Enhancing the efficacy of neonicotinoids against mosquitoes and overcoming resistance issues

Abstract

BackgroundNeonicotinoids are potential alternatives for targeting pyrethroid-resistant mosquitoes, but their efficacy against malaria vector populations of Sub-Saharan Africa has yet to be investigated. Here we tested and compared the efficacy of four neonicotinoids alone or in combination with a synergist against two major vectors ofPlasmodium.ResultsUsing standard bioassays, we first assessed the lethal toxicity of three active ingredients against adults of two susceptibleAnophelesstrains and we determined discriminating doses for monitoring susceptibility in wild populations. We then tested the susceptibility of 5532Anophelesmosquitoes collected from urban and rural areas of Yaoundé, Cameroon, to discriminating doses of acetamiprid, imidacloprid, clothianidin and thiamethoxam. We found that in comparison with some public health insecticides, neonicotinoids have high lethal concentration, LC99, reflecting their low toxicity toAnophelesmosquitoes. In addition to this reduced toxicity, resistance to the four neonicotinoids tested was detected inAn. gambiaepopulations collected from agricultural areas where larvae are intensively exposed to crop-protection neonicotinoids. However, adults of another major vector that occurred in urbanized settings,An. coluzzii, were fully susceptible to neonicotinoids except acetamiprid for which 80% mortality was obtained within 72 h of insecticide exposure. Importantly, the cytochrome inhibitor, piperonyl butoxide (PBO), was very effective in enhancing the activity of clothianidin and acetamiprid providing opportunities to create potent neonicotinoid formulations againstAnopheles.ConclusionThese findings suggest that to successfully repurpose agricultural neonicotinoids for malaria vector control, it is essential to use formulations containing synergists such as PBO or surfactants to ensure optimal efficacy.