﻿108 BULLETIN 1369, V. S. DEPARTMENT OE AGRICULTURE 



5.13. In 1921-22 the cattle were all examined and grubs extracted 

 on December 16 and January 17, the average per head being 3.55, 

 In 1922-23 the grubs were all extracted on November 28, Decem- 

 ber 28, January 29, and March 21, the average per head for the year 

 being 11.30. During 1923-24 the cattle were gone over four times 

 and an average for the year of 7.5 grubs per animal was found. 

 During the last three seasons the work was done very thoroughly, 

 yet it appears that enough flies entered the pasture from adjoining 

 farms to keep up the infestation. It is thought that this is a rather 

 peculiar case, however, on account of certain local conditions. 



Duncan, Hewitt, and Jardine (^8) have reported a similar ex- 

 perience on a farm in Ireland. The average number of grubs was 

 materially lowered after the first year's destruction, but for several 

 succeeding years it remained rather constant, though relatively low. 



The writers have observed a number of instances, however, where 

 well-isolated dairymen and breeders have largely, if not completely, 

 eradicated the pest from their herds by systematic destruction of 

 the grubs. 



In attempting to control the insect on the individual farm it is im- 

 portant to destroy the grubs in the young stock, and also to kill those 

 larvae which reach the backs rather late in the season. 



POSSIBILITIES OF ERADICATION BY SYSTEMATIC DESTRUCTION 



OF GRUBS 



For many years the possibilities of completely eliminating this 

 destructive pest from given areas have been presented. In 1896 

 Osborn (73), after discussing methods of destroying the grubs, says: 



While it is certain that this insect could be practically exterminated in the 

 United States in a single year, we realize fully the great difficulty in getting 

 every person owning cattle to know or appreciate the need of using the neces- 

 sary means . . . We can not close this sketch of remedies without present- 

 ing a plan which, though it may be styled fanciful or ideal, must if carried out 

 result in the extermination of the pest and the saving, we believe, of not less 

 and probably more than $50,000,000 per year to the farmers of the United 

 States. 



He then briefly outlines his plan of having all cattle examined 

 and the grubs extracted or destroyed by chemical treatment. Other 

 authors have presented somewhat similar suggestions, but until re- 

 cently it would appear that the knowledge of the seasonal history 

 of the two species of grubs in this country has been too meager to 

 make possible the formulation of very definite plans. From studies 

 which have been made in various parts of the world on this problem 

 it appears certain that eradication from considerable areas, if not 

 from entire countries, can be accomplished and that such effort would 

 be very remunerative to the dairy and livestock industries. In con- 

 sidering the possibilities for eradication the following facts should 

 be borne in mind: 



1. Both species of Hypoderma confine their attack almost ex- 

 clusively to domestic cattle. It is probable, however, that in vicini- 

 ties where bison range these grubs might readily be carried over in 

 numbers in such herds. Horses and goats are the only other hosts 

 which would have to be considered at all, and the writers' observa- 

 tions clearly indicate that they would not play a part in perpetuating 

 this species if all grubs were destroyed in bovines. 



