EFFECTIVE POPULATION-SIZE AND PERSISTENCE OF ANOPHELES-ARABIENSIS DURING THE DRY SEASON IN WEST-AFRICA

The way that the malaria vectors Anopheles arabiensis and An.gambiae s urvive the dry season in sub-saharan Sahel or northern Savanna areas o f Africa remains enigmatic. We examined this problem by calculating th e effective sizes (N(e)) of An.arabiensis populations for several loca tions in West Africa. An indirect/genetic procedure was used, comparin g gene frequencies at several time intervals. The amount of drift whic h occurred provides an estimate of N(e). Most estimates of N(e) were a pproximately 2000 individuals, probably close to the yearly minimum. T his supports the hypothesis that populations of An.arabiensis in this region are continuous throughout the year, with many individuals survi ving through the dry season, perhaps in a physiologically altered stat e, rather than extinction or severe bottlenecks during the dry season, followed by recolonization by a few individual survivors or immigrant s in the subsequent rainy season.