THE CATTLE GRUBS OR OX WARBLES Q9 
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 larvee 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 larve 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 larve 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 | 
apphed 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 show I 
that the ointments and powders are relatively more effective 
against the larvee 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 larve; but, on the other 
hand, that the percentage of mortality is higher in larve 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 larvee when they are actually brought into con- 
tact with the insecticide. Exact observations on the mortality among 
third-stage larve 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 
It is the common belief that the cattle grubs must be fairly well 
matured before they can be successfully removed by hand. The 
expression is often heard, “the grubs are not yet. ripe.” 
