Population dynamics of anophelines in a malathion treated village in the intermediate zone of Sri Lanka.

Abstract

As part of research programme on malaria transmission in Sri Lanka, a study was made of man-biting anophelines at Nikawehera, a village on the border of the intermediate and dry rainfall zones. Weekly mosquito collections by night human bait (NHB) were performed inside and outside four fixed stations from October 1992 till March 1993. Houses in the village were treated with malathion by the Anti-Malaria Campaign in October and at the end of January 1993. An. culicifacies and An. tesselatus were the most abundant species. An. culicifacies was probably the only species responsible for malaria transmission. An. culicifacies densities varied between stations and reflected differences in availability of breeding places. An. culicifacies aggressivity is closely related to the rainfall pattern, increasing after the first monsoon rains in November and reaching a peak in late December--early January. Vectorial capacity, however, decreased during the first weeks of the rainy season. The maximum vectorial capacity was found in January. The night biting cycle of An. culicifacies showed a peak between 20.00 and 23.00 h. Since the introduction of electricity in the village, people go to bed later. This might reduce the impact of impregnated bednets on malaria transmission. The results show that malathion spraying as performed now is not very effective. The timing of the spray rounds should be improved. In order to limit malaria transmission, we suggest to advance the malathion spraying campaign of January with one month.