Environmental factors associated with larval habitats of anopheline mosquitoes (Diptera: Culicidae) in irrigation and major drainage areas in the middle course of the Rift Valley, central Ethiopia

Background & objectives: Larval control is an integral part of malaria vector management in Ethiopia andelsewhere. For effective larval control, a sound understanding of the factors responsible for spatio-temporalvariation in larval production is essential. A study was thus conducted to characterize larval habitats of anophelinemosquitoes in irrigation and major drainage areas between Adami Tulu and Meki towns, in the middle course ofthe Ethiopian Rift Valley.Methods: Aquatic habitats were sampled for anopheline larvae and the associated environmental variables(water temperature, turbidity, water current, water pH and other variables) were measured, characterized andanalyzed.Results: Microscopic identification of the late instars (III and IV) of anopheline larvae collected throughout thestudy period yielded nearly 47.6% Anopheles pharoensis, 32.1% An. arabiensis, 17.1% An. squamosus and only3.2% of other species (An. coustani and An. cinereus). Larvae of the local malaria vectors, An. arabiensis andAn. pharoensis were most abundantly sampled from sand pools and natural swamps, respectively. Logisticregression analysis detected four best predictor variables associated with larval abundance of malaria vectorspecies. Thus, relative abundance of An. arabiensis larvae was significantly and inversely associated with aquaticvegetation and water current, whereas the relative abundance of An. pharoensis larvae was significantly andpositively associated with water temperature and the presence of algae in the water bodies.Conclusion: Dry season anopheline larval habitats such as riverine sand pools that are created and maintainedby perennial water bodies and their associated water development projects need to be considered in vectorcontrol operations.