MATERIALS AND METHODS

At Chipinda Pools, mosquito collections were made at various bush-sites in the vicinity, the most prolific of which was close to a small stream and about zoo yards from the Lundi river. On Lone Star Ranch the collections were made on high ground in savannah woodland with numerous large scattered rock formations, and on the edge of a pan in the same area.

Mosquitoes were collected, mainly as they came to bite, by a team of Africans; others were collected resting on vegetation. The collections took place usually for three hours after sunrise and for 3-6 hours after sunset. Collections at Chipinda Pools occupied approximately 1,115 man-hours and those at Lone Star Ranch 450 man-hours. The methods used in the storage and processing of mosquitoes for attempted virus isolation have been described in earlier reports from this laboratory (De Meillon et al., 1957; Kokernot, Heymann et al., 1957; Kokernot, De Meillon et al., 1957). Haemagglutinationinhibition (HI) tests were done according to the methods of Clarke and Casals (1 958), in which dilutions of sera were tested against 8 units of antigen, and neutralization (N) tests were made by the method of Smithburn et al.(1959), in which undiluted serum was tested against an estimated 100 LD 50 of virus. The mixtures were inoculated intracerebrally into infant mice 2-3 days old.