﻿THE CATTLE GRUBS OR OX WARBLES 113 



and have been determined and mapped with a fair degree of accu- 

 racy in several parts of the country. In general the duration of 

 infestation of the backs of cattle with H. hovis is longer than with 

 H. lin-eatuni, owing to the longer developmental period required by 

 H. hovis. 



Temperature, humidity, cloudiness, and drainage are important 

 factors in natural control. Host resistance as acquired by age 

 is also an important factor in holding down the abundance of 

 Hypoderma. No important insect enemies or diseases affecting 

 Hj'poderma have been found. 



The most effective time for the practice of control procedure is 

 during the period of development of the larvse in the subcutaneous 

 tissues of the back. Destruction of t^he larvae may be accomplished 

 by hand extraction with or without the aid of forceps. In the case 

 of certain breeds of cattle extraction of the grubs is very difficult. 



Tests of the application of washes, powders, and ointments to the 

 backs of the cattle and also the injection of substances into the cysts 

 containing the larvae show that each of these methods of treatment 

 is effective if certain materials are used. Among the most effective 

 should be mentioned: Derris used as a wash, as an ointment, or as 

 a powder; iodoform used as an ointment; pyrethrum applied as an 

 ointment; benzol and carbon tetrachloride injected into the grub 

 cysts; fine tobacco applied in powder form and nicotine dust applied 

 dry. 



No adverse effects on the host have been observed in this country 

 from the destruction of the grubs in the backs of cattle with suitable 

 insecticides. 



The cost of extraction or treatment depends on the skill of the 

 operator but in all cases it is small compared with the benefits 

 derived. 



Experiments with the application to the feet and legs of cattle of 

 certain insecticides and repellents by means of wading vats show 

 that with the materials used control was not brought about, and indi- 

 cate that attack directed against the eggs or young larvae in this way 

 will not be successful. 



Results of individual effort against cattle grubs is likely to be dis- 

 appointing, especially if the work is not thoroughly done and if 

 untreated cattle are in close proximity to the treated herd. 



Systematic treatment of all infested cattle in a neighborhood either 

 by extraction or by the use of insecticides appears to be a practical 

 method of control or eradication. Although these methods are best 

 adapted to dairy or farm conditions it is probable that they may be 

 modified so as to be applied successfully to range cattle. 



In order successfully to combat the insects by destroying the 

 larvae in backs of cattle it is-necessary to treat all infested cattle at 

 intervals of not to exceed 35 days. The first treatment must be given 

 before the earliest larvae have' matured and left the host. In most 

 parts of the United States it is necessary to treat the animals four 

 times during a season to reach all of the larva?. The time of begin- 

 ning the treatments in different parts of the country is indicated in 

 the discussion of seasonal history. 



08252'— 26 8 



