﻿THE CATTLE GKUBS OR OX WARBLES 87 



The construction of sheds is advisable where they will perform 

 the double service of protecting the stock against heel jflies and from 

 adverse climatic conditions. 



REPELLENTS AGAINST HEEL FLIES 



For many j'eai-s various ill-smelling applications have been used 

 with the view of protecting cattle from the attack of heel or warble 

 fjies. Prior to the last few years, during which our knowledge of 

 the life history of these pests has clearly showed that the eggs are 

 not deposited on the backs of the cattle, it was the custom to use 

 various repellent smears and washes upon the backs of cattle. As 

 it is now known that the eggs are deposited largely on the legs and 

 lower portions of the body, the futility of this practice is at once 

 evident. Inquiry into the results of the application of fly sprays 

 has led the writers to conclude that the claims that they are efficient 

 against grubs are unfounded. 



The fact that the adults of Hypoderma do not partake of food 

 would suggest that their reaction toward attractant and repellent 

 chemicals or other substances would be less than in those species 

 which have the senses developed to aid them in finding food or breed- 

 ing places. The writers' experiments and observations along this 

 line seem to bear out this conclusion. It appears probable that the 

 application on the animals of materials which tend to cover the hair 

 or mat it together may aifect oviposition more than those materials 

 possessing various odors supposed to be repellent. The experiments 

 in this field, however, have not been sufficiently extensive to enable 

 final conclusions to be drawn. 



During 1919 a dairy herd of 61 animals was used in tests of the 

 application of repellents and solvent solutions, as follows : 2 per cent 

 compound solution of cresol, 10 per cent solution of acetic acid, un- 

 diluted fuel oil (petroleum), and a mixture of 1 gallon of fish oil 

 with 1 pint of commercial pine tar. These materials were applied 

 to the legs of cattle, some with a spray pump and others with a 

 brush. The applications were made at about 4-day intervals during 

 the period when heel flies were active. While the treatments were 

 being administered heel-fly eggs were found on several of the treated 

 animals. Some were even present on the legs of those treated with 

 petroleum, and on those treated with a mixture of fish oil and pine 

 tar. 



Observations made incidentally in the experiments discussed under 

 "Destruction of eggs or larva? by the use of wading vata" indicate 

 that the application of 2 per cent coal-tar creosote dips at 4-day in- 

 tervals has no marked effect in repelling flies. The same is true of 

 wading-vat experiments with arsenical solutions. 



On a number of occasions whei-e cattle waded and got their feet 

 and legs well covered with mud the flies wci-e found to deposit their 

 eggs freely on the legs above it. The ai)plication of gummy mate- 

 rials to the entire animal has not been tried, but this would hardly 

 seem feasible from a practical viewpoint. 



DESTRUCTION OF EGGS OR LARV^ BY THE USE OF WADING VATS 



The fact that a consideralilc pciccntagi" of the eggs of Hypoderma 

 are laid on the lower legs at once suggests the possibility of destroy- 



