Mar., 1917] Distribution of Warble Flies in Ohio 173 



Discussion of H. bovis. — Hypoderma bovis appears to be 

 much the most abundant species in the state, comprising 

 nearly 83.5 per cent of all the specimens. In the northeastern 

 section, 257 specimens, or nearly 53 per cent of all the specimens 

 were obtained. This should not be taken to indicate that the 

 northeastern section is more heavily infested than any other. 

 When the collections made in the vicinity of the Ohio Station 

 are excluded, the northeastern and northwestern collections 

 of H. bovis specimens are about equal, that of the latter com- 

 prising 100 grubs. It may be pointed out, however, that the 

 fly seems to be more generally distributed in the northeastern 

 section. A study of the map shows much larger number of 

 herds free from infection in the northwestern section than in 

 any other section of the state. 



As only one collection of 3 specimens came from vSouth- 

 eastern Ohio, very little can be said of the distribution of bovis 

 in that section. In southwestern Ohio, bovis was taken in 

 five counties. Eight separate collections were made from these 

 five counties, comprising 38 specimens. 



It was hoped that a sufficient number of specimens could 

 be obtained to compare the relative annual abundance. But 

 the number of localities represented and specimens obtained 

 the first year are too meager for such a comparison. Many 

 stockmen, however, claim that there were fewer grubs during 

 the late winter and spring of 1916 than of 1915. 



The earliest collections containing fourth stage grubs were 

 received early in Aiarch from northeastern Ohio. The earliest 

 specimen (one fourth stage grub) came from Ashtabula County. 

 At this date it was the only grub to be found in the cattle's 

 backs. Later (May 3) most of these cattle were reported to be 

 infested. The latest collections were received on June 6 and 10, 

 from southwestern Ohio. In the Ohio Station herd one warble 

 was observed on July 14. On July 20, the grub had emerged. 

 As only H. bovis grubs have been taken from the Station herd 

 for more than three years, it is assumed that this specimen was 

 a representative of H. bovis. Thus H. bovis grubs may be 

 emerging from the first of March until the middle of July. 

 The greatest number of fourth stage grubs were received during 

 April and the next largest number during May. The length 

 of the season in which the grubs make their appearance is of 

 very great importance in deciding what time of year is best 

 to undertake the eradication of the grubs. 



