SEASONAL FLUCTUATIONS IN POPULATION DENSITES OF <i>BULINUS SENEGALENSIS</i> AND <i>B. TRUNCATUS</i> (PLANORBIDAE) IN TEMPORARY POOLS IN A FOCUS OF <i>SCHISTOSOMA HAEMATOBIUM</i> IN NIGER: IMPLICATIONS FOR CONTROL

Abstract

Annual and seasonal changes in population densities of Bulinus senegalensis Müller 1781 and B. truncatus (Audouin, 1827) were studied in temporary pools of the west sahelian zone in Niger in relation to environmental factors. B. senegalensis is present in the temporary pools whatever their duration, whereas B. truncatus inhabits only the more persistent pools. B. senegalensis populations develop mostly during the rainy season when the water temperature is warm. B. truncatus is most abundant after the rainy season when the water temperature is cooler, but this snail may increase when the water temperature is warmer during unusual rainy seasons with low and intermittent rainfall. Field observations suggest that interspecific competition is exceptionally occurring in the pool colonized by both B. senegalensis and B. truncatus. The implications of these observations on treatment and retreatment schedules for schistosome infection in people and on snail control in temporary pools are discussed.