Spatial distribution and habitat characterization of anopheline mosquito larvae in western Kenya

Studies were conducted to characterize larval habitats of anopheline mosqui toes and to analyze spatial heterogeneity of mosquito species in the Suba D istrict of western Kenya. A total of 128 aquatic habitats containing mosqui to larvae were sampled, and 2,209 anopheline and 10,538 culicine larvae wer e collected. The habitats were characterized based on size, pH, distance to the nearest house and to the shore of Lake Victoria, coverage of canopy, s urface debris, algae and emergent plants, turbidity, substrate, and habitat types. Microscopic identification of third- and fourth-instar anopheline l arvae did not yield any Anopheles funestus or other anophelines. A total of 829 An. gambiae s.l. larvae from all habitats were analyzed further by rDN A-polymerase chain reaction to identify individual species within the An. g ambiae species complex. Overall, An. arabiensis was the predominant species (63.4%), and An. gambiae was less common (31.4%). The species composition of An. gambiae s.l. varied significantly among the sampling sites throughou t Suba District. The larval habitats in the southern area of the district h ad a higher proportion of An. gambiae than in the northern area. Multiple l ogistic analysis did not detect any significant association between the occ urrence of anopheline larvae and habitat variables, and principal component analysis did not identify key environmental factors associated with the ab undance of An. gambiae. However, significant spatial heterogeneity in the r elative abundance of An. gambiae within the Suba district was detected. Whe n the effect of larval habitat locality was considered in the analysis, we found that the distance to the nearest house and substrate type were signif icantly associated with the relative abundance of An. gambiae. Future studi es integrating derailed water chemistry analysis, remote sensing technology , and the ecology of predators may be required to further elucidate the mec hanisms underlying the observed spatial variation of anopheline larval dist ribution.