﻿THE CATTLE GRUBS OR OX WARBLES 99 



applied at times with two boards hinged at one end. From 1 gallon 

 of water usually not more than 3 pints of infusion was obtained. 

 Serious objections to the use of this decoction are the labor involved 

 in preparing it and the great variability in the strength of the infu- 

 sion obtained. These objections would cause the investigator or 

 stockman to turn to the standardized solutions of free nicotine or 

 nicotine sulfate, but the results obtained with these substances when 

 used at strengths which would not endanger the host were unsatis- 

 factory. Nicotine sulfate at a strength of 0.4 per cent when injected 

 into the cysts of the grubs gave a mortality of only 50 per cent, and 

 free nicotine at a strength of 0.52 per cent with soap added resulted 

 in a mortality of 84 per cent. These strengths are greater than 

 would be advisable for use as general washes on the backs of cattle. 

 The toxicity, to larvae in different stages, of materials applied to 

 the backs of cattle is a point of importance. It is necessary, of 

 course, to kill a high percentage of all stages of larvae present at the 

 time of treatment, but for several reasons it is desirable that treat- 

 ment be made with a view of destroying the grubs while small. To 

 gain some information on this question a study of the percentage of 

 mortality among the different stages was made. For comparison 

 the percentages of mortality among the grubs in the fourth and fifth 

 stages treated with fairly effective larvicides were compared. The 

 materials used were grouped according to method of treatment. 

 These groups and the mortality of the larvae in each were as follows : 

 Cysts injected with syringe or oil can, fourth stage 91.01 per cent, 

 fifth stage 81.21 per cent; ointments applied to the opening in the 

 skin, fourth stage 84.34 per cent, fifth stage 93.32 per cent; dusts 

 applied to the openings in the skin, fourth stage 83.33 per cent, fifth 

 stage 88.05 per cent; washes applied to backs of cattle, fourth stage 

 90.29 per cent, fifth stage 68.77 per cent. These figures should not be 

 taken to indicate the relative merits of the different methods of 

 treatment. They are of value, however, because they clearly shoAv 

 that the ointments and powders are relatively more effective 

 against the larvae of the fifth stage than against those of the fourth, 

 probably owing to the larger apertures in the skin, which permit the 

 materials more readily to gain access to the larvae; but, on the other 

 hand, that the percentage of mortality is higher in larvae of the 

 fourth stage than in those of the fifth when the insecticides are in- 

 jected into the cysts or applied as washes to the backs of the cattle. 

 It appears that the younger stages are somewhat more easily killed 

 than the fifth-stage larvae when they are actually brought into con- 

 tact with the insecticide. Exact observations on the mortality among 

 third-stage larvae have not been made in a sufficient number of 

 specimens to form a reliable basis for conclusions, but for the pur- 

 pose of comparing the relative susceptibility of the three stages to 

 various treatments, it may be said that the mortality runs about 92 

 per cent in the third stage, 89 per cent in the fourth stage, and 83 

 per cent in the fifth stage. 



EXTRACTION OF GRUBS BY HAND 



Tt is the common Ijelief that, the catllc gi-uljs must be fairly well 

 matured before they can Ix' succ(^ssrully removed by hand. The 

 expression is often heard, " the grubs are not yet ripe." 



