a vector of equine

encephalomyelitis and its relation

to sleeping sickness in humans

has stimulated interest in mosquito control to reduce the incidence of this disease. Although

malaria is of little importance in

the Northwest, it has been endemic in the upper Willamette

Valley in Oregon for over 100

years (1^6).

The mosquito problem of the

Pacific Northwest is largely agricultural and recreational in character (17i). Mosquitoes affect

the farmer, his family, his employees, and his livestock. They

cause financial losses to stockmen,

dairymen, and general farmers.

Mosquitoes, by constant annoyance, cause livestock to lose

weight and reduce milk flow. They

often drive livestock from lush

pastures to barren hillsides and

thus further reduce flesh gains.

Annoyance from mosquitoes is a

severe trial to fruit pickers, and

may cause them to refuse to work

in the fields.

The use of recreational areas

at some beach and mountain resorts is greatly restricted by mosquito annoyance at the very time

of year when the most people are

on vacation. The losses from reduction of property values and

attendance at amusement parks,

and from injury to livestock are

frequently much greater than the

cost of mosquito control.

Mosquito control is a specialized subject and one that requires

sound judgment, a background of

entomology, some training in engineering and, because of the innumerable personal contacts, an

understanding of human psychology. Above all one must know the

different species, their life histories, and habits, in order to

apply practical measures against

them. In mosquito control one

can do the right thing, but do it

at the wrong time, and so meet

with failure.

SURVEYS

Before an effective mosquitocontrol program can be undertaken, a survey must be made of

the area. Such a survey must be

made by an entomologist or a specialist having knowledge of the

biology and habits of mosquitoes,

and of the diseases they carry. In

addition to finding out where the

mosquitoes are and what species

are present, information must be

obtained on their breeding places,

and such other data that entomologists, sanitary engineers, and
MOSQUITOES OF THE NORTHWESTERN STATES 25

mosquito-abatement engineers

will need in planning a control

program.

If the mosquito-control project

is aimed at the reduction of malaria or equine encephalomyelitis,

the presence of the disease itself

indicates in some measure the

species involved. A study of the

distribution of the disease serves

to point up the problem, and a

survey of mosquito species aids

in developing the plan of procedure and estimating costs.

When relief from mosquito annoyance is the main consideration, a

survey is necessary to determine

the limits of the infestation and

the relative importance of each

species, since more than one kind

is usually present. Even in one

county of the lower Columbia

River Valley the problem is complicated by mosquitoes that breed

in snow-water, floodwater, artificial containers, and permanent

ponds.

A mosquito survey is begun by

collecting and identifying both

larvae and adults during a mosquito outbreak. Because the flight

range may be unknown, this collection should extend for some

distance beyond the limits of mosquito annoyance. Since mosquitoes

have no regard for municipal,

county, or State boundaries, it is

sometimes necessary to control

them in one State or county to

protect the citizens of another.

Some mosquito-abatement districts maintain collections of

identified species of mosquitoes

found locally. These collections

are of use in quickly identifying

species brought in for determination and for educational purposes.

A survey of the breeding places

should determine their extent and

nature, whether permanent or

temporary, as well as the topography and natural drainage of

the area. At least one entire mosquito breeding season is necessary

for such studies. Two or three

seasons is even better. In the Fayette Valley of Idaho dorsalis predominates in May and nigromaculis in July and August. Along

the Columbia River flood crests

vary greatly from year to year,

or they may occur two or

three times during one season.

Each flood stage produces its

brood of mosquitoes and, because

of their habit, the relative abundance of the species may vary with

the height of the flood. Several

years of study are required,

therefore, before reliable averages can be determined. Fairly

effective control operations can

be started before such an extensive survey is completed, but

without adequate information

control may be highly wasteful

and may result in loss of public

confidence.

HATO) COLLECTIONS

Collecting mosquitoes while

they are biting is the simplest

and most direct method of determining the proportions of the

different species. Such collections

are usually made with a chloroform tube or other type of killing

bottle. One procedure is to stand

or sit at the selected place and,

after allowing a minute or two

for the mosquitoes to accumulate,

to collect them as they alight over

a 10-minute period. Three 10-

minute periods may be totaled

and multiplied by 2 for the hourly

rate. One person working alone

can collect the mosquitoes landing on the front of his trousers.

If two are working together, one

can collect those alighting either

on the shirt or bare back of his

companion.

When mosquitoes are abundant,

the numbers caught can be increased by placing a short paper
26 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE

funnel, or guard, in the mouth of

the collecting tube. The collector

can then catch the next specimen

without waiting for the first one

to succumb to the chloroform

fumes. The guard also conserves

the strength of the chloroform

and prevents the loss of spscimens

when the mouth of the tube is

turned downward. In heavily infested areas 100 or more mosquitos have been taken in 10

minutes with a tube of this sort.

When two or more persons are

to make collections at different

places, they should make a preliminary collection at one place

to determine the relative attractiveness and dexterity of the different collectors, since much variation 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

made daily, weekly, or biweekly.

For data on comparative abundance in different parts of the area,

or at different times of the year,

collections should be made under

conditions as nearly uniform as

possible.

Collections made during tha

first flight period (just at dusk)

may average much higher than

daylight collections. The numbers

will vary with climatic conditions.

We have compared hand collections with those made with a

New Jersey light trap in a total

of 10 hours of hand collecting for

10 minutes at hourly intervals

(133). Approximately threefourths as many female mosquitoes have been taken as with

the light trap in 60 hours. In

hand collecting, however, one seldom obtains the rare species, and

practically no males, as are taken

with the light traps.

TRAP COLLECTIONS

For most species the New Jersey light trap (lOi) (fig. 15) is

FIGURE 15.—A New Jersey light trap in

operation.

very useful for obtaining samples

of mosquito populations. Th ?

traps are placed at strategic

places throughout the area and

are usually operated on one or

more nights each week. They

should be hung in an open space,

with the light itself 5 or 6 feet

from the ground, and they should

not be placed near a street or
MOSQUITOES OF THE NORTHWESTERN STATES 27

other competing light. These

traps are of no value in controlling mosquitoes in an area;

they serve only as a sampling device as an aid in determining

the effectiveness of a control

program.

The number of mosquitoes

caught per night in a trap frequently runs into the hundreds

and, since many other kinds of insects are also found in the killing

bottles, the task of separating and

identifying the material is often

difficult. Rare species and males

not taken while biting appear in

the light-trap collections.

The different species are not

equally attracted to the lights.

They are comparatively ineffective in trapping Aedes in the

Northwest. Our highest record

for vexans and sticticus was 444

individuals in one night, even

though they were very abundant

in the area. In southeastern Oregon as many as 1,700 mosquitoes

were taken in a trap in one night.

Of these, 945 were Aedes dorsalis

and the rest Anopheles freeborni,

Culex tarsalis, and Culiseta inornata. We have taken more than

1,200 mosquitoes, mostly tarsalis

from one trap in the Yakima

Valley.

Reeves and Hammon (117)

have designed a large box trap,

mounted on a two-wheel automobile trailer, for collecting live

mosquitoes. This is a modification of the New Jersey light trap

in that the insects do not have to

pass between the blades of a fan

and are kept alive instead of being killed in a cyanide jar. As

many as 1,055 mosquitoes have

been collected in one of these

traps in a single night.

Animal-baited traps have been

used in the Tropics (95), but so

far as we know they have not

been used in the Northwest.

A mechanical trap (fig. 16) has

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

advantages over the New Jersey

light trap. The trap is operated

by a gasoline motor and does not

depend on electricity or darkness

for effectiveness. This rotary

trap catches all flying mosquitos

that happen within its collecting

range, and by this means an exact

number of cubic feet of atmosphere per time unit can be sampled. A trap equipped with two

nets and operated at 55 r.p.m.

removes the insects from approximately 500,000 cubic feet of air

per hour. By mounting a cone of

this trap on the fender of an

automobile (fig. 17) (126), one

can take continuous samples of

mosquito populations while traveling at dusk. A serious disadvantage of this type of trap is

that it may injure the specimens

when they are unattended for

long periods.

COLLECTIONS OF LARVAE

The collecting of larvae in mosquito surveys is done mainly to

locate breeding places and determine their importance. Such

collections also show the comparative abundance of the different

species. The presence or absence

of larvae determines whether an

area should be treated with a larvicide. If larvae cannot be found,

we recommend against treating a

"likely looking" area. Sometimes

the productivity of a breeding

area can be measured by placing

cloth nets or screen cages over

the water.

Breeding places are of two general classes, permanent and temporary, but the status of a given

area may change over a period of

time. Anopheles, Culex, Culiseta,

and Mansonia occur typically

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

the Northwest breed in areas that

are flooded only a few weeks in

the year. Because most of these

floods occur but once a year, Aedes

has only one brood a year, but

where floods are more frequent

a brood follows each flooding.

utes, and after several hours the

small larvae can be seen readily

in strong light. Several factors

little understood complicate this

technique. Apparently the elements of time, dryness of soil

(166), species of mosquito, and

temperature all influence the

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

from soil.

Because of deep snow in the

high mountains, it is often impossible to get to those breeding

areas in June before the mosquitoes have emerged from the

snow water. It is sometimes possible to obtain data from these

areas by taking samples of soil

from dry depressions late in the

summer and flooding them with

water in the laboratory. Some experience is required, however, before one can become adept in

choosing just the right sample

for flooding. If eggs are present,

and if they have been laid several

weeks before the sample is taken,

they will hatch within a few minhatching of these Aedes mosquitoes.

COLLECTIONS OF EGGS

In areas where mosquitoes lay

their eggs on the ground, the extent of the breeding areas can be

determined by sampling the top

layers of soil and debris (27). It

is impossible to recover many

eggs without examining and separating a large volume of soil.

The samples of soil and debris

are dried until almost dusty,

passed through a mesh sieve, and

then through a modified grain

cleaner (fig. 18) (86) to concen-
30 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE

trate the eggs in a very small

quantity of soil. The eggs can be

picked out of the infested soil

under a microscope, with a moistened camel's-hair brush. This is

best done by spreading the soil

over a white background.

A grain cleaner 24 inches wide

is used as a basis for the separator. It consists of four shaker

sieves, a roll screen, and an air

blast. The sifted soil is placed in

the hopper and, as it feeds down

over the shaker sieves, the coarse

material is removed by 14-, 30-,

and 40-mesh sieves. The eggs and

the soil particles of the same size

pass through these sieves, but the

80-mesh sieve below separates the

particles of material that are

smaller than the eggs, which drop

down the opening into the roll

screen. On the way down some of

the light particles the same size

as the eggs are blown out by a

breeze from the fan. The turning

motion of the roll sieve causes the

eggs to pass endwise through the

60-mesh roll screen. As they slide

down the chute to the catch pan,

waste material passes out of the

lower end of the roll.

The meshes used are suitable

for concentrating eggs of sticticus

and vexans. It has also been used

for obtaining eggs of dorsalis, although the mesh of the selecting

sieve is slightly large for them.

To sieve out the eggs of other

species sieves of larger or smaller

mesh can be used. The separator

can be equipped with a 14-horsepower electric motor, or can be

operated by hand with a crank.

The separator recovers about

90 percent of the eggs from the

soil, and the final product may

contain from 10 to 200 eggs per

cubic centimeter of soil. In the

lower Columbia River Valley the

average number of vexans and

sticticus eggs is about 85 per

cubic centimeter.

To prevent the eggs from drying out, each 100 cubic centimeters of soil containing eggs

should be moistened with 8 to 15

cubic centimeters of water, depending on the type of soil.

Husbands (7) has used a vacuum-cleaner suction device for

picking up eggs in pasture areas

and has developed technique for

separating them from the gathered soil and debris.

ENGINEERING SURVEYS

Surveys in connection with

mosquito-control projects should

include an engineering survey to

determine the possibility of eliminating the breeding places. Reclamation of land, diking against

floods, and maintaining water

levels are permanent solutions to

the problem. Such a survey will

determine whether such methods

are feasible and the approximate

cost. Will the local budget justify

drainage or other construction, or

is the use of insecticides the only

practicable measure? Will increased land values and recreational advantages offset the cost

of mosquito control? The legality

of the proposed work and the

need for obtaining easements on

private property must also be

considered. An engineering survey to answer such questions v^ill

provide a background upon which

to base an effective control

program.

CONTROL OF LARVAE

ELIMINATION OF BREEDING PLACES

Wherever possible and practicable we recommend the control

of larvae by eliminating the

breeding places by draining, diking, and sanitation, or by maintaining permanent water levels.

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

maintained, control workers must

be on the lookout for Anopheles,

Culex tarsalis, and Mansonia,

which breed in permanent ponds.

Drainage undoubtedly is one of

the quickest and best methods of

controlling mosquito species in

the Northwest, but construction

and labor costs are usually prohibitive. It is highly advantageous in several locations in the

Pacific Northwest. Many of the

tidal-marsh breeding areas along

the seacoast can be freed of Aedes

dorsalis mosquitoes by digging

ditches to connect the numerous

pot holes in the marshes with the

main channels of streams (fig.

19). The pot holes are drained of

water as the tide ñows out, and

the mosquito larvae are carried

along to deeper water, where they

perish before becoming pupae or

adults. Such ditches need cleaning every year.
32 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE

Ditches have been highly effective also in the Coast Range of

Oregon and Washington (131),

where the rainfall is abundant at

all seasons. Early in the spring

innumerable temporary woodland

nools of rain and seep water are

heavily infested with Aedes aboriginis and fitchii. Most of this

country is rugged and so thickly

overgrown as to be nearly impenetrable. If these areas can be

opened up with hand labor and

connected by ditches to some

stream or other drainage, the

mosquito pest can be greatly reduced. This tyne of work is semipermanent and requires a certain

amount of annual maintenance.

Very little ditching has been

done along the Columbia River

bottomlands, because most of the

breeding areas are flooded directly from the river or by water

backing up into swales and

sloughs. However, a few isolated

saucer-shaped swales have been

ditched at the lower end so that

the water quickly drains out of

them as soon as the flood subsides. If the flood is of short duration, the mosquito larvae are

carried out of the swale into

deeper water, where they are destroyed. These ditches also allow

fish to enter the infested swale

and devour the larvae.

Many acres of bottom lands

along the lower Columbia River

have been diked against the annual floods of the river. The

financial justification of such

work lies in the increased value

of the land for agricultural purposes; nevertheless, diking of

this acreage has reduced mosquito

breeding to a minimum.

Sanitation as a mosquito-control measure includes the destruction of tin cans and other artificial

containers in which Culex pipiens

and Culiseta breed. It also includes the treatment of fire barrels 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

ponds, the removal of aquatic vegetation and other shelter for the

larvae. Septic tanks must be inspected for leaks and unused

wells and cisterns for the presFiGURE 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,

stigmatosoma, and pipiens and

Culiseta incidens are usually

abundant in log ponds late in the

summer.

Thousands of acres of land in

the Northwest which have become valuable through irrigation

are now producing mosquitoes so

abundantly as to present a serious menace to man and beast. In

these areas wise use of water and

an effective device for manipulating water levels are imperative.

Most of the irrigated hayfields

in the valleys of eastern Washington, Oregon, and Idaho, which

produce myriads of mosquitoes,

have an unlimited water supply

early in the spring. When water

is applied in excessive amounts

without provision for adequate

drainage, optimum breeding conditions exist for several species

of Aedes and Anopheles, and for

Culex tarsalis.

The problem is to furnish an

adequate supply of water to the

fields and dry them up within

a week's time to reduce the

mosquito nuisance. The border

method of irrigation (28) not

only meets this problem but is

also economical in water consumption. In this method the

fields are divided into a series of

strips by low levees, or dikes,

running parallel to the general

slope of the land. Water is turned

into the upper end of each strip

from a larger border ditch and

flows across the strip in a thin

sheet. When the strips have been

flooded for a few days, the flow

of water is checked. The mosquito larvae either die on the dry

surface or are carried into drainage ditches, which may be stocked

with mosquito-killing fishes or

treated with a larvicide.

The border method of irrigation, which makes short-period

flooding possible, is a better farming practice than any other irrigation method, because it provides an efficient and comparatively cheap means of controlling

mosquitoes. It also prevents the

growth of such weeds as foxtail

barley and marsh grass, commonly found growing where irrigation has been excessive.

In mountainous areas there are

many small depressions that have

no natural drainage. Early in the

spring they are flooded to a depth

of several inches with icy water,

which drains from the surrounding banks of snow. This water is

frequently teeming with mosquito

larvae, and in many inaccessible

areas adults may emerge even

before roads and trails have been

cleared of snow (fig. 21). Treatment of these depressions with a

larvicide, such as DDT wettable

powder, in September and October will control these larvae.

The manipulation of water

levels to reduce mosquito abundance can be done in two ways.

Small dams can be constructed

across the outlets of the lakes and

ponds to hold the water level

constantly high and thereby prevent the deposition of eggs along

the upper margins (fig. 22). Satisfactory control can also be effected on the upper margins by

digging ditches parallel to the

contours to collect the seepage,

and secondary ditches may be dug

to transport the seepage to the

main channels of streams, or to

ponds. Mosquitoes may later oviposit at the upper margins, but

the eggs cannot hatch, since all

free water quickly flows off. This

method of control, however, is

limited to very special situations.

In some isolated areas where

thickly matted jungles of willow

brush furnish maximum protection for egg laying, vexuns and

sticticus have been controlled for

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 temthis 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 developclimate of the breeding site, since ment. This type of control can be

shade, humidity, and freedom considered no more than temporfrom 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

soon return. However, pasturing

stock and some annual clearing in

these areas will reduce their capacity for producing mosquitoes.

USE OF LARVICIDES

Where it is not feasible to eliminate mosquito-breeding places,

control may be accomplished by

treating them with a larvicide.

Before DDT and other recently

developed insecticides were available, petroleum oil was used

against all species and paris

green against Anopheles, A light

distilled fuel oil (No. 2) was

widely used, but it was not consistent in its effectiveness because

it was made from different types

of crude petroleum.

Recently three spreading agents

have been found particularly effective when added to No. 2 fuel

oil (Knipling, Gjullin, and Yates

87). They are sulfonated sperm

oil (Nopco 1216), a phthalic glyceryl alkyd resin (Triton B1956), and an 18-carbon-chain

complex amine (Amine 230X).

When 3 to 5 percent of one of

these spreaders was added to this

oil, adequate coverage and satisfactory control were obtained

with about 6 gallons, instead of

the usual 20 to 50 gallons, of oil

per acre on fresh water.

Pyrethrum larvicides, as developed by workers in New Jersey (Ginsburg 38), are very beneficial under certain conditions.

They are soap emulsions of pyrethrum extract in kerosene, and

are particularly adapted for use

in garden pools containing valuable aquatic plants and fish,

where other mosquito larvicides

might be harmful. They are

sprayed over the surface of pools

at the rate of about 50 gallons

per acre or 1 quart to 200 square

feet of surface. A concentrate

containing 66 percent of kerosene, 0.07 percent of pyrethrins,

0.5 percent of an emulsifier, and

33.5 percent of water can be purchased, and diluted with 9 parts

of water. This larvicide is not

recommended for use in the extensive willow flats along the

Columbia River.

With the advent of DDT in

1942-43, the scope of chemical

control of mosquito larvae was

greatly enlarged. Other materials,

such as TDE, BHC, lindane, toxaphene, aldrin, and dieldrin, developed since that time have also

been tested.

DDT in oil solution has been

widely employed as a mosquito

larvicide (fig. 24). Concentrations

of 1 to 5 percent in fuel oil No.

2, Diesel oil, or kerosene, with or

without auxiliary solvents and

spreaders, will control mosquito

larvae. Except where resistance

has been developed, (18, ^1, 88,

1U8,169), they are effective when

applied at the rate of 0.05 to 0.4

pound of DDT per acre, depending on the species, the type of

water, the amount of vegetation,

and other factors. Emulsifiable

concentrates are also satisfactory

when diluted with water to give

the required dosage, although they

are not recommended where fish

and wildlife are involved. A concentrate containing 25 percent of

DDT, 65 percent of xylene or

other solvent, and 10 percent of

Triton X-100 or other emulsifier

is satisfactory. The effectiveness

of DDT-oil solutions has been increased by the addition of 0.25 to

0.5 percent of Triton B-1956.

Long-lastinir larvicidal action can

be obtained, especiallv in local

and restricted areas where annlications of 1 to 2 pounds of DDT

per acre does not present hazard

to wildlife.

TDE, also called DDD. is particularly 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

emulsifiable concentrates may be

formulated the same way as those

containing DDT, and can be applied at the same dosages.

BHC and lindane compare favorably with DDT and are superior where mosquitoes have

become resistant to DDT. Dosages of 0.05 to 0.1 pound of the

gamma isomer per acre are

recommended.

Toxaphene has been found an

effective substitute for control of

DDT-resistant mosquito larvae in

California and Florida. It is

more toxic to fish than is DDT.

and a dosage of 0.2 to 0.4 pound

per acre is necessary for control.

Investigations with chlordane

in the Northwest are incomplete,

but preliminary data indicat'e that

0.2 to 0.4 pou"d per acra will provide satisfactory control.

Dieldrin is one of the most effective mosquito larvicides. A

dosage of 0.1 pound per acre is

satisfactory. It is recommended

for use by experienced operators,

but not by the general public because of its high toxicity to man,

animals, and wildlife.

All these larvicides are effective, economical, and safe for use

over large areas when applied by

aircraft if the operation is closely

supervised by specialists and

trained pilots. DDT is usually applied at the rate of 0.1 to 0.2

pound per acre. A good solvent

and carrying agent for 20 percent of DDT is a methylated

naphthalene such as Velsicol

NR70, Solvesso No. 3, or Shell

42 (161). Lindane is used at the

rate of 0.05 to 0.2 pound per acre,

technical BHC at the same rate

of gamma isomer.

EPN has recently given excellent control of larvae in California, when applied as an emulsion or wettable powder spray

at tha rate of 0.075 pound of

EPN per acre (Gjullin AOa). Mos-
MOSQUITOES OF THE NORTHWESTERN STATES 39

quito Abatement Districts in California uèed EPN successfuly during the 1952 mosquito season.

At the present time we have

had very little experience with

allethrin, the new synthetic compound chemically related to the

pyrethrins (Gjullin iOa), the active constituent in pyrethrum. It

appears to be almost as effective

as pyrethrins.

MATERIALS FOR CONTROLLING

MOSQUITO LARVAE

Floodwater, irrigation water, tidal water,

rain pools, and permanent ponds,—

No. 2 fuel oil, 25 to 50 gallons par

acre.

No. 2 fuel oil with 3 to 5 percent

of an emulsifier, 3 to 6 gallons per

acre.

5-percent DDT-oil solution. For use in

aircraft, 1 to 3 quarts per acre; for

ground equipment dilute to 1 to 2

percent of DDT and apply 1 to 2

gallons per acre.

25-percent DDT emulsifiable concentrate. For application by airplane,

dilute with 4 parts of water and use

1 to 3 quarts per acre; for ground

application dilute to strength recommended for the oil solution.

Snow water.—Any of the treatments

described above or a DDT solution,

emulsifiable concentrate, or wettable

powder applied to the breeding areas

late in the fall before the ground

is covered with snow. Apply 0.5 to 1

pound of DDT per acre.

Log ponds,—DDT emulsion prepared as

described above, but applied about

once a month as needed. A dosage of

3 quarts per acre or about 0.2 part

of DDT to 1 million parts of water

in the pond.

Fire barrels,—25-percent DDT emulsifiable concentrate, 1 cup to each barrel two or three times a year.

Tree holes,—50-percent DDT wettable

powder, 1 or 2 tablespoonsful to each

cavity once or twice a year. Such cavities can also be filled with sand, or a

hole can be bored at the bottom to

allow drainage.

Ornamental pools and rain barrels,—

1-percent pyrethrum emulsifiable concentrate, 1 tablespoonful to 50 gallon!

of water as needed.

We have observed several

ground-inhabiting beetles that aie

predaceous on Aedes eggs {150),

The carabids Trechus chalybaeus

Dej., Agonum pusillum (Lee),

Pterostichus algidus Lee, and

Bembidion sp. destroyed the

greatest number, 8 to 15 eggs per

individual per week.

CONTROL OF ADULTS

Before DDT and other new insecticides became available, mosquito-control measures were

usually directed against the larvae, because the insects were most

vulnerable in that stage. These

new materials, however, are

equally effective against the

adults.

Screens (16-mesh), head nets,

repellents, aerosols, and space and

residual sprays are all used for

protection against mosquito annoyance.

REPELLENTS

During World War II several

new mosquito repellents were developed (128, 158, 160), When

properly applied to exposed skin,

about 12 drops for the neck, face,

and both hands, they will prevent

mosquito bites for 2 hours to half

a day, depending on the person,

the species of mosquito present,

and mosquito abundance. The best

known of these repellents are

dimethyl phthalate, Rutgers 6-12,

and Indalone, and mixtures of

them, usually 6 parts of dimethyl

phthalate and 2 parts each of

Indalone and Rutgers 6-12. We

have tested a number of these repellents against several species of

mosquitoes in the Northwest and

believe a mixture is superior to

the same materials used alone.
40 HANDBOOK 46. U. S. DEPARTMENT OF AGRICULTURE

These materials can also be

sprayed lightly on field garments

(fig. 25) to make them repellent

for several days {127).

FIGURE 25.—Work clothingbeing 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

and Rutgers 6-12, and 4 parts of

the n-propyl ester of N, N-diethylsuccinamic acid; and (2) 6 parts

of dimethyl phthalate, 2 parts

each of dimethyl carbate and

Indalone.

Since the repellents are solvents for paints, varnishes, and

plastics such as watch crystals,

nylon fabrics, and fountain pens,

they should be used with caution.

Care should be taken not to apply

them too liberally on the forehead, as they will sting if they

get into the eyes.

SPACE SPRAYS

Protection against mosquitoes

can be obtained with space sprays.

Practically all the commercial ñy

sprays containing pyrethrum,

DDT, methoxychlor, certain organic 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 26.—Using an aerosol bomb to

kill mosquitoes within a home.

when on camping trips (fig. 27)

and when traveling from place to

place during the mosquito season.

A few seconds' release of the

aerosol will kill all mosquito species in an ordinary-sized room,

tent, or trailer. It is not hazardous

to humans if used as directed on

the container. An aerosol formula

much in use contains 0.4 percent

of pyrethrins, 1.6 percent of refined kerosene, 3 percent of DDT,

5 percent of cyclohexanone, 5 percent of motor oil (A.A.E. 10),

and 85 percent of Freon-12. Many

modified formulas containing pyrethrins, allethrin, DDT, meth-
MOSQUITOES OF THE NORTHWESTERN STATES 41

oxychlor, and synergists are now

available. A recently recommended aerosol formula contains 2 percent of DDT, 0.6 percent of allethrin, 5 percent of alkylated

naphthalene, 7.4 percent of deodorized kerosene, and 42.5 percent

each of Freon-11 and Freon-12.

Jersey mosquito larvicide (34-)

(see page 37) is also used as a

space spray against adult mosquitoes out of doors at the rate

of 15 to 25 gallons per acre.

Space sprays are effective for

only a few hours, but have been

used very successfully for outdoor

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

Mechanically generated aerosols, fogs, mists, sprays, and

smokes are now widely used out

of doors. Many home owners,

small-fruit farmers, and resort

managers reduce mosquito annoyance to a minimum with these

new devices. The best results are

obtained when the work is done

by experts such as mosquitoabatement superintendents or

licensed pest-control operators.

DDT-oil solutions can be used for

this purpose but some prefer a

pyrethrum-allethrin mixture because of its rapid action against

mosquitoes and low toxicity to

warm-blooded animals. The New

social functions and picnics, and

in and about amusement centers.

Where practical to treat late each

afternoon, this is an excellent

way of gaining relief from annoyance, even though large numbers

of mosquitoes are in the neighborhood. Fruit pickers and lumber and road crews also benefit

from their use.

The new insecticides, such as

BHC, lindane, chlordane, aldrin,

and dieldrin, are also effective as

space sprays, but these materials

are highly toxic and can harm

those using them, as well as those

living within the treated areas.

We must, therefore, caution
42 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE

against their use by uninformed

and untrained persons. For outdoor space spraying in the Northwest, a 5-percent DDT emulsion,

oil solution, or the New Jersey

larvicide is recommended until

additional information is obtained

on the other materials.

The use of aircraft is an economical and safe way to disperse

sprays over large areas to kill

adult mosquitoes (3). An oil solution containing 5 to 20 percent

of DDT and from 10 to 20 percent of a heavy oil (S.A.E. 30 to

50) in kerosene is an excellent

formula for use by aircraft.

Larger pay loads may be obtained by using a concentrate

containing 25 percent of DDT, 10

percent of a wet±ing agent (such

as Triton X-lOO-or equal parts of

Span 20 and Tween 20), and 65

percent of xylene. Both the oil

solution and the concentrate are

applied at the same dosage of 0.1

to 0.2 pound of DDT per acre.

All applications from aircraft

should be directed by specialists

and trained pilots. DDT concentrates should not be used over

water where they would be hazardous to fish.

RESIDUAL SPRAYS

The stability, or long-time residual effectiveness, of DDT makes

it possible to apply a spray on

the interior surfaces of homes to

kill mosquitoes that come in contact with these surfaces for several months (fig. 28). This

method is particularly adapted to

control of Anopheles mosquitoes,

because of their habit of entering

homes and other buildings, but it

can also be used against Culex

pipiens and tarsalis and some of

the house-frequenting Aedes in

the Northwest. DDT residual

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.

An oil solution or emulsion, applied at the rate of about 1 gallon

per 1,000 square feet, is preferred.

The spraying of all vegetation

to a height of about 10 feet (fig.

29), as well as the surfaces of

the buildings and the screens, to

leave a residue of DDT where the

mosquitoes rest will reduce mosquito annoyance in mountain

camps (66). Applications of 2 to

3 pounds of DDT per acre have

given good control for 10 days

and sometimes for as long as 45

days. If the area to be protected

is surrounded by extensive breeding areas, enough mosquitoes may

fly into the treated areas to be

annoying for 2 hours at dusk, but

they will be killed later as they

settle on the treated foliage.

Emulsifiable concentrates are preferred for use in mist blowers and

either emulsifiable concentrates

or wettable powders for use in

orchard sprayers. Water is added

to give a 5- to 10-percent emulsion

or a 2.5-percent wettable-powder

suspension.

A dosage of II/2 pounds of lindane per acre gives about the

same control as 2 pounds of DDT.

Space sprays containing 0.2 to

0.4 percent of pyrethrins or allethrin applied at dusk will give

excellent control when used in

conjunction with the heavier residual spray.

CONTROL OF

RESISTANT MOSQUITOES

The only known mosquito vector of disease that appears to

have developed a high resistance

to insecticides on the West Coast

is Culex tarsalis in California.

Up to the end of 1951 no resistance by tarsalis had been observed in the Northwest. While

no specific recommendations are
44 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE

made for the Northwest, if resistance develops toxaphene, lindane,

aldrin, heptachlor, dieldrin,

chlordane, EPN, NPD, or malathon may be considered for use.

EQUIPMENT FOR

APPLYING INSECTICIDES

Hand sprayers of the flit-gun

type are satisfactory for spraying small puddles to kill larvae

or for use indoors against adult

mosquitoes. Aerosol bombs are

best for applying space sprays

within enclosures. Areas of an

acre or more can be treated with

a 3- or 4-gallon compressed-air

sprayer or knapsack sprayer

{H-3). Paint-type sprayers, which

produce an atomized spray, can

also be used in such places.

Power equipment of various

types is used in extensive lowlands and marshes. This equipment includes orchard-type sprayers, mist blowers, heat-generated

aierosol and fog machines, and devices attached to the exhaust of

trucks or jeeps (^S, 108).

Aircraft {3) is both effective

and economical for treating large

areas to kill both larvae and

adults (fig. 30). Excellent results

have been obtained with small

aircraft over extensive floodwater lowlands along the Columbia River and in large irrigated

sections. Most commercial aircraft operators can be relied on

to do an effective and safe job.

NATURAL ENEMIES

OF MOSQUITOES

Many insects, fishes, birds, and

other organisms prey upon mosquito larvae {6Ip). However, the

only natural enemies of appreciable value in control programs

are the minnows Gambusia affinis

and Fundulus (119). These fish

thrive best in warm parts of the

country, but may establish some

tolerance to freezing for short

periods west of the Cascade

Mountains. We have introduced

Gambtisia into the Northwest

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 important Aedes breeding grounds in

this region are dry the greater

part of the year, these fish are

of little practical use here. However, they do keep Culex and

Culiseta larvae in check in log

ponds until the water becomes

too polluted for the fish. They

can be used also in permanent

ponds and ornamental pools inhabited by Anopheles and Culex

tarsalis.

Rarely we have observed Pianaria maculata Lindy, a fiat worm

15 mm. long, feeding on larvae

in the laboratory. In restricted

quarters these worms easily captured the larvae by wavering

about the container. After a larva was captured it appeared unable to release itself, even with

some assistance from the observer. In our limited observations each worm devoured one

to two larvae per day.

Adult mosquitoes have a number of natural enemies, such as

certain birds, bats, and predaceous insects (65). Undoubtedly

swallows, some night-flying birds,

bats, dragonflies, and damsel flies

eat large numbers, but they seem

to have little effect in reducing

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 mosof 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, postpronotum; 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 .

UPPER.tî'Tf^Z

ANTENNAL TUFT

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 twobranched; postclypeal hair bifurcate at middle to base; frontoclypeus 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. ^. ^«^t. ^^ u'fu^ ^^?li ^^' .^"-^ Claspettes bilobed, with 2 (someFemale.—Palpi as long as pro- times 3) spines on ventral lobe

boscis, dark brown. Mesonotum and usually with 2 spines on dorwith 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 shortlowish 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 species are very similar to those

of punctipennis. Minor variations

are given in the key.

Distribution^ biology^ and importance,—Anopheles freeborni is

widely distributed in open and

wooded country throughout the

Northwestern States (2), It occurs in clean, sunny water,

wherever suitable breeding places

are found. Comparatively large

populations develop in irrigated

areas in the Yakima Valley in

Washington and in the vicinity of

Scappoose, Prineville, and Klamath Agency, Oreg. It has been

found in abundance in the irrigated section of west-central

Idaho. This species, the most important malaria carrier in the

Western States, is prevalent also

in the Willamette Valley in Oregon, where most of the malaria

cases in this region have occurred.

Western equine encephalomyelitis

has been isolated from it in nature.

The females hibernate in root

cellars, barns, outbuildings, and

other sheltered locations. They

emerge from these places by the

latter part of February ^ in the

warmer parts of this region, but

few eggs are laid before April

or May. Larvae have been taken

along the margins of rivers,

creeks, and irrigation ditches and

in ponds, sloughs, and roadside

ditches from early in May until

frost. Apparently the females

mate before going into hiberna-»

tion, because the males do noti

overwinter. The adults are sometimes found in fairly large numbers early in September. It is frequently associated with Culex

tarsalis.

ANOPHELES OCCIDEISTALIS (Dyaii

and Knab)

Anovheles oceidentalîi^ Dvar and

Knab, Biol. Soc. Wash. Proc.

19: 159. 1906.

Female.—Similar to freeborni,

except for slightly more contrasting stripes on the mesonotum, darker and more pronounced wing spots, and the presence of a spot of pale scales at

the apex of the wing.

Male genitalia (fig. 36, F).—

Similar to genitalia of freeborni, except for the smaller number of hairs on the base of the

claspers and the slightly longer

and more slender lobes of the

ninth tergite.

Larva.—Only minor characters

are available for separating

the larvae of this species from

freeborni and punctipennis. The

postclypeal hairs have 2 to 3

stout branches near the middle.

The frontoclypeal is banded and

the antepalmate hairs on segments 4 and 5 are usually single

and unbranched.

Rozeboom {12S), in recent

work in Montana on anophelines,

claims that the mosquito east of

the Rocky Mountains hitherto

called occidentalis is earlei. An

additional character he has used

to differentiate between the two

species is that the egg of earlei

is barred whereas that of occidentalis is plain.

Distribution^ biology^ and importance.—This mosquito has been

found in small numbers in southern Oregon, in the mountains of

northern Washington and Idaho,

and near the southeastern border

of Idaho. The larvae have been

found alone and also associated

with the other three species of

Anopheles in this region. They

have also been taken with Culex

tarsalis and Culiseta inornata.

Breeding places usually contain

moss and algae, but larvae have

been observed in open grassy

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

FRANCISCANVS McCracken

Anopheles franciscanus McCracken, Ent. News 15: 12. 1904.

Anopheles pseudopunctipennis

var. franciscanus King and

Bradley, Human Malaria, 65

pp. 1941.

Anopheles pseudopunctipennis

franciscanus Aitken, Calif.

Univ. Pubs. Ent. 7 (11) : 327.

1945.

Female.—Palpi as long as proboscis, black-scaled with white

rings at the joints of the apical

end of the two preceding segments. Mesonotum with a median

pruinose gray stripe bordered by

dark bands; the median stripe

with hairlike gray scales and a

tuft of whiter ones anteriorly.

Wing scales black, with yellowishwhite scales forming spots as

follows : Costa and subcosta with

two on the apical half, the subcosta with two additional ones

on the basal half; second vein

with a small one near the cross

vein and a small one before the

apex of the upper branch; third

vein with a small one at the base

and a large one in the middle;

fourth vein with a small one at

the cross vein and a small one at

the apices of the forks ; fifth vein

with a small one at the base and

a large one extending into the

lower fork, small ones at the

apices of the forks and a small

one near the middle of the upper

fork ; sixth vein with a long spot

at the base. Legs black, the tips

of the femora and tibia with paleyellowish scales.

Male genitalia.—Claspette bilobed with 2 slender spines on

the ventral lobe and 2 or 3 broad,

leañike spines on the dorsal lobe.

Mesosome with very small nonserrated leaflets. Ninth tergite

with low conical processes.

Larva.—Both the inner and

outer clypeal hairs of the larvae

of this species are single and unbranched, and the postclypeal

hairs are also single and long.

The abdominal palmate hairs on

segments 3 to 7 are well-developed

and serrate. In the race franciscanus the posterior spiracular plates

are not developed into "tails," but

are rounded.

Distribution^ biology^ and impartance.—This species has been

found rarely in the extreme southwestern part of Oregon and in the

vicinity of Medford. The larvae

are usually associated with freeborni along streams in sunny

pools containing algae. Very little

information is available regarding its habits in the Northwest.

ANOPHELES PUNCTIPENNIS (Say)

Culex punctipennis Say, Acad.

Nat. Sei. Phila. Jour. 3: 9.1823.

Anopheles perplexens Ludlow,

Canad. Ent. 39: 267. 1907.

Female.—Palpi as long as the

proboscis, dark brown. Mesonotum with pruinose gray stripe

bordered by dark bands; the

median stripe with hairlike gray

scales and a tuft of whiter ones

anteriorly. Wing scales black,

with yellow ones forming spots

as follows: A large one on the

basal third of the costal margin,

which involves the base of the

second vein before the fork; a

smaller one on the apex of the

wing, which involves both forks

of the second vein; third vein

with a spot at apex or near the

middle or completely dark-scaled ;

fourth vein with two spots on the

base and one spot on each fork;

sixth vein with one spot in the

middle. Legs black, the tips of the

femora and tibia with pale-yellowish scales.

Male genitalia (fig. 36, G).—

Claspettes bilobed, usually with

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 segdorsal lobe. (The number of ment longer than wide, and dorspines 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 imLarva.—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 imporally 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).—

N. Y. Ent. Soc. Jour. 15: 213 f ^^^^ ^^ .,^^^1 ^?'''^^ ^^^ 29QY ^ ux. J.U. ^xo. low convex With 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 beand basal white bands forming low the apex, the filament narsmall 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. Upand 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, taperfore tarsus. ing with pectén reaching two-
MOSQUITOES OF THE NORTHWESTERN STATES 57

FIGURE 37.—Male genitalia: A, Aedes dorsalis; 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

a small tuft near the tip, the last

tooth sometimes stouter and

slightly detached. Anal segment

as long as wide, anal plate reaching nearly to ventral line; gills

small and budlike.

Distribution^ biology, and importance.—This species has been

found in only a few small areas

in Oregon and Washington. The

larvae develop in open, unshaded

water and are sometimes associated with dorsalis. Correspondents report the eggs as very resistant to adverse conditions. It

is an early-season species, the

adults appearing in June. They

will bite during the day, as well

as during the hours of darkness.

Rees (109) reports it flying 10

miles from its breeding place in

Utah. It is of little importance in

the region.

AEDES DORSALIS (Meigen)

Culex dorsalis Meigen, Syst. Bes.

Bek. Eur. Zwei, Ins. 6: 242.

1830.

Aedes melanimon Dyar, Ins.

Ins. Mens. 12: 126. 1924.

Female.—Mesonotum yellowish

white with a median brown

stripe, or with only a few brown

scales medianly; posterior brown

half lines and side lines may or

may not be present. Abdomen

with apical and basal white bands

and complete or partial median

white line; the last onç or two

segments may be entirely whitescaled. Wing scales black and

white; the costa first, third, and

fifth veins with more black scales

than the others. Legs with dark

and pale scales ; tarsi dark with

apical and basal white bands on

all but last two segments of midtarsus and last three segments of

fore tarsus.

Male genitalia (fig. 37, A).—

Side pieces about three times as

long as wide ; apical lobe rounded,

and somewhat shortened apically,

the surface clothed with rather

long setae; basal lobe prominent,

slightly constricted at the base,

and covered with short setae, a

stout spine on the margin and a

smaller adjacent spine. Claspette

straight, hirsute, and constricted

just before the apex, with 2 long

and 1 short setae at the constriction, the filament broadly expanded in a rounded rectangular shape

at the middle.

Larva.—Antennae spinose.

Both pair of head hairs single.

Abdomen stout with few hairs;

lateral tufts triple on segments

1 and 2 and double on the rest.

Comb on eighth segment with

many scales in a triangular patch.

Air tube tapering, about 3x1;

pectén evenly spaced to near middle of the tube, with a multiple

tuft set close to end of pectén.

Anal segment slightly longer

than wide; anal gills either budlike or, if longer, bluntly pointed

and seldom as long as the

segment.

Distribution, biology, and ¿mportance.—This is one of the most

important and widely scattered

pest mosquitoes in the Northwestern States. We have not found

it in the northern half of Idaho.

The larvae develop in open, sunny

areas that are flooded by saline,

alkaline, or fresh water. They

thrive in water of high alkalinity.

It is the only species that breeds

in the salt marshes in this region

and is one of the most abundant

and troublesome species in irrigated meadows and in grasslands

that are inundated by floodwater.

A. dorsalis larvae are sometimes

associated with those of nigromaculis and campestris in the

more alkaline waters and with

vexans in fresh water. Rees {111)
MOSQUITOES OF THE NORTHWESTERN STATES 59

reports that seven successive

broods have been taken from the

same locality during a single season, and that the eggs may remain viable for 2 or 3 years. The

high temperatures in midsummer

in the inland valleys cause the

adults to emerge in about 5 days

after the land has been flooded.

It is a persistent biter, even in

midday and will enter houses to

obtain blood meals. It is very annoying to livestock. Adults are

readily attracted to light traps

and are strong fliers. Rees (109)

has observed them 22 miles from

their breeding grounds. Western

equine encephalomyelitis and St.

Louis encephalitis viruses have

been isolated from this species in

nature, and it has been demonstrated as an experimental vector

for Japanese B and California

encephalitis viruses.

AEDES CANADENSIS (Theobald)

Culex canadewsis Theo., Mon. Culic. 2: 3. 1901.

Female. — Mesonotum reddish

brown with pale-yellow scales

around the margins. Abdomen

black without basal white bands

or with narrow indistinct ones;

the sides with triangular white

spots. Wing scales all dark. Legs

black; hind and midtarsal segments apically and basally whitebanded; fore tarsus banded on

segments 1 and 2 ; last segment of

hind leg entirely white-scaled.

Male genitalia (fig. 37, B).—

Side pieces slightly more than

twice as long as wide ; apical lobe

large, low, and broadly rounded

with short bladelike setae; basal

lobe long, with many short setae.

Claspette cylindrical and setose, a

larger seta before the apex; the

filament narrow, linear, pointed,

and slightly shorter than the

stem.

Larva.—Antennae spinose. Upper head hairs 6 to 7, lower 4 to

5; lateral abdomen hairs usually

double on segments 1 to 5 and

single on 6. Comb on eighth segment with 25 to 40 scales in an

irregular patch. Air tube 3x1;

pectén even, reaching beyond onethird of tube, followed closely by

tuft of 4 to 6 medium hairs. Anal

segment longer than wide; anal

gills pointed and about as long as

the segment.

Distribution^, biology^ and importance.—This species breeds in

woodland pools. It has not been

taken in Oregon, but has been

collected in large numbers in

northern Idaho and has also been

taken in Ferry, Okanogan, and

Grant Counties, in Washington.

It is the predominating species

around Payette Lake in Idaho.

The larvae can be found in temporary forest pools which are

flooded by melting snow. They

seem to prefer laying their eggs

in depressions containing decaying leaves and other debris. We

have also found a few at high

elevations in open meadows. The

species bites severely and is a considerable pest, especially in late

afternoon in large wooded areas.

AEDES MGROMACULIS (Ludlow)

Grabhamia nig7^omaculis Lud.,

Geo. Wash. Univ. Bui. 5: 85.

1907.

Female.—Proboscis of female

ringed with white. Mesonotum

with varying shades of yellowish

scales, a broad median bronzybrown stripe, and brown sides.

Abdomen black with basal segmental bands and median stripe

of yellowish scales; the lateral

spots usually concolorous with the

median stripe. Wing scales pale

and dark, the dark predominating. Femora and tibiae partially

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

the hind tarsus rarely all white,

the white band on the first segment broadly extended by scattered white scales.

Male genitalia (fig. 38, A).—

Side pieces twice as long as wide ;

apical lobe absent; basal lobe a

small elevated area with many

rather short setae. Claspette with

a cylindrical stem and a short

setae near the outer end ; the filament narrow and as long as the

stem.

Larva.—Both pairs of head

hairs single and antennal tuft

small. Comb on eighth segment

with about 9 thornlike scales. Air

tube 2 X 1 ; pectén extending well

past the middle, with 3 stout detached teeth; a small tuft near

the tip. Anal segment longer than

wide and ringed by the plate.

Anal gills pointed and longer

than the segment.

Distribution, biology^ and importance.—This species is found

associated with dorsalis, idahoensis, and vexans in open irrigated or flooded meadows in

prairie or open country. It has

been found in only south-central

Washington, but is more common

in the semiarid plains of Oregon

and Idaho. It is most numerous in

the lower Payette River district

of western Idaho. It is also an

important pest in some other irrigated sections. It is a persistent

daytime biter. Apparently it

breeds continuously throughout

the season and is associated frequently with dorsalis. This species is a strong flier. Experimentally it has transmitted western

equine encephalomyelitis and St.

Louis and Japanese B encephalitis viruses.

AEDES FLAVESCENS (Müller)

Culex flavescens Müller, Faun.

Ins. Fried, p. 87. 1764.

Female.—Mesonotum yellowish

to brown with a broad median

stripe of slightly darker brown

scales. Abdomen covered with

dull-yellow scales or with a dark

median line and sides partially

black-scaled anteriorly. Wing with

a mixture of black and yellow

scales. Legs brown with a mixture of yellow scales; tarsi with

broad basal white band.

Male genitalia (fig. 39, D).—

Side pieces more than twice as

long as wide; apical lobe prominent rounded with many setae;

basal lobe a rugose, slightly elevated area with many setae, a

stout spine and several long setae

near the base, the lobe extending

nearly to the base of the apical

lobe. Claspette lightly hirsute

with three stout setae on the inner margin of the base; the filament angularly expanded to a

rounded point near the base.

Larva.—^Upper head hairs usually 3 to 4, lower usually double.

Lateral abdominal hairs double

on segments 6 to 8. Comb on

eighth segment with many long

spinelike scales in a triangular

patch. Air tube tapering, about

3x1; pectén reaching middle,

with 2 detached teeth followed by

a tuft of 4 to 6 hairs. Anal segment slightly longer than wide.

Anal gills about as long as the

segment.

Distribution, biology, and importance.—This is a typical plains

species, and has been taken in

limited numbers in widely separated places east of the Cascade

Mountains, but it rarely occurs in

sufficient numbers to be a serious

pest. Larvae have been found in

meadow pools and marshes in the

vicinity of alkaline flats. It is a

fierce day-time biter and attacks

both man and beast. We have observed it biting in full sun and

during a breeze of about 7 miles

per hour. Hearle (59) has reported 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)

Culex excrucians Wlkr., Ins.

Saund., p. 429. 1856.

Aedes aloponotum Dvar, Ins.

Ins. Mens. 5: 98. 1917.

Female.—Tori with inner surfaces predominately white-scaled.

Mesonotum yellowish white with

a median brown stripe, varied

pattern of brown and white scales

or completely reddish-brown

scales. Mesepimeral bristles absent or rarely there may be one.

Abdomen black with basal segmental white bands and frequently with scattered white scales.

Wings predominantly darkscaled with pale scales intermixed. Legs black with tarsal

white bands broad on hind legs

and usually absent on last segment of mid tarsus and last two

segments of fore tarsus.

Male genitalia (fig. 37, E).—

Side pieces about three times as

long as wide; apical lobe prominent with small setae; basal lobe

slightly raised, rugose, and extending to the base of the apical

lobe, the surface covered with

short setae. Claspette hirsute except at the apex; the filament

angularly expanded to a sharp

point near the base.

Larva.—Upper head hairs multiple, lower usually double. Lateral abdominal hairs long and

stout, usually double on segments

1 and 2 and single on the rest.

Comb on eighth segment with

many scales in a triangular patch.

Air tube slender, about 4x1;

pectén not reaching the middle,

with 2 to 3 large detached teeth;

tuft with 4 to 6 large hairs. Anal

seermei^t lonorer than wide: r)late

extending about three-fourths of

the distance down the side, and

with a single long hair on the

posterior angle. Anal gills pointed and slightly longer than the

segment.

Distribution, biology, and importance.—This species is widely

distributed at low elevations in

mountainous areas in the Northwestern States and is found in

both open and semiwooded areas.

We found it in the Cascade Mountains and in Lake and Klamath

Counties of Oregon, as well as

through the wooded section of

southern Idaho, but it is more

abundant in northern Idaho and

in Washington. The larvae have

been taken also in roadside

ditches bordered by brush, in potholes in open meadows, and in

other temporary pools. It is sometimes as^ociatf^d with Mchn and

hexodontus. The adults appear

later than do those of many of

the Aedes, sometimes not until

July. The species is important

only in local areas and then only

for a short time.

AEDES FITCHII (Felt and Yovmg)

Cidex fitchii Felt and Young, Science (n.s.) 20: 312. 1904.

Female.—Torus with white

scales on dorsal half. Mesonotum

yellowish white to light brown,

with a broad median brown stripe

or variable pattern of brown and

light scales. Wings dark-scaled,

usually with an admixture of

white scales along the costa. Mesepimeral bristles none to two,

rarely three or four. Abdomen

black with basal white bands, and

sometimes with apical white

scales which may extend into a

median white line. Legs black,

tarsi with basal white bands on

all except the last two segments

of fore tarsus and first segment

of mid tarsus, the white bands

broader on the hind legs.

Male genitalia (fig. 39, B).—

Side pieces about three times as

long as wide; apical lobe prominent and slightly elongated, the

surface clothed with long setae
64 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE

bordered by a number of shorter

ones; basal lobe triangular,

densely tubercular with many

setae, those at the margin of the

base longer and preceded by a

spine. Claspette lightly hirsute

except at the apex, the filament

short and sickle-shaped with a

notch at the base.

Larva.—Upper head hairs 3 to

4, lower 2 to 3. Lateral abdominal

hairs usually double. Comb on

eighth segment with many scales

in a triangular patch. Air tube

slender and tapering, four or

more times longer than wide with

closely set pectén teeth to middle

of tube and tuft of 3 to 5 long

hairs set close to end of pectén,

occasionally one or more teeth

may be slightly detached. Anal

segment longer than wide; plate

extending nearly to ventral line

and with a pair of long hairs near

posterior angle. Anal gills long

and pointed.

Distribution^ biology^ and importance.—Aed&s fitchii is most

prevalent in mountainous regions,

but has also been taken near sea

level. The larvae usually appear

early in spring in flooded meadows

or potholes in semiwooded areas.

It is present over most of Oregon,

Washington, and Idaho, wherever

suitable breeding situations are

found. We have found it associated with increpitits, excrucianSy

and pullatus,

AEDES INCREPITUS Dyar

Aedes increpitus Dyar, Ins. Ins.

Mens. 4: 87. 1916.

Female.—Torus without white

scales on dorsal half. Mesonotum

yellowish white to light brown,

with a broad median brown stripe

or variable pattern of brown and

light scales. Mesepimeral bristles

one to five. Wing dark with white

scales along the costal area. Legs

black, tarsi with basal white

bands on all except the last two

segments of fore tarsus and first

segment of midtarsus, the white

bands broader on the hind legs.

The absence of white scales on

the dorsal surface of the torus

easily distinguishes this species

from fitchiL

Male genitalia (fig. 37, G).—

Side pieces more than three times

as long as wide; apical lobe

prominent and bluntly pointed

with a few small inwardly directed setae ; basal lobe a small rugose

elevated area with short setae,

which extends halfway to the

apical lobe. Claspette lightly hirsute except at the apex; the filament angularly expanded to a

sharp point near the middle.

Larva.—Antennae well spined

all over. Upper head hairs usually

2, occasionally 3; lower 1 or 2.

Lateral abdominal hairs 1 or 2

long hairs on each segment. Comb

on eighth segment with 25 or

more scales in a triangular patch.

Air tube about 21/2 x 1, pectén

not reaching the middle of tube

with a tuft of 4 to 6 hairs. Anal

segment as long as wide; plate

extending only about two-thirds

down the sides with lateral edges

uneven. Anal gills pointed and

only about as long as the segment.

Distribution^ biology^ and importance.—This is a common species that is generally distributed

over the plains areas of Oregon,

Washington, and Idaho. The larvae have been taken also in open

meadows and small pools in seniwooded country fro:T\ sea level to

an elevation of about 6,000 feet.

Near Portland the larvae have

been found developing in pools

filled by rain in March. The larvae may be associated with fitchii,

but sometimes they occur alone.

This species is one of several

found at higher and wooded elevations that contribute to the

serious discomfort of m.an and
MOSQUITOES OF THE NORTHWESTERN STATES 65

animals. It is a persistent biter,

but prefers shaded situations.

AEDES MPHADOPSIS Dyar and Knab

Aedes niphadopsisDysiYSLndKnah,

Ins. Ins. Mens. 5: 166. 1918.

Female.—Mesonotum with a

median brown stripe and usually

with posterior half-lines; the

margins, sides, and antescutellar

space with white scales. Lower

mesepimeral bristles two or three,

or rarely none. Abdomen black

with basal white bands with or

without a median line of white

scales. Wings with a mixture of

pale and dark scales, the dark

predominating. Legs with a mixture of pale and dark scales.

Male genitalia (fig. 39, C).—

Side pieces about three times as

long as wide, apical lobe small,

elongate, narrowly attached, bare

or with a few small setae; basal

lobe small, elevated into a transverse ridge at the base with a

row^ of 3 or 4 stout hairs preceded oy a short spine at the margin.

Claspette lightly hirsute on the

basal half, the filament expanded

in a gradual curve near the middle.

Larva.-—Both pairs of head

hairs usually single, occasionally

double. Comb on eighth segment

with 10 to 12 scales in an irregular double row. Air tube nearly

4x1; pectén teeth not extending

to the middle with the last 2 or 3

teeth detached and followed by a

large tuft. Anal segment longer

than wide; plate not reaching

middle of side. Anal gills short or

budlike.

Distribution^ biology^ and importance.—This species has been

found in Klamath County in Oregon and in Fremont, Custer, and

Jefferson Counties in Idaho. The

adults were present in large numbers in Custer County. Larvae

were collected at the edge of

drainage ditch in the open country below Klamath Falls in

March by Elwood Seaman and by

Don Rees in shallow, alkaline

pools in valleys of south-central

and southeastern parts of Idaho.

We have not found it abundant

enough to constitute a pest, although it readily bites both man

and animals. It has been reported

as able to fly several miles.

AEDES IDAHOENSIS (Theobald)

Grabhamia spencerii var. idahoensis Theob., Mon. Culic. 3 :

250. 1903.

Aedes idahoensis Howard, Dyar,

and Knab, Mosq. N. and Cent.

Amer, and W. I. 4: 727. 1917.

Female.—Mesonotum with a

broad reddish-brown stripe, usually separated by a fine line of

grayish scales ; faint posterior

half-lines present or absent; sides

and antescutellar space with grayish-white scales. Lower mesepimeral bristles absent. Abdomen

black with broad basal white

bands. Wing with costa, first,

third, and fifth veins dark-scaled,

the other veins with pale scales.

Legs mostly pale-scaled; femora,

tibiae, and some of apical tarsi

partially dark-scaled outwardly.

Male genitalia.—The characters

of the male genitalia of this species are the same as those of

stictictos.

Larva.—Both pairs of head

hairs single. Comb on eighth segment with 9 to 20 scales in a very

irregular patch. Air tube stout,

about 21/2 X 1 ; pectén closely set

teeth to middle or slightly beyond,

the last two teeth detached and

followed by a small tuft. Anal

segment longer than wide; plate

nearly reaching ventral line. Anal

gills pointed and as long or longer

than the segment.

Distribution^ biology^ and im^

portance.—This species is present

in a few places in Washington

and along the eastern border of
66 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE

Oregon on the treeless plains or

in low mountain areas. It has

been found in largest numbers in

Bannock and Bear Lake Counties,

in southern Idaho, where it is an

important daytime pest. The larvae usually develop in irrigated

areas, but have been taken in

pools of high alkalinity. We have

found it associated with dorsalis

and increpitus in spring and early

in summer. It is important locally

and for a short period late in

spring.

AEDES VENTROVITTIS Dyar

Aedes ventrovittis Dyar, Ins. Ins.

Mens. 4: 48. 1916.

Female.—Torus with integument of outer side yellow to black.

Mesonotum brown, darker centrally, a fringe of yellowish scales

around the margin. Lower mesepimeral bristles absent. Abdomen black with basal white bands,

which may be narrow or absent

medianly. Wing scales dark, with

or without a mixture of white

scales extending outwardly from

the bases of the veins. Legs black

with a mixture of pale scales ; the

tarsi mostly black.

Male genitalia.—The characters

of the male genitalia of this species are the same as those of

sticticus.

Larva.—Both pairs of head

hairs single. Comb on eighth segment with 6 to 9 thornlike scales

with basal spinules in an irregular row. Air tube tapering, about

21/2 X 1; pectén reaching nearly

to middle of tube with two detached teeth and with the tuft of

5 to 6 hairs near middle of tube.

Anal segment longer than wide,

with plate nearly reaching ventral line. Anal gills long and

pointed.

Distribution^ biology^ and int'

parlance.—This species has been

taken in central Washington and

southeastern Idaho. The larvae

develop in pools in mountain

meadows at high elevations.

Little is known about its habits

and distribution.

AEDES IISTRUDENS Dyar

Aedes intrudens Dyar, Ins. Ins.

Mens. 7: 23. 1919.

Female.—Torus with integument of outer side yellow or light

brown. Mesonotum uniformly

bronzy brown or occasionally

with indications of median brown

stripes. Lower mesepimeral

bristles one to five. Hypostigial

spot of scales present or absent.

Abdomen black with broad basal

white bands; venter completely

white-scaled. Wing scales dark,

with or without a small patch of

pale scales at base of costa. Legs

black with a mixture of pale

scales ; the tarsi mostly black.

Male genitalia (fig. 37, I).—

Side pieces about three times as

long as wide; apical lobe prominent rounded with numerous

rather long setae ; basal lobe represented by a large spine at the

base of one side and two spines

on a raised projection on the

other. Claspette with basal half

hirsute and forming a sharp projection ending in stout setae at

middle. The apical half slender;

the filament angularly expanded

to a sharp point at the middle.

Larva.—Upper head hairs usually 4, lower 2 or 3. Lateral abdominal hairs double on first segment and single on second to

sixth. Comb on eighth segment

with 10 to 15 scales in an irregular double row. Air tube 21/2x1;

pectén reaching the middle with

2 to 3 detached teeth followed by

large multiple tuft. Anal segment

longer than wide ; plate extending

to near ventral line and ventral

margin deeply incised. Anal gills

short and bluntly pointed.
MOSQUITOES OF THE NORTHWESTERN STATES 67

Distribution, biology, and int'

portance.—Aedes intrudens larvae have been found in small

numbers in snow-water pools in

low mountainous areas of southeastern Idaho and in northern

Oregon. It is typically a forest

species and usually survives there

as adults from May until midAugust. It is rarely abundant

enough to be of much importance.

It is a vicious biter day and night.

AEDES HEXODONTUS Dyar

Aedes hexodontus Dyar, Ins. Ins.

Mens. 4: 83. 1916.

Aedes cyclocerculus Dyar, Ins.

Ins. Mens. 8: 23, 1920.

Aed0s leuconotips Dyar, Ins. Ins.

Mens. 8: 24. 1920.

Female.—Mesonotum yellowish

to light golden brown, with paired

dark-brown lines and posterior

half-lines. Lower mesepimeral

bristles, 2 or 3. Abdomen black

with basal segmental white bands.

Wings dark-scaled with patch of

2 or 3 to many pale scales at base

of costa in about 95 percent of

specimens. Legs black with femora partially pale-scaled.

Male genitalia (fig. 38, B).—

Side pieces three times as long as

broad; apical lobe long and

rounded with short curved setae ;

the basal lobe flatly conical with

numerous setae and a long curving spine near the base. Claspette

pilose, slightly curved and expanded near the middle; the filament shorter than the stem,

slightly expanded at the middle

and terminating in a blunt curved

point.

Larva.—Antenna sparsely

spined. Both pairs of head hairs

usually in multiples of 2 or 3.

Comb on eighth segment with 5

to 9 scales in a row. Air tube

3x1; pectén fine and even and

not quite reaching the middle of

the tube. Anal segment slightly

longer than wide and ringed by

the plate. Anal gills pointed and

longer than the segment.

Distribution, biology, and int'

portance.—Aedes hexodontus is a

mountain species usually associated with communis and fitchii.

It is not so widely distributed as

these species in the Northwest

but in some areas it is very abundant and an important pest. Large

numbers of the larvae develop in

meadows in the Cascade Mountains in the vicinity of Mount

Adams and Rainier National

Park in Washington and in the

Mount Hood and Diamond Lake

areas in Oregon. This species has

also been taken in various places

in Idaho. In shaded areas it is a

vicious biter during the day.

AEDES CATAPHYLLA Dyar

Aedes cataphylla Dyar, Ins. Ins.

Mens. 4: 86. 1916.

Aedes pearyi Dyar and Shannon,

Wash. Acad. Sei. Jour. 15: 78.

1925.

Female.—Torus with integument of outer side dark brown or

black. Mesonotum gray around

the sides with golden-brown

scales in the middle, which sometimes show faint dark lines. Scutellum with pale-yellowish scales.

Lower mesepimeral bristles 2 to

7. Hypostigial spot of scales usually present. Abdomen black with

basal segmental white bands.

Legs black with a mixture of pale

scales; the tarsi mostly black.

Wing scales dark with pale scales

at base of costa and first vein.

Male genitalia. — Side pieces

about three times as long as wide.

The filament of the claspette expanded in a gradual curve near

the middle. The other characters

as in impiger.

Larva.—Both pairs of head

hairs single. Comb on the eighth

segment in two irregular rows.
68 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE

Air tube about 3x1, taperiner,

with evenly spaced pectén teeth

to the hair tuft, and beyond the

tuft there are 3 to 5 widely spaced

teeth. Anal segment longer than

wide; plate small, only reaching

about two-thirds of the distance

down the.sides. Anal gills as long

or longer than the segment.

Distribution^ biolof(y^ and importance.—This species is found

only in a few places in mountain

areas of Oregon, Washington, and

Idaho. The eggs hatch very early

when first covered with melting

snow. The adults have been taken

as early as May and are usually

abroad before associated species.

It is a vicious biter, and will bite

in bright sunshine.

AEDES ISEARCTICVS Dyar

Aedes nearcticus Dyar, Canad.

Arct. Exp. Rept. 3 (C) : 32.

1919.

Female. — Mesonotum bronzy

brown with or without a mixture

of yellowish-white scales around

the sides and two lighter colored

patches of scales centrally, the

entire surface with many black

bristles. Scutellum with pale yellowivsh scales. Lower mesepimeral

bristles 3 to 8. Abdomen black

with basal segmental white bands.

Wing scales dark with a patch of

pale scales on the base of the

co^ta. Leor« black with fe^iora and

tibiae partially pale-scaled.

Male genitalia (fig. 37, F).—

Side pieces about three and onehalf times as long as wide ; apical

lobe roimded. the surface with a

few small setae; basal lobe conically sloped to the basal edge, with

long setae and a spine at the

margin, the rest of the surface

bare or with a few small setae.

Claspette hirsute on basal half,

the filament angularly expanded

to its maximum width near the

base.

Larva.—Antennae sparsely

spined.—Both pairs of head hairs

single. Lateral abdominal hairs

multiple on first segment and

double on second to fifth. Comb

on eighth segment 8 to 14 scales

in two irregular rows. Air tube

about 214 X 1 ; pectén on basal

third followed by multiple tuft.

Anal segment as long as wide.

Anal gills stout and several times

the length of the segment.

Distribution^ biolos(y^ and importance.—This species occurs in

a few places in the high mountainous areas of Oreeron, Washington, and Idaho. The largest

numbers have been found in

Mount Rainier National Park in

Washington and near Diamond

Lake in Oregon. The larvae hatch

with the first melting snow. The

species is too rare to be of much

importance.

AEDES STICTICVS (Meîgen)

Floodwater Mosquito

Culex sticticws Meigen, Svst.

Beschr. Zweifl. Ins. 7: 1. 1«38.

Culex hirsuteron Theob. Mon.

Culic. 2: 98. 1901.

Aedes aow'y^ns Dvar and Knab

Ins. Ins. Mens. 5: 165. 1918.

Aef^^'' f^^p/vnlis ^Meio*.). T^^^warrls

in Wytsman, Gen. Ins. 194:144.

1932.

Aedes aldrirhn Dyar and Knab,

U. S. Nati. Mus. Proc. 25: 57.

1908.

Female.—Mesonotum yellowish

white, with two golden-brown

stripes and posterior half-lines;

the anterior stripes separated bv

a narrow median line of pale

scales, which is sometimes indistinct or absent. Lower mesepimeral bristles absent. Abdomen

black with basal white bands.

Winer scales dark with or without

a patch of pale scales on the base

of the co^ta. Legs black with femora and tibiae partially palescaled.
MOSQUITOES OF THE NORTHWESTERN STATES 69

Male genitalia (fig. 38, C).—

Side pieces nearly three times as

long as wide ; the apical lobe large

and rounded with short, curved

setae; the basal lobe expanded,

semidetached apically; the outer

surface with short setae, a large

spine at the base and an adjoining

tuft of long setae. Claspette cylindrical and slightly tapered at the

apex with one or two spines at the

midpoint of the inner side; the

filament short, broad, expanded at

the middle, and terminating in a

blunt, curved point

Larva.—Upper head hairs 2 or

3, lower 1 or 2. Lateral abdominal

hairs variable, usually multiple on

first segment and double on

second to sixth. Comb on eighth

segment with many scales in a

triangular patch. Air tube stout,

21/^x1; closely set, even pectén

teeth to near middle of tube, with

a multiple tuft set close to pectén.

Anal segment broader than long;

plate extending nearly to ventral

line. Anal gills long and pointed.

Distribution^, biology^ and importance.—This is one of the most

important pest mosquitoes in the

Northwestern States. It breeds in

large numbers in the brushy bottom lands along the Columbia

River. It is also found along some

other rivers in northwestern

Washington and northern Idaho.

The larvae, which are almost invariably associated with those of

vexans, are found in large numbers for about 100 miles below

Bonneville Dam, when the annual

spring flood of the Columbia inundates the bottom lands. The

adults disperse for a distance of

15 to 20 miles or more and remain a serious pest to man and

livestock throughout the summer.

The eggs may remain viable for

at least 3 or 4 years if not reached

by normal floods. This species

has been found capable of transmitting western equine and St.

Louis encephalitis viruses.

AEDES PULLATUS (CoquiUett)

Culex pullatus Coq., Ent. Soc.

Wash. Proc. 6: 168. 1904.

Female.—Torus with integument of outer side black to dark

brown. Mesonotum with yellowish-brown scales; a narrow bare

median line with parallel stripes

of brown scales, each stripe

bordered by a broader stripe with

a few dark scales ; with or without

narrow, bare, curved posterior

half-lines. Lower mesepimeral

bristles 1 to 5. Hypostigial spot of

many white scales. Abdomen black

with basal white bands. Wings

dark-scaled with patch of pale

scales at base of costa. Legs black

with femora and tibiae partially

pale-scaled.

Male genitalia (fig. 37, H).—

Side pieces about three and onehalf times as long as wide ; apical

lobe prominent and somewhat

elongated, by ventral surface covered with numerous setae; basal

lobe represented by a large spine

at the margin and two adjacent

smaller spines. Claspette with

basal half large, hirsute, and

forming a rounded projection at

the middle, the apical half slender ;

the filament angularly expanded to

a rounded point near the middle.

Larva.—Upper head hairs 5 to

7, lower usually 4; hairs short

and tufts set close together.

Lateral abdominal hairs long, and

double or triple on first to fifth

segment and single on sixth.

Comb on eighth segment with

many scales in a triangular patch.

Air tube 3x1, pectén teeth closely

set, not reaching the middle,

closely followed by large 6- to 7-

haired tuft. Anal segment longer

than wide, not ringed by the plate.

Anal gills saclike and two or three

times longer than the segment.
70 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE

Distribution, biology, and im^

portance.—This species has been

taken in a number of places in

the high forested mountainous

areas of the Northwest. The larvae are usually found in melting

snow pools, most frequently associated with communis but also

with punctor and fitchii. The

adults emerge rather late and

are severely annoying for only a

short time after emergence. They

will bite during the daylight

hours in shade.

AEDES TRICHURUS (Dyar)

Culex trichurus Dyar, N. Y. Ent.

Soc. Jour. 12: 170, 244. 1904.

Female.—Torus with integument of outer side yellow to light

brown. Mesonotum with a median

brown stripe expanded to width

behind the middle; sides and margins with grayish-white scales.

Lower mesepimeral bristles 3 to

6. Hypostigial spot of few to

many white scales. Abdomen

black with basal segmental white

bands. Wing scales dark, with

patch of 2 or 3 to many pale

scales at base of costa. Legs black

with femora pale-scaled beneath.

Male genitalia. — Side pieces

three times as long as wide;

apical lobe prominent and angularly rounded with a few setae;

' basal lobe small with conical center portion covered with setae

and an adjacent elevated portion

bearing two long spines. Claspette with long, cylindrical, curved

stem slightly expanded before the

apex; the filament short and

conical, with a series of transverse ridges.

Larva.—Upper head hairs usually double, lower single. Lateral

abdominal hairs triple on first segment, double on second and third,

and single on fourth to sixth;

other hairs few and small. Comb

on eighth segment in double row.

Air tube stout and about 3x1;

pectén reaching basal fourth of

tube with 4 to 5 widely separated

detached teeth, and multiple hair

tuft within the pectén, and an additional small tuft on dorsal and

lateral surfaces of siphon. Anal

segment as long as wide, with

plate nearly reaching ventral

line. Anal gills ensiform and

slightly longer than segment.

Distribution, biology, and ¿mportance.—This mosquito occurs

in timbered areas at high elevations in Idaho and near Mount

Adams in Washington. The larvae have been found associated

with those of fitchii, increpitus,

cinereus, and communis in pools

formed by melting snow. Although a severe biter, this species

does not occur in large enough

numbers to be of much importance.

AEDES COMMVmS (DeGeer)

Culex communis DeG., Mem. des.

Ins. 6, pi. 17, figs. 2 and 5. 1776.

Female.—Mesonotum dull-yellow or gray-scaled with a narrow

pale median line separating paired

dark-brown lines, and with posterior brown half-lines. The coloration is variable and may be

brown-scaled centrally with a mixture of pale scales and a border

of grayish-yellow scales. Lower

mesepimeral bristles 2 to 5. Abdomen dark brown with basal white

bands. Wings dark-scaled, with a

patch of 2 or 3 to many pale scales

at base of costa in about 85 percent of specimens. Legs dark with

femora partially pale.

Male genitalia (fig. 39, A).—

Side pieces about three times as

long as wide; apical lobe large

rounded with many long spinelike

setae; basal lobe small, quadrilateral in outline, partially detached at base, the surface with

some small setae, several larger

curved ones and a stout spine on
MOSQUITOES OF THE NORTHWESTERN STATES 71

the margin. Claspette lightly hirsute on the basal half, the apical

half more slender; the filament

angularly expanded to its maximum width near the base.

Larva.—Both pairs of head

hairs single. Lateral abdominal

hairs double on first to fifth segment and single on the sixth.

Comb on eighth segment with

many scales in a triangular patch.

Air tube stout and about 21/2 x 1 ;

pectén evenly spaced to near middle of tube; tuft of 4 to 6 hairs.

Anal segment longer than wide;

plate extending only about twothirds the distance down the sides.

Anal gills lanceolate and considerably longer than the segment.

Distribution^, biology^ and importance.—This is one of the most

widely distributed species in high

mountain areas of the Northwest.

In many localities it is present in

large numbers and is a serious

pest. It breeds in flooded mountain meadows and woodland pools

left by melting snow, and around

the margins of mountain lakes.

The larvae may occur along or

associated with pullatus, cataphylla, intrudervs, fitchii, and hexodontus. In Oregon it is numerous

throughout the Cascade and Blue

Mountains. It is abundant in the

Cascade and other mountain

ranges in Washington and northern Idaho, and is present in

smaller numbers in central and

southern Idaho. The adults are

sometimes seen late in May and

may occur until mid-August. They

are vicious biters and, although

they will attack during the day,

are generally more active at dusk.

AEDES PIONIPS Dyar

Aedes pionips Dyar, Ins. Ins.

Mens. 7: 19. 1919.

FemaZe.—Tori with white

scales. Mesonotum with dull-yellow or white scales, two broad,

well-defined, dark-brown stripes

and posterior half-lines, the median stripes separated by a line

of pale scales. Lower mesepimeral

bristles 1 to 4, or rarely none.

Abdomen with or without narrow

basal white bands. Wing scales

dark with small patch of pale

scales at base of costa in about

85 percent of specimens. Legs

black with femora partially palescaled.

Male genitalia.—The side piezas

are slightly longer than those of

Aedes communis. There are no

other taxonomic differences in

the genitalia of these two species.

Larva.—Antennae long and

well spined. Upper head hairs

usually 5, lower 4. Comb on eighth

segment arranged in a large triangular patch. Air tube about

21/^ x 1; pectén not reaching the

middle and followed by large multiple tuft. Anal segment about as

long as wide, with the plate reaching only about half the distance

down the sides, and with notched

lateral edges. Anal gills long and

pointed.

Distribution^ biology^ and importance.—This is a rare species

in the Northwestern States. The

larvae have been found only in

small pools in high mountain

meadows of south-central Idaho

at an elevation of over 7,000 feet.

Very little is known about it, and

because of its rarity it is of no

economic importance.

AEDES IMPIGER (Walker)

Culex impiger Wlkr., Brit. Mus.

List Dept. 1: 6. 1848.

Female.—Tori with integument

varying from black to yellow.

Mesonotum with a median oblong

area of brown scales, usually in

the form of a broad stripe or

paired stripes; margins grayish

white. Lower mesepimeral bristles

1 to 3, or rarely none. Wing
72 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE

scales dark with patch of 2 or 3

to many pale scales at base of

costa. Legs black with femora

pale-scaled beneath.

Male genitalia.—Side pieces

about four times as long as wide,

apical lobe small elongated and

narrowly attached with a few

short spines; basal lobe small,

elevated into a transverse ridge

at the base with a row of long

setae and a slender spine at the

margin; claspette lightly hirsute

except at the apex, the filament

angularly expanded to a sharp

point near the base.

Larva.—Antennae short and

spined. Upper and lower hairs

single. Lateral abdominal hairs

double on first to fourth segments

and single on fifth and sixth.

Comb on eighth segment with 15

to 25 scales. Air tube about 21^

X 1; closely set pectén teeth not

reaching the middle, followed by

tuft of 3 or 4 hairs. Anal segment

longer than wide ; plate extending

about halfway down the sides and

covered with minute spines. Anal

gills pointed and only about as

long as the segment.

Distribution^ biology, and iiwportance.—This species occurs in

small numbers in Washington and

Idaho. The larvae are usually associated with other Aedes larvae

in pools in semiwooded areas at

the higher elevations. It is too

rare to be of any importance.

AEDES ABORIGimS Dyar

Northwest Coast Mosquito

Aedes aboriginis Dyar, Ins. Ins.

Mens. 5: 99. 1917.

Female.—Mesonotum yellowish

to light golden brown, with paired

dark brown stripes and posterior

half-lines. Lower mesepimeral

bristles 1 or 2. Abdomen black

with basal white bands widening

at the sides. Wings dark-scaled in

about 95 percent of specimens.

Legs black.

Male genitalia (fig. 37, D).—

Side pieces three times as long as

broad; apical lobe long and

rounded with short curved setae ;

the basal lobe flatly conical with

numerous setae and a long curving spine near the base. Claspette

pilose, slightly curved, and expanded near the middle; the filament shorter than the stem,

slightly expanded at the middle

and terminating in a blunt curved

point.

Larva.—Antennae sparsely

spined. Head hairs, upper usually

3 to 4 and lower 2 to 4. Lateral

abdominal hairs 1 to 2 long hairs.

Comb on eighth segment with

about 30 scales in a patch. Air

tube around 3x1; pectén fine and

even and not reaching the middle,

the tuft consists of 4 to 6 large

hairs. Anal segment about as long

as wide; anal plate extending to

near ventral line; anal gills

pointed and longer than the

segment.

Distribution, biology, and int'

portance.—^Large numbers of this

species are found in the dense

timbered coastal areas of Oregon

and Washington, where the winter precipitation is very high. It

is also common at moderate elevations in the Cascade Mountains

and in other mountain areas in

Washington and northern Idaho.

The larvae are found associated

with communis, cineretos, and

fitchii in small temporary rain

pools. It is of economic importance only in a few restricted

situations in the Olympic Peninsula of Washington.

AEDES CINEREUS (Meigen)

Aedes einerens M e i g. Syst.

Beschr. Eur. Zweif. Ins. 1: 13.

1818.

Female.—Mesonotum clothed

with reddish-brown scales. Lower

mesepimeral bristles absent. Abdomen black without white bands
MOSQUITOES OF THE NORTHWESTERN STATES 73

or with narrow partial or complete ones ; the lateral spots usually joined to form a line. Wing

scales dark. Legs dark brown.

Coxa of front leg with white

scales and a central patch of

brown scales on the anterior

surface.

Male genitalia (fig. 38, E).—

Side piece twice as long as wide,

broad, and sharply tapered to the

densely spined apex. Clasper subapically inserted, with forked

arms of unequal length. Claspette

two-branched with 3 spines at

apex of each branch.

Larva.—Both pairs of head

hairs in tufts of 5 or more, the

tufts set close together. Lateral

abdominal hairs double on first

and second segments, single and

long on the third to sixth. Comb

on eighth segment in a double

row. Air tube slender, about 4 x

1; pectén extending past middle

of tube with about 3 detached

teeth; tuft small. Anal segment

longer than wide, gills very long

and lanceolate.

Distribution^ biology, and importance.—This mosquito is found

throughout the partially wooded

areas of the Northwestern States.

It breeds in shaded pools, and the

larvae are usually found associated with other species of Aedes

in March and early in April; it

appears a little later than its associates. In some mountain areas

it is the predominating species

and is a serious pest; it is found

in smaller numbers at lower elevations. The females attack both

during the day and at dusk, but

they stay close to the ground in

the grass or underbrush. The

adults are not found very far

from their breeding places. Apparently their flight range is very

limited, since Freeborn (30)

states that they prefer to walk

rather than fly, and when flying

remain close to the ground. This

species is a severe biter but important only in local areas.

AEDES VEXAISS (Meigen)

Culvex vexans Meig. Syst. Beschr.

Eur. Zweif. Ins. 6: 241. 1830.

Female.—Occiput with patch

of flat black scales bordering top

edge of flat white lateral patch.

Mesonotum clothed with bronzybrown scales, paler at the base of

the wings and around antescutellar space. Lower mesepimeral

bristles absent. Abdomen black

with centrallv indented basal

white bands. Wing scales brown.

Legs black ; all the segments of

the hind tarsus, the first four segments of the mid-tarsus, and the

first three segments of the fore

tarsus narrowlv white-banded.

Male genitalia (fig. 38, F).—

Side pieces twice as long as wide,

clasper long, broad, and divided

near the apex, the short arm with

a stout spine. Claspette short and

capitate with dense crown of

spines. Filament absent.

Larva.—Upner head hair usually 2 or 3 and lower double. Lateral abdominal hairs 2 to 3 on

first to third segment; 2 on

fourth and fifth and single on the

sixth. Comb on eighth seorment

with 10 to 25 or more scales in

an irregular double row. Air tube

3x1; pectén reaching past the

middle with 1 to 3 detached teeth

and a small multiple-haired tuft

near end of pectén. Anal segment

longer than wide. Anal gills

pointed and longer than segment.

Distribution^ biology, and importance.—This species is found

over the greater portion of the

Northwestern States. It is one of

the most important pest snecies

in both irrigated and flood-water

area8, and occurs near sea level,

as well as in mountain meadows.

It is present in overflow areas

along many rivers, but is most
74 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE

abundant on the bottom lands

along the Columbia River and its

tributaries for about 100 miles

below Bonneville Dam. In this

region the larvae are found associated with those of sticticus in

the partially open, brushy, or

wooded areas that are flooded by

the annual spring rise of these

rivers. The adults sometimes disperse for distances of 15 to 20

miles or more from their breeding places and are a serious pest

to man and livestock for 3 to 4

months during the summer. Along

the Columbia River several hatchings may occur, depending on the

number of floods, since all eggs

do not necessarily hatch with the

first flooding. More than one generation may occur in the irrigated sections and there the

larvae are associated with nigromaculiSy dorsaliSy and idahoensis.

In mountain areas they are usually found with increpitus and

cinereus. The females enter

houses and will feed there during

the hours of darkness. They also

bite at mid-day in shaded areas.

This species has been found naturally infected with western

equine encephalomyelitis and has

been experimentallv infected with

St. Louis encephalitis virus.

AEDES VARIPALPUS (Coquille«)

"Western Tree-hole Mosquito

Culex varipalpus Coq., Cañad.

Ent. 34: 292. 1902.

Female.—Palpus black-scaled

with the tip broadly white-scaled

and a few white scales at apex of

second segment. Mesonotum

brown with a median anterior

patch, and narrow posterior

curved lines of yellow scales ; the

margins with a mixture of pale

scales and scutellum with broad

white scales. Abdomen black with

median triangular dorsal and lateral patches of white scales. Wing

scales dark with a patch of white

scales at the base of the costa.

Legs black, with white bands involving both ends of all but the

last two joints of the fore and mid

tarsi, which are black, and the last

joint of the hind tarsus, which is

white.

Male genitalia (fig. 38, D).—

Side pieces three times as long as

wide; the apical lobe absent; the

basal lobe narrow with long

spines basally and short setae extending to apical fourth of side

piece. ClasDette with cylindrical

stem, the filament narrow, ligulate and as long as the stem.

Larva.—Antennae slender without spines and with a single hair

on the middle. Both pairs of head

hairs small and either single or

double. Comb on eighth segment

with about 12 scales in an irregular double row. Air tube about

3x1; pectén evenly spaced on

basal third and with tuft near the

middle. Anal segment about as

long as wide. Anal gills enlarged,

spatulate, and about four times

as long as segment.

Distribution^ biology^ and importance.—This small mosquito

breeds in water-filled holes in

practically any kind of tree.

Reeves {IH) reports finding it

also in rock pools and wooden receptacles under trees. The larvae

may be found in midwinter in

this region if temperatures below freezing do not prevail for

long periods. In summer the

aquatic stage is completed in

about 3 weeks. The species occurs

in the western half of Oregon and

Washington, but is seldom very

abundant. The largest numbers

are found in the foothills of the

Coast Range and the Olympic

Mountains in Washington, li is a

vicious biter but has a restricted

flight range. It has been found an

experimental vector of western

equine encephalomyelitis.
MOSQUITOES OF THE NORTHWESTERN STATES 75

Genus MANSONIA Blanchard

MANSONIA PERTVRBAm (Walker)

Culex perturbans Wlkr., Ins.

Saund., 428. 1856.

Female.—Mesonotum with narrow, curved, pale-yellow scales,

with or without two faint silverylongitudinal lines. Abdomen black

with narrow basal segmental

white band, sometimes lacking

medianly or consisting of scattered black and white scales on

the last few segments. Wing

scales broad, black and white intermixed. Legs black with a mixture of white scales; the hind

tibiae with a white ring on the

outer third; the first joints of all

tarsi with a narrow basal white

ring and a broad median white

ring; all other tarsal joints with

the basal half white-scaled.

Larva.—Antennae long and

slender with large tuft beyond the

middle and short pair of hairs not

far beyond the tuft. Dorsal head

hairs in multiple groups. Lateral

comb of the eighth segment of 10

to 12 spines in a single irregular

row. Air tube short, broad at the

base. Attenuated apically and

fitted for piercing, a pair of hair

tufts near the middle. Anal segment much longer than wide,

ringed by the plate, the dorsal

tufts of two unequal groups of

hairs on each side. Anal gills

slender and shorter than segment.

Distribution^ biology^ and importance.—Many adults of this

species are present near Scappoose, Oreg., in some years. Larvae probably occur in cattail

swamps in the area but none have

been taken. They are difficult to

find, because, unlike other mosquito larvae, they attach to the

succulent roots of aquatic plants

by their siphons and come to the

water surface only for emergence

as adults. The winter is passed in

the larval stage. The pupae also

attach to roots. The adults emerge

for several weeks in the summer

and are extremely vicious biters.

Adults have also been taken in

small numbers in Washington and

Idaho. Fortunately, they are so

rare that they are of little importance. Howitt et al. (69) has

shown this species may transmit

eastern equine encephalomyelitis

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)

Culex territans Wlkr, 1856. Insects Saundersiana, Dipt., 1:

428.

Culex apicalis Adams, of Dyar

and other authors, not of

Adams.

Female. — Mesonotum brownscaled with median indistinct

nearly bare lines and usually with

two median spots of yellowish

scales. Abdomen black-scaled

with apical segmental white

bands. Wing scales all black. Legs

black, the undersurface partially

white-scaled.

Male genitalia (fig. 36, D).—

Side piece more than twice as

long as wide ; subapical lobe with

two large rods, a spine and five

hooked filaments. The first three

partially serrated. Tenth sternite

prominent, the apex broad, extending beyond the mesosome and

terminating in a row of short

setae. Mesosome halves with relatively even, oblong outlines terminating apically in a rounded,

serrated margin, the halves

joined by a sclerotized band near

the apex.

Larva.—Head hairs single or

double. Antennae large, cylindrical, and spined. Lateral abdominal hairs multiple on first and second segments and double on third

to sixth; secondary hairs numerous and well-developed. Comb on

eighth segment with numerous

scales in a triangular patch. Anal

segment twice as long as wide

and anal gills about as long as the

segment. Air tube long and tapering, about 7 X 1 ; pectén of 12 to

14 teeth on basal third of tube

with four pairs of prominent

tufts beyond pectén, and also

sometimes a small fifth pair near

the apex.

Bohart (10) found that C.

apicalis consisted of two species.

He used this name for the species

found in California and Arizona,

but applied the name ''territans''

to the more widespread species

which occurs in other parts of

North America.

Distribution^ biology^ and iwiportance.—This species is well

distributed in the Northwestern

States. The larvae have been collected in semishaded and in open

grassy pools. They are never

found in large numbers. The females feed on cold-blooded animals, such as frogs, and are not

known to attack man or other

warm-blooded animals.

CULEX PIPIENS (Linneaus)

Northern House Mosquito

Culex pipiens L., Syst. Nat., ed.

10: 602. 1758.

Female.—Mesonotum brownscaled. Abdomen black with basal

segmental white bands, which are

widest at the middle and at the

sides. Wing scales all brown.

Legs brown-scaled.

Male genitalia (fig. 36, C).—
MOSQUITOES OF THE NORTHWESTERN STATES 77

Side pieces more than twice as

long as wide, subapical lobe with

8 appendages, beginning at the

apical end ; a seta, a leaf, 3 setae,

and 3 rods. Tenth sternite prominent and extending beyond the

mesosome, and the apex semicircular and densely crowned

with stout spines. Mesosome

halves each with ends of 3 processes projecting outwardly past

the outer edges of the tenth sternite.

Larva.—Both pairs of head

hairs multiple. Antennae large,

spinose, cylindrical, and constricted beyond the tuft. Lateral

abdominal hairs multiple on first

and second segments and double

on third to sixth ; subdorsal hairs

of segments 3 and 4, single or

double. Comb on eighth segment

with numerous scales in a triangular patch. Anal segment

longer than wide and gills slightly

longer than the segment. Air tube

gradually tapering, about 5x1;

pectén about 12 teeth on basal

fourth followed by 4 pairs of hair

tufts, the subapical pair more

dorsal and out of line than the

others.

Distribution^ biology^ and impartance,—This species is occasionally present in large numbers

in some communities in the western parts of Oregon and Washington. It seldom occurs in the

eastern half of these States. The

larvae breed in temporary and

permanent pools and in artificial

containers. Because of its habit

of developing in any polluted

place provided by man, it is often

abundant and annoying around

homes and industrial plants. It

enters houses freely and overwinters in basements, root cellars, and other shelters. The flight

range is short and, if breeding

places are not great in number

and widely scattered, the area affected is small. Western equine

encephalomyelitis and St. Louis

encephalitis viruses have been recovered from this species in nature and experimentally it has

been shown to be a vector of

Japanese B encephalitis virus.

CVLEX TARSALIS Coquille«

Culex tarsalis Coq., Cañad. Ent.

28: 43. 1896.

Female.—Proboscis ringed

with white. Tori with inner surfaces, and basal segment of flagellum with ventral surface bearing many white scales. Mesonotum dark brown with white

scales around the margins and 2

narrow white lines extending

posteriorly from median white

spots. Abdomen black with basal

segmental white bands; venter

with pale scales, each segment

marked with a dark-scaled V- the

apex anteriorly directed. Wing

scales dark with some white

scales on the costal veins. Legs

black, the femora and tibia with

a line of white scales on the sides,

the tarsi with a ring of white

scales at both ends of all joints

except the first 1 or 2 on the front

and middle legs.

Male genitalia (fig. 36, B).—

Side pieces more than twice as

long as wide ; subapical lobe usually with five appendages, beginning at the apical end; a seta, a

narrow leaf, a seta, and two rods.

Tenth sternite prominent, well

chitinized, and extending beyond

the mesosome, the broad apex

crowned with short pointed spines

medianly and short, broad, blunt

ones outwardly. Mesosome halves

each consisting of inner swordlike blade and an outer 4-pronged

process.

Larva.—Both pair of head

hairs multiple. Antennae long

and curved, basal two-thirds

spinose and enlarged. Lateral abdominal hairs triple on third to

sixth segments. Comb on eighth
78 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE

segment with numerous scales in

a triangular patch. Anal segment

slightly longer than wide ; gills as

long as segment and bluntlypointed. Anal plate without bristles. Air tube slender and about

5x1; pectén on basal third followed by 5 pairs of tufts, none

displaced or out of line.

Distribution^ biology^ and im^

portance.—This (fig. 2) is one of

the most abundant and widely

distributed mosquitoes in the

Northwestern States. It has been

collected in every county in Oregon and from all but a few counties in Washington and Idaho. It

occurs in largest numbers in

poorly drained irrigated areas

where water accumulates. It is

readily found around Klamath

Lake, along the John Day River,

and elsewhere in eastern Oregon.

In Washington it is common in

Yakima and Okanogan Valleys,

and in western Idaho it is very

numerous in the lower Boise and

Payette River Valleys. It is also

abundant around American and

Bear Lakes, in Idaho. The larvae

are associated with anophelines,

Aedes dorsalis, and Culiseta inornata. The females pass the winter

in hibernation. Culex tarsalis has

been shown to be infected in nature with both St. Louis encephalitis and western equine encephalomyelitis in several areas and is

capable of transmitting these diseases to chickens. It has been experimentally infected with Japanese B and California encephalitis

viruses.

CULEX STIGMATOSOMA Dyar

Culex stigmatosoma Dyar, U. S.

Nati. Mus. Proc. 32: 123. 1907.

Female,—Proboscis ringed

with white. Tori without scales

and basal segment of flagellum

brown-scaled. Mesonotum with

bronzy-brown scales intermingled

with paler ones and forming no

definite pattern. Abdomen black

with basal segmental white

bands; venter pale-scaled, each

segment marked with a median

oval dark-scaled spot. Wing scales

all dark. Legs black, the tarsi

with a ring of white scales on

both ends of all joints except the

first one or two of the front and

middle legs.

Male genitalia (fig. 36, A).—

Side pieces more than twice as

wide as long; subapical lobe usually with 6 appendages, beginning

at the apical end—a seta, a leaf,

a seta, and 3 rods. Tenth sternite

prominent, well sclerotized, and

extending beyond the mesosome,

the apex semicircular and densely

crowned with slender spines, with

a few slightly heavier ones on the

outer margin. Mesosome similar

to mesosome of tarsalis.

Larva.—Both pairs of head

hairs multiple. Lateral abdominal

hairs triple third to sixth segments and subdorsal hairs, 3-

branched, on segments 3 and 4.

Comb on eighth segment with

many scales in a patch. Anal segment about as long as wide ; anal

plate indented and with row of

short bristles near apex ; anal gills

broad and as long as segment. Air

tube about four to five times as

long as wide; pectén on basal

third followed by five pairs of

hair tufts, but apical one usually

very small; subapical one sometimes out of line.

Distribution^ biology^ and im^

portance.—In western Oregon

and Washington the larvae of this

species are usually associated

with tarsalis or other species of

Culex and Culiseta. It has not

been taken in the pastern half of

these States or in Idaho. Western

equine encephalomyelitis has been

isolated in nature from this species, but it is probably of little importance as a vecto?:* because of its

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 maccrackenaey 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 folFemale.—Mesonotum dark lowed by a black ring, apical segbrown 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

separated but indicated by two

large groups of small spines.

Eighth segment without spines or

with one spine at center of basal

margin.

Larva.—Both pairs of head

hairs multiple, the lower with

about three long hairs, the upper

more numerous and shorter. Air

tube stout, about 2x1; pectén

with a few basal teeth followed

by long hairs that extend nearly

to apex of tube; a paired tuft

near base of tube between rows of

pectén. Anal segment ringed by

the plate with 2 anterior tufts of

ventral brush arising from a cleft

in the plate and a small patch of

short bristles near apex of the

plate. Anal gills slightly longer

than segment.

Distribution^ biology^ and importance.—This species is rare in

the Northwest; it has been taken

only in a few places in southwestern Oregon. The larvae were

found associated with larvae of

incidens and territans in pools

overgrown with vegetation.

CULISETA INCIDENS (Thompson)

CuUseta incidens Thompson,

Kongl. Sven. Eng. Resa. 6,

Dipt.: 433. 1868.

Female.—M esonotum with

dark-brown scales and a mixture

of yellowish scales some of which

form partial longitudinal lines or

spots. Abdomen black with basal

segmental white bands. Wing

scales dark, aggregated into

patches on the fork and base of

the second vein, the fork of the

second and fourth vein, the upper

fork of the fifth and the middle of

the sixth veins. Legs dark brown

with narrow faint white rings on

the bases of some of the tarsal

joints, the femora and tibia with

narrow white rings at their

apices.

Male genitalia (fig. 39, F).—

Side piece more than twice as

long as wide, apical lobe a small

elevated area with a number of

small setae and a long spine;

basal lobe small and conical with

small setae, the apex with 2 stout

spines. Lobes of ninth tergite

slightly separated, and each bearing 5 to 8 rather long setae.

Eighth segment with 5 to 8

spines on basal margin.

Larva.—Both pairs of head

hairs multiple, lower tufts longer

than the upper. Lateral abdominal hairs multiple on first and

second segments and double on

third to sixth. Air tube stout

about 2x1; pectén with a few

basal teeth that have 1 or 2 minute denticles, teeth followed by

long hairs to apical third of tube ;

and a multiple tuft near base between rows of pectén. Anal segment ringed by the plate with

several tufts of ventral brush

puncturing the plate and a small

1- to 3-haired tuft on lateral

posterior margin. Anal gills

slightly longer than segment.

Distribution^ biology^ and importance.—This species is widely

distributed at lower elevations in

the Northwestern States. The

largest numbers occur in Oregon

and Washington west of the Cascade Mountains, but it is common

also in southern Idaho. The larvae

breed in both permanent and

semipermanent pools and in artificial containers. They are associated with inornata and tarsalis.

Only the females hibernate. They

occasionally attack man, but they

are of little importance as a pest.

The species has been reported as

favoring animals for blood meals,

although it is seldom abundant

enough to be a pest of livestock.

It has been infected experimentally with western equine encephalomyelitis and St. Louis and

Japanese B encephalitis viruses.
MOSQUITOES OF THE NORTHWESTERN STATES 81

CVLISETA mORlSATA (Williston)

Culex inornatus Williston, U. S.

Dept. Agr., Div. Ornith. and

Mam., N. Amer. Fauna 7: 253.

1893.

Female.—Mesonotum with

mixture of brown and yellowish

scales, usually with 2 fine, pale,

median posterior half lines and

pale obscure longitudinal stripes.

Abdomen black with broad basal

segmental bands widening at the

sides, the last segment entirely

pale scaled. Wing scales dark

brown with mixture of pale scales

on the anterior veins. Legs with a

mixture of brown and pale scales.

Male genitalia (fig. 39, G).—

Side pieces stout conical, less

than twice as long as wide ; apical

lobe absent or faintly indicated;

basal lobe conical and prominent,

with 2 or 3 spines on the apex and

small setae on the sides. Lobes of

the ninth tergite broad, rounded

projections with 10 to 14 short,

thick spines. Eighth segment

without row of spines on basal

margin.

Larva.—Both pairs of head

hairs multiple, the lower with 3

or 4 long hairs, and upper multiple and shorter. Lateral abdominal hairs multiple on first and

second segments and double on

third to sixth. Air tube stout, 3

X 1 ; pectén of 10 to 12 stout teeth

followed by long hairs that extend nearly to apex of tube, the

teeth with 3 to 4 outstanding

denticles; paired tuft large and

arising from base of tube between the rows of pectén. Anal

segment ringed by the plate with

2 to 3 anterior tufts of ventral

brush piercing the plate and a

tuft of 1 to 2 long hairs on its

lateral posterior margin. Anal

gills longer than segment with

tips rounded.

Distributionj, biology^ and importance.—This species is widely

distributed in the Northwestern

States. It occurs in largest numbers in poorly drained irrigated

areas. Under such conditions the

larvae are usually found with

those of freeborni and tarsalvs. It

is also found in shaded pools in

forests at elevations up to 6,000

feet. It seldom bites man, but can

become a pest of livestock because

of its long breeding season and

wide distribution in irrigated

areas. The females hibernate, and

Rees {111) believes that some

larvae may overwinter, since they

are very resistant to low temperatures. Western equine encephalomyelitis has been isolated from

this species in nature. Experimentally, it has been shown to

transmit St. Louis and Japanese

B encephalitis viruses.

CVLISETA MORSITANS (Theobald)

Culex morsitans Theob., Mon.

Culic. 2: 8. 1901.

Female.—Mesonotum brown

with a mixture of yellowish scales

around the margins, a pair of

faint nearly bare median stripes,

and posterior yellowish white

half-lines. Abdomen brown-scaled

with scattered yellowish-white

scales, most heavily concentrated

along the apices and bases of segments, or these may occasionally

form basal pale bands only. Wing

scales dark with pale scales at the

base of the costa. Legs dark with

faint white rings at both ends of

the tarsal joints.

Male genitalia (fig. 39, H).—

Side pieces conical, more than

twice as long as wide ; apical lobe

absent; basal lobe prominent and

conical, with 3 to 5 spines on the

apex and small setae on the sides.

Lobes of the ninth tergite with

broad projections each with 6 to

12 slender setae. Eighth segment

with a group of small spines centrally on basal margin.
82 HANDBOOK 46, U. S. DEPARTMENT OF AGRICULTURE

Larva.—^Upper head hairs multiple, lower double. Lateral abdominal hairs multiple on first

and second segments, single and

long on third to sixth. Air tube

about 6x1; pectén 6 to 9 teeth

on basal fourth; a small paired

tuft at base between the rows of

pectén. Anal segment longer than

wide and ringed by plate. Anal

gills slender and longer than the

segment.

Distribution^, hiologyj, and ¿mportance.—This rare species has

been found in small numbers in

Kittitas and Yakima Counties in

Washington and in Columbia,

Clatsop, and Klamath Counties in

Oregon. It has been reported

from Franklin County, Idaho.

The larvae have been collected

from unshaded pools grown up

with rank grass and fed by fresh

water. This mosquito is not

known to bite man, and very little

is known about it.

CVLISETA IMPATIENS (Walker)

Culex impatiens Wlkr. Brit. Mus.

Dipt. List 1: 5.1848.

Female.—Mes on o turn with

brown and yellowish scales, two

fine pale lines extending posteriorly from median pale patches

and a variable pattern of other

pale scales. Abdomen black with

basal segmental white bands.

Wing scales brown and aggregated to form faint spots at the

forks of second and fourth veins,

and the bases of the second and

third veins. Legs black, the femora white tipped.

Male genitalia (fig. 39, E).—

Side pieces stout conical, about

twice as long as wide ; apical lobe

a small slightly elevated chitinized area with long setae; basal

lobe large and conical in outline,

the apex rounded with 1 large

spine-like seta and several smaller

ones. Lobes of the ninth tergite

only slightly separated and each

bearing about 10 long setae.

Eighth segment with a row of 20

to 40 short stout spines on basal

margin.

Larva.—Both pairs of head

hairs multiple and long. Lateral

abdominal hairs multiple on first

to fifth segment and double on the

sixth. Air tube stout, 2x1;

pectén of 8 to 9 teeth on basal

fourth, followed by long hairs

that nearly reach apex of tube;

paired tufts large and arising

close to base between rows of

pectén. Anal segment wider than

long, ringed by the plate with 2

to 3 of the anterior tufts of ventral brush puncturing the plate,

and with a tuft of small hairs

near posterior margin. Anal gills

bluntly pointed and longer than

the segment.

Distribution^ biology^ and im*

portance.—This species has been

found in small numbers in a few

timbered sections of Oregon and

Washington and in Fremont

County, Idaho. The larvae usually

develop in shaded spring- or

snow-fed pools. The overwintered

females can usualy be found in

the woods very early in spring on

warm days. They are said to prefer animals for food, but will bite

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

in the Northwest.

'^vescens

• 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

(1) AlTKEN, T. H. G.

1937. THE DISTRIBUTION OF CALIFORNIA ANOPHELINES WITH REMARKS ON

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(2)

1945. STUDIES ON THE ANOPHELINE COMPLEX OF WESTERN AMERICA. Univ.

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1948. THE USE OF AIRCRAFT IN THE CONTROL OF MOSQUITOES. Amer.

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(4)

1952. INSECTICIDES AND EQUIPMENT FOR CONTROLLING MOSQUITOES. Amer.

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(5) APPLEWHITE, K. H., and CROSS, H. F.

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(6) BARBER, M. A.

1928. THE FOOD OF CULICINE LARVAE. U. S. Pub. Health Serv. Rpts.

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(7) BATES, MARSTON.

^ 1949. THE NATURAL HISTORY OF MOSQUITOES. 379 pp. New York.

/^(8) BisHOPP, F. C.

1951. DOMESTIC MOSQUITOES. U. S. Dept. Agr. Leaflet 186, 8 pp., rev.

(9)

1951. TODAY'S PROBLEMS IN CONTROLLING MOSQUITOES AND THE LATEST

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^/(lO) BOHART, R. M.

1948. THE SUBGENUS NEOCULEX IN AMERICA. Ent. Soc. Amer. Ann. 41:

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(11) BRADLEY, G. H., and KING, W. V.

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(12) BUDDINGTON, A. R.

1941. THE NUTRITION OF MOSQUITO LARVAE. Jour. Econ. Ent. 34: 275-281.

(13) CARPENTER, S. J., MIDDLEKAUFF, W. W., and CHAMBERLAIN, R. W.

1946. THE MOSQUITOES OF THE SOUTHERN UNITED STATES EAST OF OKLAHOMA AND TEXAS. Amer. Midland Nat. Monog. No. 3, 292 pp.

(14) CHAMBERLAIN, R. W., RUBIN, H., KISSLING, R. E., and EDISON, M. E.

1951. RECOVERY OF A VIRUS OF EASTERN EQUINE ENCEPHALOMYELITIS FROM

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(15) CHAMBERLIN, J. C, and LAWSON, F. R.

1945. A MECHANICAL TRAP FOR SAMPLING OF AERIAL INSECT POPULATIONS.

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1950. KNOWN FACTORS CAUSING VARIATIONS IN RESULTS OF INSECT REPELLENT TESTS. Mosquito News 10: 126-132.

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1947. A STUDY OF THE INSECT REPELLENTS USED AS SKIN TREATMENTS BY

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1950. THE TOXICITY OF SEVERAL INSECTICIDE RESIDUES TO MOSQUITOES COMMON IN THE PACIFIC NORTHWEST. Mosquito News 10: 132-134.

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1946. PREHATCHING APPLICATIONS OF DDT LARVICIDES ON FLOODWATER

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GJULLIN, C. M., LINDQUIST, A. W., and BUTTS, J. S.

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