Aquatic habitats of the malaria vector, Anopheles funestus in rural south-eastern Tanzania

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Abstract Background In rural south-eastern Tanzania, Anopheles funestus now dominates malaria transmission, mediating nearly nine in every ten new malaria infections. However, little is known about the ecological requirements and survival strategies of this mosquito species in the wild. Methods Potential mosquito aquatic habitats were systematically searched along 1000 m transects radiating from the centers of six villages in south-eastern Tanzania. All water bodies were geo-referenced, characterized and examined for presence of Anopheles larvae using standard 350mls dippers or 10L buckets. Larvae were collected for rearing, and the emergent adults identified to generic or species level, to confirm habitats containing An. funestus . Results One hundred and eleven (111) habitats were identified and assessed from the first five villages (all <300m altitude). Of these, 36 (32.4%) had An. funestus larvae co-occurring with other mosquito species. Another 47 (42.3%) had other Anopheles species and/or culicines but not An. funestus , and 28 (25.2%) had no mosquitoes. There were three main habitat types occupied by An. funestus, namely: a) small spring-fed pools with well-defined perimeters (36.1%), b) medium-sized natural ponds retaining water most of the year (16.7%), and c) slow-moving waters along river tributaries (47.2%). The habitats generally had clear waters with emergent surface vegetation, depths > 0.5m and distances < 100m from human dwellings. They were permanent or semi-permanent, retaining water most of the year. Water temperatures ranged from 25.2 to 28.8°C, pH from 6.5 to 6.7, turbidity from 26.6 to 54.8 NTU and total dissolved solids from 60.5 to 80.3 mg/L. In the sixth village (altitude >400m), very high densities of An. funestus were found along rivers with slow-moving clear waters and emergent vegetation. Conclusion This study has documented the diversity and key characteristics of aquatic habitats of An. funestus in south-eastern Tanzania, and will form an important basis for further ecological studies towards improved control strategies. Given the observed characteristics, An. funestus habitats in the area can indeed be described as fixed, few and findable. Future studies should therefore investigate potential of targeting these habitats with larviciding or larval source management to complement malaria control efforts in areas dominated by this vector.

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