BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE 61 
Preliminary studies conducted in cooperation with the Oak Ridge, 
Tennessee National Laboratory, under contract with the Atomic En- 
ergy Commission, indicate that gamma rays from radio-active cobalt 
have the same effect on flies as do X-rays. This method of causing 
sterility would be much more practical than X-rays. Cooperative 
studies with a commercial electric company also indicate that cathode 
rays will cause sterility of the flies. 
Dips Evaluated for Control of Cattle Ticks 
Most of the research on control of ticks on cattle has been devoted 
to the evaluation of dip formulations of toxaphene and DDT-lindane 
wettable powder preparations. Much of this work was done in co- 
operation with commercial companies. Toxaphene (0.5 percent) and 
DDT-lindane (0.5 percent DDT-0.025 percent lindane) formulations 
are now recommended for use as sprays. However, when vats are 
charged with them they tend to deteriorate, resulting in decreased 
efficacy and greater hazard to the animals. A considerable number 
of cattle have been killed in Texas, Florida, and in Central America 
because toxaphene emulsion dips have deteriorated in vats within a 
few weeks or months after they were charged. Basic studies on the 
cause of such deterioration have been undertaken. By microscopic 
examination of the dips at regular intervals during the season, follow- 
ing routine dipping of cattle, sheep, and goats, it was noted that the 
emulsion particles tend to coalesce. Samples of hair from dipped 
cattle were also analyzed for toxaphene following each dipping. 
These studies showed that as the emulsion particles became larger 
there was an increase in the amount of toxaphene deposited on the 
hair of the dipped animals. 
Two commercial preparations of emulsifiable toxaphene are under 
study. From the standpoint of stability in vats these are much su- 
perior to other products marketed in the last few years. 
Improved Sprays for Controlling Flies Affecting Livestock Sought 
In further research on the control of horn flies a new insecticide 
known as Q-137 (l,l-dichloro-2,2-bis (^-ethyl phenyl) ) has been eval- 
uated on cattle. It appears to be equal in efficacy to methoxychlor, 
DDT, toxaphene and other insecticides now used for controlling this 
pest. Xo information is available, however, as to whether the in- 
secticide accumulates in fat of cattle or is excreted in milk in hazard- 
ous quantities. 
A series of tests with DDT for horn fly control in Florida on herds 
of cattle indicate that the insect has not acquired any significant 
resistance to DDT in these areas. The same concentration and amount 
of DDT used in 1945 were applied in 1951. The periods of effective- 
ness of the treatments were approximately equal. 
A search for new insecticides and repellents for the stable fly have 
continued. Sulfoxide and n-propyl isomer were tested in combina- 
tion with pyrethrum and applied as mist sprays to cattle. These 
two synergists, which step up the potency of the insecticide, were 
equal in performance to piperonyl butoxide. It was noted that the 
degree of protection afforded was extremely variable, depending ap- 
parentl} T on the prevailing temperature and amount of sunshine. 
