have rested on an insecticide-treated surface
often have the urge to leave a treated house at
daybreak.

~
window

trap

screen —

door

Figure 34. Window Trap

Carbon Dioxide Traps

Solidified carbon dioxide (dry ice) will
attract large numbers of some mosquito
species. An economical portable mosquito bait
trap utilizing dry ice as an attractant has been
developed in California. This trap (Fig 35),
made from a 12-inch lard can with two in-
wardly directed screen tunnels, is baited with
about 3 pounds of dry ice wrapped in
newspaper. It is effective in capturing large
numbers of Culex tarsalis.

screen cone — dry ice

Figure 35. Carbon Dioxide Trap

Insect Nets

Insect nets are used to collect mosquitoes
from grass and other vegetation. This type of
collection is valuable in determining the
abundance of those species, such as Aedes
vexans, Ae. sollicitans, Ae. taeniorhynchus,
Ae. nigromaculi, and Ae. triseriatus, which
rest on vegetation.

Daytime Resting Places

Adults of many species are inactive during
the day, resting quietly in dark, cool, humid
places. Careful counts of mosquitoes in
daytime shelters give an index to the
population density of these mosquitoes. This
method is especially useful for anopheline
mosquitoes and is commonly used for
Anopheles quadrimaculatus and An. freeborni.
It is also of value in estimating populations of
some culicines such as Culex quinquefasciatus,
C. tarsalis. and Culisela melanura. The shel-
ters are also a source of specimens for various
tests. Mosquito resting stations are divided
into two general types: natural and artificial.

Natural Resting Stations

These are the resting stations usually
present in houses, barns, stables, chicken
houses, privies, culverts, bridges, caves,
hollow trees, and overhanging banks along
streams. With experience one becomes capable
of evaluating the suitability of shelters as adult
mosquito resting stations. Dwellings,
especially when unscreened, often prove to be
satisfactory resting stations. They are
especially important when mosquito-borne
diseases are being investigated. Under such
conditions they furnish an index to the number
of mosquitoes which could bite man and
transmit encephalitis, malaria, or other
disease.

Artificial Resting Stations
Suitable resting stations may not be

49


MOSQUITO COLLECTION RECORD

Locality, Smithville Date July 20
Collector John Doe Supervisor LB. Jones

LARVAL COLLECTIONS

Station No. of No. of Larvae Larval Description
Number |{ Collection Dips Larvae per Collections Collection
Collected Dip Site
1 July 19 10 15 LS Rain Barrel Backyard
101 Main
Street
2 July 19 30 75 2.5 Temporary South end of
Rain Bugle Marsh
Puddles

12 July 19 60 30 0.5 Grassy South end of

LL Margin Blue Lake

(Front side)

ADULT COLLECTIONS

Station Date of Type of Females per Landings No. of Females
Number | Collection | Collection | Trap Night per Minute (Resting
Station)
1 July 20 | Light Trap 6
15 July 19 Biting 45
Collection
9 July 19 Daytime 20
Resting
Station
(Reverse side)

Figure 38. Mosquito Collection Record

54


or cotton and a layer of plaster of Paris or
cardboard. For safety reasons, instead of
cyanide, a layer of plaster of paris saturated
with ethyl acetate can be used. Some workers
use paradichlorobenzene or dichlorvos plastic
strips in the killing jar. Frequently a
perforated paper cup is placed in the mouth of
the killing jar to hold the specimens, keep
them dry, and make removal easier.

The mosquito light trap is mounted on a
post, or hung from a tree, so that the light is
about 6 feet above the ground. It should be
located 30 or more feet from buildings in open
areas near trees and shrubs. It should not be
placed near other lights, in areas open to
strong winds, or near industrial plants that
give off smoke or other fumes. The traps are
operated on a regular schedule from 1 to 7
nights per week. They are turned on just
before dark and turned off after daylight. An
automatic time clock or photoelectric cell can
Start and stop the trap, or it can be turned on
and off by hand. The collection should be
removed each morning and placed in a
properly labeled box, sorted and identified.

The CDC miniature light trap (Fig. 36) was
developed for greater portability in making
live mosquito catches in remote areas which
could not otherwise be sampled (Johnston et
al. 1973). This small plastic trap was field
tested, resulting in catches of about one half as
many mosquitoes as the New Jersey trap, or
its modification, the American light trap used
in California. It has been used with success in
collecting Culicoides and Phlebotomus. It
collects a high percentage of mosquitoes in
proportion to “trash insects" and many more
females than male specimens, a desirable
feature in collecting mosquitoes for virus
studies. Both the American and CDC
miniature light traps exclude many large
insects.

The CDC miniature light trap weighs only
1 3/4 pounds. It can be disassembled readily

51

for easy transport and has a collapsible
catching bag. The large plastic aluminum
canopy protects the operating mechanism, even
in the heaviest rainstorms. It can be operated
with one 6-volt battery or four 1 1/2-volt
flashlight "D” cells, which provide sufficient
power for one night. The Aristo-Rev No. I
motor, which is available from hobby shops,
has given between 15 and 25 nights of service
before wearing out.

Wide differences have been noted in the
reactions of different species of mosquitoes to
light. Light trap collections must therefore be
used in conjunction with other methods of
sampling mosquito populations. They have
proven very useful in measuring densities of
some of the culicine mosquitoes, such as
Aedes sollicitans, Ae. vexans, Ae.
nigromaculis, Culex tarsalis, and
Coquillettidia perturbans. Some anophelines,
especially Anopheles albimanus, An. crucians,
An. atropos, and An. walkeri, are also readily
taken in light traps. Anopheles
quadrimaculatus, however, is seldom taken in
significant numbers. Aedes aegypti is rarely
collected in light traps. Pratt (1948) and
Provost (1959) have reported that light trap
collections of many species of mosquitoes
show fluctuations on a 4-week cycle correlated
with the dark and bright phases of the moon.
The largest collections are made during the
dark phase.

LARVAL MOSQUITO SURVEYS

Mosquito larvae are found in all types of
aquatic habitats from warm, brackish, seaside
marshes to the pure, cold, melted snow water.
They are found in such diverse locations as
rivers, lakes, ponds, crab holes, pitcher plants,
eave troughs, funeral urns, bottles, cans,
reservoirs, tree holes, old tires, and junk
automobiles.

The inspector must assume that mosquitoes


available in
satisfactory
population. It ma:
special shelters or
etc., as artificial

sufficient numbers to give a
evaluation of the mosquito
y be necessary to construct
to use boxes, barrels, kegs,
1 resting stations. Many
different types of artificial shelters have been
used. They should always be placed near the
suspected breeding places in shaded, humid
locations. Mosquitoes enter such shelters at
dawn, probably in response to changes in light
intensity and humidity and ordinarily do not
leave until dusk. Artificial shelters built as
boxes, each side one foot long and painted red
on the inside, or as artificial privies 4 feet
square and 6 to 7 feet high, have been used
successfully in the United States.

Light Traps

Many mosquito species are attracted to
light. This reaction makes it possible to sample
adult populations between dusk and dawn. The
New Jersey mosquito light trap, developed in
the 1930’s, has been widely used in obtaining
data on the density and species composition of
mosquito populations.

The American mosquito light trap (Fig. 36)
has been developed by the Bureau of Vector
Control, California Department of Public
Health, as a modification of the New Jersey
light trap. It was redesigned to reduce capture
of moths and other "trash insects" and to
permit construction from easily available parts
(Mulhern 1974)

Mosquito light traps attract adults from a
considerable area when the traps are placed
away from competing light sources. As the
mosquitoes reach the light, they are blown
downward through the screen funnel into a
killing jar or mesh bag suspended below the
trap. The light and fan are usually powered by
alternating current, but batteries are used for
remote locations. The killing jar is made from
a pint or quart fruit jar or plastic container. A
layer of sodium or potassium cyanide is placed

50

FOUR SIZE D
PLASTIC FLASHLIGHT
RAIN BATTERIES

GUARD

PLASTIC CYLINDER

{Contaiaing ent.
motor & fan blade)

A. CDC MINIATURE LIGHT TRAP

16” ————|
Chain tor
hanging. Electric light
bulb — 25 watts,

Hood of 20 9 140-120 volts. T

gal. iron .

inside white, VO 6

outside dark 4

green. !
Space to admit mos wr
quitoes covered by
galv. iron hardware
floth, %" mesh to Fan motor
exclude large insects 360 ev. ffi
abreckers to suppor an blades
top, of 1/8" x1"
band iron spaced Capacity as
equally about tube Sober ears P.
{shown out of 90- volts. 2,
{ahown out of 29, meenh bronze screen. 16
One extended to
support light bulb.

Tupe of 20 98

galv. iron
Dark green.

‘Mason
iar
V pint.

Plaster of Paris 7

Sawdust Cyanide

f}——_ 10°"—— 4

B. AMERICAN LIGHT TRAP

Figure 36. Mosquito Light Traps

in the bottom, covered with a layer of sawdust


proceed slowly and carefully in searching for
mosquito larvae. If the water is disturbed, or
a shadow is cast on them, the larvae often dive
to the bottom. Anopheline larvae are collected
by a skimming movement of a dipper with one
edge pressed just below the water surface. The
stroke is ended just before the dipper is full,
because larvae will be lost if the dipper runs
over. Where clumps of erect vegetation are
present, it is best to press the dipper into such
clumps with one edge depressed so that the
water with the surface-floating Anopheles
larvae flows gently into the dipper. Culicine
larvae such as Aedes vexans, Ae. stimulans,
Ae. sollicitans, Ae. taeniorhynchus, or the
species of Psorophora, require a quicker and
deeper motion of the dipper, since these larvae
hang down from the water surface and are
more agile. Some species, e.g., Ae. aegypti,
are more likely to dive below the water
surface when disturbed.

Inspection for Ae. aegypti requires a careful
search for, and examination of artificial
containers in which these domestic mosquitoes
breed. Such inspections are usually made
premises-by-premises, checking bottles, tin
cans, automobile tires, and all other water
containers. The Ae. aegypti index is obtained
by dividing the total number of premises
inspected into those in which larvae are found.
Collection of the Ae. aegypti larvae can be
made with a dipper, but it is more frequently
accomplished by means of a wide-mouth
pipette.

Inspection for Ae. triseriatus and Ae.
sierrensis involves searching for tree holes and

53

artificial containers in which these larvae
occur. Such breeding places are often too
small to admit an ordinary dipper, but water
can be removed by means of a suction bottle

An inspector should always record the
number of dips and the number of larvae
found, as in the record form on Figure 38.
The larvae are transferred to small vials by a
wide-mouth pipette and preserved for later
identification. It is possible to get an
approximate idea of the larval density by
computing the number of larvae of each
species per dip. The number of dips required
will depend on the size of the area, but for
convenience they should be made in multiples
of 10. Inspections should be made at intervals
of one to two weeks during the breeding
season because areas which are entirely free of
larvae at one time can have many larvae at
other times. Laboratory identifications of
specimens are tabulated on the record form as
shown in Fig. 39.

Variations in the procedure described above
are required when inspecting for certain
species. For example, Mansonia and
Coquillettidia larvae remain below the water
surface throughout their development. These
larvae are found by pulling up aquatic plants
(cattail, sedges, pickerelweed, etc.) and
washing them in a pan of water. A search of
the bottom muck and trash from the area
where the host plants have been uprooted can
be productive. This material should be scooped
up and examined in pans of clear water. Other
methods for collecting Mansonia larvae are
described by Bidlingmayer (1959).


reporting for informational and budgeting pur-
poses. A schematic map is used for orientation
and for locating and recording larval breeding
places and adult sampling stations. A contour
map should show streets, roads, railroads, as
well as ponds, lakes, streams, and other water
areas.

The schematic map (Fig. 31) illustrates the
type of information needed for a small project.
When larger areas are to be protected, it is
best to have a master schematic map and
large-scale area maps showing details for
planning drainage and other control operations
in the field. Urban mosquito control programs
require detailed maps in which each block is
numbered. The master schematic map will
show the areas to be protected, the possible
flight range of mosquitoes from different
larval habitats, and the degree of penetration
into areas to be protected. All larva and adult
stations are shown by symbols and numbers.
Counts made at these stations at regular
intervals permit evaluation of the mosquito
problem at any time by indicating the
abundance of mosquitoes, the species
involved, the flight range, and the areas
requiring high priority for treatment.

ADULT MOSQUITO SURVEYS

Purpose

The number and relative abundance of the
various mosquito species in a community can
be estimated by surveys of the adults. By
consulting references on the habits of the
different species, the vector control specialist
can determine where to look for the larval
habitats and decide the need for a control
program Adult mosquito information
indicates the best times and places to use space
spray equipment. It is also a source of reports
to supervisors and the public concerning the
extent of the problem and results of control

45

operations. Interpreting mosquito survey
reports correctly results in the most efficient
use of manpower, materials, and equipment.

Equipment

The equipment required for a survey
consists of a collecting tube (also known as an
aspirator), a killing tube, pill boxes, cases for
live mosquitoes, field record forms or
notebook, flashlight, and map (Fig. 32). Var-
ious kinds of traps and other collecting devices
can also be used.

The killing tube can be made from a glass
or plastic tube of any convenient size. Test
tubes about |-inch diameter by 7 inches long
are preferred. Pour about an inch of plaster of
paris mixed with water into the bottom of the
tube and allow the plaster to dry. Add
sufficient ethyl acetate to saturate the plaster of
Paris. Then press two or three discs of blotting
paper (cut slightly larger than the tube) down
over the plaster. Close the tube with a cork or
tubber stopper. The collecting tube will stay
effective for several weeks and can be
recharged when necessary by removing the
discs and adding more ethyl acetate. Some
workers wrap the base of the killing tube with
adhesive tape to lessen the chance of breakage:
some add a paper cone (base up) inside the
mouth of the tube to trap specimens more
easily. The addition of crinkled tissue paper to
the tube helps keep specimens dry, and, by
preventing their getting broken, makes
identification easier.

A simple aspirator is prepared from a
section of rigid plastic (or glass) tubing 12
inches long with an inside diameter of about
3/8 of an inch. One end of the tube is covered
with fine cloth netting or metal gauze and then
inserted into a piece of rubber tubing 2 to 3
feet long (Fig. 32). A flashlight-battery-
operated aspirator is described by Sudia and
Chamberlain (1967).


spicata) and salt-meadow cord grass (Spartina
patens), than in the lower areas where water
stands for longer periods of time characterized
by growths of rushes (Juncus spp.) and marsh
grass (Spartina alterniflora). These results
have been confirmed by later research of many
workers including Elmore and Fay (1958) who
have worked out characters for identifying first
stage larvae of the salt-marsh mosquitoes
(Aedes solicitans and Ae. taeniorhynchus).

Egg Separation Machines

Egg separation machines were developed as
early as 1938 by C.M. Gjullin for separating
eggs of Aedes vexans, Ae. sticticus, and Ae.
dorsalis from soil and debris. Horsfall (1956)
developed an entirely different technique
which involves mechanical agitation, washing,
screening out, or sedimentation of debris and
flotation of the eggs in saturated salt solution.
The samples of sod, leaves, and other ground
material are taken by cutting around a board 6
inches square with a sharp trowel. They are
then put into plastic bags and stored,
sometimes for months, in a cool room. The
various species of Aedes and Psorophora can
be identified by microscopic examination of
live or preserved eggs (Ross and Horsfall
1965). This egg-separating technique has been
used by many mosquito control districts to
locate prolific breeding places of Aedes and
Psorophora mosquitoes. These areas are then
treated with insecticides, often by prehatch
treatment.

Oviposition Traps

Ina study of container-breeding mosquitoes,
Fay and Perry (1965) showed that several
species of mosquitoes were attracted to black
jars containing water and would lay eggs ona
hardboard paddle placed in these oviposition
traps or “ovitraps” (Fig. 40). Technicians were
trained to identify the eggs of Ae. aegypti from
those of Ae. triseriatus and other container--

56

bleeding mosquitoes. The eggs of Aedes
(Stegomyia) aegypti and Aedes (Stegomyia)
albopictus are very similar. In surveys they
are listed as Aedes (Stegomyia). The only way
to separate them is to hatch the eggs and
identify the larvae or reared adults. The
ovitrap method of surveying or surveillance
appears to be more sensitive and economical
than larval or adult surveys of Aedes aegypti.
It was used extensively in the United States,
Puerto Rico, and the Virgin Islands in 1967
and 1968 during the Aedes aegypti Eradication
Campaign, in Thailand in 1968 and 1969, and
in dengue contro! on Guam in 1975.

Figure 40. Oviposition Trap with Paddle

Reiter Gravid Trap

The Reiter gravid trap samples female
Culex mosquitoes as they come to ovipost
Reiter, et al., 1986). It therefore is selective
for females which have already taken at least
one blood meal. If mosquitoes are being
collected for virus isolation, there is a higher
probability of collecting infected mosquitoes.
Gravid trap counts might also have a higher
correlation with disease transmission. The


MOSQUITO IDENTIFICATION RECORD

Locality, Smithville Date Received July 20
Determined by. George Abbot Date July 24
|
Station Date of Type of Mosquito No. of No. of No. of
Number Collection || Collection Species Larvae Males Females
1 July 19 Larval 10 Aedes 15
aegypti
5 Ae. triseriatus
2 July 19 Larval 50 Ae. vexans 7s
25 P. ferox
12 July 19 Larval 12. A. quad. 30
18 A. punct.
1 July 20 Light Trap | 5 Culex pipiens 1 Culex 5 C. pipiens
1 A. quad. pipiens 1 A. quad.
15 July 19 Biting 40 Aedes vexans 40 Ae. vexans
Collection 5 P. ferox 5 P. ferox
9 July 19 Daytime 20 A. quad. 20 A. quad
Resting
Station

Figure 39. Mosquito Identification Record

MOSQUITO EGG SURVEYS

Egg surveys are undertaken primarily to
locate the larval habitats of salt-marsh,
floodwater, and irrigated field mosquitoes in
the genera Aedes and Psorophora. These
mosquitoes lay their eggs on damp soil in
Places subject to intermittent flooding, not on
the surface of standing water, as do Anopheles
and Culex. Therefore, two entirely different
types of egg surveys have been carried out
with these temporary pool mosquitoes: sod
sampling and egg separation.

Sod Sampling
Sod sampling was carefully studied and

55

reported by Bradley and Travis (1942). They
cut samples containing 8 square inches of soil
and vegetation, trimmed to a thickness of
about an inch, and stored them for a week or
more to allow the embryos time to develop
within the eggs. The sod samples were then
placed in glass jars and flooded with water and
the larvae were identified as they hatched. The
use of sod sampling as an adjunct to larval
surveys in delimiting breeding areas has led to
important economies in larvicidal and ditching
operations. Frequently sod sampling has
revealed much heavier concentrations of salt-
marsh mosquito eggs in higher areas of the
marshes subject to intermittent flooding,
overgrown with salt-marsh bermuda (Distichlis


have adapted themselves to a wide variety of
aquatic situations. It is necessary to obtain
information regarding the general breeding
habits of the species known or suspected to be
present in the area prior to initiation of larval
surveys. An experienced person may be able
to spot the probable mosquito-breeding places
in a specific area by means of a tapid
reconnaissance survey. These places should be
carefully numbered and marked on the map.
More detailed inspection is then required to
determine the specific breeding sites and
establish permanent larval sampling stations.
Larval surveys show the exact areas in which
mosquito larvae occur and their relative
abundance. For this reason they are of special
value in control operations.

Equipment for Larval Mosquito Surveys

A white enamel dipper about 4 inches in
diameter is most often used for collecting
mosquito larvae (Fig. 32). The handle of such
a dipper may be extended to a convenient
length by inserting a suitable piece of cane or
wood. Many special dippers are used for
specific purposes, being designed so that their
capacity can be directly related to the water
surface area examined. Thus, the number of
larvae per square foot or square meter may be
computed with reasonable accuracy.

Some inspectors prefer white enamel pans
to dippers. A convenient size for a pan is
about 14 inches by 9 inches by 2 inches deep.

Such a pan is used to sweep an area of water
until half full. It will then float in the water
while the larvae are removed.

Inspection of small artificial containers or
cisterns can call for a flashlight or mirror with
which to reflect light into the shadowed area.
Largebulb pipettes, siphons made of rubber
tubing,” or suction bottles (Fig. 37) are
sometimes used to remove water from small,
inaccessible locations such as tree holes. The
water can be put in a dipper or pan and the

52

Figure 37. Suction Bottle

larvae counted and collected. Wide-mouth
pipettes (eye droppers) are used for removing
larvae from a dipper or pan. Small vials,
preferably with screw caps, will hold the
larvae until they can be identified or mounted
on slides. Screenbottom spoons or tea strainers
can be substituted for pipettes if the larvae are
to be transferred to widemouth bottles or
disposable polystyrene (€.g., Styrofoam (R)
cups. Either 95% alcohol, or 100% cellosolve,
is a satisfactory preservative, but 70% alcohol
is in common use. An extensive account of
equipment for collection of mosquito larvae is
given by the World Health Organization
(1975).

Inspection Procedures

In the larger ponds and lakes, mosquito
larvae are usually found where surface
vegetation or debris are present--ordinarily
only in the marginal areas. It is necessary to


populations. In making biting collections or
counts, part of a person’s body is exposed by
rolling up sleeves or trousers, or by removing
the shirt. The person should sit quietly for a
designated period of time, usually 10 or 15
minutes. Mosquitoes are collected with an
aspirator either by the collector or a coworker.
In many parts of the tropics it is customary to
make biting collections about sundown from a
domestic animal, such as a large cow or horse.
If collections are made at night, a flashlight is
required. Whether counts are made from
human beings or animals, it should be
recognized that certain individuals are more
attractive to mosquitoes than others. It is
therefore, desirable for the same person or
animal to be used throughout a given survey.
Collections must be made at regular intervals
and at approximately the same time of day, so
that biting rates at different stations may be
compared to show trends in mosquito
populations.

Biting collections should not be made from
humans in areas where encephalitis activity is
likely. With day-biting species, the index may
be based upon the number of mosquitoes
alighting upon one’s clothing in a given time
interval (the landing rate), rather than those
actually in biting position. This is more
practical when populations are very high, and
is useful for a rapid check of mosquito
abundance before and after control efforts.
The landing-rate method has been used
especially with certain species of Aedes or
Psorophora found in salt marshes, rice fields,
and the arctic and subarctic tundras.

Bait Traps

Animal bait traps, or stable traps (Fig. 33),
have been used extensively in the West Indies,
South America, and other parts of the world.
Bait traps are somewhat expensive to build,
transport and maintain, but a series of these
traps will collect live mosquitoes over a wide

48

area for a whole night, without large numbers
of other insects, and in areas where electric
power is not available. Animal bait traps must
be of sufficient size and strength to hold the
bait animal comfortably and permit its
convenient entry and removal. A considerable
portion of the sides of the trap is covered with
screen wire in order that mosquitoes may be
attracted to the bait animal. V-shaped entrance
slots make it easy for mosquitoes to enter and
bite but difficult for them to find their way out
after feeding. Two types of openings, the
Egyptian and Caribbean (Fig. 33), are widely
used. The animal is generally placed in the
trap in the evening and left overnight. The trap
is inspected early in the morning and the
mosquitoes counted and/or collected. Horses,
mules, donkeys, calves, sheep, and hogs have
been used as bait.

Caribbean
opening

Egyptian
opening

Figure 33. Animal Bait Trap

Window Traps

Window traps (Fig. 34) employing the same
principle as the animal bait trap are sometimes
used. The humans sleeping inside serve as
bait. The entrance slots can be mounted in the
windows of the buildings with the screen cages
inside to catch mosquitoes as they enter. More
frequently, in malaria control programs, the
cages are placed outside, for mosquitoes which


¢ a aacamniacetome
ASPIRATOR FOR COLLECTING ADULTS
PIPETTE FOR TS
PICKING Cs Funnel
UP LARVAE ky G9
KILLING
TUBE FOR
AOULTS
<>
PLASTER
OF PARIS
JAR FOR
LIVE LARVAE
ena FLASHLIGHT
Q i_ BATTERY-OPERATED
ASPIRATOR
PILL BOX
FOR ADULTS
RUBBER BOOTS
S| DIPPER FOR
FOR NLIGHT COLLECTING
COLLECTING LARVAE
ADULTS
VIAL FOR
LARVAE
& PUPAE
(inside tabel
4 Alcohot

Figure 32. Equipment for Mosquito Surveys

Small pill boxes or salve boxes are
convenient for holding dead mosquitoes until
they can be identified. The mosquitoes should
be placed between layers of facial tissue with
enough additional tissue to prevent damage to
the specimens as they are carried about or
shipped to a laboratory for identification.

47

Excellent discussions and pictures of survey
techniques and equipment are included in
articles by Sudia and Chamberlain (1967);
Bidlingmayer (1959); and Service (1976).

Biting Collections
Collecting mosquitoes as they bite or land
to bite is a convenient method of. sampling


4
H
’
1
'
'
'
t
'
'
‘
'
1
2

&
>
BK
Py
g
So
9 :
\ G) | PROTECTED AREA
! Hy
‘ rhs
‘
\
‘ oO m
‘ .
\ ! > -G
. ©|
N
. y
.
4 y
{Oo} Y 4c i} aad |
CHAPEL 4 «

2 LIMITS OF

¢ POPULATED AREA =~ ame
x

3

CONTROL LIMITS ~

aout stations L\
LARVAL STATIONS (@)

LIGHT TRAPS @

° 1

SCALE IN MILES.

Figure 31. Schematic Map Showing Mosquito Sampling Stations

46



Harris County Mosquito Control District in

Houston, Texas has used these traps
successfully in their SLE © surveillance
program.

UTILIZATION OF SURVEY DATA

Data from surveys are correlated with
reported disease prevalence or complaints of
pest mosquitoes. It is only after reviewing all
of this information that the health officer or
vector control specialist can make an
intelligent decision as to the need for a control
program and the type of control operations that
will be most effective and economical. The
conclusions, together with a request for funds,
can then be presented to the appropriate local
officials.

Inspections must be continued routinely
once a mosquito-control project is under way.
Information from such inspections serves to
show the progress of the control operations.
The effectiveness of a mosquito-control project
cannot be measured in terms of the number of
feet of ditches constructed or the number of
gallons of insecticides used. While these are
useful statistics, it is the actual population of
mosquitoes that is significant. If the mosquito
population is reduced to a satisfactory level,
there should be accurate data showing this
reduction. On the other hand, if mosquito
populations remain high, these facts should be
known so that control work can be intensified.
It is always advisable to inspect some
comparable breeding areas beyond the control
zone at regular intervals in order to learn the
normal fluctuation of various species
throughout the season.

During World War II, malaria control

57

officials felt that "satisfactory control"--i.e.,
the mosquito population level at which malaria
would not be transmitted--would be reached
when resting station collections of A.
quadrimaculatus contained no. more than 10
females per station in the control zone.
Similarly, Reeves (1965) has indicated that
little or no transmission of Western equine or
St. Louis encephalitis occurred in California
when light trap collections of Culex tarsalis
contained no more than 10 females per trap
per night.

Some authorities have worked out a
correlation between mosquito annoyance and
the numbers captured in light traps. In New
Jersey, for example, it was determined that
general annoyance did not ordinarily occur
until the number of female mosquitoes of all
species exceeded 24 per trap per night.
Standards for biting-or landing-rate collections,
as well as for other sampling methods for
adult mosquitoes, can also be established. It
must be cautioned, however, that survey data
are seldom absolute and interpretations must
be made for each specific situation. Numbers
of mosquito larvae found in surveys are more
difficult to correlate with pest problems or dis-
ease hazards. However, larval surveys reveal
the specific sources of mosquito production.
This information is helpful to the control
supervisor as it enables him to apply effective
larvicides to the right places at the right times.
Data over a period of time may also serve to
justify the use of permanent control measures.
The more expensive operations, such as filling
and draining, should be undertaken only after
due consideration has been given to the effect
on the local environment in relation to the
benefits realized from the mosquito control.