B—Lancaster Farming, Friday,' Feb. 8, ISIS'?
HERE USDA RESEARCHERS are administering
radioactive ET-57, a phosphate insecticide to a test animal,
using a drenching gun. A Geiger counter, held by the
worker in the center, keeps a constant check on the radio
activity. Radioactive ETS7 was given to cattle to determine
residues remaining in the various tissues and in the milk,
the rate at which the chemical is eliminated from the
animal’s body, how it travels within the animal and how
it kills grubs (USDA Photo)''
New Chemicals Kill Cattle Grubs
While Inside Infected Animals
The search for a chemical that can be given to cattle
orally or by spraying to destroy cattle grubs inside the ani
mal body has turned up two insecticides that may be just
what scientists have been looking for, U. S Department of
Agriculture reports
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Most promising of these finds
is ET-57, a phosphate compound
that is given to cattle by mouth as
a drench or in a large cylindrical
pill. It dissolves and passes
through the walls of the digestive
tract, quickly circulating in body
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Maggots
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LIFE CYCLE OF THE HEEL FLY. Heel
flies begin to chase cattle during the first
warm days of spring. The cattle run fran
tically to escape these insects, which can
not bite or sting. The female flies lay their
eggs on the short hairs of the animal’s
heels. In a few days the eggs hatch and
the larvae, or maggots the cattle grubs
burrow through the various body or
gans and muscular tissue of the infested
fluids to all parts of the animal
The ability of the chemical to
permeate the animal’s body tis
sues distinguishes it as a “sys
temic” insecticide.
Cattle grubs the larvae of
heel flies usually enter the
bodies of cattle near the heel and
burrow upward through the flesh.
They are apprently killed when
the animals are treated with
ET-57. If this insecticide is admin
istered before the grubs reach the
animal’s back, damage to the
flesh is reduced and the grubs do
not make holes in the hide.
The other systemic that has
performed well against cattle
grubs in preliminary tests is
Bayer 21/199. This chemical, also
a phosphate compound, is admin
istered by spraying over the ani
mal. The way this insecticide gets
into the animal body to kill the
grubs has not been fully deter
mined, but at least some of the
chemical is known to be absorbed
through the skin.
USDA scientists know much
less about 21/199 than they do
about ET-57, but results to date
are encouraging. An insecticide
such as 21/199 that can be
sprayed on is easier to use, es
pecially on range cattle, than one
that must be given by mouth.
Neither ET-57 nor 21/199 is
available commercially, and these
chemicals are not yet recom
mended for cattle-grub control.
Additional research is needed
on their possible toxic effects on
treated animals, on whether they
leave any toxic residues in meat
or milk, and on practical meth
ods and timing of treatments.
Cattle grubs cost the U S live
stock industry an estimated $lOO
million to $2OO million every
year. They damage both hides and
flesh of beef animals. Packing
losses due to these parasites
sometimes run as high as $7 to
$8 per carcass.
The only insecticide now being
used to kill cattle grubs is rote-
Larva
iiiiiil
none, derived from the tropical
derris plant. This chemical has no
systemic action. Used as a spray,
wash, dip, or dust, it kills a high
percentage of the grubs once they
have reached the backs of infest
ed animals. But by that time the
parasites have already damaged
the flesh and hide of their hosts.
Various other insecticides and the
chemical phenothiazme. widely
tested for use against cattle
grubs, have proved ineffective.
Experiments made early in
1955 by entomologists of USDA’s
Agricultural Research Service at
Corvallis, Ore., first showed the
systemic grub-killing powder of
ET-57. Technical name for this
chemical is 0,0-dimethyl 0-2,4,5-
tnchlorophnyl phosphorothioate.
The studies made so far indi
cate that a single dose at the rate
of 100 milligrams of ET-57 for
each kilogram of the treated ani
mal’s body weight will kill prac
tically all cattle grubs present in
the animal. This amounts to a
dose of about 1.6 ounces for an
animal weighing 1,000 pounds.
Best time for treatment seems to
be near the end of the heel-fly
season in midsummer.
Administered at this rate, the
chemical does not appear to be
toxic to the animal and causes no
off-flavors in the meat. USDA re
searchers believe, however, that
on the basis of present evidence
the insecticide should not be
given to beef animals less than
30 days before slaughter, to pre
vent any possibility of traces of
the chemical remaining in the
meat. It appears unlikely at pres
ent that ET-57 can be recom
mended for dairy cattle if their
milk is to be sold Rotenone can
be used for effective control of
cattle grubs in producing dairy
animals.
The Oregon and Texas Agricul
tural Experiment Stations have
cooperated with USDA in testing
the meat of treated animals for
off-flavors due to ET-57. Their
results show no apparent flavor
cattle. Finally they reach the underside of
the skin on the animal’s back, where they
stay for 35 to 60 days, breathing through
the holes they make in the hide. As the
grubs mature they fall to the ground and
burrow into the soil to pupate. About three
to II weeks later, depending on the tem
perature, they emerge as heel flies. When
the female flies lay their eggs, the cycle
begins again. (USDA Photo) (
Rhoads Sells Bull
Jerome H. Rhoads, Kirkwood,
has sold the registered Guernsey
hull, Rhoadsacres Actor’s Merit,
according to the American Guer
nsey Cattle Cluh.
This bull was sold to Robert
F. Mendenhall, Avondale, Pen
nsylvania.
changes, even when the test ani
mals were slaughted only 10 days
after treatment. At that time an
estimated two parts per million of
the chemical was still present m
the fat.
The effectiveness of ET-57 in
killing cattle grubs has been
tested in beef animals by USDA
and several state agricultural ex
periment stations, notably that of
Oklahoma. A number of other
states have shown an active in
terest in the’ research on cattle
grub systemics.
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