1.A local strain of yellow fever virus was carried through 5 cycles in the laboratory using saimiri monkeys as hosts and the mosquito Haemagogus capricornii as vector.
2.This is a laboratory reproduction of what may be a local transmission mechanism of jungle yellow fever, as both saimiri monkeys and haemagogus mosquitoes have been implicated in the epidemiology of the disease by field studies.
3.The extrinsic incubation period in Haemagogus capricornii under the conditions of these experiments was 20 to 24 days at room temperature (24°–27°, mean 25.4°C.); and 13 to 15 days at a constant temperature of 30°C.
4.A virus strain was used that had been subject to a minimum of laboratory manipulation. Adult white mice of the standard strain used in yellow fever studies were found to show an irregular susceptibility to intracerebral inoculation of small amounts of this virus, but 3- and 5-day-old mice were highly susceptible. The strain was highly virulent for saimiri monkeys: 8 of the 10 animals infected by mosquito bite died in the course of acute infections.
5.Only a certain percentage of specimens of Haemogogus capricornii became infected after feeding on monkeys with virus in circulation. The percentage infected in a particular experiment appeared to depend on (a) the amount of virus originally ingested by the mosquitoes and (b) the environmental temperature at which the mosquitoes were kept. The possible effect of virus strain and of the genetic constitution of the mosquitoes was not studied.
6.The correlation between factors governing haemagogus infection in the laboratory and the habits of the mosquito judged by field studies, is discussed. The mosquito seems to require a high environmental temperature to become infected, and its habit of flying in the canopy zone of the forest means that it is subject to relatively high temperatures in nature. The correspondence in habits between this species of mosquito and saimiri monkeys in the Villavicencio area is close.