﻿THE CATTLE GRUBS OR OX WARBLES 



93 



of the larvse in situ. In such cases the observations were continued 

 for several weeks to determine the eifect on the host of the destruction 

 of the grubs bj^ this method. In order to make accurate observa- 

 tions on tlie killing power of the various materials used, most of 

 these were administered after the major part of the grubs had 

 reached the fifth or last stage. In most cases a sufficient number of 

 grubs were in the younger stages so that the effect of the various 

 materials upon them could be determined. The tests indicated that, 

 although the younger stages may be more susceptible to the action 



Fig. 35. — Injecting HypuUcrma cysts with chemicals by means u 



I an oil can 



of the insecticides, in those stages they are probably more protected 

 against the materials, since the apertures in the skin are usually 

 much smaller. 



]\Iost of the tests in which the results Avere carefully checked are 

 given in Tables 11 and 12. It Avill be observed from a study of the 

 results that a number of the materials Avill produce a mortality above 

 80 per cent. The writers are of the opinion that materials which 

 will not accomplish the destruction of at least 80 per cent of the grubs 

 present should not be considered as practicable. On the other hand, 

 some of these materials which gave a very high percentage of de- 

 struction are not adapted to use in general practice on account of the 

 cost. 



