Five insecticides have EPA label approval
for application as ULV aerosols by ground
equipment; chlorpyrifos, malathion, naled,
pyrethrum, and resmethrin. These insecticides
are listed in Table 3 (Rathburn and Boike
1975).

ULTRA-LOW VOLUME AERIAL
APPLICATIONS

Aircraft have been used for many years to
apply insecticide dusts, pellets, sprays, and
aerosols. Since 1964, aerial ULV has been
used many times for controlling mosquitoes in
disaster areas and for controlling epidemics of
mosquito-borne disease. The ULV method was
used in 1966 to kill infected Culex pipiens
quinquefaseiatus during the Dallas, Texas,
epidemic of St. Louis encephalitis; in 1967, to
kill species of Aedes, Psorophora, Culex, and
Anopheles in a 3-million acre flooded area in
Texas; in 1969, in Ohio to kill Aedes vectors
of LaCrosse encephalitis during an epidemic;
in 1972 and 1974 in New England to kill
species of Aedes, Coquillettidia and Culiseta
during an outbreak of eastern equine
encephalitis; in 1975, in North Dakota and
Minnesota to kill infected Culex tarsalis during
an outbreak of western equine encephalitis;
and in 1975 in Guam and Puerto Rico to
control the vectors of dengue.

The aerial ULV technique uses the
application of 0.5 to 3.0 ounces of highly
concentrated insecticide per acre for the
control of adult mosquitoes. These insecticides
are currently approved for adult mosquito
contro! by the ULV method of application
from airplanes: malathion at 3.0 fluid ounces
per acre, naled at 0.5-1.0 fluid ounce per acre,
and resmethrin at 3 fluid ounces per acre. On
occasion, car paint spotting and bee kills have
occurred as a result of ULV aerial
applications.

Special aircraft equipment for the ULV
involves special tanks, electrically-driven

pumps, spray booms, and 8001 to 8008 Tee-

Jet nozzles or other specialized delivery and

nozzle systems. In general, airplane ULV

applications should be made only under the

following conditions (Kilpatrick 1967):

(1) when temperatures are below 80°F

(usually early morning).
with droplet size of not more than 50
to 60 microns MMD (Mass Median
Diameter); no more than 10% of the
droplets should exceed 100 microns. In
some areas damage to car paint has oc-
curred when larger droplets were
dispersed or more than 10% of the
droplets exceeded 100 microns.
Effectiveness against adult mosquitoes
requires 10 or more drops per square
inch. Determination of droplet size
should be made by depositing a sample
of the aerosol on a silicone-/or Teflon-
coated glass slide and measuring the
droplets under a microscope with an
ocular micrometer. Other droplet
measuring systems are available.

(3) by multi-engine aircraft flying at a
height of 100-150 feet, at speeds of
about 150 miles per hour or more, with
swath widths of 300-1000 feet with
pump pressures and nozzle sizes and
positions adjusted to provide the proper
droplet size. Single-engine fixed wing
and rotary wing aircraft are undesirable
for this technique because of their
slower air speed and resulting problems
with droplet breakup. There are ad-
ditional safety factors with single-
engine aircraft and with their limited
"pay load" which need to be
considered when used in urban areas.

2)

THERMAL FOG AND DUST
APPLICATIONS

Thermal fog applications have been used
successfully for adult mosquito control for

71


larvae of Culex tarsalis may be abundant
among the dominant species found in these
poor drainage situations. This species was
found in such situations in an area endemic for
western equine encephalitis in west Texas
(Harmston ef al. 1956) and similar
relationships have been seen in many other
irrigated areas. Drainage is now being con-
sidered more carefully in the design of
irrigation systems partly because it has become
necessary to reclaim the waste water, and in
the future more efficient design and
maintenance of drainage systems in irrigation
should serve to minimize mosquito production.
Other recent developments in irrigation
include the development and refinement of
sprinkler irrigation systems, which will
probably reduce mosquito production in
irrigated areas. Sprinklers apply water
uniformly and more conservatively than other
surface irrigation methods, but mosquito
problems have been found where the land was
improperly prepared, application was poorly
managed, and water was allowed to
accumulate: Center-pivot irrigation systems are
being widely accepted by farmers in the
United States, and are extending irrigation in
the arid western United States (Splinter 1976).
Recent studies have shown that there is a
strong correlation between good irrigation
practices, high crop yield, and low mosquito
production, and conversely, poor water and
land management practices, low crop yield,
and high mosquito production indices are also
strongly associated. Because of the economic
benefits that can be demonstrated, it is less
difficult to encourage practices which will also
diminish the production of vector mosquitoes.
The use of sewage effluent for irrigation is
becoming an accepted practice, and the high
nitrogen content of this waste makes it
valuable in agricultural and horticultural
pursuits. Where such effluent has
been used for irrigation, pronounced changes

62

may occur in the larval mosquito populations,
including species composition, relative
densities, and the introduction of new vector
species. The association of Culex mosquitoes
with waste water of high organic content is
well known, a fact which has been demon-
strated in these situations.

Because of diked dredged spoils areas, a
serious mosquito control problem exists along
some of the navigable waterways of the United
States. The problem is due to production of
Aedes sollicitans, a salt-marsh mosquito, in
spoil material dredged from the waterways in
the course of their maintenance. Among the
states experiencing mosquito production with
diked dredged spoils are Louisiana, Texas,
California, and the Atlantic Coastal states on
the inland waterway.

Spoil material from the dredge is a liquified
substance consisting of silt, sand, and a large
percentage of water for conveyance purposes.
The normal practice has been to deposit some
of this material in a designated site and allow
it to dry. Once dry, the material may be
bulldozed into a dike so that a large basin is
created, into which more spoil material will be
pumped. Spoil material does not spread
uniformly but produces a "waffle" effect of
high and low portions. The lower ones tend to
hold precipitation, become vegetated quickly
and provide excellent oviposition and
development sites for Aedes sollicitans. As the
spoil dries, it often becomes cracked due to
shrinkage. The cracks collect precipitation,
and may become productive Aedes sollicitans
habitats. Spoils sites range in size from a few
to more than 1,000 acres.

Various methods have been used to reduce
mosquito production associated with these
spoils areas, including plowing, harrowing,
scraping, and other mechanical means of
altering the topography. Research is needed to
determine other naturalistic methods of control
of mosquitoes in diked dredged spoils deposits.


TABLE 2 (continued)

—

INSECTICIDE

APPLICATION

} (Active Insecticide/Acre)
ee | Senin ramen _

Bacillus thuringiensis
israeliensis

Follow label
directions.

Many formulations of
Bactimos, Teknar, et
al.

Pyrethrins and
synergist

Tossits

Proprietary

Compounds:
proprietary compounds such as AROSURF
MSF and Golden Bear GB-1111 and GB-1356
are registered for mosquito control. These

Special

larvicides have given good control at
application rates of 1-5 gallons per acre. They
have low toxicity to plants and to non-target
aquatic organisms. They act to suffocate larvae
and pupae and thus eliminate the problem of
resistance to organophosphate insecticides.
Insect Growth Regulators: Insect growth
regulators have been studied intensively in
recent years. Some of them have been called
insect developmental inhibitors, or juvenile
hormone-like materials. Some like methoprene
(Altosid) cause mortality in the pupal stage,
Others like diflubenzuron (Dimilin) prevent
molting. Altosid is available as emulsion,
granules, briquets, and pellets. These do not
kill eggs, first stage larvae, pupae, or adults,
but they do kill second, third, and fourth stage

67

Many formulations, follow label directions. After
ingestion, toxins released by the bacteria cause
paralysis of midgut and death within a day.

larvae and prevent development of pupae.
Dimilin is available as a powder which
prevents hardening of the cuticle and molting.
None of the insect growth regulators produce
the quick kill associated with many other
larvicides.

Lavicidal Bacteria: Bacillus thuringiensis
israeliensis is a bacterial compound used to
control mosquito larvae. It is sold
commercially under many trademarks as
Bactimos, Teknar, and Vectobac in various
formulations as liquids, granules, flowables,
and briquets. After ingestion by the larvae,
the bacteria liberate toxins that cause paralysis
of the midgut to occur within a few hours and
death in about a day. The microorganisms
released into the environment do not self-
perpetuate, so re-application is required. This
larvicide does not harm the environment -- fish
and other aquatic organisms, plants, wildlife,


salt-marsh mosquito breeding, with a minimum
effect on the natural environment.

Land management practices which were
discussed under “reservoirs” apply equally to
smail ponds and impoundments. Shorelines
with a 3:1 gradient and without emergent
vegetation are desirable. Farm ponds are
usually constructed with one portion gently
sloping and shallow so that livestock can have
easy access to the water. Mosquito production
has been observed on many farm ponds in the
United States and the important breeding sites
were commonly shallow, vegetated portions of
the impoundment.

Sewage lagoons and stabilization ponds have
produced abundant populations of Culex
tarsalis and Culex pipiens quinquefasciatus
mosquitoes. Culex pipiens quinquefasciatus
prefers water with high organic content for
oviposition, and Cx. tarsalis will tolerate this
source as well. It has been found that mosquito
production could be lessened by keeping
lagoons free of aquatic vegetation, and by
keeping the banks free of emergent vegetation.
A minimum operating depth of three feet has
been recommended to preclude mosquito
production. Breeding has been observed in
partially filled, vegetated lagoons; in such
cases, rapid filling with sewage effluent would
serve as a control measure.

BIOLOGICAL CONTROL

Biological control implies the destruction of
larvae by predators or pathogens. Control of
mosquito larvae by various biologic means has
been the subject of considerable research and
has shown much promise, but in practice,
mosquito fish are used most often in control
programs today. The pathologic agents under
study have shown varying degrees of success
in field trials, but as yet none are practical or
have been licensed for mosquito control.

Larvivorous fish offer the greatest
opportunity in biological control at this time,

and a number of mosquito abatement districts
propagate and distribute the mosquito fish
(Gambusia affinis) and the guppy (Poecilia
reticulata) for control of larvae in cisterns,
garden pools, ponds, and livestock watering
tanks.

In New Orleans, Marten (1990) reported
elimination of Aedes albopictus \arvae from
tire piles by introducing the copepod
Macrocyclops albidus. Some workers have
reported varying degrees of success in
controlling larvae of Aedes aegypti, Ae.
albopictus, and Ae. triseriatus with the large
predatory larvae of Toxorhynchites.

CHEMICAL CONTROL
Larval Control

If areas cannot be drained or filled at
reasonable cost, and mosquito control by
predator fish, impounding, or other naturalistic
methods is not possible, larviciding may be
required. Larvicidal control is of primary
importance in areas where control of disease-
carrying mosquitoes is necessary, particularly
in situations with extensive flooding following
natural disasters such as hurricanes or
prolonged rainy seasons. Where chemicals
are used for larviciding, it is recommended
that the larvicide be with a different chemical
from that used for adult control. For example,
it may be desirable to use temephos (Abate) as
a larvicide and malathion as an adulticide. The
degree of control with larvicides differs with
the various species of mosquitoes, degree of
pH and pollution of the water, and type and
amount of vegetation present. Table 2 lists
insecticides and dosage rates currently being
used to control mosquito larvae.

Types of Formulations

The synthetic organic insecticides can be
applied as dusts, pellets, granular
formulations, suspensions of wettable powders,
solutions or emulsions. Dusts have been used


Naturalistic control of. mosquitoes on
wetlands, along the Atlantic seaboard and in
California, has been the subject of much work
and research since the early 1900’s. For many
years, the wetlands were thought of as
wastelands because their role in the ecosystem
and their economic contributions were not well
understood. Recent studies have shown that in
addition to the production of salt grass hay,
the salt marshes are valuable nursery areas for
several species of fish and crustaceans.
Intensive studies have been accomplished in
California, Utah, New Jersey, Delaware, and
Florida, for the control of saltmarsh Aedes and
for the enhancement and protection of the
environment. In all instances, consideration
has been given to mosquito control, fish and
wildlife interests, and agriculture. The original
approach for mosquito control on salt marshes
was drainage and miles of ditches were dug
for this purpose. As knowledge of marsh-
plant-mosquito production developed, it was
seen that there was a high-marsh area which
was subjected to intermittent tidal flooding,
and this section of the marsh produced mos-
quitoes abundantly. The low-marsh portion
received frequent flooding, making it
unfavorable for oviposition for  salt-marsh
Aedes. Thus, the low-marsh was not the
source of the problem, but had been indis-
criminately ditched for mosquito control
purposes (Provost 1974).

Two basic methods of marsh management
for mosquito control are being used: water
level management and management of the
open tidal marsh. Both of the foregoing
depend on the knowledge of the biology and
ecology of Aedes sollicitans and Ae.
taeniorhynchus. These saltmarsh mosquitoes
lay their eggs on soil or plants, never on the
water surface.

Water level management has been used
successfully on salt marshes in Utah, New
Jersey, and Florida. The areas under control

63

were located near human population centers
and were intermittently flooded, producing
large numbers of mosquitoes. To correct this
situation, the problem areas were diked
appropriately to maintain the desired level of
flooding. A pump may be required to fill the
area or to add water when indicated. With a
constant water level, optimum oviposition sites
for salt-marsh mosquitoes are eliminated.

Other marsh areas indicate a need for open
management techniques. Canal systems are
developed to connect any section of isolated
marsh with tidal waters. The important
concept in this method is to bring circulation
or tidewater into isolated marsh areas, which
may hold floodwater or rainfall, within 1-2
days following the flooding. Minnows
predaceous on mosquito larvae are provided
access to all regions of the marsh as well
(Provost 1974).

The Open Marsh Water Management
(OMWM) concept (Ferrigino et al. 1975) is an
important source reduction approach. OMWM
is employed in marsh areas which are situated
either slightly above the spring tide line, or
slightly below it. Three basic modifications
can be made, and they can be used separately
or in conjunction. They are tidal ditches,
ponds, and pond radials (short ditches). In
some areas, a series of depressions are
arranged in a linear distribution. Such de-
Pressions could be connected with a ditch to
the nearest source of tidal flow in order to
provide circulation. Some depressions could be
linked to others by short lateral lines which
would eventually connect to the main ditch. In
other areas, several depressions might be
arranged in a roughly circular fashion. In this
case, a pond would be constructed by
connecting all the depressions together and
deepening them in the process. Smaller
depressions, near the pond, could be tied into
the pond by means of radials. All of these
modifications serve to reduce the potential for


TABLE 2 (continued)

INSECTICIDE

Malathion
57% EC

RATE OF

APPLICATION
(Active Insecticide/Acre)

Up to 13 oz/acre

Mix 2.5 oz of malathion 57% with water to make 1
gallon. Apply up to 5 gal./acre depending on
flotage and vegetation. (intermittently flooded
areas, stagnant water, temporary rainpools).

1 Temephos (Abate)

0.05-0.1 ib/acre

Apply 5-10 Ib. of 1% Abate sand and celatom
granular per acre.
Apply 2.5-5 ib. of 2% Abate sand and celatom

granular per acre.
Apply 1-2 Ib. of 5% Abate sand and celatom

granular per acre.

Temephos (Abate)

0.1-0.5 Ib/acre

In some tidal water, marshes, and water with high
organic or pollution content apply up to 25 Ib. of
2% Abate sand and celatom granular, or up to 10
Ib. of 5% Abate sand and celatom granular.

Temephos (Abate)

0.016-0.948 Ib/acre

Mix 0.5--1.5 oz. of Abate 4E per gal of water.
Apply at 1 gal./acre.

0.2-1 gallon/acre

Apply as single layer monomolecular film to cover
water surface.

Methoprene
(Altosid SR 10
Altosid G
Altosid Briquet
Altosid Pellets)

3-5 gallons/acre

34 oz. Altosid SR10
per acre

8-10 Ibs. Altosid G per
acre

1 Altosid briquet per
100 square feet

Apply from air or ground to cover water surface.

Mix 3-4 gallons of 10% Altosid in 4 to 5 gallons
of water and apply to 1 acre. Use 8-10 ibs. of
Altosid G per acre. Use Altosid Briquet 1/100
square feet. Kills 2nd, 3rd, and 4th stage larvae,
not pupae or adults.

Diflubenzuron
(Dimilin)

Re

0.02-0.04 Ib/acre

Interferes with formation of larval cuticle, inability
to moult successfully.



THE CONTROL OF MOSQUITOES

INTRODUCTION

Mosquito control activities are important to
the public health, and responsibility for
carrying out these programs rests with state

and local governments. The federal
government assists states in emergency
situations and provides training and

consultation in vector and vectorborne disease
problems on an ongoing basis as requested by
the states. The current interests in ecology and
the environmental impact of control measures,
and the increasing problems that have resulted
from insecticide resistance emphasize the need
for "integrated" control programs. An
integrated approach to mosquito control
involves accurate and complete assessment of
the problem and the employment of control
measures that are best suited to the situation.
Mosquito control measures generally used in
this approach include any one or a com-
bination of techniques aimed at: (1)
eliminating mosquito-producing habitats, (2)
control of mosquito larvae by chemical means
or by predatory fish, and (3) chemical control
of adult mosquitoes. In addition, experimental
efforts aimed at new alternative means of
mosquito control are under way, including use
of parasites and other pathogens, predators,
and sterile male and other genetic techniques.
These alternative methods, however have not
been used extensively in public health
mosquito control.

In many situations the application of
insecticides is still necessary to achieve
acceptable control. Persons with

responsibility for the application of pesticides
are regulated by the Federal Environmental
Pesticide Control Act which became law in
October 1972. This act is the amended Federal
Insecticide, Fungicide, and Rodenticide Act

(FIFRA) of 1947, and specifics that all
pesticides must be classified for "general use"
or “restricted use."

General-use chemicals are those which can
be safely handled by home owners, farmers or
others without special training. Restricted
chemicals are those which can be handled only
by trained and qualified people because they
could be dangerous if carelessly applied.

The amended FIFRA requires persons who
apply restricted-use pesticides to be certified as
competent after passing an examination, or to
work under a certified person’s supervision.
The certification examination is usually given
by a state agency. In preparing for this
examination, the U.S. Department of Agricul-
ture and the U. S. Environmental Protection
Agency have published a core manual on
general standards entitled "Apply Pesticides
Correctly.” All persons applying restricted-
use pesticides will be expected to understand
information in the core manual. In addition,
mosquito control workers who apply pesticides
must pass a competency examination covering
insects of public health importance. Special
manuals for mosquito control personnel have
already been prepared in some states.

NATURALISTIC CONTROL

Naturalistic control, as used in this Manual,
refers to all commonly employed methods of
mosquito control other than chemical or
biological. These "naturalistic" methods
include mainly those which involve the physi-
cal or mechanical alteration of topography or
the management of water. Elimination or
reduction of mosquito larval habitats by these
methods is often termed “source reduction.”
Although control of larvae by chemical or
other means might also be considered "source
reduction," such methods will be considered

1. Office of Pesticide Programs, U. S. Environmental Protection Agency, Washington, DC 20460.

58


TABLE 3--INSECTICIDES CURRENTLY USED FOR CONTROL OF ADULT
MOSQUITOES WITH ULTRA-LOW-VOLUME GROUND EQUIPMENT.
Modified from Rathburn and Boike (1975) and Evans (1992)

(These recommendations are guidelines only. User must ensure that insecticides are applied in s

with label and local, state and federal regulations).

IRMULATION/
LABEL

Dursban Dow Mosquito
Fogging Concentrate

At vehicle speed of 10 mph, 2/3 to 1 1/3 fl.
oz./min. Maximum flow rate 0.3 to 0.62
gal./hour.

Cythion ULV
Concentrate

At vehicle speed of 5 mph, 1-2 fl. oz./min.
Maximum flow rate of 1 gal./hour.

At vehicle speed of 10 mph, 2-4 fl. oz./min.
Maximum flow rate of 2 gal./hour.

10% Dibrom 14 in HAN

1% Dibrom 14 in fuel oil
with 1% Ortho additive

At vehicle speed of 10 mph, 6-12 fl. oz./min.
Maximum flow rate of 6 gal./hour. At this
rate persons may have serious irritation of
eyes and respiratory tract.

At vehicle speed of 10 mph, 40 fl. oz./min.
Maximum flow rate of 20 gal./hour.

5% pyretrhins -- 25%
piperonyl butoxide

naled* (Dibrom)
pyrethrum

At vehicle speed of 5 mph, 2--2.25 fl.
oz./min. Maximum flow rate of about 1
gal./hour.

At vehicle speed of 10 mph, 4--4.5 fl.
oz./min. Maximum flow rate of about 2
gal./hour.

| (Scourge)
2-4% (3.3 Ib/gal.)
z.- f 7 RAN - Heavy

Nowe mph = miles per hour fT. oz. - fluid ounce:

At vehicle speed of 5 mph, 9 fl./oz./min. of
2% finished formulation.

omatic Naphtha.

*With naled, tank pressure should not be greater than 1.5 Ibs. psi because of overatomization and poor mosquito control.
**Lower concentrations of this product should become available in the near future.

69

trict compliance


pets, and humans.

Pyrethrins: Larvicides containing
pyrethrins are sometimes used to control
mosquito larvae in lily ponds, and other
situations with valuable vegetation. Tossits
are gelatinous capsules containing 1%
pyrethrins which can be tossed into small
bodies of water such as stagnant pools, small
ditches, catch basins, cisterns, and small
marshy areas. The application rate is
approximately one tossit per 100 square feet,
per six inches of depth.

ADULT CONTROL

Control of adult mosquitoes by space
spraying of any kind is only temporary since
mosquitoes from nonsprayed areas can move
rapidly into the sprayed area following spray
applications. Also, aquatic stages are usually
not affected by space spraying and new adults
will continue to emerge.

Spraying operations are conducted during
the late afternoon and early evening, at night
or in the early morning when the air is cool
and wind velocity does not exceed 6 miles an
hour. If air movement is excessive, the small
droplets used in space spraying are dispersed
so swiftly that effectiveness is reduced or pre-
vented. Similarly, during the middle of a hot
day the droplets are dispersed by rising
currents of warm air known as thermals. At
night there may be an inversion of air
temperatures so that small droplets are held
close to the ground, usually producing
excellent control of mosquitoes.

Outdoor space treatments with ground
oraerial applications have been carried out
effectively against many species. Susceptible
populations of mosquitoes can be reduced

68

effectively by space application of insecticides
listed in Tables 3 and 4.

ULTRA-LOW VOLUME
APPLICATION WITH GROUND
EQUIPMENT

Ultra-low volume (ULV) application with
ground equipment is becoming the most
frequently used method of adult mosquito
control in the United States and can be very
effective in vector control. Ultra-low volume
treatment is defined as the application of less
than 2 quarts of insecticide per acre, usually
0.5 to 3.0 ounces per acre. Beginning in 1970,
great advances were made in the development
of ultra-low volume equipment and a number
of ULV ground application models are now
sold commercially. Ultra-low volume
equipment utilizes insecticide concentrate
without a diluent or carrier resulting in savings
in fuel, loading time, and cost of the fuel oil
required in thermal foggers. Other advantages
of ULV aerosols are that they do not produce
the dense fogs--as do thermal fogs -- which
constitute a traffic hazard by reducing
visibility. The ground ULV machine is
relatively small. Its insecticide tank commonly
holds 5 to 10 gallons and it is usually mounted
on a small vehicle, such as a 1/2 ton pickup
truck.


as mosquito larvicides, but they are light in
weight and subject to drifting in air currents
causing spotty application, and they may not
penetrate vegetation to reach the water. Pellets
and granular formulations have larger particle
size, so they slip through leaves or dense
vegetation to reach the water surface to kill the
mosquito larvae. Wettable powders are fre-
quently used in prehatch treatment of areas for
the control of mosquito larvae. Wettable
powders can be applied to snow, ice, or earth
in dried-up mosquito-breeding areas seeded
with eggs of temporary pool mosquitoes. Oil
solutions can be sprayed on water surfaces to
kill both anopheline and culicine larvae and
pupae, particularly in waters with high organic
content. Water emulsions have been employed
extensively to treat irrigated waters, as in rice
fields, since oil solutions are toxic to
cultivated plants. The water in the emulsion
serves as a carrier for the insecticide.

Larvicidal Chemicals

Organic Phosphorus Insecticides (OP
compounds): These chemicals came into
general use after World War II, particularly

after the emergence of the problems of
resistance of mosquitoes to the chlorinated
hydrocarbons and of environmental
contamination. Soon after application, most
organophosphates combine with water and
break down into compounds which do not
contaminate the environment.

At the present time, chlorpyrifos
(Dursban(R)) and temephos (Abate(R)); are
among the most widely used organophosphate
larvicides. Malathion has also been used
effectively. The degree of control varies
widely with the species of mosquito, degree of
Pollution of the water, and type and amount of
vegetation present (CDC 1973). Temephos is
a safe and effective larvicide against most
species of mosquito larvae. At recommended
dosage rates, it usually does not kill predators
(including fish) of mosquito larvae. It has been
used to control mosquito larvae in rain barrels
holding potable drinking water, in bird baths,
and in animal watering devices. Chlorpyrifos
(Dursban(R)) has given control of Culex larvae
in polluted water, such as dairy drains and
industrial waste water accumulations (Mulhern
1974),

TABLE 2-INSECTICIDES CURRENTLY USED IN MOSQUITO LARVICIDING

(These recommendations are guidelines only. There are many formulations available. The following are a
few in current use. User must ensure that pesticides are applied in strict compliance with label and local,
State, and federal regulations).

—

INSECTICIDE

|

RATE OF
APPLICATION
(Active Insecticide/Acre)

| Organophosphates 0.4-1.6 oz/acre in Dilute with water or oil for use in hand and power
chlorpyrifos water or oil sprayers, mist applicators, and aerial spray
(Dursban) equipment. Use 0.4 to 0.8 oz/acre for light (or no)
to medium vegetation and 0.8 to 1.6 oz/acre for
medium to heavy vegetation cover.
—

65


seepage through the dam which is frequently
observed. When such seepage occurs, it should
be properly drained into the main outfall
below the dam, or the resultant accumulation
may become a mosquito habitat.

Irrigation systems are among the largest
contributors to the mosquito problem in the
western United States (USDA 1967). Mosquito
Production has been recorded from every
aspect of the irrigation system, with sources
off the irrigated field being the most important
and difficult to control.

An irrigation system typically begins with
an impounded reservoir which stores water
and releases it as needed into the main
distribution canal and through a series of
smaller channels or laterals until it reaches the
area requiring irrigation. Ideally, the unused
water or runoff will be channeled into drain
collection ditches, and finally returned through
a main drain to the original source of the
water or to a stream. Reservoirs that are
drawn down sharply during the mosquito
Producing season generally do not cause
mosquito problems.

Irrigation distribution canals in
themselves are not major sources of mosquito
production. Usually the water in the canals is
in constant motion and does not Provide the
permanence or stability needed for ideal
oviposition sites or larval development.
Canals are usually 6-12 feet deep and steeply
banked, factors which tend to preclude
Mosquito production.

The important sources of Mosquitoes in the
distribution system are seepages emanating
from unlined canals. There are several
solutions to the seepage problems, and all of
them are expensive to install. For large canals,
the installation of a lining is probably the only
Practical method. Concrete linings are the
usual choice because of their durability but
polyethylene sheeting and other impervious
materials have been used successfully. The

61

Bureau of Reclamation has installed laterals on
certain projects in underground conduits where
surface canals would be aesthetically
objectionable. This is also a water conser-
vation technique, since it has been estimated
that as much as 75% of the water entering the
distribution system is lost before it reaches the
target because of seepage, evaporation and
waste (USDA 1967).

In the past, irrigated fields were frequently
observed to be abundant mosquito producers.
Unlevelled fields with surface depressions and
Poor drainage at the low end of the field
Created mosquito habitats. Currently, the
Bureau of Reclamation requires that fields be
levelled, conditioned, and Properly prepared
for efficient irrigation before water is
delivered to new systems.

Close-growing crops, such as alfalfa, and
wildflooded pastures Produce mosquitoes
abundantly, whereas a row crop, such as
cotton, does not. Fields of some crops (e.g.
Sugar beets and fruit orchards) usually do not
produce mosquitoes because Over-application
of water will result in damage to these crops,
and irrigation is carefully managed. Corn, on
the other hand, is a row crop with a deep root
system which tolerates much moisture,
resulting in poor irrigation Management and
associated mosquito production. Over--
application usually occurs with runoff
accumulating at the low end of the field and in
toadside ditches. Aedes, Culex, Culiseta, and
Psorophora larvae are commonty found in
agricultural waste water.

Efficient drainage Systems are uncommon in
irrigation agriculture. Once water reaches the
field, there is likely to be little or No provision
for removing the excess and abundant
Mosquito production may occur at the low end
of the field and in adjacent roadside ditches.
These ditches which often receive irrigation
drainage, are not designed to dispose of such
drainage efficiently. Throughout its range the


many years. Thermal fogs require the addition
of a fuel oil carrier and depend on a high
temperature system to produce the fog
droplets. Tests have shown ULV and thermal
fogs to be similar in effectiveness.
Disadvantages of thermal fogs include the
hazard of the dense fog produced and the
expense of carrying and using the fuel oil
carrier.

In past years there has been much interest
in the use of dusts for adult mosquito control,
and they can be effective. Tests with ground-
dispersed dusts (19% and 7.5%) of carbaryl
have produced 99% reduction of adult salt-
marsh mosquitoes at dosages of 0.2 and 0.3
pounds of carbaryl per acre.

OTHER METHODS OF ADULT
MOSQUITO CONTROL

Residual treatment outdoors for mosquito
control does not always produce good results.
However, limited relief from biting mosquitoes
can, at times, be obtained in small city parks,
playgrounds, picnic areas, patios and yards.
Water suspensions or emulsions with a low
percent of insecticide (rather than oil solutions)
are used in order not to “burn” vegetation.
These applications can be made with power
Sprayers or with hand sprayers, using nozzles
which provide a broad fan or cone and a
coarse spray, such as the Tee-Jet 8004. The
insecticides used for such outdoor applications
include Punt (containing pyrethrin).

Residual spraying is a primary method of
controlling mosquitoes that breed in catch
basins. In many large cities with thousands of
catch basins along the edges of the streets,
surveys indicate that often one catch basin in
every ten holds enough water to produce
broods of mosquitoes of the Culex pipiens
complex. The application of petroleum oils or
granular insecticides to these catch basins is
not the complete solution to this type of

72

Mosquito control because a single rain shower
produces enough runoff to flush the larvicide
into the storm sewer. Therefore, a special
nozzle has been developed which produces a
radial spray pattern and coats the walls of the
catch basin with insecticide. Some of the
insecticides used are not readily soluble in
water and the residual insecticide may remain
on the walls of the catch basin for weeks or
months. It kills the adult mosquitoes as they
rest on the walls after they emerge from their
pupal cases, while their wings and body
harden sufficiently for flight.

The organophosphate insecticide,
dichlorvos, is formulated into resin strips
which release an insecticide vapor. Usually
one resin strip per 1000 cubic feet
(10’x10’x10’) provides good control of
mosquitoes for 3 to 4 months. Results of tests
with such strips for control of adult
mosquitoes in catch basins, cisterns, etc. have
been variable. Studies in Savannah, GA and
elsewhere have shown good control as tested
with caged Culex pipiens quinquefasciatus for
11-18 weeks when one resin strip was wired to
the grating of a catch basin (CDC 1973).

ENVIRONMENTAL ASPECTS
Assistance should be sought from competent
conservationists, fish and game specialists, and
others in planning control measures in areas
where delicate ecosystems could be disrupted
by mosquito control practices. In mosquito
control only those pesticides approved by the
EPA for the planned use should be considered.

PERSONAL PROTECTION FROM
MOSQUITOES

People can protect themselves from
Mosquitoes by using proper window screens,
protective clothing and repellents. The
ordinary window screen with 16x16 or 14x18


and moving at 5 or 10 mph at the
recommended label dosage. Field-collected,
caged specimens (100-150/cage) are hung 6 ft
above the ground at stations 150-300 ft from
the point of discharge of the machine along
each of three streets (270-300 ft apart). Ten to
15 minutes after exposure the cages are
removed and the insects are transferred to
holding cages, given food and held for a 24-
hour female mortality count. Seventy percent
or better kill is expected. If the kill at either
150- or 300-ft station is less than 70%, then
the equipment and timing of application of
insecticide should first be examined, and
adjusted. If, after these adjustments have been
made, the kills are still unsatisfactory, then a
change of insecticide should be recommended.
Bioassay tests for larvicides are of less
value than sampling of natural larval habitats
for larvae before and after an application is
made. A useful technique to improve
reproducibility of larval sampling is that of

placing numbered stakes at various sites and
then taking a prescribed number of dips at the
site each time it is sampled. A 70% or greater
reduction in the number of larvae per dip is
expected.

For years larval and adult mosquitoes have
been tested for resistance to insecticides with
kits purchased from the World Health
Organization. These tests required large
numbers of specimens, were usually conducted
in the laboratory, and were subject to
procedural variables such as temperature and
humidity or age of the chemicals or test
papers. Therefore, Brogdon and coworkers
(1987, 1989) proposed the development of
Nonspecific Esterase (NSE) Microplate Assay
tests which permit: tests conducted in the
field; analysis of single insects; up to thirty
assays from a single insect; and fast and
accurate methods which can be read in the
field with the naked eye, at considerably lower
costs than the WHO Bioassay kits.

PUBLIC RELATIONS

To be of maximum effectiveness, mosquito
control must be understood and supported by
the people for whom protection is provided.
People who are informed about mosquito
biology and control are more likely to
mosquito-proof their homes, and to control
mosquito breeding places on their own
property. In reaching the public it is helpful to

work through officials of established
organizations and agencies, such as the
schools, PTA’s, Agricultural Extension

Service, the Grange, and civic groups. If
newspapers and local radio and television
stations are approached and the program is
explained to them, they may be willing to
devote a portion of their activities to a
discussion of mosquito control, frequently as
a free public service. In some areas school

74

children have taken home "check lists” to
“check off” on their own property such typical
mosquito-breeding places as tin cans or
bottles, old automobile tires, stopped-up
gutters, low ditches or a farm pond. Exhibits
at local, county or state fairs are used by some
mosquito abatement districts and attract par-
ticular attention if they include live mosquito
eggs, larvae, pupae and adults--one way to
teach large groups about the life history of
these insects. Some mosquito control
organizations buy a page of a local newspaper
once a year and print their annual report, with
well-selected photographs to illustrate typical
activities, in a mass medium read by thousands
rather than the more expensive annual report
sent to a select few who may file it away with
or without reading it.


cases the two elements should be considered
together because the bulk of the associated
larval production occurs at or near their
interface. This concept was clearly shown to
be true by the Tennessee Valley Authority
(TVA) for malaria control. The interaction of
water level management on reservoirs, along
with the proper preparation of reservoirs
before impoundment, proved that anopheline
vector production could be greatly reduced.
The valuable lessons learned from TVA
malaria control are still valid and should be
considered by the major water resource
developers in the planning, construction,
operations, and maintenance of reservoirs.
Mosquito problems on TVA projects have
been minimized because mosquito biology and
ecology are well understood, and naturalistic
control measures are integrated into reservoir
operation (USPHS and TVA 1947).

Water and land management practices for
mosquito control can be more easily
understood and appreciated if viewed in
relation to specific types of water resource
developments, such as reservoirs, irrigation
systems, wildlife refuges, and navigable
waterways.

Reservoirs are developed for multipurpose
uses such as hydro-power generation, flood
control, municipal and industrial water supply,
outdoor recreation, and fish and wildlife
interests. All types have caused mosquito
problems. If a reservoir is not to cause
mosquito problems, the following requirements
must be satisfied: (1) proper preimpoundment
preparation of the reservoir, (2) correct
management of the pool level, and (3) proper
maintenance of the shoreline.

Proper preimpoundment preparation of the
reservoir is the most satisfactory means of
eliminating potential mosquito producing
habitats. Preparation involves shoreline
conditioning, brush and vegetation removal,
and providing for drainage. Preimpoundment

60

preparations are the most desirable of available
methods because any modifications attempted
after filling are not easily made and are more
costly.

Shoreline conditioning involves steepening
the gradient in places which would otherwise
be very shallow after the reservoir
impoundment. Shallow vegetated areas
produce mosquitoes prolifically and must be
deepened wherever practicable. A shoreline
gradient of 3:1 has been found to deter the
establishment of emergent vegetation.
Mosquito-producing habitats are commonly
observed in the shallows of the upper reaches
of a reservoir and in tributary embayments.
Clearing of brush and vegetation within the
zone of recession removes potential mosquito
habitats. Much vegetation is not water tolerant
and should always be cleared from the
shoreline prior to impoundment and
“rebrushed" during drawdown periods.

Another aspect of reservoir preparation
which minimizes potential mosquito larval
habitats is the installation of drains in natural
depressions, borrow pits, and dikes. Water is
frequently trapped in such sites within the
summer fluctuation zone of a reservoir and
when the pool level is drawn down, they can
retain water and become serious mosquito-
producing situations which must be controlled
chemically.

Maintenance of the pool level and the
contiguous land areas are important parts of
mosquito control on reservoirs. The
manipulation of the pool level through
fluctuations was demonstrated by Hess and
Kiker (1943) to be effective in minimizing
anopheline mosquito production. The spring
surcharge and subsequent drawdown serves to
strand flotage such as plant parts and
accumulated debris, which, if not removed
from the reservoir pool, would create prolific
mosquito habitats.

Another maintenance consideration is


separately in the section on biological and
chemical control.

For ecological reasons, naturalistic control
methods are generally considered to be more
desirable than dependence on chemical control.
Further, the emergence of widespread
resistance of mosquitoes to the commonly used
pesticides has, in some areas, necessitated
virtually full reliance on the use of source
reduction methods. It should be remembered
that all source reduction methods require some
manipulation of the environment, and all must
be examined prior to use for possible
undesirable effects on the aquatic or terrestrial
environment. While naturalistic control
techniques are effective, for environmental,
economic or other reasons they may not
always be feasible.

Source reduction today often requires an
environmental impact statement, a permit from
the U.S. Army Corps of Engineers, and
compliance with the following laws: Clean
Water Act of 1972, 1977, and 1987 (sections
404 and 401), U.S. Fish and Wildlife
Coordination Act, Endangered Species Act,
National Historic Preservation Act of 1966,
National Environment Policy Act of 1969, and
Coastal Zone Management Act of 1972.
Source reduction methods commonly used
include filling, deepening, draining, ditching,
management of water levels, shoreline
maintenance, management of aquatic and
inundated vegetation, and others. Impounded
reservoirs, irrigation systems, navigational
dredging, and natural wetlands present special
problems in the production of mosquito
breeding sites, as well as opportunities for
mosquito control by environmental
manipulation.

Filling, a method of mosquito habitat
elimination, implies placing soil and similar
compactable materials into depressions, pot
holes, and low lying areas.

Deepening is a method used to modify
impoundments or other depressions which are
intended to hold water permanently. A
backhoe, dragline, or other mechanical method
may be used to deepen shallow and marginal
areas and to increase the slope of the
shoreline. The resulting steep, clean shoreline
precludes or reduces growth of emergent
vegetation. These modifications are frequently
made on borrow pits to reduce mosquito
breeding potential.

Draining of standing water is another
method of larval control. This involves open
ditching, use of subsurface drains, or
pumping. Each technique has a_ specific
application, and its use depends on the size of
the area to be drained, the terrain, soil type,
and economic feasibility.

Open drainage ditches are used throughout
the United States and are a common means of
salt-marsh mosquito control. For example, in
New Jersey much of the tidal marsh was
ditched for mosquito control about 1910-1920,
although the ditching was often improperly
installed. Subsequent to research on the “high”
and "low" salt marshes, new ditching concepts
have emerged which are more efficient. These
will be discussed in more detail below.

Water and land management, i.e., the
management of surface water and contiguous
land areas, plays a very important role in the
control of mosquito larvae, and poor
management commonly leads to severe
mosquito problems (USDA, 1967). This can
apply to entire watersheds or to collections of
waste water, precipitation runoff, irrigation
water and other impounded water. As water
becomes a more highly valued resource, water
management practices are being revised to
conserve and recycle water.

When considering control of mosquito
larvae, it is difficult to separate water
management from land management. In most

1. Office of Pesticide Programs, U. S. Environmental Protection Agency, Washington, DC 20460.

59


TABLE 4. INSECTICIDES CURRENTLY USED FOR ADULT MOSQUITO CONTROL
WITH GROUND FOGGERS, MISTERS, AND DUSTERS.

(These are guidelines only. User must ensure that insecticides are applied in strict compliance with the label

and local, State and Federal regulations).

INSECTICIDE DOSAGE (Active Insecticide/Acre)
carbary! (Sevin) 0.2-1.0 Ib/acre
chlorpyrifos (Dursban) 0.025-0.05 Ib/acre
fenthion (Baytex) 0.01-0.1 Ib/acre
malathion 0.075-0.2 Ib/acre
naled (Dibrom) 0.02-0.1 Ib/acre
propoxur (Baygon) 0.05-0.07 Ib/acre
pyrethrins (synergized) 0.002 =0.0025 Ib/acre
remethrin (Scourge) 0.0035 Ib/acre

Dosage based on swath width of
300 feet. Apply as mist or fog
between dusk and dawn. Mists
are usually dispersed at rates of
7 to 25 gallons per mile at a
vehicle speed of 5 mph. Fogs
are applied at a rate of 40
gal./hr. dispersed from a vehicle |}
moving at 5 mph; occasionally

80 gal./l hr. and 10 mph.

Finished formulations for

thermal foggers contain from

0.5 to 8 oz. per gallon actual
insecticide in oil. For

nonthermal foggers or misters,
water emulsions can be used.
Dusts can also be applied with
ground equipment.

Performance requirements for ground ULV (2)
equipment have been published as follows
(American Cyanamid Co. 1972):

(1) The ULV cold aerosol nozzle for (3)
dispersal of malathion to control adult
mosquitoes must have the minimum
capability of producing droplets in the
5 to 27 micron range. Large droplets
May permanently damage automobile (4)
paint. The average diameter should not
exceed 17 microns. Determination of
droplet size should be made by (5)
depositing a sample of the aerosol on a
silicone-coated glass slide and
measuring the droplets under a
microscope with an ocular micrometer.

70

Tank pressure should not be less than
2 to 3.5 pounds nor greater than 6
pounds per square inch (psi).

Flow rate must be regulated by an
accurate flow meter. Flow meter data
such as that in Table 3 should be
recorded at the end of each day’s oper-
ation.

The nozzle should be in the rear of the
truck and pointed upward at an angle
of 45° or more.

Vehicle speed should not be greater
than 10 miles per hour. Some
agencies have obtained: special local
need (24.C) authority to treat at 20
mph.


wal

ne ae ne ET

meshes to the inch will keep out most
mosquito species. Frequently, mosquitoes
follow people into buildings or enter on the
human host. For this reason, screen doors
should open outward and have automatic
closing devices. Residual insecticide
applications on and around screen doors give
added protection.

Long-sleeved clothing of tightly woven
material offers considerable protection against
mosquito bites. Sleeves and collars can be kept
buttoned and trousers tucked in socks when
mosquitoes are biting. This type of protection
may be necessary for people who must work
in areas where infected vector mosquitoes are
particularly abundant. The use of mosquito
netting to protect infants in their cribs may
also be indicated in high risk circumstances.

Relief from mosquito attack may usually be
obtained by applying insect repellents to the
skin and clothing. A number of these have
given adequate protection against mosquitoes.
Effective protection may be obtained through
the use of diethyl toluamide (Deet, Off). Use
repellents with 25% to 30% (or lower)
concentration of diethyl toluamide. Adverse
affects have been reported in infants or
sensitive adults treated with high
concentrations of diethyl toluamide. Re-
pellents are available as liquids in bottles,
pressurized spray cans, and in stick form.

When applied to the neck, face, hands and
arms, liquid repellents will prevent mosquito
bites for 2 hours or more, depending on the
person, species of mosquito attacking, and
abundances of mosquitoes. These repellents
can also be sprayed on clothes to make them
repellent. Many repellents are solvents of
paints and varnishes, plastics, such as watch
crystals, rayon fabrics and fountain pens.
Diethy] toluamide will not affect nylon. Care
should be taken not to apply repellents to the
eyes, to the lips, or to mucous membranes.
Clothing can be treated with aerosols of

permethrin (Permanone) and allowed to dry
for 2-4 hours before its worn to repel or kill
mosquitoes.

Pressurized aerosol insecticide dispensers
can be used in the home to kill adult
mosquitoes. Most of these contain pyrethrum
or allethrin because these insecticides have low
human toxicity and cause a quick knockdown
of mosquitoes. These aerosol dispensers may
also contain a synergist such as piperonyl but-
oxide and another insecticide such as diazinon
to kill the insects. Release of the aerosol for a
few seconds usually kills most insects in an
ordinary-sized room, tent, or trailer. These
aerosols are not hazardous if used as directed
on the container, except in rare cases where
persons are allergic to pyrethrum or the
synergist.

METHODS FOR ASSESSING
CHEMICAL CONTROL OF
MOSQUITOES

Evaluating the results of the treatments
applied as larvicides and adulticides is
important to any control effort. Resistance to
the insecticide being used may become a
problem, or improper application techniques
may reduce the effectiveness of the method, or
possibly increase the risk of killing nontarget
species.

The basic approach used in evaluating
larviciding or adulticiding applications is
comparison of the number of specimens per
collection made before and after the
application. For this purpose collections should
be made on each of several days before and
after the application and as many sampling
sites as possible should be included.

Another useful method is that of bioassay
tests with caged specimens. A bioassay test for
space sprays may be done by using the
following technique:

Treatments may be applied by fog, dust,
mist, or, ULV machine mounted on a vehicle

73