Preferred resting surfaces of dominant malaria vectors inside different house types in rural south-eastern Tanzania

Abstract

Malaria control in Africa relies extensively on indoor residual spraying (IRS) and insecticidetreated nets (ITNs). Indoor residual spraying typically targets mosquitoes resting on walls, and in

few cases, roofs and ceilings, using contact insecticides. Unfortunately, little attention is paid to

where

malaria vectors actually rest indoors, and how such knowledge could be used to improve IRS. This study investigated preferred resting surfaces of two major malaria vectors, Anopheles funestus and Anopheles arabiensis, inside four common house types in rural south-eastern Tanzania. The assessment was done inside 80 houses in south-eastern Tanzania across four villages. In each house, resting mosquitoes were captured using Prokopack aspirators from walls, undersides of roofs, floors, furniture, utensils, clothes and bed-nets. Overall, only 26% of An. funestus and 18% of An. arabiensis were found on walls. In grass-thatched houses, 33-55% of An. funestus and 43-50% of An. arabiensis rested under roofs, while in metal-roofed houses, only 1620% of An. funestus and 8-30% of An. arabiensis rested under roofs. Considering all data together,

approximately

40% of mosquitoes rested on surfaces not typically targeted by IRS, i.e. floors, furniture, utensils, clothes and bed-nets. These proportions were particularly high in metal-roofed houses (47-53% of An. funestus; 60-66% of An. arabiensis). While IRS uses contact insecticides to target adult mosquitoes on walls, and occasionally roofs and ceilings, significant proportions of vectors rest on surfaces not usually sprayed. This gap exceeds one-third of malaria mosquitoes in grass-thatched houses, and can reach two-thirds in metal-roofed houses. Where field operations exclude roofs during IRS, the gaps can be much greater. In conclusion, there is need for locallyobtained data on mosquito resting behaviours and how these influence the overall impact and costs

of IRS.