Uses of various DDT formulations for the control of insects affecting animals

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Title:
Uses of various DDT formulations for the control of insects affecting animals
Physical Description:
9 p. : ; 27 cm.
Language:
English
Creator:
United States -- Bureau of Entomology and Plant Quarantine
Publisher:
Bureau of Entomology and Plant Quarantine
Place of Publication:
Washington
Publication Date:

Subjects

Subjects / Keywords:
DDT (Insecticide)   ( lcsh )
Insect pests -- Control   ( lcsh )
Genre:
federal government publication   ( marcgt )
non-fiction   ( marcgt )

Notes

General Note:
Caption title.
General Note:
"E-714 ; March 1947."
General Note:
Typescript.
Statement of Responsibility:
Division of Insects Affecting Man and Animals.

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 030292650
oclc - 780068557
System ID:
AA00025139:00001

Full Text


IMarch 1947


United States Department of Agriculture
Agricultural Research Administration
Bureau of Entomology and Plant Quarantine



USES OF VARIOUS DDT FORMULATIONS FOR THE CONTROL OF
INSECTS AFFECTING ANIMALS

Division of Insects Affecting Man and Animals


Five types of DDT formulations are employed in the control of
animal pests---dusts, wettable powders, emulsions, oil solutions,
and aerosols._/ In weighing the relative merits of each of these
types and the plaae each may have in this field, it is first of all
necessary to consider such important factors as effectiveness,
toxicity to animals, cost of treatment, and ease of application.
Such factors must be considered in relation to the several kinds
of parasites to be controlled and to the different hosts on which
the treatment is applied. Furthermore, the conditions under which
these materials will be employed vary greatly in different sections
of the country and at different seasons of the year. To complicate
matters even more the five types of preparations differ in compo-
sition, physical properties, and type of equipment used for their
application.

In view of the above, it is understandable that confusion and
uncertainty exist in the minds of research workers, extension
personnel, manufacturers, distributors, and consumers regarding
the type of DDT material that should be employed for the control
of various animal parasites. This paper summarizes the observa-
tions and experiences of the Bureau of Entomology and Plant Quaran-
tine with the different types of formulations. It is recognized,
however, that the place each of these types has in the field of
insect control cannot be clearly defined at present, and that
further research and practical experience may lead to information
that will require modification of the opinions and suggestions
that are offered.

Detailed directions for use are not given. The purpose of
the paper is to explain the characteristics of the various types
of DDT formulations now being marketed, and to discuss briefly
some of the advantages and disadvantages of each.



]/ Technical DDT having a setting point of 89C. is generally
used for all formulations, except for certain types of aerosol
preparations. For liquefied-gas aerosols a product having a melting
point not less than 1030C. is used.





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Caution.--The toxicity of DDT is too low for it to be regarded
as an acute or caustic poison, and a 10-percent DDT dust has been
used extensively in the control of body lice on man without any ill
effect. Nevertheless, it should be handled as a poison. Food and
utensils should not be contaminated by it, and the hands should be
washed thoroughly after it has been handled. Oil solutions can be
absorbed through the skin; therefore extended exposure of the skin
to such solutions should be avoided, as should also unnecessary
exposure to aerosols. When DDT insecticides are applied in barns
and similar structures, care should be taken to avoid deposits on
food that is to be fed to animals, especially those producing milk.

Dusts

Dusts containing DDT may be formulated with various kinds of
materials. The type of material, the size of the particles, and
other physical characteristics have a bearing on the performance
and possibly on the effectiveness of the product. Most of the
experimental work has been done with mixtures containing pyro-
phyllite or nonfibrous talc. Light, fluffy materials, or those
which are liable to pack in the duster, may not perform satisfac-
torily or be fully effective. DDT dusts are employed less exten-
sively than sprays against insects affecting animals. The dusts
are recommended, however, in concentrations up to 10 percent for
use on animals (except cats) infested with certain lice and fleas.

Dusts are considered especially desirable for louse control
on cattle and hogs in cold climates, where dips or sprays might
prove harmful to the animals and where satisfactory control can
be obtained even though two treatments may be required. However,
with the equipment that is available at present, dusts are gener-
ally less effective than sprays, because it is more difficult to
obtain thorough and equal distributions of the insecticide on the
host with the dust. Where dusts can be employed effectively,
their use is encouraged, because of ease of application and safety
to animals. However, excessive inhalation of dusts by the opera-
tors and animals being treated should be avoided as much as possible

Wettable Powders

Wettable powders consist of finely ground DDT plus an inert
carrier, or diluent, such as pyrophyllite or talc, to which a
wetting agent has been added. When mixed with water the prepara-
tion is used as a spray which contains the powder suspended in
the water. The properties and performance of such a spray will
depend on the characteristics of the diluent, the method of mix-
inf7 the diluent with the DDT, the kind of wetting agent, and the
type of water used. The ingredients may differ in various






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commercial products; therefore, it may be desirable to observe
and appraise the settling and wetting properties of a material
before using it extensively.

Certain types of products settle out of suspension more
rapidly than others and may clog spray nozzles. Pyrophyllite,
nonfibrous talc, and certain types of clays have been found best
suited as the base for wettable powders. The various types of
powders do not behave the same in all kinds of water. The wetting
agent plays an important part in keeping the powder in suspension,
and its performance may be affected by the characteristics of the
diluent or by the type of water used, especially if the water is
extremely hard or highly alkaline.

To insure equal distribution and uniform dosage of the
insecticide, it is necessary to see that the solid material does
not settle out while the spray is being applied. This requires
agitation in the spray tank or dipping vat. When the suspended
material has a tendency to cake, reagitation is of particular
importance in dips.

Notwithstanding the known and possible adverse characteris-
tics of some of the wettable powder preparations, there are ex-
cellent products of this kind on the market. As.will be brought
out later, a wettable powder is considered the preferred type of
DDT preparation for use on a number of animals.

Emulsions

DDT emulsion concentrates contain DDT, an organic solvent,
and a water-miscible emulsifier. The concentrate is diluted with
water to obtain the desired strength of DDT for application as a
residual-type surface spray or for use on animals as a spray or
dip. In emulsions the DDT is in the form of a dispersed solution,
as contrasted with wettable-powder sprays, in which the particles
are suspended in water. here, as in the case of wettable oowders,
the diluted spray or dip is largely composed of water.

Various solvents and emulsifying agents are employed in the
preparation of DDT emulsions. Some solvents may injure washers
and similar fittings used in sprayers. Certain solvents may also
constitute a fire hazard. Little is known regarding the toxicity
to animals of many of the solvents and emulsifying agents, wken
they are employed alone or in combination with each other or with
DDT. Many solvents that rmay be used in making emulsions are of
such a nature that they should not be applied directly to animals.
In general, the use of high-boiling aromatic solvents should be
avoided. Only a few specific materials have been tested












sufficiently to demonstrate that they can be used safely on ani-
mals, and then directions for their use must be carefully observed.

Furthermore, the stability of the emulsion may vary. Certain
materials that emulsify readily with ordinary water may not emulsi-
fy with hard or highly alkaline waters. Emulsions of this kind
may "break" quickly in such waters, so that the emulsion concen-
trate will either rise to the surface or sink to the bottom, depend-
ing on its specific gravity. 'When unstable emulsions are a:.:lied
to animals as sprays, certain of the animals nay be subjected to
highly concentrated solutions, others to correspondingly low con-
centrations. Animals treated with an emulsion in which the con-
centrate has risen to the surface upon br:i. r. ; y be exposed to
high concentrations, especially if th-- are dipped in it. Such
hazards are largely avoided in dips whfen the oil phase settles to
the bottom. The solvents used in li-.ter-than-water concentrates
may evaporate, and thus a 1'-.ge proportion of the DDT precipitates
and sinks to the bottom of the vat. The heavier-than-water and
stable types of emulsions are therefore also advantageous Irom this
standpoint. However, the heavier-than-water types might be the
more hazardous when employ; as sprays, since the liquid is fed
from near the bottom of the spray tank, except when atomizing types
of sprayers are used

The total amount of spray applied to an enir.al should be
considered. Too much emphasis has been given to concentrations of
DDT in the s: y without due consideration to he amount of liquid
and the actual amount of DDT applied.

This very brief review of the characteristics of DDT emulsions
as a class should show the user, retailer, and manufacturer that
difficulties may be encountered in connection with their unconsidered
and wide-scale use on animals. Cases of injury to livestock through
the use of emulsions attributable to one or more of the factors
mentioned have been reported. On the other hand, no reports of
injury from the use of DDI wettable powders have come to our atten-
tion. For this reason the Bureau of Entomolcy and Plant .-iiarantine
considers that, in the interest of .',.ety, DDT wettable po'.'.ders are
in general the preferred treatment for pest control on livestock,
except in cases where emulsions are distinctly more effective or
otherwise distinctly advantageous for the control of the parasite.

In closely supervised large-scale tests f-ecially prepared DDT
emulsion concentrates were applied to livestock for the control of
external parasites without harm to the animals. Light aromatic
solvents, such as xylene or toluene, were used with Triton X-100
(an aralkyl polyether alcohol) as the emulsifier in tests on cattle,
sheep, and goats, and soluble pine oil was used in other tests on






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sheep, goats, and horses. These tests and other observations
suggest that DDT emulsion concentrates containing only ingredi-
ents known to be of a low order of toxicity, and which form a
stable emulsion when mixed with water, may be used on animals
without harmful effects and may be expected to give effective
control of the parasites which are susceptible to DDT.

DDT emulsions have been employed for the control of insects
on animals in many localities throughout the nation during the
past seasons. In experiments for the control of certain external
parasites on sheep and goats, specific emulsions were found to be
superior to the DDT wettable powders because of better penetration.
For the control of other pests, such as the horn fly and lice on
cattle, the wettable powders proved to be equal to or more effEc-
tive than emulsions.

For use as sprays by the average farmer or small livestock
raiser, emulsions may offer certain advantages over wettable
powders. They are easily mixed and readily applied with equip-
ment generally available, such as ordinary garden-type pressure
sprayers or small hand sprayers. Emulsions may also be more
suitable than a wettable powder for use in the home to control
household pests. Those who require only small quantities of
insecticides may prefer to have on hand one material and equip-
ment that is suitable for treating the home as well as livestock,
In view of these and other factors, and because DDT emulsions may
be procured for use on animals, the following suggestions and
cautions, based on present knowledge and experience, are offered;

(1) The emulsion should first be tested in the t'p of
water that will be used for diluting the spray, to deter-
mine whether a stable emulsion will result. The oil phae
should not break; it should remain as a milky suspension
for about 12 to 24 hours, and, when it rises to the surface
or settles to the bottom of the container, a creary layer
should be formed, not a clear oily layer. All other
factors being equal, the most desirable emulsion from the
standpoint of safety is one in which the oil phase remains
as a milky suspension for more than 24 hours. To decrease
the possibility of improper mixing, the concentrate should
tend to be miscible with water without agitation, although
every emulsion should be stirred thoroughly while it is
being prepared and before each use.

(2) Emulsions for use in a dipping vat should preferably
be of stable type or of the heavier-than-water type that
can be readily reemulsified. Emulsions that have proved
satisfactory for charging dipping vats have been used






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repeatedly for several months without recharging, as have
also the wettable powders.

(3) The concentration of DDT to employ for dips will vary
with the kind of pest. The following concentrations are
suggested: Against horn flies on cattle, sheep ticks, and
sheep and goat lice, 0.2 percent; against cattle and hog
lice and certain ticks, 0.5 percent.

(4) Where emulsions are employed as sprays for control of
horn flies, the concentration of DDT in the diluted spray
should not exceed 1.5 percent. This high concentration
should be applied in small amounts, usually at a rate of
about 1 pint for the average-size cow. For treatment of
lice on cattle, where it is important to obtain adequate
and thorough wetting of the animal, a minimum of 0.5
percent DDT is suggested and approximately 2 quarts per
animal may be required. Thorough applications are neces-
sary to control both horn flies and lice. In sections of
the country where experience has shown that satisfactory
horn fly control on cattle may be obtained with lower
concentrations than the minimum mentioned above, a thorough
treatment with 0.25 percent DDT is suggested. However,
this low concentration is not highly effective against lice,
and it is usually desirable to control this insect at the
same time that cattle are treated for flies. More effective
control of mosquitoes and other biting insects, where they
occur as livestock pests, may also be expected with higher
concentrations of DDT. For the control of hog lice a
thorough application of 0.5 to 0.75 percent DDT emulsion
is suggested.

(5) It is desirable to mix only the quantity of emulsion
sprays that will be used during the day or for a particular
job. If an excess has been prepared and set aside, it should
be stirred thoroughly before it is used.

An emulsion for use on cattle, containing in the concentrate
form 25 percent of DDT, 65 percent of xylene, and 10 percent of
Triton X-100, has been discussed in E series publication 675
(Use of DDT in Control of Flies on Cattle and Around Farm Buildings).
Present information indicates that the percentage of DDT in the
diluted spray suggested in that publication (2.5 to 5 percent) is
unnecessarily high, and the lower percentages discussed in this
paper (0.25 to 1.5 percent) should be employed.

A DDT-soluble pine oil emulsion has been recommended by the
Bureau as a dip for the control of sheep ticks (E-679, Control of





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the Sheep Tick by a Single Dippi. :, in DDT Emulsion). This
emulsion in concentrate form consists of 1 part of DDT in 5 parts
(by weight) of soluble pine oil. When diluted to contain 0.2
percent of DDT it is recommended for the control of sheep and goat
lice, as well as sheep ticks. The same emulsion at a strength of
0.4 percent DDT has been sigested for the treatment of horses
infested with winter horse ticks.

An emulsion preparation oontai:/inj 1 percent of DDT in the
final dilution has also been recommended for the control of head
lice and crab lice on man (E-685, Control of Human Lice). This
preparation was widely used by our armed services during the war
for the control of lice and scabies,

"I_ *lut ions

Kerosene and other petroleum oils have been widely employei
as carriers for DDT sprays. For residual or long-lasting sprays
and for space applications the kerosene-base solutions are satis-
factory for use in homes and barns. In using them one should
give consideration to the fire hazard that may be involved. Kero-
sene or other oil solutions of DDT are not recommended for applica-
tion to livestock in quantities needed to provide lasting effects
against flies or other insects. DDT in oil is readily absorbed
through the skin of animals, and it is well known that excessive
amounts of oil alone oan be harmful to livestock and other animals.

Oil sprays containing py 'ethrumn or other toxicants, such as
certain thiocyanates, have been used on livestock for many years
to provide temporary relief fror. flies. These sprays were applied
in small quantities with mist-type hand sprayers or other atomizing
equipment. Usually the amount applied did not exceed 1 ounce per
animal, and much of this was not actually deposited on the animals.
The deposit which remained was largely on the outer coat of the
animal and ordinarily did not wet the Akin.

This type of spray has been largely replaced by DDT residual
sprays. However, because of its slow action, DDT may not prevent
biting by mosquitoes, deer flies, and stable flies, and the insects
may or may not be killed after they have fed on the treated animals.
The spraying of barns and animals will give excellent control of horn
flies and house flies, and will also greatly reduce annoyance
caused by stable flies and mosquitoes. Under certain circumstances,
where the spraying of barns and animals with DDT residual sprays
does not give adequate relief from flies and mosquitoes, the ordi-
nary types of livestock sprays are still in demand. Where such a
spray is needed, the addition of low concentrations of DDT (no
more than 0,5 percent) to other insecticides which act more rapidly,






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such as pyrethrum or certain thiooyanate compounds, will increase
the effectiveness of the spray. Experience points rather definite-
ly to the conclusion that DDT may be used in such sprays in con-
centrations up to 0.5 percent, without harmful effects on animals.

When oil-base sprays containing a rapid-knock-down agent and
0o5 percent or less of DDT are sold for use on livestock, it is
important that the label should caution users to employ a mist
spr.- and not to wet the skin of the animal with the oil spray.
The quantity per application should not exceed 1 ounce of spray for
an average-size cow. Satisfactory water-base sprays of this kind
could, of course, be employed in the same manner. It is emphasized,
however, that the Bureau recommends the application of DDT residual-
type sprays for horn fly control, because such a treatment is the
most effective and practical method known for the control of this
insect. Spraying of barns with this type of spray is also recommend-
ed, and only where experience has shown that the ordinary types of
livestock sprays are necessary as supplemental treatments does the
Bureau suggest their use.

Aerosols

Various methods are being used for producing aerosols, or
smokes or fogs containing small particles of insecticides, which
remain suspended in the air for some time. The most common method
of dispensing insecticidal aerosols is by releasing a liquefied
gas, such as Freon-12 (dichlorodifluoromethane) containing the
insecticide. This method was invented by employees of the Bureau
and is covered by patents assigned to the Secretary of Agriculture.
The gas serves mainly as the propellant for the insecticide and
diffuses in the air after its release. Aerosols may also be pro-
duced mechanically or by means of heat.

The aerosols are intended primarily for the control of flying
insects such as flies and mosquitoes, and if DDT is used in them
it is frequently combined with pyrethrum or other insecticides
causing rapid paralytic action. The use of aerosols for the con-
trol of insects affecting animals is still in the experimental
stage. Like mist or space sprays, they provide only temporary
relief. The aerosol is not considered an economical or effective
means of applying residual deposits of DDT.

The use of small containers, such as the customary 1-pound
bomb, of gas-propelled aerosols for the temporary control of fly-
ing insects affecting animals is not considered praotioal. In
well-constructed barns and similar buildings the release of gas-
propelled aerosols from special devices or installations has
aided in killing flies and related pests. Their use under these






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circumstances may provide temporary relief in much the same way
as do the ordinary oil-base sprays.

Tests with heat-generated aerosols containing DDT have
suggested that they may reduce the numbers of flies in barns or
similar locations. However, the effect is usually considered
temporary. Certain of the machines producing such aerosols,
known as fog generators, can be adjusted to produce a rather wide
range of particle sizes and, under certain conditions, are reported
to deposit sufficient DDT to give considerable lasting effect.
VWhether or not this type of aerosol is economical for this purpose
will depend on the circumstances under which it is employed and
the cost of the labor involved in applying the treatment as compared
with conventional methods. In general, the information available
is not sufficient to justify specific recommendations at present.




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