Anopheline mosquito (Diptera: Culicidae) ecology in relation to malaria transmission in the inner and outer terai of Nepal, 1987-1989.

The ecology of Anopheles mosquitoes in relation to malaria transmission was studied at sprayed and unsprayed villages and two unsprayed cattle sheds in the inner terai of Sindhuli District, Central Region, and at two unsprayed villages and one cattle shed in Kanchanpur, Far Western Region of Nepal, from August 1987 to August 1989. Anopheles maculatus was the most abundant of 26 anopheline species collected in Sindhuli District; however, An. fluviatilis was collected most frequently at human bait and was infected most frequently with malaria sporozoites. Residual house spray controlled the indoor resting abundance of the endophilic resting species and protected the population from malaria during midsummer, but had less effect on exophilic resting species and those abundant after and before spray application during the fall and spring, respectively. Malaria at the unsprayed village was detected predominantly in adults of both sexes, perhaps because young children retired early and frequently slept indoors under bed nets during the early evening period of elevated anopheline host-seeking activity. Malaria transmission was verified by the collection of sporozoite infected An. fluviatilis and An. maculatus during spring at cattle sheds in the forested Churia Hills and during the summer monsoon season within the unsprayed village. An. culicifacies was the most abundant of 12 anopheline species collected in Kanchanpur District. Few females of all species were collected at human bait positioned in or out of houses or had human positive blood meals; none were infected with sporozoites. Malaria incidence was higher in the study village positioned along the forest-rice field ecotone than in the cleared rice growing area.