BULLETIN" 1218, U. S. DEPARTMENT OF AGRICULTURE. 



When the larvae were in the prepupal stage or had already pupated 



no more water was added and the media usually became quite dry 



before the adults emerged. It was found that the adults would soon 



denude themselves if left more than an hour or so in the rearing jars. 



Tabanid eggs collected in the field hatched very readily in the 



laboratory, but it was found that 

 the. period of incubation was con- 

 siderably shorter in cases where 

 they were exposed to high tempera- 

 tures in direct sunlight. The 

 eggs were taken to the laboratory 

 on a portion of the vegetation or 

 object to which the mass adhered 

 and suspended over about a half 

 inch of water in a glass vial an 

 inch in diameter. A cotton stop- 

 per was placed in the vial to pre- 

 vent any intrusion of predators 

 or escape of emerging parasites. 

 Upon hatching, the larva? dropped 

 to the water. Tabanus punctifer 

 larvae would remain near the sur- 

 face; T. phaenops larvae would 

 remain more deeply submerged. 

 The number of eggs was deter- 

 mined in most cases by counting 

 the larvae. In the case of badly 

 parasitized egg masses the egg- 

 shells had to be counted. Egg 

 masses of T. phaenops often be- 

 came detached and dropped into 

 the water, where they failed to 

 hatch. This can be avoided 

 largely by leaning the vials at 

 an angle. 



Larvae collected in the field were 

 placed with mud in vials or jars, 

 several being in one container, and were carried to the laboratory 

 with very little fatality. 



OVIPOSITION CAGES. 



It has been found very difficult to get Tabanus punctifer and 

 T. phaenops to bite a host in captivity. A screen-wire cage 5 feet 

 high and 10 feet square was constructed partly over water near a 

 sluggish stream. The cage contained water plants and other vege- 

 tation upon which it was hoped the flies might oviposit. A calf 

 1 months old was placed in the cage September 1, 1917. About 300 

 flies (T. phaenops), including 8 or 10 males, were captured and 

 released in the cage. The last flies were introduced September 11. 

 On September 15 all were dead. No eggs were found and no flies 

 were observed biting the calf. They appeared to be occupied in 

 a constant effort to escape. Ovipositions were obtained, however, 

 in a smaller cage (fig. 7). A rearing pan of galvanized iron 4 



Fig. 7. 



-Oviposition cage used in securing 

 horse-fly egg masses. 



