BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE 93 
observed that the grub population had been reduced about 84 percent 
in comparison with untreated herds in the same locality. 
The possibility of using sulfur-cube dip in cattle grub control was 
investigated. This dip is now being used for louse control, and the 
advantage of a treatment with a dual purpose is obvious. Single 
dippings killed a low percentage of grubs, but two dippings at 17- 
attd 19-day intervals killed 67.3 percent of them. This indicates the 
desirability of further experiments in which the number and interval 
of the dippings are varied. 
EXTERNAL PARASITES OF SHEEP, GOATS, AND CATTLE 
Progress was made in the study of wetting agents for increasing 
the efficiency of sulfur dips for the control of goat lice. Combinations 
of two or three different wetting agents were found to be superior to 
any single agent. Twenty such combinations can now be recommended 
as giving the maximum toxicity and better retention of sulfur on the 
skin and hair of the animal. Forty-nine other formulas tested were 
found undesirable. 
In cooperative tests with local ranchmen approximately 7,000 head 
of cattle were dipped in a sulfur-cube dip for the control of the 
resistant, blood-sucking, short-nosed ox louse. This was determined 
as a satisfactory control. Tests were also initiated to determine the 
effect of feeding sulfur to infested animals for the control of lice. This 
treatment has frequently been advocated by stockmen and others. 
After 6 months the infested animals which received a daily ration of 
5 grams of elemental sulfur for every 100 pounds of live weight con- 
tinued to show louse infestation. Treated and untreated animals were 
placed in dark stalls for 3 months each, but no difference in louse 
infestation was noted, as has been sometimes claimed. 
FLY SPRAYS 
Sixteen new materials were tested against flies that are troublesome 
about dairies. Of these, 4 displayed toxicity to cattle but none of 
them exerted a sufficient effect on the flies to warrant further investi- 
gation. A total of 88 materials were tested for their poisonous effect 
on houseflies and only 6 were found which caused greater than 20 
percent mortality in 24 hours. A total of 64 carbon compounds were 
tested to determine their repellency toward houseflies and only 4 of 
them showed strong repellent properties. These tests are being con- 
tinued. It has been determined that the best method of preparing 
home-made fly sprays is to dilute the ordinary commercial 20-to-l, 
or 30-to-l, pyrethrum concentrate with kerosene, and that a good 
quality spray can be made in this way for approximately 42 cents 
per gallon. This method is probably more economical for the fanner 
than extracting the pyrethrum flowers himself. 
MOSQUITOES 
At the invitation of the Tennessee Valley Authority the Bureau 
cooperated with that organization and other Federal agencies to de- 
termine methods of controlling malaria mosquitoes which would not 
adversely affect wildlife in the Tennessee Valley. The following 
agencies were invoved : Tennessee Valley Authority. Fish and Wild- 
life Service, Public Health Service, and Bureau of Entomology and 
