Anopheles arabiensisis an important malaria vector species in Africa. IRS and insecticide impregnated nets (ITNs/LLINs) are the most advocated mosquito control tools for their proven efficacy in reducing malaria transmission. Mosquito control interventions are bound to result into changes among target populations, which may subsequently have an impact on vector control strategies. It is important, therefore, while assessing effectiveness of existing and newer insecticide and repellent compounds to evaluate the resulting responses if such tools are to remain effective.
A series of experimental hut trials were conducted to determine the responses of wild free flying Anopheles arabiensis against; DEET, lambdacyhalothrin, permethrin, actellic, DDT in indoor substrates and Permethrin impregnated blankets. Primary outcomes in examining the responses were mortality, blood-feeding inhibition and treatment-induced mosquito exit.
From the trials, very high mosquito mortality rates were recorded in actellic (86%) and DEET (82%) compared to DDT (81%), permethrin (77%) and lambdacyhalothrin (76%) sprayed huts. DEET recorded the highest mosquito blood feeding inhibition rates (44%). There was a reduction in mosquito entry into huts in the first two weeks post spraying suggesting a spatial effect of freshly sprayed chemicals. Although less effective in killing (25-35%) mosquitoes, pyrethroid treated blankets moderately reduced blood feeding (30-50%).
Actellic and DEET showed highest potential as IRS compounds. Despite moderate feeding inhibition tendencies against An. arabiensis retained by permethrin treated blankets and nets, there may be less potential for these products owing to the documented behavioural avoidance of An. arabiensis to treated surfaces.
Stephen Magesa (KCMC) & Mark Rowland (LSHTM)
Robert Malima (NIMR, Tanzania) & Steve Lindsay (Durham University)