﻿THE CATTLE GRUBS OR OX WARBLES . 85 



access to it. Large numbers of grubs and pupse are destroyed by 

 the walking of the cattle, especially in pastures where the animals 

 are concentrated. 



ARTIFICIAL CONTROL 



In considering control or eradication it should be borne in mind 

 that the flies do not feed, nor have any habits been noted which 

 could be utilized in accomplishing their destruction. The flies 

 also do not seem to be sensitive tO' the presence of foreign materials 

 on the host, and therefore are not easily repelled. The egg stage 

 is comparatively short, hence slyij treatment directed against it must 

 be applied frequently. During the greater part of the year the 

 larvae are protected within the body of the host; that is, from the 

 time of penetration immediatel}^ after the hatching of the eggs 

 to the appearance of the third-stage grubs in the subdermal tissues 

 of the back. There is, however, a rather definite period, usually 

 not exceeding four months, during the fall, winter, and spring, 

 varying according to latitude, during which the grubs are localized 

 in the backs of the cattle where they may be reached through the 

 apertures in the skin. The fact that both species are practically 

 incapable of developing in hosts other than cattle is also a point 

 of distinct advantage in any control procedure attempted. 



POSSIBILITIES OF CHECKING THE SPREAD OF HYPODERMA 



■No effort has been made in this country to check the spread of 

 either species of Hypoderma. In fact H. lineatuni appears to have 

 long since established itself in all parts of the United States where it 

 is capable of existing. FI. hovh, on the other hand, is much more re- 

 stricted in distribution and it appears that it is capable of becoming 

 much more widely disseminated in this country. 



It is probable that H. bovis, which at this time occurs west of the 

 Mississippi Eiver only in scattered localities in the Northern States, 

 may cover that region solidly and extend its range well south along 

 the mountain ranges. Hewitt (^f', 4-3, and 44) and others have 

 stated that Hypoderma appears to be increasing in abundance in 

 Manitoba. The importance of H. hovis as a cattle pest is sufficient 

 to warrant serious consideration of ways and means of checking its 

 spread in this country. It may not be advisable to take legal steps 

 to meet the situation.' but certainly stock raisers should recognize the 

 danger of bringing cattle infested with //. hovis into regions where 

 that pest does not exist, and take due precautions to destroy all grubs 

 which reach the subcutaneous tissues of the backs during the spring 

 and summer folloAving the arrival of the cattle. Certain uninfested 

 foreign countries have enacted legislation designed to prevent the es- 

 tablishment of Hypoderma. Australia {2)^ for instance, has a law 

 prohibiting the introduction of cattle from the United States, the 

 British Isles, and othei- infested countries except during the period 

 from December 1 to May HI. Present knowledge of the seasonal 

 history of Hypoderma shows clearly that siu-h a restriction would 

 not give a complete protection against tlie introduction of the pesis. 

 It would apjjear, however, thai some system by which the animals 

 could be kept under surveillance and all gi'iihs deslroyi'd during 

 the period of one full year after inijoriation would he cHective. 



