United States Department of Agriculture
Agricultural Research Administration
Bureau of Entomology and Plant Quarantine
DDT SPRAYS FOR THE CONTROL OF THE GULF COAST TICK--
A PRELIMINARY REPORT
By E. B. Blakeslee and W. G. Bruce
Division of Insects Affecting Man and Animals
Tests conducted by the Bureau of Entomology and Plant Quaran-
tine in 1945 and 1946, in cooperation with the Florida Agricultural
Experiment Station, indicate that the Gulf Coast tick (Amblyomma
maculatum Koch) can be effectively controlled on cattle by the use
of full-coverage DDT sprays (1). In a test at St. Augustine, Fla.,
in 1945, the ticks on animals treated with a 2.5-percent LDT spray
were so severely affected by the DDT residues that many of them
never reached the ears of the animals. Some ticks were able to at-
tach but did not survive long enough to begin engorgement, and only
a negligible number lived to become corr:'-letely engorged.
In 1946 an effort was made to verify the observations of the
previous year and to determine the relative effectiveness of sprays
and ear smears under ranch conditions. A 2.3-percent DDT spray was
compared in field tests with two of the most effective ear smears
known. One of these ear smears, designated as Savannah No. 5, was
an experimental material containing 7.5 percent of DDT, which had
been used with considerable success for the two previous years.
This material resembled a slightly sticky cold cream, and repre-
sented an attempt to eliminate some of the disagreeable features of
viscous resins used in other smears. The other ear smear, known as
stock 1037 (2), contained 5 percent of DDT in a semifluid base of
nondrying resins. The 2.3-percent DDT spray, was made by mixing 2
pounds of 50-percent wettable DDT powder in 5 gallons of water.
Three lots of animals were treated in each test, one with each
ear smear and one with the spray. A fourth lot of untreated animals
was used as a check. The ear smeirs were applied to both the inside
and outside of the animals' ears and thoroughly rubbed in with the
bare hands. The spray was applied with a small power sprayer, and
the animals were wet thoroughly on all parts of the body, about l1
to 2 pints of spray being used per head.
In one test, at St. Augustine, Fla., the indicated control of
ticks was 68 percent for Savannah No. 5 And ` percent for both
stock 1037 and the DDT spray. In another test, at Indiantown, Fla.,
the indicated control was 85 percei;t for vanah N. 5, 3" percent
for stock 1037, and 90 percent for the Li--y. Further evidence
h' 5~ V9J7
of the effectiveness of DDT sprays against this tick was also ob-
tained in a ranch test in southern Florida, where a severe tick in-
festation was brought under complete control by a 2.3-percent DDT
spray applied on September 4.
Suggestions for Use
Although a number of questions connected with the use of DDT
sprays on cattle for the control of the Gulf Coast tick have not
been fully answered, the results of the tests are considered suffi-
ciently definite to justify their adoption by stockmen on a trial
basis. The severity of tick infestations varies so widely between
different parts of the country, and sometimes between different
parts of the same ranch, that is is impossible to make a blanket
recommendation for all conditions. Tests show that the DDT spray
is as effective as ear smears, and that it will give satisfactory
control for about 1 month. It is believed that in most of the
Southeast two applications of sprays during the active tick season
will give satisfactory control, the first to be applied about the
latter part of July or early August, and the second a month later.
It should be emphasized, however, that the DDT spray is a treatment
for preventing the attachment of ticks and the resulting lesions
that predispose screwworm infestations. Therefore, its success de-
pends on keeping an effective DDT residue on the animals during the
active tick season. Many herds of cattle are now being treated with
DDT sprays for the control of other pests, such as biting flies,
mosquitoes, and lice, and their use against ear ticks will require
only slight modification in the schedule of dosage and timing now
The minimum spray concentration required for tick control has
not been determined. All the 1946 tests were made with a 2.3-percent
DDT spray, and it is suggested that for the present at least this
concentration be used, especially where ticks are extremely trouble-
some. The concentration should not be reduced below 1.5 percent,
the strength now recommended for the control of other external para-
sites of cattle in the Southeast. Whether or not the lower concen-
tration will prove effective against ticks is not known. The 2.3-
percent DDT spray can be made by mixing 2 pounds of wettable powder,
containing 50 percent of DDT, in 5 gallons of water. Use 1 pound of
the powder in 4 gallons of water to prepare a 1.5-percent spray.
A few animals may be sprayed with hand equipment, but a small port-
able power sprayer with a satisfactory agitator will be useful for
treating larger numbers.
(1) Blakeslee, E. B., Tissot, A. N., Bruce, W. G., and Sanders, D. A.
1947. Experiments with DDT for the control of the Gulf Coast
tjik-A preliminary report. Jour. Econ. Ent.
(2) Rude, C. S.
1946. A new remedy for the control of the Culf Coast tick.
U. S. Bur. Ent. and Plant Quar. E-686, 3 pp.
UNIVERSITY OF FLORIDA
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