BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE 85 
a normally mild winter the pest is able to survive as far north as 
Valdosta, Ga., but during severely cold seasons the overwintering 
line is about 100 miles south of that locality. 
HORN FLIES 
The results obtained with an automatically operated fly trap dur- 
ing the second season of tests with this device continue to show its 
effectiveness in controlling horn flies on dairy and range cat tie. On a 
large ranch near Fort Worth, Tex., the infestation of herds in pas- 
tures where these traps were in operation seldom exceeded 150 flies 
per head, whereas that of herds in circumjacent pastures where no 
traps were operated was 3,500 to 4,000 flies per animal. 
Experiments were continued on the development of a method of 
controlling horn flies by feeding cattle certain insecticides which 
pass unabsorbed through the alimentary tract of the animal and 
render the feces unsuited for the development of horn fly larvae. 
Feeding phenothiazine at a minimum rate of 22 milligrams per kilo- 
gram of body weight was found effective in preventing horn fry 
development; however, this chemical appears unsuitable for this 
method of horn fly control since it causes a discoloration of the ani- 
mal's milk, and continuous feeding or slight overdoses have a tend- 
ency to disturb the digestive processes or physical condition of the 
animal. Another chemical has been discovered which when admin- 
istered in doses of 8.8 milligrams per kilogram of body weight is 
as effective as phenothiazine in preventing horn fly breeding and so 
far has not shown any ill effect on test animals. 
CATTLE GRUBS 
A practical method has been developed for treating range cattle 
for cattle grubs. It consists in applying to the backs of the infested 
animals a wash composed of 12 ounces of derris or cube powder, 4 
ounces of soap, and 1 gallon of water. The cattle are run through 
chutes, and about one-third of a quart of the wash is distributed 
evenly over the back of each animal and then thoroughly rubbed 
in with the hands, the application requiring about 2 man-minutes per 
animal. In the more northern sections better results are obtained 
if the wash is warmed before the cattle are treated. In the southern 
parts of the country, where cattle do not carry a very heavy winter 
coat, about one-third less derris or cube will give almost as good 
results as the larger quantity. 
EXTERNAL PARASITES OF SHEEP, GOATS, AND CATTLE 
Continued research on methods of controlling various external 
insect parasites of animals has shown that a dip consisting of 100 
pounds of wettable sulfur plus a wetting agent and 10 pounds of 
cube or derris powder containing 5 percent of rotenone in 1,000 gal- 
lons of water will kill all species of adult lice attacking sheep, goats, 
and cattle in the United States. This dip will also destroy the adults 
of the sheep tick, and tests so far indicate that it is effective against 
horse lice. In connection with the experiments with wettable sulfur, 
wetting agents have been developed that permit the use of sulfur in 
alkaline water without causing flocculation. 
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