Efficacy of six neonicotinoid insecticides alone and in combination with deltamethrin and piperonyl butoxide against pyrethroid-resistant Aedes aegypti and Anopheles gambiae (Diptera: Culicidae)

Background: In this study, carried out on pyrethroid-resistant Aedes aegypti and Anopheles gambiae, different combinations containing pyrethroid deltamethrin, piperonyl butoxide (PBO) synergist and six neonicotinoid insecticides (acetamiprid, nitenpyram, thiamethoxam, clothianidin, imidacloprid and thiacloprid) were tested. The bioassays were carried out by tarsal contact on impregnated paper on Ae. aegypti and with impregnated pieces of netting on An. gambiae.

Results: The combination of deltamethrin and PBO was synergistic against pyrethroid-resistant Ae. aegypti (LHP) and An. gambiae (VKPR) strains, with 43 and 57% mortality respectively, versus 17 and 12% with deltamethrin alone. On LHP Ae. aegypti, the deltamethrin + PBO + neonicotinoid mixtures generated insecticide efficacies that were either greater (group 1) or lower (group 2) than the deltamethrin + PBO mixture. The tricomponent mixtures made with thiamethoxam, nitenpyram and thiacloprid (70.7, 64.9 and 55.9% mortality respectively) belong to group 1. Group 2 consists of mixtures made with imidacloprid, clothianidin and acetamiprid (28.9, 32.9 and 34.3% mortality respectively). The nettings impregnated with the three tricomponent mixtures of group 1 confirmed the excellent efficacy of these mixtures against An. gambiae VKPR (87-89% mortality).

Conclusion: Deltamethrin + PBO + neonicotinoid (group 1) mixtures induce interesting, efficient synergies, most valuable for the management of mosquito resistance to insecticides.