34 BULLETIN 597,, U. S. DEPARTMENT OP AGBICULTUBE. 



time thev would attach to a piece of paper or stomach section or even 

 to one another. This is only a temporary attachment, however, and 

 apparently no attempt at feeding takes place. 



The studies of Brauer. Xuman. and Guyot indicate that the larva? 

 molt during their development and that there are at least three 

 stages. Xo experiments have been reported as to the exact time that 

 larva? remain within the body of the horse, although apparently they 

 spend about 10 months in this parasitic stage. On some occasions, 

 as will be observed in Table I, well-developed larva? were disclosed on 

 post-mortem examinations in early fall. The indications are that- 

 some larva? are not sufficiently developed to pass out in time to pro- 

 duce adults and that they succumb to low temperatures. There are 

 various factors that apparently tend to influence the extension of lar- 

 val periods. "When gross infestations occur the development is 

 markedly slower than in those horses containing only a few larva?. 

 Laxative foods have a greater tendency to discharge well-developed 

 larvae than foods of a non-laxative nature, as is observed in comparing 

 autopsies of livery and pastured animals. Since there is such a wide 

 range of variation in the ages of larva? within the eggs at which they 

 are capable of being ingested it is possible that this may tend to 

 prolong the period during which the last-stage larva? drop. 



SUBMERGENCE OF LARVAE. 



Last-stage larva? removed from horses immediately after death 

 remained alive and active from 21 to 33 days when submerged in 

 water, but when submerged for only 6 days they would not attempt 

 pupation. These periods are considerably decreased if larva? are 

 not removed shortly after the death of the animal. 



PUPA PERIODS. 



The larva? drop naturally with manure, burrow only enough for 

 protection, and normally pupate within a dav or two. The periods 

 of dropping extend over a long time and very few larva? are 

 found in droppings. It is a difficult matter to rear larva? taken 

 in jDOst-mortem examinations, and this is best undertaken in the late 

 summer or early autumn, when the greatest number of larva? are 

 fully developed. With such larva?, used in the experiments, the pu- 

 pa periods have been observed to vary from 27 to 13 days, with an 

 average of 38 days. 



EFFECT OF DEATH OF HOST UPON GASTROPHILUS LARViE. 



The resistance of larva? and the death of horses from infectious 

 diseases naturally suggest the fate of larva? during the period when 

 they normally drop. In experiments larva? were not kept with the 

 animals during the decay, but were removed in autopsies, separated 



