THE CATTLE GRUBS OR OX WARBLES 89 
similar to those used in the experiments described above. They con- 
cluded that the treatments had a very material effect on the infesta- 
tion the following season. Since only 10 animals were used in the 
| test the great variation in the degree of infestation may readily be 
due to causes other than the effect of the treatments. Subsequent ex- 
periments conducted by the Bureau of Animal Industry, however, 
are said to show that a satisfactory degree of control may be brought 
about in range cattle through the use of wading vats (68). 
Studies of the distribution of the eggs of both species of Hypo- 
derma made by the writers show that a large percentage of the eggs 
are deposited elsewhere than on the legs. This is particularly true 
with H. bovis, which deposits many eggs above the hock joint. It is 
also the case with the deposition of eggs on dairy or quiet farm cattle 
by H. lineatum. As has been pointed out in preceding pages, the 
flies often approach such cattle while lying down and deposit large 
numbers of eggs on the escutcheon, tail, and elsewhere, all of which 
would be unaffected by dips apphed in wading vats. 
LABORATORY TESTS OF DIPS ON EGGS OF HYPODERMA LINEATUM 
Several authors have suggested the use of sprays or washes con- 
taining materials designed to dissolve the attachment of eggs of cer- 
tain species of Oestridae. Acetic acid is one of those which has been 
advocated for this purpose. ‘Tests were conducted during 1919 in 
which eggs of H. lineatwm were submerged in a 10 per cent solution 
of acetic acid for periods varying from 3 minutes to 5 days. Follow- 
ing this treatment the eggs were allowed to dry for periods ranging 
from 30 minutes to 13 days, and then the firmness of attachment of 
the eggs to the hairs was tested by scraping and pulling them with 
a dissecting needle or forceps. In every instance the eggs were found 
to be firmly attached. In most cases the eggshells would tear in two 
without their attachment to the hair being disturbed. 
Hairs bearing eggs of H. lineatwm were also submerged for a few 
seconds. in 2 per cent coal-tar creosote dips and kept in incubators to 
determine if the eggs would be destroyed. In one of these tests 29 
eggs were submerged three times for an instant in 2 per cent creosote 
dip at 3 p. m. and then placed in an incubator at 90° F. The fol- 
lowing morning one larva had hatched and was very active. During 
the day a total of 21 larve hatched from these eggs and were appar- 
ently normal. Twenty eggs from the same lot mentioned above were 
given three dippings as in the previous lot and on the following 
morning they were again dipped in 2 per cent creosote dip and 
returned to the incubator. These did not begin hatching until the 
afternoon of March 25, a full day later than those in the previous 
lot which were submerged but once. Sixteen or seventeen larva, 
however, hatched from the 20 eggs and all were apparently normal. 
Another series of 26 eggs which were about one-half through their 
normal period of incubation were dipped in a 2 per cent solution of 
a coal-tar creosote dip and placed in an incubator. From these, 19, 
or 73.08 per cent, of the eggs hatched normally. In still another test 
34 eggs were dipped in 2 per cent creosote dip before they were due 
to hatch. An hour later 10 larve had hatched and were active. No 
other larve emerged, thus making a hatch of 29.4 per cent, whereas 
in a check lot the hatch was 31.3 per cent. 
nd caoaeer bate deieabaein aa amet eee pe TEESE TED EP re ~ 
A NE a ee ae 
