340 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I25 



behavior of the flies. Upon returning to consciousness, a few flies were 

 observed mating, and numerous females assumed a position as though 

 they were biting. It was first beheved that the position of the females, 

 with the mouthparts directed perpendicular to the jar, was merely an 

 attempt to establish equilibrium. However, when the flies were re- 

 leased into the large outdoor cage, a high percentage of the flies at- 

 tacked the human subject and took blood voraciously. Within 4 to 6 

 hours, a number of the flies that had fed also oviposited. 



With more hopeful prospects for success in the establishment of 

 the colony, another cage, about one and one-half times the size of the 

 first, was constructed over a natural stream in which Simulium 

 ochracemn and 5". fnetallicum were breeding (pi. 20, fig. 2). This 

 cage was also stocked with various combinations of flies, and similar 

 foods were presented. With the inauguration of the second cage, flies 

 were generally exposed to the carbon-dioxide treatment or to re- 

 frigeration before being introduced into the oviposition cage. 



Of over 20,000 ^. ochraceum, metallicum, and callidum that had 

 been chilled prior to being introduced into the cages, about 30 percent 

 took blood meals, although none oviposited. In 460 trials run with 

 carbon-dioxide treatment, more than 65,000 flies of the same species 

 were treated. About 40 percent took blood meals, and of these, about 

 20 percent oviposited. Some of the females deposited up to a thousand 

 eggs (an abnormally high number), but none of the eggs developed 

 to form larvae. This may indicate that the eggs were sterile or that 

 they were adversely affected by the gas. 



Approximately 8,800 reared adults of S. exigimm were introduced 

 into the laboratory and field cages, both without treatment and after 

 exposure to carbon-dioxide gas or refrigeration. Of 3,400 that had 

 been treated, 31 pairs of flies mated, 7 flies took blood, and 290 fed 

 on sugar. Of the 5,400 that had not been treated, 27 pairs mated, but 

 none took blood or sugar. No flies of this species oviposited in cap- 

 tivity. Representatives of other definitely zoophilic species did bite 

 man readily after exposure to carbon-dioxide gas. One such species 

 was S. rubicundulum. However, no egg deposition took place. 



In 1 95 1, when other experiments and duties precluded the possi- 

 bility of continuing with the problem of establishing the colony, it 

 was reluctantly abandoned. Apparently, the anthropophilic species of 

 black flies of the Yepocapa region, like so many other insects that do 

 not normally inhabit confined areas, resist colonization. Perhaps some 

 simple expedient will, in the future, revolutionize this problem. How- 

 ever, the use of carbon dioxide to induce oviposition by captive 

 Simulium species does signal a way toward further possible experi- 



