Oviposition by African malaria vector mosquitoes

Abstract

Blood-fed females of the Anopheles gambiae species complex, most of which would have been A. gambiae Giles sensu stricto, were collected from a freshwater locality in coastal Kenya and used for laboratory studies of their temporal patterns of oviposition. Contrary to previous reports these patterns were not found to be constrained to the early hours of the night but varied widely, evidently dependent on the time of blood-feeding and on subsequent temperatures but not on endogenous activity rhythms of any circadian nature other than daytime inhibition. After two days at mean temperatures ranging from 26·25 to 28·1°C the combined results of ten nights showed a build-up from dusk to a peak in the hour following midnight, falling more steeply towards dawn. In combination with patterns derived from mosquitoes re-fed at 20–21.00 hours and 05–06.00 hours this indicated oviposition with a mean 44–47 hours after blood feeding. Considered in the context of available relevant field evidence, temporal patterns of oviposition by A. gambiae in the field in the warmer lowlands of Africa would be expected to show an initial, more abrupt peak in the early night (contributed mainly by females which had failed to oviposit on the night when first due), followed by a more diffuse peak. Patterns would be dependent on local conditions of blood-feeding, temperature and distance from daytime resting sites.