92 ANNUAL KK1MJKTS OF IJKI'AKTMKNT OF A( IKIC I" LT V KF, 1940 
widely tried by slock owners, most of whom arc enthusiastic about it. 
Experiments were conducted to find wound protectors even more ef- 
fective thai! diphciiylaminc. and these tests involved the treatment 
of some 1.700 HTcwworm cases under field conditions. In addition, 
133 oj her chemical compounds which appear promising as screwworm 
larvicides were given preliminary laboratory tests. 
Reinfestations of a chemically treated wound with screwworm eggs 
have never been recorded so long as the wound was strongly acid or, 
in other words, maintained a pH value of G.O or below. On the 
other hand. oviposition increased at a pi I value of 6.4 and continued 
to increase as the wound lost its acidity until maximum oviposition 
was reached when a wound showed a pH valie- of 7,0 
In a search for fundamental factors involved in protecting a wound 
from screwworm attack it was demonstrated that repellency was one 
of the most important. It was observed repeatedly that the increase 
in protection afforded a treated wound was in direct ratio to the 
increase in repellency of the material used for treatment. For exam- 
ple, p-nitrophenetole showed a repellency of 69.5 percent and a wound 
protection of 19.96 da} r s, pine-tar oil a repellency of 62.8 percent and 
a protection of 16.95 days, and diphenylamine a repellency of 4*J.7 
percent and a j)roteetion of 14.68 days. Two of the materials, p-nitro- 
phenetole and diphenylamine, are larvicides. The former is also an 
ovicide, whereas pine-tar oil has little if any ovicidal or larvh idal 
properties. 
In experiments on larvicides and ovicides for destroying screw- 
worms, it was found that benzene containing 5 or 10 percent thio- 
phene, or 10 percent naphthalene, and undiluted tolvene is superior 
to undiluted benzene as a larvicide, while xylene and p-cymene are 
inferior. P-nitroanisole and o-nitrophenol killed 100 percent of the 
eggs of the screwworm fly. 
Great variations in protection from screwworm reinfestation in like 
individuals treated with the same wound protector were observed, 
and were found to be due to the factor of the individual animal 
or its inherent disposition and reaction to fly attack. 
HORN FLIES 
Satisfactory results were obtained for the second season with the 
automatically operated cattle-fly trap. It was found that cattle 
quickly learned to use a trap to relieve themselves of flies, and in- 
festations were reduced from 3.000 to 4.000 flies per head in unt rapped 
pastures to 200 flies per head in trapped pastures. 
To make t his met hod of control available to -lock owner-, a circular 
was issued describing the use and construction of the trap. A public- 
service patent ha- been granted on this trap. 
A- a result of <» s tests with the medication of cattle for the preven- 
tion ol horn flies breeding in their droppings, it was found that of 
the 29 chemicals used in these tots rolenone was by far the most 
effective. Rotenone, however, is expensive and for that reason may 
be impracl ical. 
CATTLK GRIHS 
Iii cooperation with ranch owner- and the Texas Agricultural K\- 
perimenf Station and Extension Service further studies were made 
on the control of cuttle grubs in range animals. On some of these 
ranches where experimental control work is in the third year it was 
