The new insecticides for controlling external parasites of livestock

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Title:
The new insecticides for controlling external parasites of livestock
Physical Description:
28 p. : ; 27 cm.
Language:
English
Creator:
Knipling, E. F
United States -- Bureau of Entomology and Plant Quarantine
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United States Department of Agriculture, Agricultural Research Administration, Bureau of Entomology and Plant Quarantine
Place of Publication:
Washington, D.C
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Rev.

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Subjects / Keywords:
Livestock -- Parasites -- Control   ( lcsh )
Insecticides -- Testing   ( lcsh )
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federal government publication   ( marcgt )
non-fiction   ( marcgt )

Notes

Statement of Responsibility:
compiled by E.F. Knipling.
General Note:
Caption title.
General Note:
"E-762, Second revision."
General Note:
"June 1951."

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University of Florida
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All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 030294006
oclc - 780165844
System ID:
AA00025174:00001

Full Text


STATE 6 -l L3OARD

June 1951 E-762, Second Revision

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



THE NEW INSECTICIDES FOR CONTROLLING
EXTERNAL PARASITES OF LIVESTOCK

Compiled by E. F. Knipling,
Division of Insects Affecting Man and Animals


The available information on the insecticidal efficiency and toxicology
of new insecticides used for the control of external parasites of livestock has
been summarized in two previous issues of this publication (December
1948 and April 1949). They also contained suggestions regarding uses
for these new materials. Further information has since been obtained
by the Bureau of Entomology and Plant Quarantine, the Bureau of Animal
Industry, the Food and Drug Administration, State experiment stations,
and others, which has resulted in a number of changes in these suggestions.
This publication has therefore been revised again to include the most
recent information on the use of DDT, benzene hexachloride, lindane,
chlordane, toxaphene, methoxychlor, TDE, and piperonyl butoxide for
controlling livestock pests.
The major objectives of this report are (1) to summarize the results
of research that has been conducted and, insofar as possible, to compare
the performance of the different materials against various livestock pests;
(2) to summarize briefly the available knowledge regarding the toxicity of
the insecticides to animals, as well as on residues in meat and milk when
different insecticides are applied to animals; and (3) to recommend or
suggest specific uses and restrictions for the new materials.
Many new insecticides and insecticide preparations are being applied
to livestock. It has not been possible to investigate all of them thoroughly
for their many potential uses. For this reason it is difficult at this time
to determine with finality which materials and formulations will give
maximum effectiveness, safety, and economy. Before such conclusions
can be reached, consideration must be given to the parasites involved,
types and age of animals, methods of application, stability of specific
formulations, climatic conditions, and other factors. Further research
on the various new materials, including those not recommended at this
time, is under way by several agencies, and as more information is
obtained, changes in recommendations or suggestions may become
necessary or desirable.







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RESULTS OF TESTS WITH VARIOUS NEW INSECTICIDES

In this paper the performance of DDT will not be discussed under a
separate heading. Most of the information obtained by various investigators
on this insecticide has been published. However, DDT will serve as a
basis of comparison for the performance of other new insecticides.

Benzene Hexachloride and Lindane

Technical benzene hexachloride consists of several isomers. All the
isomers are crystalline products. The gamma isomer is the most
effective against insects and other external parasites. When benzene
hexachloride first became commercially available, most manufacturers
formulated insecticides made from a technical product containing 10 to
12 percent of the gamma isomer. The 50-percent benzene hexachloride
wettable powder therefore contained 5 to 6 percent of the gamma isomer.
Recently there has been a trend in industry to produce benzene hexa-
chloride of higher gamma content, and some manufacturers now have a
product containing 36 to 40 percent of the gamma isomer. One containing
95 percent of the gamma isomer was also available experimentally for
some time, However, for about 2 years the almost pure gamma isomer
has been on the market under the common name "lindane." Although
more costly than the technical material, this product has several advantages
and its use for livestock pests is encouraged by the Bureau. Most of the
research on benzene hexachloride insecticides during this period has been
with lindane.
The Bureau's tests have been chiefly with the wettable powders and
emulsifiable concentrates containing xylene. In general both types of
formulations have been equally effective. Tests with benzene hexachloride
products of varying gamma-isomer content have been made against a
number of livestock pests. It appears that the insecticidal effectiveness
is due almost entirely to the gamma isomer.
The technical product as manufactured has a persistent musty odor,
but with the development of lindane the objectionable odor has been largely
overcome.
In the discussion of tests with benzene hexachloride insecticides the
concentrations are, for the most part, given in terms of the gamma isomer
whether different types of the technical product or lindane were used.

Cattle Lice

From the standpoint of initial killing action, benzene hexachloride is
one of the most effective insecticides for controlling lice on cattle. It
kills the eggs as well as the motile forms by contact, and it also acts as
a fumigant. Complete ovicidal effect requires a gamma concentration







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of 0.1 percent. It is likely that lower concentrations, as used for con-
trol of the motile forms, will not kill a high percentage of the eggs.
Benzene hexachloride has been tested against the short-nosed cattle
louse (Haematopinus eurysternus (Nitz.)), the long-nosed cattle louse
(Linognathus vituli (L.)), and the cattle tail louse (H. quadripertusus
Fahrenh.). Complete control of the first two species was obtained when
animals were thoroughly treated with wettable-powder sprays containing
0.06 percent of the gamma isomer. A single thorough treatment with a
spray containing 0.03 percent of the gamma isomer in either low gamma
or lindane grades has given good control, but in tests conducted in Texas
this concentration did not always give complete control. Both concentra-
tions have given good initial control of the cattle tail louse in a limited
number of tests. Apparently complete control of this species has been
obtained with a spray containing 0.12 percent of the gamma isomer.

Goat Lice

Benzene hexachloride dips made with wettable powders and emulsion
concentrates have been tested against red and yellow lice (Bovicola spp.)
on Angora goats. At 0.025 percent of the gamma isomer a single dipping
eliminated lice from the herd. Excellent initial control was obtained with
0.006-percent dips, but several months after treatment a few lice were
present. DDT dips at 0.2- and 0.25-percent concentrations have given
complete control of these lice.

Hog Louse

Benzene hexachloride is also effective against the hog louse
(Haematopinus adventicius Neum.). A single thorough treatment with
a wettable-powder spray containing 0.025 percent of the gamma isomer
has given good but not complete control in a limited number of tests.
Other workers have reported complete control at 0.05- and 0.06-percent
concentrations.

Sheep Tick

In Oregon benzene hexachloride wettable-powder dips containing
approximately 0.006, 0.025, and 0.06 percent of the gamma isomer have
provided complete control of the sheep tick (Melophagus ovinus (L.)).
Thorough treatments with wettable-powder sprays containing 0.025 to
0.05 percent of the gamma isomer (4 to 6 quarts per mature sheep with
long fleece) were effective in limited tests, although complete control
was not attained until several weeks after treatment. However, ground
derris rotenone2 5 percent), at rates of 4 and 8 ounces in 100 gallons of
dip, also gave complete control, and this seems to be the most economical
treatment for controlling this pest.










Lone 3tar I'ick

'> nzene hexachloride sprays made with wettable powders and
emulsion concentrates have been tested against the lone star tick
(Amblyomma americanum (L.)) on cattle at gamma-isomer concentrations
from 0.012 to 0.18 percent. All stages of the tick have been killed with
as little as 0.03 percent of the gamma isomer. However, even at 0.18
percent the residual action has not been marked. At Kerrville, Tex., a
0.06-percent spray protected animals for about 4 days, but after 1 week
some ticks began to engorge. Concentrations higher than 0.06 percent
did not seem to prolong the protection to any marked degree. In com-
parative tests DDT failed to kill all engorged ticks at a concentration as
high as 1.5 percent. However, DDT provided better protection against
reinfestation than did benzene hexachloride. The control obtained with
sprays containing 0.5 and 0.75 percent of DDT after 2 weeks was com-
parable with that obtained after 1 week with 0.06 percent of the gamma
isomer. The 0.75-percent DDT spray provided 75 percent control after
2 weeks. In view of the initial action of benzene hexachloride and the
residual action of DDT, much of the research on ticks has been conducted
with a mixture of these insecticides. Concentrations of 0.025 percent of
the gamma isomer and 0.5 percent of DDT have been employed.

Winter Tick

Sprays containing benzene hexachloride have been tested on cattle
and sprays or washes on horses for control of the winter tick (Dermacentor
albipictus (Pack.)) in the vicinity of Kerrville. Good control of all stages
was obtained with a gamma-isomer concentration as low as 0.012 percent.
Concentrations of 0.03 and 0.06 percent protected animals against reinfesta-
tion for about 2 weeks. DDT emulsions and Wettable-powder sprays failed
to kill all engorged ticks at concentrations up to 2.5 percent, but 0.5- to
0.75-percent concentrations provided protection for about 4 weeks.
Mixtures of benzene hexachloride and DDT as used for the lone star tick
provided an excellent control for the winter tick.

Ear Tick

In laboratory and field tests benzene hexachloride was effective against
the ear tick (Otobius megnini (Duges)) when applied as a spray. Sprays
containing 0.025 and 0.03 percent of the gamma isomer plus 0.5 percent
of DDT have given good control for 2 to 3 weeks. The Bureau of Animal
Industry (Farmers' Bulletin No. 980, The Spinose Ear Tick and Methods
of Treating Infested Animals) has shown that benzene hexachloride in a
pine oil-xylene solution will control this parasite.






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Gulf Coast Tick

Tests against the Gulf Coast tick (Amblyomma maculatum Koch)
indicate that benzene hexachloride is about as effective against this
species as against the lone star tick, and that mixtures containing
0.025 percent of the gamma isomer and 0.5 percent of DDT will give
good control of this species for 2 to 3 weeks.

Flies

Benzene hexachloride is highly toxic to the horn fly (Siphona irritans
(L.)) and the house fly (Musca domestic L.). Sprays at gamma con-
centrations of 0.025 and 0.05 percent applied on cattle for the control
of horn flies generally become ineffective in 4 to 14 days, as compared
with 3 to 4 weeks for 0.5-percent DDT. In laboratory tests conducted
at Orlando, Fla., deposits of technical benzene hexachloride or lindane
containing approximately 25 to 50 mg. of the gamma isomer per square
foot gave nearly complete control of house flies exposed for 2 hours as
long as 9 weeks after treatment. DDT applied at 50 mg. per square foot
was completely effective at the end of 36 weeks against flies of normal
susceptibility. DDT-resistant house flies showed only slight resistance
to benzene hexachloride, and in field tests good results were obtained
for 2 to 6 weeks with lindane applied at the rate of 25 to 50 mg. per
square foot. However, lindane and other benzene hexachloride insecti-
cides do not possess the long-lasting residual killing power formerly
obtained with DDT. Although DDT-resistant flies are susceptible to
lindane and benzene hexachloride, there are indications that resistance
to these materials may also become a serious problem.
Benzene hexachloride has been rv- rted to provide some control of
horse flies and deer flies. In tests conducted in Texas against Tabanus
abactor Philip, most of the flies feeding on cattle 1 day after treatment
were killed. However, the spray contained approximately 0.25 percent
of the gamma isomer. Tests against mixed species near Sil-sbee, Tex.,
showed no mortality of flies feeding on cattle 24 hours after treatment
with sprays containing 0.15 percent of lindane. In Georgia some success
against tabanids was indicated with mixtures of benzene hexachloride
and methoxychlor. However, further tests in this area are necessary
to determine whether such treatment offers practical control.

Screw-Worm and Fleece Worms

Benzene hexachloride is highly effective as a larvicide for lh..
screw-worm (Callitroga americ: : (C. ar.! P.)) and fleece worms
(Phormia regina (Meig.) and otht r second.:: blow flies. Formulations
containing lindane have recelrntly been recommended for controlli these
insects. (See E-813.)






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Common Cattle Grub

Benzene hexachloride has given some kill of the common cattle grub
(Hypoderma lineatum (De Vill.)). Its performance is erratic, however,
and available formulations cannot be depended upon to provide satisfactory
control at concentrations that are considered feasible from the standpoint
of economy or safety. Regular spraying of cattle at 2-week intervals
during the heel fly season, with preparations containing about 0.06
percent of the gamma isomer did not prevent animals from becoming
infested with cattle grub larvae.

Chlordane

Chlordane has been employed extensively for the control of certain
household pests, and is also being used against various insects and ticks
affecting livestock. Rather extensive tests have been conducted with this
insecticide against most of the major pests of livestock.
Chlordane is a viscous liquid, readily soluble in a number of solvents.
Both wettable-powder preparations and emulsions have been used. Under
some conditions this insecticide acts as a fumigant as well as a contact
insecticide.

Cattle Lice

Chlordane, in both wettable-powder (50-percent) and emulsion-
concentrate (25- to 50-percent) formulations, has been found to be equal
to or more effective than DDT for controlling several species of lice on
cattle. Complete control of both long-nosed and short-nosed lice was
obtained with 0.5-percent sprays, A 0.25-percent spray gave good but
not complete control of lice with one treatment. The cattle tail louse
also appeared to be as susceptible to chlordane as to DDT. However,
an insufficient number of tests have been conducted to determine the
value of chlordane in practical control.

Goat Lice

-hlordane and DDT were found to be equally effective against red
-c. yellow g.at lice in tests conducted in Texas. A single treatment
in 0.1- to 0.25-percent chlordane dips, prepared from either wettable
powder or emulsifiable concentrate, provided complete control, and no
reinfestation occurred for at least 4 months. At 0.05-percent con-
centration both materials controlled all motile forms, but some animals
were found infested when examined 4 months later.






-7-


Hog Louse

In one test with a few animals chlordane gave apparently complete
control of hog lice when applied as a wettable-powder spray at 0.2-percent
concentration. DDT in the same test gave good initial control, but a few
lice were found after 3 weeks.

Sheep Tick

Dips containing 0.05, 0.2, and 0.5 percent of chlordane gave complete
control of sheep ticks. DDT also gave complete control, but chlordane
eliminated the insects more quickly. When applied as a spray at 0.2- to
0.5-percent concentration, chlordane was superior to DDT and comparable
with benzene hexachloride at 0.025 to 0.05 percent gamma-isomer con-
centration.

Lone Star Tick

Chlordane has been tested against the lone star tick on goats and
cattle at concentrations of 0.25, 0.5, 0.75, and 1.5 percent. All con-
centrations gave complete or almost complete control of the flat stages,
and the 0.5- and 1.5-percent concentrations gave nearly complete kill of
all stages. DDT failed to kill all the engorged forms at 1.5-percent con-
centration. At the same concentrations the two insecticides gave about
equal protection against reinfestation. (The performance of DDT in
these tests has been mentioned on page 4.)

Gulf Coast Tick

Limited investigations indicate that the Gulf Coast tick and the lone
star tick are about equally susceptible to chlordane, both from the
standpoint of initial and residual toxicity.

Winter Tick

Chlordane is distinctly superior to DDT against the winter tick on
cattle and horses. Complete or nearly complete control of all stages
has been obtained with 0.5-percent sprays, whereas DDT at 1.5 percent
killed only a small percentage of the engorged forms. Chlordane also
gives better protection against reinfestation. At 0.5 and 0.75 percent
chlordane prevented reinfestation for about 2 months as compared with
1 month for DDT. Chlordane as a 5-percent dust has also proved
superior to DDT.






-8-


Flies

Chlordane has been tested on animals exposed to horn flies in cages,
and has also been used in field tests on dairy animals in Texas and beef
animals in Kansas. The tests in Kansas were conducted in cooperation
with the State experiment stations and colleges of Kansas and Missouri
and the Livestock Loss Prevention Board of Kansas City. Wettable-
powder sprays at concentrations of 0.25 and 0.5 percent, applied at the
rate of approximately 2 quarts per mature animal, gave good control of
horn flies and protected the animal for about 3 and 4 weeks, respectively.
There was no clear-cut difference in effectiveness between DDT and
chlordane, although chlordane appeared to be slightly inferior.
Chlordane is more toxic than DDT to house flies. Its residual action
is long lasting but not equal to that of DDT. In laboratory tests at
Orlando, Fla., surface treatments with chlordane at the rate of 200 mg.
per square foot, applied in acetone solution, gave complete or almost
complete kill of flies exposed for 2 hours as long as 28 weeks after
treatment. However, DDT was still completely effective against sus-
ceptible flies after 36 weeks, even at the low rate of 50 mg. per square
foot. DDT-resistant flies are in general of normal susceptibility to
chlordane. Field tests in Florida have shown chlordane to be one of the
best substitutes for DDT against DDT-resistant flies. There is recent
evidence, however, that house flies have developed resistance to chlordane
where this insecticide is being used for fly control.
Chlordane applied at concentrations as high as 2 percent did not pro-
tect cattle from attack by tabanids, Tabanus abactor Philip, but it did
cause 100 percent kill of feeding flies on the first day and 60 percent on
the second day after treatment.

Screw-Worm and Fleece Worms

Chlordane is highly effective against screw-worm larvae, although it
is not equal to lindane. Chlordane also protects sheep from attack by
fleece worms when used in sprays containing 0.5 to 2 percent of the
insecticide. In general, results have been comparable to those obtained
with toxaphene.

Common Cattle Grub

When emulsions and wettable-powder suspensions containing up to 1.5
percent of chlordane were applied to cattle, either as a wash or with a
high-power sprayer, the mortality of cattle grubs was less than 20 per-
cent. Dusts containing up to 5 percent of chlordane also proved ineffective.
Sprays containing 2 percent of chlordane applied to cattle at 2-week
intervals apparently did not protect animals from attack by adults of the
cattle grub, or heel flies.






-9-


Toxaphene

Toxaphene is one of the newest insecticides being offered to the public
for livestock-pest control. It is a waxy material, with no objectionable
odor, and readily soluble in most of the common solvents used in insecti-
cide formulations, including petroleum oils. In most of the tests wettable
powders and emulsion concentrates were used. The wettable powders
contained from 25 to 40 percent of the toxicant, and the emulsion con-
centrates from 25 to 65 percent, with xylene or kerosene as the solvent.

Cattle Lice

When tested as sprays at concentrations of 0.25 and 0.5 percent,
toxaphene gave results that were comparable with those obtained with
DDT and chlordane against both short- and long-nosed cattle lice and the
cattle tail louse.

Goat Lice

Toxaphene was at least equal, and perhaps superior, to DDT and
chlordane against red and yellow goat lice. In limited tests apparently
complete control was obtained with dips containing 0.05 percent of the
insecticide. Dips at 0.1- to 0.25-percent concentration have kept goats
free of lice for at least 4 months.

Hog Louse

Only one test, on a few animals, has been run with toxaphene against
the hog louse. A wettable-powder spray at 0.2-percent concentration
gave apparently complete control of the lice, being superior to DDT and
comparable with chlordane.

Sheep Tick

Against the sheep tick toxaphene was superior to DDT when used as
either a dip or a spray, but it was less effective than benzene hexa-
chloride or chlordane. In a few tests complete control was obtained
with dips containing 0.05, 0.2, and 0.5 percent of toxaphene. However,
its action appeared to be slower than that of the other insecticides.

Lone Star Tick

Toxaphene was superior to DDT and equal to chlordane, but less
effective than benzene hexachloride, against the engorged forms of the
lone star tick. Its residual effect provided protection against reinfestati'






-10-


comparable with that given by DDT and chlordane. Sprays at 0.5-percent
concentration gave control of all stages and good protection against rein-
festation for 2 weeks.

Winter Tick

Toxaphene was superior to DDT and comparable with chlordane against
the winter tick on cattle and horses, when employed as either a spray or
a dust. Good control of all stages and protection against reinfestation
for about 2 months were obtained with sprays containing 0.5 to 0.75 per-
cent.

Gulf Coast Tick

Extensive tests indicate that the action of toxaphene against the Gulf
Coast tick is similar to that against the lone star tick. Good control of
all stages resulted when cattle were dipped or sprayed with 0.5 percent
of the insecticide. Good protection against reinfestation was obtained
for 2 to 3 weeks, depending on the abundance of ticks. DDT was less
effective than toxaphene in killing the engorged ticks, but the degree of
protection was similar to that obtained with toxaphene. A spray containing
0.5 percent of toxaphene appeared to be comparable to one containing
0.025 percent of the gamma isomer of benzene hexachloride and 0.5 per-
cent of DDT.

Cattle Fever Tick

In extensive tests conducted in South America- sprays containing 0.5
percent o.f toxaphene were highly effective against all stages of the cattle
fever tick present on animals. Complete protection was obtained for 3
weeks and good control for 4 weeks. Protection after 3 weeks was com-
parable with that obtained 11 to 13 days after treatment with a spray
containing 0.025 percent of the gamma isomer of benzene hexachloride
and 0.5 percent of DDT.

Ear Tick

Toxaphene was superior to DDT and comparable with chlordane and
benzene hexachloride for controlling the ear tick. Good control for 2 to
3 weeks or longer was obtained with 0.5-percent toxaphene sprays applied
in ears of infested cattle.


1/ These tests were conducted by E. W. Laake, of this Bureau, while
on leave as a consultant for the American International Association for
Economic and Social Development.






-11 -


Flies

Toxaphene at 0.5-percent concentration has given control of horn flies
similar to that given by DDT, although it is somewhat slower in killing
flies coming to treated animals, and under certain conditions might appear
to be inferior.
Toxaphene is less effective than DDT against house flies, from the
standpoint of both initial and residual action. Toxaphene as a 2-percent
spray did not protect animals from attack by tabanids or stable flies.

Screw-Worm and Fleece Worms

Toxaphene is fairly effective against screw-worms and fleece worms.
It provided excellent protection against fleece worm attack on sheep when
used at concentrations df 0.5 to 2 percent. Against screw-worms, toxa-
phene is considerably less effective than lindane.

Common Cattle Grub

In small-scale tests toxaphene did not control larvae of the common
cattle grub. A 2-percent emulsion spray applied to cattle at 2-week
intervals failed to prevent infestations.

Methoxychlor

Methoxychlor is similar to DDT in both physical and chemical
properties. Most of the tests have been made with 50-percent wettable
powders and 25-percent emulsion concentrates. In general the wettable-
powder preparations seem to be somewhat more effective than the
emulsions.

Cattle Lice

Sprays containing 0.5 percent of methoxychlor gave good control of
short-nosed and long-nosed cattle lice. Methoxychlor also gave results
comparable with those of DDT for controlling the cattle tail louse.

Hog Louse

Methoxychlor was effective against the hog louse and comparable with
DDT, but a single treatment with 0.2-percent spray did not give complete
control.






-12-


Sheep Tick

In tests in Oregon methoxychlor controlled the sheep tick when used
as a wettable-powder dip containing 0.2 and 0.5 percent of the insecticide.
Methoxychlor appeared to be slightly less effective than DDT.

Ticks

Against ticks methoxychlor was less effective than the other chlorin-
at:. hydrocarbon insecticides. Wettable-powder sprays in strengths up
to 1.5 percent did not kill unengorged or engorged winter ticks or lone
star ticks on cattle and horses, and animals became reinfested by the
second week.

Flies

A Lethoxychlor gave good control of the horn fly on cattle. In some
tests it gave results superior to DDT; in others the duration of effective-
ness was shorter. A wettable-powder spray containing 0.5 percent of
ethoxychlor applied to dairy cattle in Texas and to beef cattle in Kansas
at he rate of 2 quarts per mature animal provided 20 to 24 days' pro-
tection, as compared with 28 to 30 days for DDT. In other tests, con-
ducted in Missouri and Kansas in cooperation with the State experiment
stations and the National Livestock Loss Prevention Board, longer pro-
tection was obtained with methoxychlor. When treated animals were
exposed to flies in cages, this material was slightly inferior to DDT in
lasting effect.
Methoxychlor has shown some promise for control of the stable fly.
In cage tests a wettable-powder spray containing 0.5 percent of methoxy-
chlor applied to cattle prevented feeding by stable flies for several days
and killed most of the flies that took blood during the first week after
treatment. When applied to cattle in practical control tests, it reduced
fly attack, but some flies fed on the first day of treatment. Most of the
Lies feeding during the first 3 days were killed. DDT at the same con-
centration did not prevent flies from feeding but killed most of the flies
that took blood during the first 3 days after treatment.
nder laboratory conditions methoxychlor applied as a residual spray
is almost equally as long lasting as DDT against both the house fly and
the stable fly. Treated screen-wire cages exposed to sunshine and
weathering remained toxic to stable flies longer than similar cages
treated with DDT. Recent tests have shown that DDT-resistant house
flies are also partially resistant to methoxychlor. In Florida, Texas,
and Georgia erratic results were obtained with methoxychlor as a
residual treatment for controlling house flies strongly resistant to DDT.






-13-


TDE

TDE (also called DDD) is another crystalline substance closely re-
lated to DDT in chemical and physical properties. The formulations
used are also similar to those of DDT. Tests conducted with both
emulsions and wettable-powder suspensions have thus far shown no
difference in effectiveness.

Cattle Lice

TDE was about equal to the other chlorinated insecticides in effective-
ness against short-nosed and long-nosed cattle lice. A 0.5-percent spray
thoroughly applied gave good control of these insects. In preliminary
tests TDE was also comparable with DDT for the control of the cattle
tail louse.

Hog Louse

In preliminary tests run on a few hogs TDE was equal to DDT in
initial kill of the hog louse. Neither material gave complete control
at 0.2-percent concentration.

Sheep Tick

TDE gave good control of sheep ticks when employed as a dip at con-
centrations of 0.2 and 0.5 percent. It was about equal to methoxychlor
but less 6-ffective than the other chlorinated hydrocarbon insecticides.

Ticks

In laboratory dipping tests against the lone star tick TDE was not so
effective as chlordane, benzene hexachloride, toxaphene, or DDT.
In a limited number of tests against the winter tick TDE was approxi-
mately equal to DDT but inferior to toxaphene and chlordane. Sprays
containing 0.5 to 0.75 percent of TDE did not kill engorged ticks but
prevented reinfestation for about 1 month.

Flies

TDE gave satisfactory control of horn flies on beef and dairy animals.
In general at 0.5-percent concentration in a wettable-powder suspension
this material was about equal to methoxychlor and slightly less effective
than DDT or toxaphene.






-14-


In laboratory tests TDE was less effective than DDT against the house
fly. Preliminary tests in the laboratory and on caged cattle indicated
that TDE was comparable with DDT in effectiveness against the stable fly.

Piperonyl Butoxide

Piperonyl butoxide alone is somewhat insecticidal, but it is of chief
interest for use in combination with pyrethrum, which is widely used in
fly sprays. The insecticidal action of pyrethrum is rapid and it is safe
for use on warm-blooded animals, but it is costly, particularly for use
on range animals. The addition of piperonyl butoxide permits reduction
in the amount of pyrethrum required to control certain insects.
Pyrethrum plus piperonyl butoxide applied as a residual spray did
not control house flies in dairy barns for more than 1 week. Piperonyl
butoxide, however, greatly increased the toxicity of pyrethrum against
house flies when used as a space spray.
Emulsions containing 0.005 percent of pyrethrins and 0.05 percent of
piperonyl butoxide, or 0.01 percent of pyrethrins and 0.1 percent of
piperonyl butoxide, gave complete initial control of the short-nosed cattle
louse, but young lice were present on treated animals after 2 weeks.
Sprays containing 0.1 percent of pyrethrins and 1 percent of piperonyl
butoxide protected animals against stable flies for 2 to 6 days. Some
protection against tabanids was also indicated, although results reported
by several investigators vary considerably. In some tests horse and
deer flies fed on treated animals within 2 days after treatment, whereas
in other tests almost complete protection was obtained for 3 to 4 days.

TOXICOLOGICAL INVESTIGATIONS

The toxicological effects of insecticides on man and animals are of
primary consideration in connection with their use for the control of
livestock pests. Some of the insecticides might prove hazardous to
persons handling them and if they are employed in excessive amounts or
if improperly formulated and mixed, there is danger that some of them
will cause harmful effects or even death when applied to livestock.
However, other, more complex toxicological problems arise in connection
with their use. When some of the insecticides are applied to livestock,
small amounts appear in the milk; and heavy and repeated applications of
all the chlorinated hydrocarbon insecticides cause the storage of chemicals
in the fatty tissues. When applied on cattle at the concentrations and
frequency usually employed for controlling livestock pests, these insecti-
cides differ considerably in the amount of chemical stored in fat or
excreted in milk.
It has recently been found that appreciable amounts of DDT or TDE
may appear in the milk of animals in dairy barns that have been treated
with these insecticides.






- 15-


The occurrence of these insecticides in milk is a matter of consider-
able concern, even though the quantity may be small. Milk is a major
item of the diet of infants, children, and many convalescent persons of
all ages. Studies conducted by the Food and Drug Administration during
the last several years have led to the conclusion that even small amounts
of DDT could in time prove hazardous to man when consumed in the diet.
A recent statement by that agency follows:
The Food and Drug Administration has the duty of protecting
the inter-State food supply from adulteration. DDT is a poison
and its use under conrrditions which would contaminate milk--a
food so universally used by infants and children--would be con-
trary to the Food, Drug, and Cosmetic Act.
Current recommendations for the control of livestock pests take into
consideration all available information on the toxicity of the insecticides
to livestock and the amount of the residues appearing in meat and milk.
The Food and Drug Administratioh has investigated the toxicology of
the various new insecticides to laboratory animals. The information
given here is taken for the most part from papers by A. J. Lehman (1, 2),
pharmacologist of that Administration. The data represent general
averages for several kinds of animals. Chemicals of high purity, rather
than the technical grades, were usually employed. Since some of the
studies are incomplete and many of the formulations differ from those
commonly employed in treating livestock, the information indicates trends
or approximate toxicity only. The Bureau of Entomology and Plant Quar-
antine, in cooperation with the Bureau of Animal Industry and the Texas
Agricultural Experiment Station, conducted most of the toxicological
studies on livestock that are reviewed in this report. Most of these
studies were carried cut at Kerrville, Tex., with funds provided under
the Research and Marketing Act of 1946.
The toxicological investigations on livestock have included studies to
determine (1) the effects on livestock of various insecticidal chemicals
and formulations of them when applied externally, (2) the amount of
insecticidal chemical secreted in milk when insecticides are applied to
dairy animals in amounts and frequency necessary to control horn flies
and other parasites, (3) the amount of milk contamination resulting from
the application of residual insecticides in dairy barns, and (4) the amount
of insecticidal chemical stored in fat when the insecticides are applied in
amounts and frequency necessary to control livestock pests. Some studies
and observations have also been made to determine whether products
from animals treated with benzene hexachloride are tainted with its odor
or taste.



sT hpiANRY RID
SATE pL Brlol,






- 16 -


DDT

The mean lethal oral dose of DDT to laboratory animals is about
250 mg. per kilogram of body weight. From the standpoint of chronic
toxicity, the Food and Drug Administration reports evidence of damage
to the liver of certain laboratory animals that are continuously fed a
diet containing 5 p. p. m. of DDT.
When applied externally, DDT in dry form shows no gross toxic
effects on laboratory animals. In solution, animals can tolerate a
single application to the skin of 3 grams per kilogram. However, re-
peated exposures to DDT in solution increase the hazards of DDT because
it is readily absorbed and stored in tissues.
As many as 10 applications of a 2-percent DDT wettable-powder
spray at 2-week intervals have produced no visible gross toxic effects
on cattle. Single treatments with wettable-powder sprays containing as
much as 8 percent of DDT can be tolerated without apparent harm to
cattle. No adverse effects have been noted with xylene-type emulsions
containing DDT at the same concentrations. However, certain solvents
have produced harmful effects when used in emulsions, and the presence
of DDT might increase the toxicity of such formulations.
Analyses have been made of many samples of milk taken from dairy
cattle treated with DDT for fly control. In 1947 weekly samples of milk
were analyzed from two herds near Kerrville, Tex., that had been treated
with 0.5-percent DDT wettable-powder spray for controlling horn flies.
Four treatments were made about 1 month apart. DDT was found in all
samples of milk. The amounts ranged from 0.1 to 2 p. p.m., and
averaged between 0.6 and 0.7 p. p.m.
In 1948 similar analyses were made of the milk from four herds in
the Kerrville area. The animals were treated as often as necessary to
control horn flies, with 1 to 2 quarts of a 0.5-percent DDT spray made
from a concentrate containing DDT, xylene, and Triton X-100. The
amount of DDT in the milk was somewhat less than in 1947, averaging
about 0.25 p. p. m.
In another experiment several dairy cows maintained under controlled
conditions were treated four times at 1-month intervals with a 0.5-percent
DDT wettable-powder spray. The DDT in the milk averaged about
1 p. p. m. during the test period. The barns were also treated with a
DDT emulsion at the concentration and frequency necessary for controlling
house flies. The amount of DDT appearing in the milk after barn spraying
increased in some cases for a day or two, but it quickly dropped to that
present after DDT had been applied to the cattle. However, the barn
sprayings did not always cause an appreciable increase in the DDT con-
tent of the milk. DDT in the milk attributed to barn sprayings occurred
in four of eight sprayings. The amount attributed to barn treatment in






-17-


one case was approximately 1.23 p. p.m. on the day after the spraying,
but dropped to about 0.25 p.p.m. on the second day. The average for
the season was calculated to be about 0.1 p. p.m.
Special tests were conducted at Kerrville, Tex., and Beltsville, Md.,
in cooperation with the Bureau of Dairy Industry and the Food and Drug
Administration to determine the degree of milk contamination resulting
from barn-spraying alone. DDT appeared in the milk from the herds in
all instances where feed and watering troughs were not covered. When
the troughs were covered or washed out with water from a pressure hose
before the spray dried-', there was little contamination of milk with DDT.
However, detectable amounts of DDT (less than 0.5 p. p.m.) were some-
times found even when these rigid precautions were taken.
Considerable information has been obtained on the storage .of DDT in
the fat of beef cattle treated with this insecticide for insect control. In
one experiment four Hereford cows, each with a suckling calf, were
treated five times at 28-day intervals with a 0.5-percent wettable-powder
spray, and four others with a 0.5-percent emulsion spray. Two of the
calves in each group were also sprayed. Two weeks after the fifth
spraying fat samples from the cows treated with wettable-powder spray
averaged 14.6 p. p.m. of DDT, and those from cows treated with the
emulsion averaged 15.2 p. p.m. The four calves treated with the sprays
averaged 52.4 p. p.m. of DDT; those not sprayed but which consumed
milk from sprayed mother cows averaged 26.5 p. p.m.
Yearling Hereford steers sprayed four times at 3-week intervals
with 0.5-percent DDT emulsion were biopsied at intervals during the
period of treatment. Fat from three animals showed an average DDT
content of lb p. p.m. after one treatment, 31.2 p. p.m. after two treat-
ments, and 32.8 p. p. m. after four treatments. In other tests four
yearling Herefords were treated once with the same spray. Fat samples
taken subsequently averaged 11.2 p. p.m. of DDT after 2 weeks,
8.1 p.p.m. after 6 weeks, 5.3 p.p.m. after 10 weeks, and 2.9 p.p.m.
after 22 weeks.

Benzene Hexachloride and Lindane

The different isomers of benzene hexachloride vary in their toxicity
to higher animals. For the gamma isomer the mean lethal dose to
laboratory animals, when administered by mouth, is approximately
125 mg. per kilogram of body weight. In oil solution it is readily
absorbed through the skin; when it is administered in this way, the
mean lethal dose ranges from 20 to 50 mg. per kilogram. The Food
and Drug Administration has found the gamma isomer of benzene
hexachloride to be about one-fourth as toxic as DDT from a chronic
standpoint, and that there is less tendency for storage of this chemical






-18-


in animal fat and it is more quickly eliminated. However, that agency
considers the beta isomer of benzene hexachloride to be especially
hazardous from the standpoint of chronic toxicity; therefore, this isomer
should be eliminated from benzene hexachloride insecticides. Although
the alpha and delta isomers are similar to the gamma in chronic toxicity,
they should also be eliminated insofar as possible, since they increase
the toxicity hazard and add little to the effectiveness of benzene hexa-
chloride insecticides.
At Kerrville high concentrations of benzene hexachloride and frequent
treatments were tested to gain information on the upper limits of toxicity.
When mature or nearly mature animals were employed, no harmful
effects were noted on 8 sheep, 8 goats, 4 cattle, 2 horses, and 2 hogs
treated eight times at 4-day intervals with a dip or spray containing 1.5
percent of technical benzene hexachloride (0.15 to 0.18 percent of the
gamma isomer). A wettable-powder preparation was used on some of
the animals and a xylene emulsion on the others. The Livestock Loss
Prevention Board of Kansas City obtained similar results on 8 animals
treated with a wettable-powder spray at the same concentration. At
Kerrville 10 cows treated nine times at 2-week intervals with a wettable-
powder spray containing 2 percent of benzene hexachloride (about 0.24
percent of the gamma isomer) showed no apparent harmful effects.
However, when a wettable powder containing 50 percent of gamma
benzene hexachloride was used, all 3 cattle treated once with a spray
containing 1.5 percent of the gamma isomer were killed, but 1 out of
3 receiving a spray containing 0.75 percent of gamma died and another
was seriously affected but recovered. A 0.25-percent gamma spray
had no ill effects.
Calves less than 3 months old are much more susceptible to benzene
hexachloride than are cattle a year old or older. Tests have not been
run to determine the relative susceptibility of calves less than 3 months
and those 3 months to 1 year old. Emulsion sprays containing 0.05
percent of the gamma isomer and xylene as the solvent killed 3 of 11
Jersey calves that were thoroughly saturated to simulate dipping.
Wettable-powder sprays of the same gamma content were apparently
less toxic, but toxic symptoms were evident in 2 of 9 calves treated
and 1 calf died.
Recently tests have been conducted with lindane, the essentially pure
gamma isomer of benzene hexachloride. Eight Jersey calves were
sprayed with an emulsion containing 0.05 percent of lindane. Only one
calf showed toxic symptoms, and it recovered. Of four sprayed with
0.1 percent of lindane, one died, one showed toxic symptoms but re-
covered, and two were unaffected. Two Hereford calves given the same
treatment showed no adverse effect. Apparently the toxicity of lindane
to calves depends on the breed and perhaps other factors. Tests on




-I


19 -


calves were made with three samples of benzene hexachloride of
different gamma content--namely, 12, 36, and 95 percent. When
diluted to the same gamma content, all three sprays were equally toxic.
Some reports have been received of death or injury to calves or
cattle treated with benzene hexachloride or lindane for pest control.
It has been difficult to determine what concentrations were used when
death occurred. These experiences emphasize, however, that the insecti-
cide should be used with care to avoid injury to cattle, particularly to calves.
Suckling pigs and lambs appear to be much more resistant than
calves to lindane sprays. In a limited nunrber of tests 0.5-percent
lindane did not harm suckling pigs and lambs about 6 weeks old.
Only limited information is available on the storage of benzene
hexachloride in fat of livestock treated for pest control. A spray con-
taining 0.25 percent of the insecticide (approximately 0.03 percent of
the gamma isomer) was applied to 8 yearling Hereford cattle at 2-week
intervals for 12 treatments. Two weeks after the last treatment fat
samples taken from these animals had an average organic-chlorine
content equivalent to 31 p. p.m. of benzene hexachloride; a month later
it dropped to 11 p. p. m. and after another month had returned to normal.
Six yearlings were sprayed with 0.025-percent lindane emulsion at
3-week intervals over a period of 6 months. No lindane was found in fat
samples taken at intervals during the treatment period.
To determine whether the use of benzene hexachloride gave off-flavor
or odor to meats of treated animals, tests were conducted with several
kinds of animals. One pig received two thorough treatments 9 days
apart with a spray containing 2.5 percent of benzene hexachloride (0.3
percent of gamma isomer). The animal was killed 2 days after the
second treatment, and 10 families cooked and tasted the meat. None of
the families detected benzene hexachloride taste, but two of them
detected the odor while the meat was cooking. Another pig was sprayed
twice 4 days apart with 1.5 percent of benzene hexachloride, and
slaughtered on the sixth day. None of the families eating the meat
reported benzene hexachloride odor or taste. In similar tests with a
goat, a sheep, and a yearling calf, one report of benzene hexachloride
flavor or odor from each animal was received. Another calf and a pig
sprayed eight times at 4-day intervals with 1.5 percent of benzene hexa-
chloride (0.18 percent of gamma isomer) and slaughtered 1 month after
the last treatment showed no marked off-flavor or odor, although some
individuals gave positive reports. In tests with six chickens exposed
for one to several weeks to roosts heavily painted with a slurry of
benzene hexachloride (12 percent gamma), conflicting reports were
received, but in one chicken marked benzene hexachloride odor was
detected. In these tests the concentration of benzene hexachloride was
in excess of that needed for controlling parasites.






-20-


In an experiment conducted in cooperation with the Missouri Agri-
cultural Experiment Station, no off-flavor or odor was detected in meat
from a cow dipped 18 times over a period of 2 years in a wettable-
powder suspension containing 0.5 percent of benzene hexachloride (0.05
percent of the gamma isomer).
No reports of off-flavor or odor ot meat from livestock treated with
benzene hexachloride for practical pest control have come to the attention
of this Bureau.

Chlordane

The acute toxicity of chlordane administered orally to laboratory
animals is reported to be about half that of DDT. However, the toxicity
of a solution applied repeatedly to the skin is reported to be greater for
chlordane. From a chronic-toxicity standpoint this insecticide is con-
sidered by the Food and Drug Administration to be about four times as
toxic as DDT, when taken in the diet of animals.
At Kerrville five sheep and five goats were dipped, and two cattle
and one horse were sprayed eight times at 4-day intervals with a 1.5-
percent chlordane emulsion, and the same numbers of animals were
treated with a wettable-powder preparation at the same strength. The
test was repeated with a new lot of chlordane, but only five sheep and
two r.igs were treated with each preparation. In the first test none of
the cattle or horses were killed with either preparation, but the five
sheep and two of the goats were killed by the emulsion and two sheep
and two goats by the wettable-powder suspension; some of the animals
died after the third treatment. In the second test none of the animals
were killed.
The Livestock Loss Prevention Board obtained similar results in
that sheep were killed by the severe treatment, and one of two cattle
sprayed with each preparation was killed.
In another test at Kerrviile 3 of 10 cattle died after four thorough
treatments at 2-week intervals with a 2-percent wettable-powder prepara-
tion. No explanation can be offered for the variable results.
Eight yearling Herefords were sprayed 12 times at 2-week intervals
with a 0.5-percent chlordane emulsion. The animals showed no toxic
symptoms, and weight gains equaled those of untreated animals.
Tests on a few young calves 2 to 6 weeks old indicate that chlordane
is .,',-ut as toxic as toxaphene when single applications are made. Of
10 calves sprayed with a 1-percent emulsion, 1 died and 9 showed no
toxic ;symptoms. Of 10 calves sprayed with a 2-percent emulsion, 4
died and 6 showed no toxic symptoms. Suckling pigs and lambs are
much more resistant than calves. An emulsion dip containing 4 percent
of chlordane did not adversely affect 2 pigs, 2 lambs, or 4 kids.






-21 -


Weekly analyses of milk samples from two dairy herds treated with
0.5-percent chlordane wettable-powder spray four times at intervals of
about 1 month showed that small amounts of organic chlorine were
present in the milk. Of 18 samples analyzed, 17 showed from 0.1 to
0.4 p. p.m. of organic chlorine. However, it is not certain that all the
organic chlorine present can be attributed to the chlordane treatment.
To obtain information on the storage of chlordane in treated livestock,
fat samples were taken from the eight yearling Hereford cattle treated
12 times with a 0.5-percent chlordane emulsion. Analyses of samples
taken 2 weeks after the last treatment showed organic-chlorine content
equivalent to 20 p. p.m. of chlordane. One month later this figure had
dropped to 4 p. p.m. and after another month the organic chlorine was
normal.
Three yearling steers were sprayed once with a 0.5-percent chlordane
emulsion. Two weeks later the fat averaged 9.1 p. p. m. of organic
chlorines compared with 6.5 p. p.m. prior to treatment. Because of
wide variations in the normal level of organic chlorine, the difference
probably can not be considered significant.

Toxaphene

Toxaphene is reported to be about four times as toxic as DDT when
administered orally to laboratory animals, the mean lethal dose being
about 60 mg. per kilogram. It is also more toxic than DDT when applied
to the skin. The Food and Drug Administration considers toxaphene to
be about as toxic as lindane, or one-fourth as toxic as DDT, from a
chronic standpoint when consumed in the diet.
At the Kerrville laboratory 20 sheep, 15 goats, 8 cattle, 4 horses,
and 4 hogs, all mature or nearly mature, were treated eight times at
4-day intervals with 1.5 percent of toxaphene. No adverse effects were
noted on any of the animals.
Mature animals showed no ill effects from single applications of
emulsion sprays containing 8 percent of toxaphene. Young calves,
however, are more susceptible. After reports were received from
Texas that toxaphene caused the death of some calves that had been
dipped in this insecticide, tests were made on calves 1 to 2 months old.
A single spraying with 1.5-percent toxaphene emulsion (containing xylenc
or kerosene) or wettable-powder suspension caused toxic symptoms in
some of the calves, and two treatments 4 days apart caused a few deaths
Eleven Jersey calves were thoroughly treated with 1-percent toxaphene
sprays, eight with a kerosene emulsion and three with a wettable-powc'
suspension. One of the calves showed toxic -ymptoms but recovered
the rest showed no harmful effects. single treatment at 0.T-percei
concentration had no 3dverse effect on 12 calves. 'er being reate






-22-


eight times at 4-day intervals one calf showed symptoms of poisoning
but recovered. Suckling pigs and lambs are much more resistant than
calves.
Field observations indicate that deaths among cattle treated with
sprays or dips containing 0.5 percent of toxaphene are due in part, if
not entirely, to the use of faulty formulations.
Milk samples from dairy herds treated four times at about monthly
intervals with wettable-powder sprays containing 0.5 percent of toxaphene
were analyzed for organic-chlorine content. Of 43 samples analyzed, 27
were negative. In the samples giving positive results, the amount of
organic chlorine ranged from 0.2 to 0.6 p. p. m. It is not certain whether
the organic chlorine present can be attributed to the toxaphene.
To determine whether toxaphene applied repeatedly to cattle will
increase the organic-chlorine content of fat, 36 yearling Hereford steers
were sprayed from 1 to 12 times at 2-week intervals with a 0.5-percent
toxaphene emulsion. There was no clear-cut evidence that the organic-
chlorine content increased significantly over that of untreated cattle, but
at no time did it exceed the equivalent of 5 p. p. m. of toxaphene. Irn. 8
similar animals on range grass that were similarly treated, 2 weeks
after the last treatment the organic-chlorine increase over untreated
animals was equivalent to 8 p. p.m. of toxaphene. Four weeks later the
organic-chlorine content returned to normal.

Methoxychlor

Methoxychlor is the least toxic of the chlorinated hydrocarbon insecti-
cides that have been investigated. The mean lethal dose to laboratory
animals when administered orally is reported to be higher than 6 grams
per kilogram of body weight. The Food and Drug Administration has also
found methoxychlor to be of low toxicity when fed in the diet to laboratory
animals. From results of tests of single and repeated applications of
methoxychlor in solution to the skin of laboratory animals, this insecti-
cide is the least toxic of the new insecticides, including piperonyl
butoxide. On the basis of tests on laboratory animals, the toxic dose
is estimated to be about 2,8oo00 mg. per kilogram of body weight for single
exposure and 600 mg. per kilogram when applied repeatedly.
At Kerrville no adverse effects were noted when sheep, cattle, hogs,
and horses were treated repeatedly with emulsions or wettable-powder
preparations containing up to 2 percent of methoxychlor. Single applica-
tions of up to 8 percent of methoxychlor showed no adverse effects on
young calves.
Milk samples collected at weekly intervals from two herds of dairy
cattle treated five and six times during the season with a wettable-
powder suspension containing 0.5 percent of methoxychlor were analyzed
for organic-chlorine content. Only 3 of 42 samples analyzed showed
organic chlorine (0.1 p. p.m.). A single spraying with 0.5-percent







- 23 -


methox.c hlor etn-iulsi0n resulted in an average deposit of 2.8 p. p. mr of
methox',chli.r in the fit of four yearling Herefords, when det rmined bA
a mrnethod specific for this insecticide. When the same spray w.,i applied
to three similar cattle twice 2 weeks apart, the method. chlor content
averaged 1.5 p p. nm. after each treatment.

TDE

The mean lethal oral dose of TDE for several laboratory animals is
reported to be about 2.5 grams per kilogram of body weight. The Food
and Drug Administration considers TDE to be somewhat less toxic than
DDT from the chronic standpoint.
At Kerrville sheep, goats, cattle, hogs, and horses showed no ill
effects when treated eight times at 4-day intervals with 1.5-percent
TDE emulsions or wettable-powder preparations. Single applications
in strengths as high as 8 percent have shown no adverse effects on young
calves.
In 1947 samples of milk taken at weekly intervals from two herds of
dairy cattle treated with TDE were analyzed for their TDE content by
the colorimetric method. The animals had been treated five times with
a 0.5-percent wettable-powder spray (approximately 2 quarts per animal).
Of 20 samples analyzed, 8 were negative and 12 showed TDE present in
amounts ranging from 0.1 to 1.2 p.p.m. TDE in similar amounts was
found in the milk taken from several herds treated in a similar manner
during 1948. When applied to dairy barns, TDE appeared in milk in
amounts at least equal to those obtained after barns had been treated with
DDT; when applied to beef cattle, it was stored in about the same amounts
as DDT. The stored chemical is persistent in the fat but seems to be
eliminated somewhat more rapidly than DDT. Four Hereford cattle
sprayed once with 0.5-percent TDE emulsion averaged 11 p. p.m. of
TDE in the fat 2 weeks later. The amounts in the fat 6, 10, and 22 weeks
after treatment averaged 5.2, 3.9, and 0.7 p. p.m., respectively.

Piperonyl Butoxide

The mean lethal dose of piperonyl butoxide administered by mouth
to various laboratory animals is reported to be about 13 grams per
kilogram of body weight. On the basis of applications to the skin of
laboratory animals, the toxic dose averages about 1.8 grams per kilo-
gram for single exposures and 200 mg. per kilogram for repeated app' -
cations. Pyrethrum, with which this material is usually combined, a. ',
is also relatively nontoxic to warm-blooded animals, especially in the
small amounts generally applied. However, the medium lethal single
dose of pyrethrins applied orally is about 1.5 grams per kilogram.






-24-


SUGGESTIONS REGARDING THE USE OF THE NEW INSECTICIDES

This publication does not give detailed directions for controlling
various livestock pests with insecticides. Rather, it contains suggestions
or recommendations on the field of use for the new insecticides in the
light of current information on their performance and the potential
hazards connected with their use. Livestock growers who contemplate
employing any of the materials should consult with workers in their own
States who are concerned with livestock-pest problems.
In view of the differences in toxicity of the various insecticides to
higher animals and in their excretion in milk, the materials useful in
controlling insects affecting dairy cattle should be considered separately
from those that m ight be satisfactory for controlling pests of other kinds of
livestock.
Precautions

Be extremely careful when storing, handling, mixing, and applying
the insecticides discussed in this publication.
Store insecticides where children, pets, and other animals cannot
reach them. Store those containing kerosene or xylene so that there
will be no fire hazard, and do not mix or spray them in the presence of
an open flame or sparks.
When handling, mixing, or applying insecticides, take proper pre-
cautions against unnecessary exposure to skin contact or breathing of
spray mist. When applying sprays continuously and repeatedly, wear a
respirator and clothing that protects the body. Change clothing frequently
and, if it becomes saturated with spray, launder the clothing before it is
worn again. Bathe or wash parts of the body with which insecticides
have come in contact.
When applying insecticides take care to avoid accidental contamination
of food and water for man and animals.
Observe carefully the suggested concentrations and rates of appli-
cation. Mix the materials thoroughly and agitate them continuously in
the spray tank. If an emulsion concentrate will not mix readily with
water and an oily film accumulates, do not use the material.
Dispose of unused sprays in such a way as to avoid hazards.
In spraying dairy barns, take special precautions to avoid contamin-
ating milk or utensils. Cover water cups and feed troughs, and cover or
remove feed while spraying.






-25-


DDT

DDT applied to dairy animals may appear in milk in quantities judged
by the Food and Drug Administration to be a potential hazard to consumers.
It may also appear in milk when dairy barns are treated with the insecti-
cide. The Bureau therefore recommends that this insecticide not be
applied to animals producing milk for human consumption. Nor should
DDT be used for fly control in dairy barns or milk-processiiL plants.
The Bureau still recommends DDT as an aid in controlling flies in other
places, and for controlling pests on livestock other than d&;r als
producing milk for human consumption,

Benzene Hexachloride and Lindane

If benzene hexachloride is to be used for controlling any livestock
pest, it is advised that wettable-powder formulations be used. Products
of high gamma-isomer content are the least objectionable from the stand-
point of odor. Lindane, the essentially pure gamma isomer, is recom-
mended in preference to the technical product. Benzene hexa-
chloride should not be applied to dairy animals. Neither should
it be applied to meat animals that are to be slaughtered
within 30 days. In view of its toxicity to calves, the gamma-isomer
concentration of either product should not exceed 0.03 percent for con-
trolling insects or ticks on them, and for cattle a year or older the
maximum should be 0.05 percent. For tick control 0.025 percent of the
gamma isomer plus 0.5 percent of DDT is suggested. For louse control
on cattle 0.03 to 0.05 percent of gamma isomer is recommended. For
control of sheep ticks on goats and sheep, a dip containing 0.025 percent
or a spray containing 0.05 percent is suggested. For louse control 0,02
percent is usually enough, but to assure complete control, especially
in recently shorn animals, 0.05 percent may be required. For control
of lice on hogs, a concentration of 0.05 to 0.06 percent in a spray or dip
is recommended.
Lindane is not recommended for repeated use on dairy cattle to con-
trol flies and ticks, although single treatments for louse control are
recommended. Lindane is recommended as a residual treatment for
spraying dairy barns or milk-processing rooms for fly control. A
deposit of 25 mg. per square foot is suggested. For other farm build-
ings 25 to 50 mg. per square foot is suggested. A special pre-'aration
known as EQ-335 Screw-worm Remedy (see E-813),conlain'n_ iindanc,
has recently been recommended for controlling screw-worms and w.-
maggots.






-26 -


Chlordane

No harmful effects on livestock have been noted or reported when
chlordane has been applied in insect-control operations. However,
toxic effects have developed in experiments with 1.5- to 2-percent sprays
applied repeatedly to livestock. There is also evidence of some storage
of chlordane in fat of cattle when applied at 2-week intervals. Additional
tests with repeated treatments at various concentrations should therefore
be conducted before recommendations are made for its use for controlling
pests on livestock, such as ticks and flies requiring repeated applications.
There is no evidence, however, of toxic effects of single or occasional
applications of 0.5-percent sprays. Therefore, single applications of
0.5-percent sprays are recommended for louse control on cattle and
hogs. For controlling lice and sheep ticks on sheep and goats, 0.25-
percent dips or 0.5-percent sprays are suggested. Sprays containing
0.5 percent of chlordane have also proved effective in preventing or
controlling wool mnaggot infestations in sheep.
Chlordane has given good results against house flies in situations
where Idequate control cannot be obtained with DDT. However, the
Lureau advises that it not be used for fly control in dairy barns, milk-
processing plants, or similar situations.

Toxaphene

From the standpoint of economy and efficiency toxaphene is considered
a good insecticide for the control of several livestock pests. Investigations
have shown that this insecticide can be used safely as a spray when applied
to livestock.
Toxaphene as a 0.5-percent spray, made from an emulsifiable con-
centrate or a wettable powder.is recommended for controlling horn flies,
ticks, and lice on beef cattle; lice on sheep, goats, and swine; and for
sheep ticks and wool maggots on sheep.
Because of the narrow safety margin of toxaphene, particularly for
calves, the insecticide is not at present recommended for use as a dip
for cattle. Investigations are under way to develop suitable dip formula-
tions that will remain stable and disperse uniformly in vats. Toxaphene
is recommended, however, for use as a dip at a concentration of 0.25
percent for controlling lice and sheep ticks on sheep and goats.
Until more information is available on the rate of excretion of toxa-
phene in milk of dairy animals treated for insect control, the Bureau
recommends that it not be applied to dairy cows. The insecticide is
also not recommended for fly control in dairy barns. For fly control
in other farm buildings, the insecticide should be applied at the rate of
200 mg. per square foot.






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Methoxychlor

Methoxychlor is recommended for controlling certain insects on dairy
animals and other livestock. Results to date indicate that for horn flies
and lice on cattle the insecticide compares rather favorably with DDT.
It is suggested that cattle be treated with sprays containing not less than
0.5 percent of methoxychlor, preferably prepared from a wettable powder.
For the control of horn flies, about 2 quarts of spray should be applied
to a mature animal. If higher concentrations are employed the amount
of spray should be reduced. For control of lice the animals should be
thoroughly saturated. Against horn flies about 3 to 3 1/2 weeks' pro-
tection may be expected, as compared with about 4 weeks for DDT
applied at the same rate.
For stable fly control on dairy cattle a tentative suggestion is to
apply a 0.5- or 1-percent spray, preferably a wettable-powder prepara-
tion, once or twice a week to the legs, belly, and lower part of the sides
of the animals. A light spraying on their backs at the same time will
make further horn fly treatments unnecessary. Other cattle on the farm
should also be treated at regular intervals for horn fly control.
For louse control on cattle and hogs a 0.5-percent concentration is
recommended for most conditions. In the Southeast, where the cattle
tail louse is prevalent, a spray containing 1 to 1.5 percent is recommended.
For controlling lice or sheep ticks on sheep and goats a dip containing
0.25 percent of methoxychlor is suggested.
Methoxychlor is recommended as a residual spray for fly control in
farm buildings, including dairy barns. Results have been erratic due to
resistance of flies to methoxychlor where resistance to DDT has developed.
A wettable-powder or emulsion spray applied so as to deposit 200 mg.
of methox-ychlor per square foot is recommended.

TDE

TDE should not be used on dairy animals. It may be used to control
horn flies on cattle and lice on cattle, swine, sheep, and goats. For
controlling horn flies a 0.5-percent concentration applied as a wettable-
powder or emulsion spray at the rate of 2 quarts per animal is suggested.
For louse control the animal should be thoroughly saturated with a spray
of the same concentration. If employed as a dip for controlling lice and
sheep ticks on goats and sheep, a concentration of 0.25 percent is
recommended.

New Pyrethrum Insecticides

Several new materials that increase the insecticidal effectiveness
of pyrethrum are available, but piperonyl butoxide is the only one that
has been investigated for controlling livestock pests. Because of the
low toxicity of pyrethrum-piperonyl butoxide ins cticides to animals,





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no hazards should ordinarily be created by their use. (If used in an oil
solution, excessive amounts of oil may prove harmful to the animals.)
This insecticide preparation should be considered for the control of lice,
horn flies, stable flies, horse flies, and deer flies on dairyanimals. For
louse control a thorough treatment with an ermulsion or wettable-powder spray
containing 0.025 percent of pyrethrins and 0.25 percent of piperonylbutoxide is
suggested. For controlling horn flies, stable flies, and horse flies on
dairy cattle, a spray containing 0.1 percent of pyrethrins and 1 percent of
piperonyl butoxide should be applied at the rate of 1 quart per animal.
This spray is also effective when applied as a mist for controlling flies
in barns or on dairy cattle. A light mist applied at the rate of about
1 ounce per cow will control flies for several hours or until the next
milking.

Other Methods of Controlling Dairy Pests

Various oil-base insecticides for application as a light mist have
been employed extensively in the past to provide temporary control of
flies on dairy cattle. These materials which contain pyrethrum, rotenone,
or an organic thiocyanate, have also been used as space sprays in barns
and elsewhere. They are again coming into wide use because of the
restrictions placed on some of the newer insecticides and because of
the occurrence of strains of house flies that are resistant to certain
insecticides. However, there is danger of harming livestock by treat-
ment with oil-base sprays. Such sprays are intended for use as mists
only and in such small quantities that the skin of the animals does not
become wet with the oil. The amount applied should not exceed 1 ounce
per animal. When mist sprays are used on dairy cattle and in dairy
barns, other cattle and other places on the farm where flies concentrate
should be treated with residual sprays of the types discussed in this
publication in order to reduce the over-all fly population to a practical
minimum.
The use of insecticides should not be relied on to give complete
insect control on the farm. Rigid sanitation, especially manure disposal,
should be practiced to prevent fly breeding. Well-screened buildings
will also aid in excluding flies and in preventing the contamination they
may cause.
LITERATURE CITED
) Lehman, A. J.
148, The toxicology of the new agricultural chemicals. Assoc.
-rood and Drug Officials Bul. 12(2): 82-89.

750. 5ome toxicological reasons why certain chemicals may or
may not be permitted as food additives. Assoc. Food
and rug Officials Bul. 14(3): 82-98.