﻿THE CATTLE GEtTBS OR OX WARBLES 



33 



Fig. 17. — Hypoderma lineatum: Pos- 

 terior stigmal plates of fifth-stage 

 larva. Greatly enlarged (Laake) 



The fly of H. bovis (fig. 20) is considerablj^ larger and much stouter than that 

 of H. lineatiim. This is especially true of the thorax, which is much broader. 

 The color is similar to that of //. lineatum, but the band of yellowish hairs 

 across the prothorax dorsally is markedly wider and the shade slightly deeper 

 than in H. lineatum. The shiny longitudinal lines of the thorax are obscured 

 anteriorly by the hair. The color of the abdominal vestiture is similar to that 

 of H. lineatum except on the terminal segments, which have a wider and more 

 sharply defined band of lemon yellow, distinctly paler than in H. lineatum. 

 The wing veins of H. iovis are of a reddish-brown color. The femora and the 

 tibige are black and well covered with black 

 and yellow hairs, and the tarsi are brown 

 and much less hairy than in H. lineatum. 



HOW THE LARV.« OF HYPODERIVU 

 LINEATUM GAIN ENTRvVNCE TO 

 THE HOST 



The method of ingress of various 

 animal parasites is often a point of 

 considerable economic importance. 

 As ha^ been indicated in the historical 

 sketch, the opinions held by various 

 investigators in regard to the way in which Hypoderma larvae enter 

 the host have been at wide variance • and even up to the present time 

 there are but few who feel certain of the method of ingress of these 

 parasites. 



During 1916 plans were laid at the Dallas laboratory to carrry out 

 a series of tests to determine accurately the way in which the larvae 

 enter the host. These tests have been continued along similar 

 lines up to date. Since a full knowledge of the habits of oviposition 

 of adult H. lineatum has been gained, it is evident that there are 

 really only two waj^s in which the larvse might get into the host, one 

 of these being by direct penetration through the skin and the other 

 by being taken in by mouth in the Qgg or young larval stage. 



The following plan, with slight modification, was carried out in 

 all of the tests : Certain animals were placed in fly-proof cages and 



thus protected from all possibility 

 of attack by heel flies during the 

 season of fly activity. To these 

 animals were administered by 

 mouth the eggs of newly hatched 

 larvae. Most of these were ap- 

 plied to the tongue or inside of 

 the lips of the host, but some were 

 placed in capsides and the host 

 made to swallow them. Certain 

 of these animals were dissected 

 at a time when the larvae should 

 be present in tlie gullets or other 

 portions of the carcass commonly infested, to ascertain if possible 

 whetlicr any of them escaped from tlie digestive ti-act. Others 

 were kept and Avatdicd the following fall, winter, and early s|)ring 

 foi- the appearance of larva; in the snixlernial tissues of the back. 

 At the time that the.se animals were being fed with the larvie and 

 eggs, others were infested on the legs or elsewhei-e by allowing 

 flies captured in nature or icared in cages to deposit eggs upon 



Fig. is. — Hypoderma bovln: Posterior 

 stlfiTnal platf;.s of flftli-stage larva. 

 Greatly enlarged (Laake) 



58252°— 20 3 



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