Efficacy of various insecticides recommended for indoor residual spraying: pirimiphos methyl, potential alternative to bendiocarb for pyrethroid resistance management in Benin, West Africa

Background Using the same insecticide for multiple successive indoor residual spraying (IRS) cycles is not recommended; instead, the National Malaria Control Program (NMCP) has decided to select another insecticide (insecticide B) in addition to bendiocarb for indoor residual spraying. Methods An experimental hut trial comparing the effectiveness of three classes of insecticides (one carbamate [bendiocarb], two organophosphates [fenitrothion and pirimiphos methyl] and one pyrethroid [lambdacyalothrin]) was conducted in Malanville, northern Benin, against wild free entered resistant Anopheles gambiae s.l. population to pyrethroids. Results Fenitrothion and pirimiphos methyl yielded the highest rate of deterrence. Their mean rates were respectively 46.6% and 35.4%. Regarding blood feeding inhibition, only fenitrothion has induced a significant inhibition rate (25.4% as mean rate). As regards the exophily rates, only lambdacyhalothrin has induced the highest rate (39.7%). Pirimiphos methyl showed the highest mortality rate and also induced a mortality rate of at least 80% in blood fed An. gambiae population after 24 h observation time. Furthermore, the huts treated with pirimiphos methyl showed the highest residual effect, followed by lambdacyhalothrin. Conclusion Benin NMCP has selected pirimiphos methyl as insecticide B to alternate or combine to bendiocarb (carbamate) because of the adverse effects of fenitrothion on the sleepers and its short residual effect on walls.