Anopheles species composition and relative seasonal abundance were measured in an irrigated division (low historical malaria incidence) and in a rain-fed division (high historical malaria incidence) of southern Sri Lanka. Twelve species of anophelines were represented in adult and larval collections with Anopheles vagus Donitz being the most abundant. In cattle-baited net trap collections, Anopheles adults were significantly more abundant in the irrigated division than in the rain-fed division. In pyrethrum-spray sheet collections, cattle-baited but trap collections and larval collections, Anopheles abundance was significantly greater in the rain-fed division. Houses were of poorer construction in the rain-fed division, where pyrethrum-spray sheet collections consisted mainly of Anopheles subpictus Grassi (98%) and Anopheles culicifacies Giles (2%). Hut trap collections also consisted mainly of An. subpictus (88%) and An. culicifacies (7%). Net trap collections consisted mainly of An. vagus (43%) and Anopheles peditaeniatus Leicester (31%). Larval collections also consisted of An. peditaeniatus (24%) and An. vagus (21%). Weak associations were found between species abundance and environmental factors explored in this study (e.g., vegetation, water quality, sunlight exposure). The greater malaria risk in the rain-fed division is due in part to the occurrence of potential vectors in relatively higher numbers.

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