﻿112 BULLETIN 1369, U. S. DEPAETMENT OF AGRICULTURE 



The distance from the gullet and viscera to the subcutaneous tis- 

 sues of the back is apparently traversed very rapidly by the larvae. 

 Soon after the larvae reach the back they cut a hole through the 

 skin. The duration of the third stage of H. lineatum after the 

 skin of the back is punctured averaged 4.5 days at Dallas, Tex., and 

 4.26 days in New York; in H. hovis it averaged 3.35 days in New 

 York. The average duration of the fourth stage of H. lineafuTn was 

 24.5 days and of H. hovis, 27.1 days. The development of the fifth 

 stage of H. Uneafum required an average of 30.3 days in Dallas, Tex., 

 and that of H. hovis about 40 days in New York. 



The total developmental period in the backs of cattle has been 

 determined with fair accuracy in many individuals at points in 

 Texas and New York. The three shortest developmental periods 

 recorded at Dallas, Tex., were between 35 and 47, between 38 and 40, 

 and between 39 and 46 days, respectively. The average at Dallas, 

 Tex., was 56.3 days in one series and 57.7 days in another, whereas at 

 Uvalde, Tex., it was 49.4 days. The developmental period of H. hovis 

 in the backs of cattle in New York was 77 days (maximum), 65 days 

 (minimum), and 72.8 days (average). 



Mature larvsa may emerge from the host at any time of day or 

 night, but the largest number as recorded by the writers emerged 

 during the middle of the forenoon. The time from emergence from 

 the host to appearance of the flies of H. lineatum at Dallas, Tex., 

 ranged from 18 to 77 days, with an average of 41.7 days. In the case 

 of H. ho-vis at Middletown, N. Y., this period ranged from 22 to 45 

 days, with an average of 31.34 days. 



Mating of the adults of H. lineatum takes place very soon after 

 emergence, and oviposition may begin a few minutes after copulation. 

 There are some distinct differences in the habits of oviposition of 

 H. lineatum and H. hovis. Among other things the flies of the latter 

 species are more persistent in their attack on the cattle and induce 

 greater fear in them. H. liiieatmn may ovipost at a temperature as 

 low as between 40 and 45° F., but oviposits freely between 55 and 

 85° F. 



The adults of H. lineatum lived in captivity from 1 to 25 days. 

 The average life of the adults of this species is about 5 or 6 days 

 and H. hovis has a similarly brief life span. 



The seasonal history of H. lineatum varies widely according to 

 latitude and other conditions. In southwestern Texas the flies may 

 appear and lay eggs in the fall or early winter so that the whole life 

 cycle may be correspondingly earlier than elsewhere in the country. 

 As the higher latitudes and altitudes are approached the various 

 stages in the life history are later. In the northern edge of the 

 United States the adults do not begin to emerge until about April 1. 

 The seasonal development of the larvae is closely correlated with that 

 of oviposition; for instance, in southwestern Texas the earliest grubs 

 may reach the backs of the cattle in July, at Dallas, Tex., in Sep- 

 tember or October, at Ames, Iowa, during January, and at Herkimer, 

 N. Y., in February. The earliest appearance of the larvae of H. hovis 

 in the backs of cattle is somewhat later than that of H. lineatum.. 

 The dates in different regions when the earliest larvae become mature 

 and leave the host, and the dates when the last larva has reached the 

 back, are matters of much importance in connection with control 



