5
Vector Control Bulletin Nd. 4
March 1974
i 20 77
MONTANA
H€4C)IJIT€IS
Part n Survey and Ground
Applied Chemical Control
MONTANA DEPARTMENT OF HEALTH AND ENVIRONMENTAL SCIENCES
Environmental Sciences Division
Environmental Services Bureau
Helena, Montana
Montana State Library
3 0864 1006 5710 8
MONTANA MOSQUITOES, PART II— SURVEY AND GROUND APPLIED CHEMICAL CONTROL
Table of Contents
I. Philosophy . ■ l
II. Mosquito Biology - Some Practical Implications 1
III. Classification of Breeding Places — ■ 3
IV. Mosquito Surveys -• 3
A. Original Basic Survey 3
B. Operational Surveys 3
1. Larval Surveys — ■ 4-
2 . Adult Surveys — • 4
V. Methods of Control 14
A. Source Reduction n
B. Pre-larviciding 5
C. Larviciding 5
D. Adult iciding 5
E. Biological Control 6
VI. Chemicals for Mosquito Control 6
VII. Equipment for Ground Application 8
A. Introduction 8
B. Types of Larviciding Equipment 8
C. Types of Adult iciding Equipment 9
D. Equipment Selection 10
VIII. Chemical Application 10
A. Equipment Calibration 10
B, Standardizing Application Rates 11
C. Computation of Acreage 12
1. For Larviciding 12
2. For Adult ic id ing 13
D. Formulations 13
E. Determining Amount of Mixed Chemical Needed 14
F. Computation of Dosage Rates 14
1. For liquid formulations given lbs/gal of
active ingredient 14
2. For liquid formulations given percent of a
active ingredient or specific gravity 15
3. For granules and dusts 15
G. Methods of Varying the Dosage Rate 15
1. Adjusting formulation strength 16
2. Varying speed of travel 16
3. Varying the discharge rate 17
MONTANA DEPARTMENT OF HEALTH AND ENVIRONMENTAL SCIENCES
Environmental Sciences Division
Environmental Services Bureau
Helena, Montana
MONTANA MOSQUITOES, PART II— SURVEY £ GROUND APPLIED CHEMICAL CONTROL
I . Philosophy
It is necessary to understand the life cycle and habits of mosquito species in
order to effectively and efficiently control mosquito populations. Detailed surveys
are essential for the planning, operation and evaluation of control programs. Survey
and evaluation are continuing processes that must accompany control, A basic tenet
for mosquito control is that only by treatment of cause (larval mosquito habitat)
rather than effect (mosquito populations) can a problem become less severe.. For this
reason and since mosquitoes require shallow standing water for development, good
water management practices /source reduction methods are the preferred approaches in
mosquito control.- As a practical matter, the use of chemicals will be required for
the temporary suppression of mosquito populations. Chemical control should assume
less importance as source reduction programs develop. In all cases, the least
environmentally disrupting approach to mosquito control should be used.
Control programs conducted by mosquito control districts organized under state
enabling legislation (R.C=M. 1947, 15-1+201 through 16-4214) have been the most
effective. Districts thus organized have more program continuity, higher levels of
financing and a more reliable source of financial support. These advantages make
environmentally sound source reduction and larviciding programs easier to attain.
The vector control specialist of the Environmental Services Bureau may be contacted
for technical advice, information or assistance in forming mosquito control districts
or for reviewing and consultation upon mosquito control programs and problems. A
pesticide applicators license, obtainable from the Pesticide Control Division of the
State Department of Agriculture, is required by all commercial and government applica-
tors who supervise the application of pesticides.
II . Mosquito Biology - Some Practical Implications
There are 43 species of mosquitoes in Montana distributed among six genera (Aedes,
Anopholes, Culex, Culiseta, Coquilletidia and Psorophora). Vector Control Bulletin #1,
Montana Mosquitoes, Part I— Identification and Biology (obtainable from the Department
of Health) may be consulted for detailed information. The most common mosquitoes are
Aedes species. Most control efforts are directed at this group. The other common
genera are Culex and Culiseta. The mosquito species Culex tarsalis is of public health
importance in Montana because it is the principle vector of human and equine encephali-
tis. Other species have also been found to be naturally infected with the virus
causing this disease.
All mosquito species have four distinct stages in their life cycle: the egg,
the larva (wiggler), the pupa (tumbler) and the adult. The first three stages require
water for development. Eggs of all species (except Aedes and Psoiophora species) and
all larvae and pupae will die if they are out of water. (Pupae can survive for short
periods in a moist environment.) For this reason, source reduction (draining, ditching,
filling, etc.) is effective at controlling mosquitoes. (See Section III, Classifica-
tion of Breeding Places).
-1~
Aedes and Psorophora species normally lay their eggs in the mud along receding
waters. (One rare Aedes species lays its eggs above the water line in tree holes or
containers) Eggs of some Aedes species will hatch if the site is flooded again that
season, others must be subjected to cold before they will hatch. Hence some species
have only one generation each year; others may have several generations. Aedes are
a temporary water mosquitCi implying that they are produced in water which is retained
on the surface for a minimum of about 7 days but which disappears during the course
of the season.. They may also be found in permanent or semi-permanent bodies of water
which have periodic fluctuations in water levels. Water which has little fluctuation
in water level will produce few Aedes „ Eggs of some Aedes species retain the ability
to hatch if flooded even after a period of 5 yeai's on dry land,, Hence two or three
dry years do not solve most mosquito problemso Several years which are successively
drier will result in se'-'eral egg lines below the high water mark. If all egg lines
were then flooded, a much larger than normal hatch could occur, Aedes over-winter in
the egg stage.
Eggs of The Culex and Culiseta species are laid in rafts on the surface of per-
manent or semi -permanent bodies of water. Eggs of Anopholes species are laid singly
on the water surface,, Eggs of these permanent water mosquitoes must have water
continuously ^o remain viable,, Whi.le Coquilletidia over-winter in the larval stage,
the Culex, Cuiiseta, and Anopholes species ovex^-winter in the adult stage in sheltered
sites, Since there is a high mortality of adults of these species during the winter,
populations of these species do not usually build up until later in the season. The
permanent water mosquitoes typically have several generations each year.-
Water temperature is the most critical factor in the hatching of eggs and in
the time required for development « Eggs of the predominant Aedes species may hatch
when the daily a'-rer'age water temperature reaches about 50° but they do not hatch in
large numbers tint II the daily average water temperature approaches 70° F. Besides
water temperature, the i?atft of larval development depends on the species and amount
of nutrien^ ,a»aiIableo Ldrvai and pupal development may be completed in as little as
5 days (moie likely ? or 8 days) in hot weather or development may take 3 weeks when
the water temperature is cooler.
Larvae pass through 4 developmental instars (stages), molting or shedding their
skin at the end of each ir.star in order to grow. Fourth instar larvae become pupae
with the next molt» Re." ognit ion of the instar that larvae are in is of practical
importance. More time is available for an operator to larvicide if earlier instars
are detected Less ir!i.?;ecticide is required to kill 3rd instar larvae than iith instar
la.rvae„ Pupae are mc-ir-e tolerant to attack by .insecticide and control is apt to be
less effect I''? it larvae ,ar'e allowed to pupateo All larvae (except Coquilletidia,
which is fairly rare) w;ist come to the surface to breathe: hence xhe effectiveness
of oils which foul the breathing apparatus and cut off the air supply.
The adult mosquitoes feed mainly at night j being most active at dawn and at
dusk, A few Aedes species will attack during broad daylight (especially if disturbed)
but most prefer shaded situations if they bite at all during daylight hours. Different
mosquito species show different host preferences, Culex tarsalis , the common encepha-
litis mosqui+Oj readily bites man but prefers to feed on birds, Culex territans
feeds exclusively on reptiles and amphib,ians ,„
The normal flight range of most Anopholes, Culex and Culiseta species is usually
considered to be one mile or less. However, studies have shown that Culex tarsalis
commonly fly from 3 to 10 miles, especially when seeking shelter in the fall. Most
Aedes species are strong fliers and range several miles from their breeding places,
_.2"
Individuals have been recaptured over 20 miles from their release site but most range
three miles or less. Mosquitoes will normally fly no further from their breeding
sites than is necessary to feed.
° Classification of Mosquito Breeding Places
Not all water produces mosquitoes. Shallow, standings sometimes stagnant water
which has emergent vegetation (that protects larvae) and bodies of water which have
gradual sloping banks are of primary concern. Large open expanses of water which
are subject to wave action, ponds which have abrupt banks and little emergent vegeta-
tion and running water usually produce few mosquitoes. As indicated earlier, water
with little fluctuation, in levels produces few Aedes species.
Mosquito breeding places may be classed as temporary, permanent or semi-permanent.
Temporary breeding pools remain for a limited period of time follov/ing each flooding.
Permanent water remains throughout the year. Semi-permanent water areas remain
throughout most or all of a mosquito season following an initial flooding.
Mosquito breeding places may also be classified as to their location. They
may be classified as on field (including surface pools, irrigation laterals and
drains) or off field (including road side ditches, or borrow pits, waste land areas,
abandoned canals and laterals, drainage ditches, natural waterways, oxbows, sloughs
and distribution systems). Over 95 percent of the total breeding area was associated
with "on field" mosquito breeding places in one irrigated area studied in Montana.
These accounted for over 70 percent of all mosquito production during the entire
season. Thus in most areas suffering from severe mosquito infestations, more than
90 percent of all mosquito production may be associated with the use of water for
irrigation.. In non- irrigated areas, spring run-off and a rising water table account
for higher percentage of the mosquitoes produced.
IV. Mosquito Surveys
Two types of surveys are widely used: the original basic survey and the opera-
tional survey.
A. Original Basic Survey. The original basic survey determines the species of
mosquitoes, their source, location and seasonal density. Mosquito control maps
are used for orientation and locating larval breeding places and adult sampling
stations o When making the original basic survey, it is advisable to record the type
of breeding place and, if known, the number of expected generations of mosquitoes
(e.g. temporary, on-field (alfalfa), 3 generations). This information is of value for
estimating the expected seasonal breeding acreage that would have to be treated each
year (as opposed to the amount of acreage that can produce mosquitoes) and for
estimating the types of control measures that may be used, the number of personnel
needed, type of equipment and amount and type of insecticide.
B. Operational Surveys. The operational survey is a continuing evaluation of
the mosquito control program and is extremely valuable in daily operations. Through
operational surveys, one refines information on control efficiency, the times that
larvae appear in each source, and the significance of each larval source according
to the production indexes. Such surveys determine the population index (showing
general fluctuations rather than determing the actual numbers of mosquitoes present).
Operational surveys may be larval or adult mosquito surveys.
-3-
lo Larval Surveys = In conducting larval surveys, a dipper approximately
U inches in diameter is scooped fairly through the surface of water near emergent
vegetation. Aedes larvae are collected by a rapid skimming movement of the dipper
with one side depressed below the water surface, ending the stroke just as the
dipper is filled. Where clumps of emergent vegetation are present, it is easiest
to collect Anopholes larvae by pressing the dipper into such clumps with one edge
depressed so that the water flows from the vegetation into the dipper. A quicker
motion is required for collection of Culicine larvae (Aedes, Culex, Culiseta and
Psorophora) than for collections of Anopholes larvae since the Culicine larvae are
more likely to dive below the surface when disturbed by shadows or movement. The
number of dips made and the number of larvae found are recorded in order to calculate
a breeding index. The breeding index may be defined as the number of larvae per
square foot of water surface. Therefore, the number of larvae collected divided by
the number of times that "4 dips are taken equals the breeding index (BI = # larvae *
# dips (h) ' Unless the mosquito production source is very large, a mosquito breeding
index of less than 1 is not normally controlled. One can determine the relative
importance of each breeding site or station by calculating the production index (breed-
ing index X the area = production index of the site or station). Both pre-treatment
and post-treatment larval counts should be made, when possible, in order to determine
control efficiency.
2. Adult Surveys. Adult surveys may be biting collections, resting collections,
or light trap, carbon dioxide or baited trap collections. Adult mosquito surveys
provide inforaation on (1) the species present, (2) the mosquito population density,
(3) the effectiveness of the control efforts throughout the season and (4) a means
of evaluating the effectiveness of specific treatments. Adult light trap collections
depend upon a phototropic response. Mosquito species differ in their response to
light; some being attracted readily, others poorly. After being attracted to the
light; a fan is usually employed to blow the mosquitoes into a bag or killing jar.
Biting collections are carried out by capturing the adult female mosquito with an
aspirator as she attempts to obtain a blood meal from a host. When making population
estimates with the bite count method, a predetermined time period is established.
The count per given period that will be tolerated by residents in an area varies from
region to region and must be determined for each area. Biting and light trap collections
are the most common forms of adult surveys. Resting station collections are made by
aspirating the adults which remain inactive during the day, resting in cool, humid
places. Resting stations may be in such sites as stables, chicken houses, culverts,
and so forth. Egg samples or egg-sod surveys are not typically made in Montana but
have been employed in large districts as a part of pre-larviciding operations,
V. Methods of Control
All methods of mosquito control require surveys to insure success. A number of
general methods are employed. In order of preference, they are good water management,
source reduction, biological control, larviciding, pre-larviciding, and adulticiding.
The one instance in which adulticiding should provide the basis of a control project
is in the event of an outbreak of mosquito-borne diseases , such as St , Louis
encephalitis or Western equine encephalitis.
A. Source Reduction. Source reduction is accomplished by the removal of free,
shallow, standing water contributing to mosquito production or by the elimination of
harborage present within that water. Source reduction or permanent control may
involve diking, ditching, draining, dredging, deepening, filling or water level
management .
B. Pre-larviciding. Pre-larviciding consists of applying approved insecticides
to areas known to produce mosquitoes but which contain no larvae at the time of
application. Granules of either the coated or clay type and containing either 1 or
2 percent concentrate (e.g. Abate, chlorpyrifos or fenthion) may be applied to the
ice of snow melt pools or to low spots that collect the annual run-off and which
are known to produce an early hatch of mosquitoes. Precisely outlining this area
depends upon experience, accurate surveys and records. Areas to be treated by
pre-larviciding should be carefully selected to insure that the insecticide will
not be flushed from the area and contaminate potable water supplies or water contain-
ing valuable resources.
C. Larviciding. It is at the larval stage of development that mosquitoes are
most effectively controlled. More mosquitoes are killed per given quantity of
insecticide by larviciding than adulticiding because mosquito larvae are concentrated
in a restricted location and less toxicant is needed to affect control, (i.e. since
insecticide is applied over given areas at approximately the same dosage whether
adulticiding or larviciding, more insecticide is required after adults disperse).
Larviciding should not be conducted without surveying a site and establishing that
mosquito larvae are present in sufficient numbers to merit control. Larviciding is
conducted by the application of fuel oil, fuel oil plus spreader, highly refined oils,
insecticide granules, emulsifiable concentrates or solutions to a body of water. The
choice of approach and chemical depends upon the registration of the chemical, its
use directions and the environmental conditions present.
Besides being of value in pre-larviciding, granules are an excellent means for
applying insecticide through heavy foilage. They will tumble through the vegetation
to the water surface rather than deposit upon the surface of vegetation as liquid
formulations do. (The use of liquid formulations in heavy cover may result in
ineffective control from the application of less than toxic amounts of insecticide
to both the water and the foliage.)
The use of fuel oil should be restricted to waste land areas not possessing
valuable vegetation. Fuel oil applied at the rate of 15 to 20 gallons per acre may
burn vegetation and leave an unsightly appearance. Fuel oil with a spreading agent
applied at 2 to 3 gallons per acre is slightly less objectionable. The more highly
refined mosquito control oils have not been reported to have this toxic effect.
When applying an insecticide for mosquito control, the applicator must insure
that the insecticide is also registered for application to crops in that area. For
example: a flooded alfalfa field containing mosquito larvae should be treated with
a chemical registered for both mosquito control and for use on alfalfa pests.
D. Adulticiding. Adulticiding is conducted through the use of thermal fogging,
misting or ULV equipment. Adulticiding is the most difficult form of mosquito control
to practice in terms of applying the correct dosage and obtaining the proper cover-
age that is necessary for efficient control. Disadvantages are that there is less
control over exposure of non-target organisms, more insecticide is used per mosquito
killed, the effect is more temporary than it is with other forms of mosquito control
and a repellent effect may occur. Routine adulticiding or adulticiding only on the
basis of telephone complaints can be a useless and expensive procedure. Nonetheless,
adulticiding can *be a valuable supplement to other forms of mosquito control. It
is widely used to combat outbreaks of mosquito-borne disease.
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Mists, fogs, and ULV applications depend upon direct contact of the insecticide
with the adult mosquitOo For this reason, they are most effective while the mosquito
is on the wing in the early morning or early evening hours. Under ideal conditions,
the wind does not exceed five miles per hour, there is a temperature of 55 to 75° F,
and the relative humidity is 50 to 80 percent. ULV application of malathion should
not be made if the temperature exceeds 82° F. Space spraying is conducted as near
as possible at right angles to the wind. Low wind currents are depended upon to
disperse the insecticide over the 300 to 4^00 foot swath width which may result under
favorable conditions with thermal fog or ultra low volume applications.
The movement of the extremely small thermal fog particles is very unpredictable.
These particles are more subject to climatic conditions than are the larger ULV or
mist particles.
ULV adulticiding (the application of H gal. or less of undiluted concentrate .per
acre) results in the distribution of more uniform particle sizes which are of a size
sufficient to kill the adult mosquito. It is the cheapest form of adult mosquito
control (about \ that of thermal fogging) and results in less environmental contamina-
tion (the use of diesel fuel is eliminated and it is only necessary to apply approximately
1/2 to 2/3 the dosage needed for thermal fogging). However, since pure or concentrated
insecticide is dispensed, chemical and equipment use directions must be followed
rigorously and the performance of the machine must be continually assessed to assure
that accidents do not occur. The hazard of spotting of automobile paint increases with
droplet size.
Misting machines disseminate a wide array of different sized particles. This may
result in wastage of some chemical but enables applicators to use the machine during
daylight hours and under more adverse wind and temperature conditions. Misters can
be used for short term residual mosquito control in parks and in bushes and trees in
rural or urban residential areas. Under these conditions the mist is directed at a
lower angle than the customary angle of 45° above the horizontal that is used when
space spraying. If vegetation is tall, the mist should be directed at the upper part
of it. The vehicle speed should be 5 mph or less when treating low sparse vegetation
and 3 mph or less when vegetation is dense. In the latter case or under hot, dry
conditions, the effective swath width may not exceed 100 feet. Under more ideal
conditions, it may be 200 feet. Although one can larvicide with misters, it is usually
best to larvicide with equipment designed for that purpose rather than attempt to
employ adulticiding equipment in this fashion. If equipped with a granule hopper,
however, mist blowers can be used to effectively larvicide with granules as well as
mist for adults.
E. Biological Control. Most forms of biological control remain in the experi-
mental stage,., The use of the mosquitofish Gambusia af finis has been effective in
Montana on a limited basis. Other experimental efforts to use fish for mosquito
control should be attempted whenever possible. The Fish and Game Department should
be notified prior to such attempts. Algae, protozoa (particularly microsporidia) ,
nematodes, fungi (e.g. Cbelomomyces) , irridescent viruses and the crystaloid toxicant
produced by the bacteria Bacillus thuringiensis are examples of experimental control
efforts not yet reaching field use.
VI . Chemicals for Mosquito Control
A variety of insecticides are registered for mosquito control. Since registra-
tions are periodically reviewed and certain restrictions may be imposed, applicators
should consult with the State Department of Agriculture and State Department of Health
and Environmental Sciences prior to using them. Label directions should be followed.
The following table indicates pesticides currently used in mosquito control.
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Pesticides Currently Employed in Mosquito Control'
a,d
Type
Application
Toxicant
Dosage
Remarks
Residual
Spray
malathion
100 - 200 mg
per square ft.
For use as an interior house treatment .
Effective for 3-5 months on wood surfaces,
Continuous
Vapor
Treatment
dichlorvos
1 dispenser per
1,000 cu. ft.
In resin; dispensers hung from ceilings. Gives
2h - months control. Do not use where
infants, ill or aged are confined or in food
preparation or serving areas.
Outdoor,
Ground
Applied,
Space
Spray
chlorpyrifos
( Dursban )
fenthion'^
(Baytex
malathion
naled
pyrethrins
( synergized)
lb /acre
0.0125
0.001-0.1
0.075-0.2
0.02-0.1
0.002-0.0025
Dosage based on estimated 300 foot swath width.
Mists and fogs are applied from dusk to dawn.
Mists are usually dispersed at 7 to 25 gal/mi.
and at a speed of 5 mph. Fogs are applied at
a rate of 40 gal/hr @ 5 mph (occasionally at
higher rates and greater speeds). Finished
sprays have 0.5-8 oz/gal actual insecticide
in oil or (with non thermal foggers) water.
In ULV ground applications'^ technical grade
malathion is used at 1-1.5 fl. oz/min at
5 mph or 2-3 fl. oz/min @ 10 mph; some ULV
pyrethrins at 2-2.25 fl. oz/min @ 5 mph or
4-4.5 fl. oz/min @ 10 mph; chlorpyrifos
fog concentrate at 2/3 - 1 1/3 fl. oz/min @
10 mph.
Larvicide
abate
chlorpyrifos^ '®
fenthion^'®>^
malathion
pyrethrin tossit
fuel oil
Flit MLO
0.05-0.1
0.0125-0,05
0.05-0.1
0.2-0.5
1/100 sq. ft.
2 to 2Q gal/A
1 to 5 gal/A...
Apply by ground or air at up to 10 quarts
finished spray /acre depending on concentration
used. Use oil or water emulsion formulations
in areas with minimum vegetative cover; granu-
lar formulations where vegetative cover is
heavy. Fenthion provides longer residual in
contaminated water at 5 times the dosage listed
Chlorpyrifos has long residual toxicity in water
with a high organic content (e.g. 12 weeks
in septic tanks) while abate is fairly labile
in polluted water.. Apply fuel oil at 15-20
gal/A in open water courses or with 0.5%
spreading agent (e.g. T-Det-MC, Dal-Com W)
apply at 2-3 gal/A. . , . . ; , . .
a Modified from "Public Health Pesticides" Technical Development Laboratories, Center fpr,.,j
Disease Control, U.S. Department Health, Education and Welfare (1973)
b Other compounds such as Lethane 384 and ronnel may have uses in.-. §s^i^ca^eg(:^pi§-ff^i^iy.f§^^.follov
label directions. a/o bstB woit vr'ivs'i's
c For use by trained mosquito control personnel only. , ,
d Adhere STRICTLY to ALL label specifications and directions,
e Do not apply to waters with valuable fish.
f Label requires a 3 week interval between applications except for adulticiding.
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VII. Equipment for Ground Application
A. Introduction
-Information on the types of equipment available for larviciding and adulticiding
is available in the American Mosquito Control Association Bulletin #2, Ground Equipment
and Insecticides for Mosquito Control, 101 pp. Only brief description of the more
conronly used types of equipment will be included herein. Bulletins such as A Guide
for the Safe Use of Pesticides and Respiratory Protection Against Pesticides are avail-
able from the Environmental Services Bureau of the State Department of Health and
Environmental Sciences; " . .. -• "
-.-cticiBy Types of Larviciding Equipment
In nearly all public health insect control projects, the compressed air sprayer,
is standard equipment. These sprayers are small 1 to 4 (usually 2 or 3) gallon cylindrical
tanks equipped with an air pump, hose and spray gun (wand and nozzle). After filling the
tank about 3/H full, air is compressed into the remaining space for use in forcing the
liquid through the nozzle. Desirable features include stainless steel construction, a
pressure gauge, a large filler opening, synthetic rubber gaskets and a pressure release
valve. (If no pressure release valve is present, turn the sprayer over and release
pressure through the nozzle before opening). A flat fan nozzle is usually used for
applying residual sprays to walls, while a hollow cone nozzle is ordinarily used for
applying insecticide to vegetation and mosquito breeding sites. A stock of spare parts
should be kept on hand.
The hydraulic power sprayers, with capacities of from 50 to 300 gallons (usually
50 - 150 gallons) can pump a maximum of from 1 to 10 gallons of spray per minute. Most
which are used for mosquito control are mounted on skids or on the beds of 3/U ton
trucks. This sprayer consists of a tank (usually with an agitator), a pump, a power
source (usually a gasoline engine), a pressure regulator and relief valve and one or
more hoses and hand guns (and/or occasionally a boom). Hoses are usually 50 to 200
feet long. For longer lengths of hose it is advisable to use one with a H inch I.D.
since there is less frictional loss of pressxire than with \i inch or 3/8 inch hose.
Two types of hand operated granule applicators are commonly used in larviciding.
One is the rotary slinger plate type of grass seeder. When used in tall grass and
cattails, the moving parts can get clogged unless a protective sheet of metal is mounted
below and ahead of them to divert vegetation. The most common type of hand operated
granulator in Montana is the "sling" seeder (horn seeder). This is a tear-drop shaped
granule bag with a tapered metal tube. An applicator feeds granules into the 3 foot
long tube and dispenses them through the adjustable gate by whipping the tube back and
forth.
Power granulators are of several types. One kind commonly used is a power driven
rotary plate type of seeder. Granules are fed from a hopper to a rotating plate by
gravity flow and slung out in a fairly uniform swath by centrifugal force. The other
type of power granulator commonly used is a modified mist blower. Granules are dis-
charged into the air exhaust duct and moving air transports the granules to the
target. Back-pack dusters can be modified in a similar manner.
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C. Types of Adult iciding Equipment
Equipment most commonly used for adult mosquito control is of three types:
Ultra low volume (ULV, misting and thermal fogging. (See Section V D, Adulticiding,
for a discussion of principles governing adulticiding with each type of equipment
and factors influencing their effectiveness and versatility.
Thermal fog generators break insecticide into aerosol sized particles by means
of blasts of hot exhaust gases. The following recommendations upon equipment for
fogging were developed by the Entomological Research Center of the Florida State
Board of Health. Mention of any brand does not constitute endorsement by the
Montana Department of Health and Environmental Sciences.
Equipment for Fogging:
Dyna Fog Sr.
1. Machine operation - Operated as recommended by the manufacturer
with respect to engine speed and formulation pressure, i.e., 6-12 p.s.i.
2, Wind and Temperature''' - Operate when air temperatures are 65
or above and in winds up to, but not greater than 3 mph.
Leco 80 & 120 ^ «
1. Machine Operation - Burner temperature: 850 - 900 F; engine
r.p.m. : 2000; formulation pressure; whatever is required to produce 40 gallons
per hour. When applying 80 gph (model 120) the burner temperature should be 1000° F.
2. Wind and Temperature - This machine can be effgctive when air
temperatures are 60*^ - but best results were obtained at 65 and above. Present
data indicate effective results in winds up to 9 mph.
Leco W
1. Machine Operation - Burner temperature: 1200°F; engine r.p.m.:
3400; formulation pressure: whatever is required to produce 40 gallons per hour
(usually 6 to 8 p.s.i.)
2. Wind and Temperature - Best results were obtained when atmos-
pheric temperatures were above SU*^ F and with winds up to 8 mph.
See Fog (Tifa SF-50)
1. Machine Operation - As recommended by manufacturer: Gas
pressure: 38 p.s.i.; steam pressure: 25 p.s.i.; water pressure 45 p.s.i.
2. Wind and Temperature - Operate when air temperatures are 70° and
above; present data indicate that this machine is effective in winds up to 5 mph.
Tifa 40-E
1. Machine Operation - Burner temperature; 1000°; formulations
pressure: 25 p.s.i.; engine r.p.m. 2200.
2. Wind and Temperature - This machine is effective at air temperatures
of 60° - 64° but best results are at 650 and above. Data indicate that the TIFA
can be used effectively in winds at least to 9 mph, but better average kills were
obtained at the lower wind velocities, as with all other machines tested.
NOTE : Recommendations with respect to wind and temperature conditions are
based only upon test results using malathion or malathion-Lethane . Similar data
for other insecticides are not presently available for most of the machines listed.
-9-
Mist blowers are essentially large capacity power driven air turbines which
drive air at high velocity through a tube. Several models discharge 5000 cubic feet
of air per minute at 150 mph. Sprays are pumped at low pressure and volume into a
discharge tube where it is atomized by a nozzle. In addition to granule hopper
attachment modifications already discussed, "mini-spin" nozzles have been inserted
into insecticide lines to disperse insecticide concentrates.
Ultra low volume equipment for adulticiding is of relatively recent origin.
Special nozzles or attachments break insecticide concentrates up into relatively
uniform particles measured in terms of microns. Advantages have already been
discussed (Section V, D).
D= Equipment Selection
The equipment selected must fit the various local needs in an area. Careful
survey and analysis of the extent and types of breeding areas will provide the basis
for equipment selection,, If an area has extensive ditches, ponds, small swamps and
temporary pools which are accessible by road, power driven sprayers and granulators
mounted on trucks or jeeps are suitable. If these areas are inaccessible,
compressed air sprayers and hand held granulators are used. Large swamps and
irrigated areas are treated with power equipment mounted on trucks; if inaccessible
they are treated with power equipment mounted on all-terrain vehicles. Where there
are extensive larval populations distributed over extensive inaccessible areas,
contracted spraying by air craft may be the most effective means of control.
Other factors that are important considerations are budgetary limitations,
labor costs and equipment versatility and serviceability. Equipment that can be
effectively operated by one man will pay for itself in one or two seasons if compared
to the labor cost of crew served equipment. A similar cost -benefit analysis can be
applied to more expensive equipment that can be operated in several ways by a crew
of two but which has the capability of covering the same area that 3 or ^ crews
cover with more inexpensive equipment. An appropriate example may be cited for
regions which have extensive sloughs (which are relatively inaccessible) and
sluggish overgrown ditches. If an all terrain vehicle (ATV) were outfitted with a
hydraulic sprayer and power granulator, the area becomes accessible and can be treated
much more rapidly. While being trailered, one could also use it to treat roadside
borrow area,
VIII„ Chemical Application
A. Equipment Calibration
Prior to any attempt to control mosquitoes an applicator must familiarize
himself with the equipment and calibrate it . To "calibrate" is to determine the
quantity of chemical that the equipment dispenses each second, minute or hour. The
quantity dispensed will vary with various equipment settings (such as RPM or pressure)
with various attachments (different disks and nozzles) and, in some cases, with the
temperature and viscosity of the chemical. Equipment manuals which accompany the
sprayers or granulators normally contain sufficient instruction for calibration
and operation and are, hence, only briefly discussed.
In calibrating compressed air or hydraulic sprayers, spray into a container
for an established period of time and measure the amount of material dispensed in
order to determine the discharge rate/second or minute. (See also Section VIII F(3),
Varying the Discharge Rate). Since the spray pattern and discharge rate vary with
the pressure being used, it is advisable to calibrate and use the compressed air
sprayer over a 30 to 50 psi pressure range. In this way, the average pressure will
be suitable for producing the delivery rate and spray characteristics for which many
nozzles are designed.
-10-
In calibrating mist blowers or thermal foggers, the tank is filled to a mark
with water or fuel oil respectively. The equipment is operated for a period of time
and the quantity of material necessary to replace that dispensed is measured. The
discharge rate is usually measured in terms of gallons per hour. (See also Section
VIII C (2), Computation of acreage for adulticiding) .
Power granulators are usually calibrated in terms of pounds of granules
dispensed per minute, hour of mile of travel at a set speed. The rate of discharge
selected will depend on the swath width that is obtained with the type of granule
selected and the recommended dosage rate of the chemical selected. (Smaller heavier
granules will give a wider swath width and the discharge rate needed will be greater).
Steps to be followed are (1) measure the swath width; (2) calculate the acreage
covered per mile of travel (swath width (in feet) X 5280 t 4-3,550); (3) multiply by
lbs of granules desired per acre (to get lbs/mile of travel); (4) multiply by the
desired rate of vehicle speed (to get lbs per hour) and (5) by trial and error
adjust the flow rate of granules to meet the desired pounds/hour. (See Section
VIII E(3), Dosage rates for granules and dusts for an example.)
In the hand operated "sling" or horn seeders, an adjustable gate regulates
the gravity flow of granules. The amount that the gate will be opened will depend
on swath width and rate of travel. These variables will be balanced against each
other as indicated in Section VIII B, Standardizing Application Rates.
Operation manuals which accompany ultra low volume (ULV) equipment should be
consulted for calibration. Flow rates are again determined by swath width and the
recommended dosage rates. Flow rates vary with the temperature and viscosity of
the insecticide and calibrations should extend over the temperature range. The
calibration of ULV equipment also includes rigorous regulation of droplet size
and coverage.
B. Standardizing Application Rates
Applying the correct volume of finished spray or weight of granules is
largely a matter of practice. Two approaches are used. One approach is based
strictly on the time required to apply the correct quantity to a given area. One
can develop a table that will show the number of seconds required to dispense required
volumes or weights over a series of areas. The other approach is based on the develop-
ment of a particular constant rate of movement by the applicator, nozzle or equipment.
The rate of movement or the time that chemical is actually being dispensed is depen-
dent upon the discharge rate of the equipment (in turn determined by nozzle type,
pressure, etc.)
In developing the appropriate rate of movement, measure and stake out a test
area and use one of the following approaches (1) fill the equipment to a certain
mark, (2) spray the test area uniformly, (3) measure the amount of material required
to fill the equipment to the original level, (U) compare with the amount of material
which should have been used and (5) adjust the rate of application accordingly.
Or, (1) place only the volume or weight of material required for treatment in the
equipment, (2) spray or granulate the test area and (3) try to adjust the rate of
travel/application so that the chemical runs out just as the area has been completely
and uniformly covered (i.e. just as the applicator reaches the stake at the other end
of a linear area or returns to the starting stake in a more circular or rectangular
area) .
C. Computation of Acreage
Since insecticide labels usually express the limits for dosage rates as pounds
or fluid ounces of active ingredient per acre, it is necessary to calculate the
acreage of each site to be treated. Methods used to compute acreage are given below.
1. Computation of acreage for larviciding
In smaller areas, the acreage may be estimated by pacing off the length
and width of the area to be treated. If the area is relatively square or rectangular,
a multiplication of length x width will give the area in square yards. (Although
the average "normal" step is about 30 inches, one can develop a step of about 36
inches with little practice). If the area is more triangular in shape than
rectangular, the length x width value should be divided by 2. It is then necessary
to convert square yard measurements to acres. This may be done by dividing the
number of square yards by 4840 (1 acre = 4840 square yards = 43,550 square feet).
It is more convenient, less time consuming and there is less chance for mathematical
error if a table such as below is consulted.
Square yards
Acres
t^ULlO^ C VOX Uk9
Acres
650
.1343
50
.0103
700
.1446
100
.0206
750
.1570
150
.0309
800
.1553
200
.0413
850
.1756
250
.0537
900
.1858
300
.0619
950
.1952
350
.0723
1000
.2055
400
.0826
2000
.4132
450
.0929
3000
.6198'
500
.1033
4000
.8264
550
.1157
5000
1.0330
600
.1239
Additional columns can be added to the table to further reduce the chances
for error and save time. One can e.g. calculate the gallons or pounds of actual
and mixed chemical required for each area involved and/or the number of seconds
the trigger valve would have to be open to deliver the required amount of chemical.
-12-
It is suggested that conversion tables be maintained in the spray vehicles.
It is further suggested that the acreage at each mosquito source be recorded. Although
the acreage at each site may vary from season to season and time to time, some ponds
have rather stable boundaries and some areas are flooded to about the same extent
with each irrigation.
For larger areas or for long ditches or borrow pits, the acreage may be
more rapidly estimated by the simple field calculation noted in formula 1 below.
This is based upon a figure of 8 feet swath width for one mile of travel.
< -1 mile (5,280 ft.) >
Approximately 1 acre (i+2,2'+0 sq. ft.)
One square mile = 640 acres.
Formula 1 Acreage Treated = mileage covered x swath width
— g
Example 1. Calculate the acreage treated by larviciding an area \ mile long and
12 feet wide.
Acreage Treated = ^ = .75 acres
8
2. Computation of acreage for adult iciding
In space treatments (misting and fogging) the acreage treated is a variable
figure dependent upon the swath width taken. The first step then is to determine
the swath width. This may be done by setting out cages of mosquitoes and adulticiding;
using visual observations of a fog; or setting out strips of paper and spraying a dye
solution (minus insecticide). While this may be practical in calibrating a machine,
an operator would not find it practical to conduct such tests routinely. As a practical
consideration, the swath widths in urban areas are usually taken as the length or
width of the city block. The approximate acreage treated by space application of
insecticides may be determined by Formula 1 above as e.g.
Example 2. Calculate the acreage treated by a mister traveling 4 miles where the
swath width is 200 feet.
Acreage Treated ■- ^ ^ - 100 acres
8
D . Formulat ions
Insecticides for mosquito control are sold in Montana in a number of formulations
(forms): emulsifiable concentrates, non-emulsif iable concentrates, granules, tossits,
(encapsulated insecticides) or as finished sprays (ready to use), Emulsifiable con-
centrates are normally mixed with water (or occasionally with fuel oil) prior to use
while the non-emulsif iable concentrates are normally diluted with fuel oil to make a
finished spray. Granules, tossits and finished sprays (such as 95% ULV malathion)
are ready to use as received.
-13-
8 ft.
Pesticide container labels give directions for dilution prior to use. The level
of dilution which you use should fall within the limits specified on the label. However
other factors need consideration: (1) The more concentrated the finished spray is, the
more closely the application rate must be controlled, i.e. slightly over or under
spraying of a more dilute solution has less effect on the amount of active ingredient
applied than slightly over or under spraying a more concentrated solution. (2) The
more carrier (oil or water) used, the less finished spray that can be held in the
spray tank. (3) The more carrier used, the higher the carrier cost.
The actual dilution used will be based upon the equipment characteristics (dis-
charge rate) and rate of application. If the equipment puts out a large volume in a
short period of time, the finished spray may be more dilute or the rate of application
very fast.
E. Determining Amount of Mixed Chemical Needed.
After determining the size of the area needing treatment (in acres), one can
determine the amount of finished spray needed. This will depend on: (1) the allowable
dosage rate (pounds or fluid ounces of active ingredient per acre) specified on the
insecticide label and (2) the degree to which the insecticide concentrate has been
diluted. The following formula may be used to determine the quantity of insecticide
needed.
Formula 2. Gallons finished _ Dosage rate x acreage treated
' spray needed Insecticide (lbs. or fl. oz.)/gal. finished spray
Example 3. A dosage rate of 0.06 lbs. of fenthion/acre is desired on U acres of
standing water in a field. The finished spray contains 0.08 lbs. of active ingredient
per gallon. (To obtain this, one could mix e.g. 2 gallons of Baytex 4 EC lb/gal)
with 98 gallons of water). How much finished spray should be used? By Formula 2:
Gallons needed = ^ ^ = 3 gallons
0.08
Formulas 3 and 4 below may be revised to determine the gallons of liquid
insecticide needed (given percent concentration or specific gravity) or pounds of
insecticide granules needed respectively.
F. Computation of Dosage Rates.
After determining the acreage treated and amount of insecticide used, one can
establish that the correct dosage rate was used. Remember, the rates applied must
fall within the limits specified on the insecticide label.
1. Dosage rates for liquid formulations given pounds active ingredient/
gallon in the finished spray may be calculated by the following revision of Formula 2:
Dosage Rate = Gallon applied x insecticide /gallon (lbs)
Acreage treated
■14-
Example 4. An area 2 miles long and 200 feet in depth was treated with 40 gallons of
fenthion emulsion containing 0.08 lbs of active ingredient /gallon. Calculate the
dosage rate.
Using Formula 1: Acreage treated = ^ = acres
8
Using Formula 2: Dosage rate = ^ "-"^ = 0.064 lbs. /acre
S 0
2. Dosage rates for liquid formulations (given various percentages).
The strengths of liquid concentrates are often given as percentage of active
ingredient rather than in pounds /gallon. Occasionally the specific gravity of the
concentrate is given. The following formula may be used.
Formula 3.
a. Dosage rate = gallons applied x wt./gal of formulation x % cone.
acreage treated
or (where given specific gravity)
b. Dosage rate = gallons applied x sp. gr. x 8.345 x % cone.
acreage treated
3. Dosage rates for granules and dusts may be calculated by:
Formula 4. Dosage rate = Pounds applied x % of concentration
acreage treated
Example 5. A 2% fenthion granular formulation is used for larviciding a swampy waste-
land area which is 1 mile long. The swath width is 16 feet. The rate of application i:
20 lbs/mile of travel (100 lbs/hour at 5 mph). Calculate the dosage rate.
Using Formula 1: Acreage treated = ^ = 2 acres
8
Using Formula 4: Dosage Rate = 20 x^0.02 = .2 lbs/acre
G. Methods of varying the Dosage Rate
There are generally three methods used to vary the dosage rate: (1) varying
the formulation strength; (2) varying speed of travel; and (3) varying the discharge
rate. Most often in space treatment, the simplest and most practical method is to use
a more or a less concentrated formulation. In this way, it is possible to maintain
the optimum speed of travel (5 mph) and the standard discharge rate giving the best
droplet size and coverage. In larviciding, it may be practical to vary the formula-
tion strength for different larger jobs where the terrain may dictate different
average speeds. There may be several reasons for wishing to vary the speed of travel.
Heavy vegetation at a particular larval station may require higher dosage rate; the
physical situation may require that a different swath width be taken, etc. In some
situations, it may be more practical to vary the discharge rate. The terrain may be
such that the speed of travel has to be temporarily reduced or such that the speed
of travel could be more rapid than normal.
-15-
1, Adjusting formulation strength
If one wished to maintain a standard discharge rate (e.g. 100 gal/hr) and
standard speed (e.g. 5 mph) over the same swath width, one could vary the dosage rate
bv varvtnj the diiuUon of insecticide concentrate. One can determine the formula-
Son sSengS needed to obtain a given dosage rate by the following rearrangement of
formula 2:
Insecticide (lbs) _ (Dosage rate) (acres treated)
gal. finished spray ~ gallons applied
Example 6. You wish to reduce the dosage rate in example 4 from 0.064 lbs/acre to
0.05 lbs/acre and still maintain a discharge rate of 20 gal/mile where due to a
200 foot swath width, 25 acres were covered each mile. Compute the gallons of 4 lb /gal
concentrate needed t; make 100 gallons of finished spray. Usxng the above formula:
Insecticide (lbs) ^ 0.05 x 25 ^ o.0625 lb/gal = 6.25 lb/100 gal.
gal. finished spray 20
Thus one would have to use 1.55 gallons of concentrate containing 4 lbs of active in-
^liZl ITr lallon to get the 6^25 lbs per 100 gallons desired in the finxshed formula-
tion. (This would amount to using 25 pints of concentrate and diluting it to 100
gallons-determined as: 1.56 gal x 16 pints/gal = 24.96 pints). NOTE: For a
different dilution swath width, discharge rate, vehicle speed or dosage rate, a
different dilution would be appropriate.
2. Varying the speed of travel
Doubling the rate of travel doubles the acreage treated and halves the dosage
rate if other variables are maintained. Conversely any decrease in speed would result
in a proportionate increase in the dosage rate. From the formulation strength, dis-
charge rate and desired dosage rate, one can compute the needed vehicle speed for any
given swath width. By rearranging formula 2, one can obtain the gallons of finished
spray needed per acre. By dividing the discharge rate (gal/hr) by gallons per acre
applied, one obtains the number of acres which need to be covered per hour. One can
then consult the coverage rate table below to determine the appropriate rate of speed
(modified from the Depts. of Air Force, Army and Navy Insect and Rodent Control Manual
and the Cascade County Mosquito Abatement District manual).
Example 7. A mister delivers 100 gal/hr of a formulation containing 0.0625 lb/gal.
The operator desires a dosage rate of 0.05 lbs/acre over a 200 ft swath width.
Calculate the appropriate vehicle speed. By substituting in a modification of
Formula 2, one obtains:
gallons _ dosage rate _ 0-05 _ Q^g gal/acres as the needed application rate for
acre ~ insecticide /gal 0.0525
the finished spray.
The acreage treated/hr at a discharge rate of 100 gal/hr = Q^f^g^^^, = ^25 acres/hr.
From the following table, one can observe that, where the swath width is 200 feet, the
appropriate speed is about 5 mph.
-16-
Rate of Coverage for G
iven Rates of Travel and Given Swath Widths
Rate of
Yards
Acreage covered/hr. for given swath widths
Travel
( mph )
Traveled
Per Hour
12.5 ft.
15 ft.
25 ft.
50 ft.
100 ft.
200 ft.
300 ft.
0.5
880
0.75
0.91
1.5
3
6
12
18
1.0
1,760
1.5
1.8
3.0
6
12
24
36
1.5
2,540
2.25
2.7
4.5
9
18
36
54
2.0
3,520
3.0
3. 6
5.0
12
24
48
72
3.0
5,280
4,5
5.4
9.0
18
36
72
108
1 i+.O
7,040
6.0
7.2
12.0
24
48
96
144
0 • u
ft flnn
7.5
9.05
15.0
30
60
121
181
5.0
10,560
9.0
10.8
18.0
36
72
144
216
10.0
17,600
15.0
18.1
30.0
60
121
242
362
In the absence of a table or with a different swath width, one could estimate
the appropriate speed of travel by the folxowing modification of Formula 1:
Speed (mph)
- Acres treated/hr. x 8 ft.
In example 7 : Speed =
swath width (ft. )
- 125 X 8
200
5 mph
If one knows the dosage rate resulting from a particular speed of travel, he
can apply any other dosage rate over the same area by changing the speed of travel. Since
speed is inversely proportional to the dosage rate, one can set up a simple ratio:
Speedj^ X Dosage Rate-;^ = Speed2 x Dosage Rate2
Example 8. A 57% Malathion EC (5 lb/gal) is to be misted over an irrigated alfalfa field
adjacent to town because of residual larval pools and extensive cover being afforded to
adults. The formulation strength and discharge rate were such that a dosage rate of 0.2
lbs/acre was delivered in town at 10 mph. The operator wished to apply 0.5 lbs/acre
over the field. Compute the appropriate speed.
0.2 X 10 = 0.5 X speedj
speed2 = ^ ^'^ = 4 mph
• 5
3. Varying the discharge rate
This method of varying the dosage rate is most often used while larviciding.
In discharging liquid formulations, the dosage rate may be varied by changing the spray-
ing pressure or nozzle tips or disks. Increasing the spraying pressure has the dis-
advantage of decreasing the droplet size and consequently increasing the potential drift
-17-
of the insecticide. A change in pressure does not result in a proportionate change
the discharge rate. (The table below illustrates this). Larger changes in the dis-
charge rate are more effectively brought about by changing the nozzle tips. The
following table (taken from the Cascade County Mosquito Abatement District Manual)
illustrates the discharge rate that various nozzle sizes emit at various pressures.
Data for Trigger-Valve Hand Guns
Rate (gal/min)
200 psi 300 psi
1+00 psi
500 psi
D-4
1.2
1.5
1.6
1.9
D-5
1.8
2.2
2.6
2.8
D-6
2.5
3.0
3.4
3.8
D-7
3.3
H.O
4.4
4.9
D-8
4.3
5.2
5.0
6.6
-18-
Selected References
Mosquitoes of Public Health Importance and Their Control (Revised 1971), PHS,
U.S. Dept. HEW
Insecticidal Equipment for the Control of Insects of Public Health Importance (1959),
CDC, PHS, U.S. Dept. HEW
Insecticides for the Control of Insects of Public Health Importance (1962), CDC,
PHS, U.S. Dept. HEW
"Public Health Pesticides" Pest Control, (April 1973), Technical Development
Laboratories, CDC, PHS, U.S. Dept. HEW
Ground Equipment and Insecticides for Mosquito Control (1968) American Mosquito
Control Association, Bulletin No. 2, Revised
Insect and Rodent Control (1956), U.S. Dept. Army, TM 5-632
-19-
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