a) 
THE CATTLE GRUBS OR OX WARBLES 85 
access to it. Large numbers of grubs and pupz are destroyed by 
the walking of the catile, 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 any treatment directed against it must 
be applied frequently. During the greater part of the year the 
larve are protected within the body of the host; that is, from the 
time of penetration immediately 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 
f 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. lineatum appears to have 
long since established itself in all parts of the United States where it 
is capable of existing. HH. bovis, 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 River only in scattered localities in the Northern States, 
may cover that region solidly and extend its range well south along 
the mountain ranges. Hewitt (42, 43, and 44) and others have 
stated that Hypoderma appears to be increasing in abundance in 
Manitoba. ‘The importance of /7. bovis 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 H. bovis 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 following 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 other infested countries except during the period 
from December 1 to May 31. Present knowledge of the seasonal 
history of Hypoderma shows clearly that such a restriction would 
not give a complete protection against the introduction of the pests. 
It would appear, however, that some system by which the animals 
could be kept under surveillance and all grubs destroyed during 
the period of one full year after importation would be effective. 
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