﻿THE CATTLE GEUBS OE OX WAEBLES 89 



similar to those used in the experiments described above. Thej^ con- 

 chided tliat the treatments had a very material effect on the infesta- 

 tion the folloTrin^ season. Since only 10 animals were used in the 

 test the great variation in the deoree 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. Un-eatum. 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 applied in wading vats. 



LABORATORY TESTS OF DIPS ON EGGS OF HYPODERMA LINEATUM 



Several authors have suggested the use of spraj^s or washes con- 

 taining materials designed to dissolve the attachment of eggs of cer- 

 tain species of Oestriclae. Acetic acid is one of those which has been 

 advocated for this purpose. Tests were conducted during 1919 in 

 which eggs of H. lineatum 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. lineatum 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 larvse 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 hatcliing 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 20 eggs whicli were about one-half through their 

 normal period of incubation were dipped in a 2 per cent solution of 

 a coal-tar creosote di]j and placed in an incubator. Fi'oni tiiese, 19, 

 or 73.08 per cent, of the eggs hatched noi-rnally. In still another test 

 34 eggs were dipped in 2 per ccnl (•re(jsot(' di|) before they were due 

 to hatch. An hour later 10 larva; had hatched imd were active. No 

 other larvae emerged, thus making a hatch of 29.4 per cent, whereas 

 in a check lot the hatch was 31.3 per cent. 



