NO. I BLACK FLIES OF GUATEMALA — ^DALMAT 339 



Most of the flies died within 5 days, but a small number lived as 

 long as 18 days. Less than i percent of the flies fed, and only one 

 S. metalliciim oviposited. This fly deposited approximately 300 eggs, 

 200 of which developed into larvae. Of the entire group, only five 

 adults emerged, three of which were males. The males fed on sugar 

 solution, but the females refused all foods. No mating or oviposition 

 was observed in the second generation and the adults finally died. The 

 great majority of the larvae had been washed away by the fluctuation 

 of the current owing to a breakdown of the water system. 



In an attempt to stimulate female flies to feed, they were introduced 

 into another mechanism (pi. 21, fig. 2) before being loosed in the 

 oviposition cage. It was an apparatus that had previously been used 

 for feeding mosquitoes (Greenberg, 1949). Each lantern-globe cage, 

 in which a number of flies were held, was kept humid by moist blotting 

 papers in the Petri dish attached at its base. The upper end of the 

 globe was covered with adhesive tape except for the central region 

 through which the food was presented to the flies. Above each globe, 

 extending from an asbestos board, there was a cylindrical heating 

 unit which could be regulated to bring any substance passed through 

 it to body temperature. A tube of appropriate diameter, containing 

 liquid food and topped with a membrane (Baudruche), was passed 

 through the heating unit and brought to rest on the lantern globe so 

 that its membrane coincided with the opening in the adhesive tape. 

 The most successful food was a mixture of blood plasma and sugar. 

 The apparatus did stimulate approximately half the flies to feed, but 

 these did not oviposit any better than did the flies that had not fed. 



During January 1950, a system was initiated whereby flies were 

 treated with carbon-dioxide gas before being released in the oviposi- 

 tion cage (Dalmat, 1950a). The flies were first placed in a museum 

 jar into which carbon-dioxide gas was introduced through a rubber 

 tube extending from a standard gas cylinder. An oxygen manometer 

 valve was used to control the quantity of gas passing through the tub- 

 ing to the fly chamber. 



Since the actual volume of gas necessary to immobilize the flies was 

 not measurable with the equipment used, the end point of treatment 

 was arrived at by observation of the fly activity. The flies were at 

 first stimulated to greater activity, and then they would topple over 

 as if dead. At the latter point, the treatment was halted and the jar 

 left open until the flies revived. The actual treatment lasted less than 

 20 seconds ; the flies usually revived in about 3 to 4 minutes. 



It appears that the gas treatment has an immediate effect upon the 



