112 BULLETIN 1369, U. 5S, DEPARTMENT OF AGRICULTURE 
The distance from the gullet and viscera to the subcutaneous tis- _ 
sues of the back is apparently traversed very rapidly by the larve. — 
Soon after the larve 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. bovis it averaged 3.35 days in New 
York. The average duration of the fourth stage of H. lineatum was 
24.5 days and of H. bovis, 27.1 days. The development of the fifth 
stage of H. lineatum required an average of 30.3 days in Dallas, Tex., 
and that of H. bovis 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. bovis 
in the backs of cattle in New York was 77 days (maximum), 65 days 
(minimum), and 72.8 days (average). 
Mature larvee 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. Inthe case 
of H. bovis 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. bovis. 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. lineatum may ovipost at a temperature as 
low as between 40 and 45° F., but oviposits freely between 55 and 
Sore ie 
The adults of H. lineatwm 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. bovis 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 earler 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 larvee 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 larve of H. bovis 
in the backs of cattle is somewhat later than that of H. lineatwm. 
The dates in different regions when the earliest larvee 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 | 
