﻿78 BULLETIN 1369, U. S. DEPARTMENT OP AGRICtJLTUEE 



The time of maximum abundance of larvse in the backs of cattle 

 varies considerably in different herds and during different years. At 

 Dallas, Tex., this maximum usually occurs, on the average, about 

 January 10, and at Uvalde, Tex., about December 15. 



The date when the last grub leaves the cattle varies considerably 

 in different herds, as well as in different localities and during a 

 series of years. This point is of little economic importance for H. 

 lineatuon in those States where H. h&vis also occurs, for the latter 

 always persists in the hosts later in the season, and the two species 

 must be dealt with as a unit. At Dallas, Tex., the date when cattle 

 become free from grubs in their backs has been determined during 

 several years. In 1915 this date was March 20 ; in 1916, April 12 ; 

 in 1917, March 18; in 1919, March 15; in 1921, March 20; and in 

 1922, March 16. At Uvalde, Tex., Mr. Parman has observed the 

 cattle to become free of grubs between January 20 and April 12. It 

 is interesting to note that Mr. Babcock found two specimens of 

 H. Uneatuni in the back of a cow at San Angelo, Tex., on March 20, 

 1924. These larvse would not have been mature in less than 15 days. 

 Since the grubs of this generation began to appear in the backs of 

 cattle in that region about August 2, there is a remarkable and very 

 unusual period of infestation of the backs of cattle of about eight 

 months. Thus it appears that there is a wider variation from year 

 to year in this respect in southwestern Texas than occurs elsewhere. 

 A very general idea of the time when all larvae of H. lineatum 

 have emerged from the cattle may be gained from the following 

 dates: March 1, southern Arizona and southern California; March 

 15', Alabama, Georgia, North Carolina, Oklahoma, and southern New 

 Mexico; April 15, Maryland, Missouri, and Nevada; May 1, Penn- 

 sylvania, Indiana, Colorado, Idaho, and Washington; June 1, North 

 Dakota and Michigan ; June 15, New York and Montana. Observa- 

 tions made by W. E. Dove in 1924 indicate that all larvse of H. 

 lineatuQn would have left the cattle in the vicinity of Aberdeen, 

 S. Dak., about May 5, and at Minot and Dickinson, N. Dak., and at 

 Moorhead, Minn., about May 10. The season, however, was more 

 advanced that spring than usual. On May 1, 1924, all grubs were 

 found to have emerged from cattle at Sioux Falls, S. Dak. 



In general the duration of the infestation of the backs of cattle 

 in H. hovis is longer than in H. lineatum. This is brought about 

 through the longer developmental period of the larvae in this situa- 

 tion and the wider spread of time between the date the first larvae of 

 H. hovis reach the back and the date the last ones appear there. 

 The writers' records indicate that the earliest larvae of H. hovis reach 

 the subcutaneous tissues from one to two weeks after those of H. 

 lineatuon. On the other hand, the larvae of H. lineatum arrive in 

 that portion of the host in much larger numbers proportionately 

 during the first month or six weeks following their first appearance. 



The writers have checked closely the' earliest appearance of larvae 

 of H. hovis in the subdermal tissues, as well as the time of dropping 

 of the last grubs in herds of cattle in New York during three seasons. 

 The earliest appearance of H. hovis was February 2 in 1923 in 

 Orange County, N. Y. In 1920' they appeared about February 26, 

 and in 1922 about Februaiy 22. At Herkimer they first reached the 

 subdermal tissues about March 8 in 1920, April 15 in 1921, and 



