﻿!rHE CATTLE GRUBS OR OX WAEBLES 91 



kept under tlie most favorable conditions, hence there is difficulty 

 in determining the percentage of mortality chargeable directly to 

 tlie treatment. The tests made show clearly, however, that Hypo- 

 derma larvae, especially in the later stages of their development, 

 are very resistant to contact insecticides. In these tests some 25 

 or 30 different materials were used. Those were selected which 

 would seem to be adapted to use in the destruction of grubs in the 

 cysts in the backs of the hosts. The period of submergence in most 

 cases was about two minutes. 



Mention will be made of only a few of the results obtained, since 

 it appears impractical to determine by this method the efficiency 

 of the various materials when applied to the warbles in the cysts. 

 In these experiments it appeared that the saponified coal-tar creo- 

 sote products gave the highest percentage of mortality within the . 

 first 24 hours. Tincture of iodine U. S. P. also gave a high per- 

 centage of kill soon after treatment. Certain other materials such 

 as iodoform with neutral carriers and 5 per cent solutions of silver 

 nitrate destroyed a high percentage of the grubs but the action was 

 slower. To illustrate the resistance of the larvae to the action of 

 certain insecticides it might be mentioned that submergence for 

 two minutes in such materials as crude petroleum and spirits of tur- 

 pentine killed a comparatively small number. 



APPLICATION OF MATERIALS TO GRUBS IN THE BACKS OF CATTLE 



Many years ago the application of various smears to the backs of 

 cattle was advocated by many, including such authorities as Ormerod 

 {71) in England. The object in view, however, was not the destruc- 

 tion of the larvse in the subcutaneous tissues but the prevention of 

 infestation. In connection with their work the present writers have 

 learned of the use by farmers and dairymen of the injection of such 

 substances as kerosene oil and turpentine into the cysts for the pur- 

 pose of destroying the grubs. Some men have practiced this method 

 for years and are well pleased with the results. In Germany the 

 warble commission {67) advocated the application of birch tar oil to 

 the grubs individually in the backs of cattle. In Ireland and Eng- 

 land, as a result of experiments carried out by Carpenter {18), the 

 application of a tobacco decoction in the form of a wash has been 

 advocated. Rene {81) advises, among other methods of control, the 

 injection of 1 cc. of tincture of iodine into the warble. 



Attempts to employ gas against the grubs in the backs of cattle 

 liave been reported on by Greve {31) and Duncan, Hewitt, and Jar- 

 dine {"28). The results were not encouraging. 



In their own work, experiments along these lines have been carried 

 out by the writers on a rather extensive scale since 1918. Most of 

 these tests have been conducted in a way which made it possible to 

 secure accurate records on the percentage of grubs destroyed by the 

 various treatments. In this work vai'ions dairy herds were utilized 

 in the vicinity of Dallas and othei- points in Texas, in Peoria, 111., and 

 in Orange and Ilei-kimer Counties, N. Y, 



Three fliffcircnt classes of materials were emi)loyed — powders, oint- 

 ments, and lijjuids. The powders were usually applied directly into 

 tlic grub holes by means of u shaker can. The ointments were in 



