Adulticidal & larvicidal efficacy of three neonicotinoids against insecticide susceptible & resistant mosquito strains

BACKGROUND & OBJECTIVES: Due to ever growing insecticide resistance in mosquitoes to commonly used insecticides in many parts of the globe, there is always a need for introduction of new insecticides for the control of resistant vector mosquitoes. In this study, larvicidal and adulticidal efficacies of three neonicotinoids (imidacloprid, thiacloprid and thiamethoxam) were tested against resistant and susceptible populations of Anopheles stephensi Liston 1901, Aedes (Stegomyia) aegypti Linnaeus, and Culex quinquefasciatus Say (Diptera: Culicidae). METHODS: Laboratory-reared mosquito species were used. Insecticide susceptibility tests were done using standard WHO procedures and using diagnostic dosages of insecticide test papers and larvicides. Adulticidal efficacy of candidate insecticides was assessed using topical application method and larval bioassays were conducted using standard WHO procedure. RESULTS: The results of topical application on 3-5 day old female mosquitoes indicated that resistant strain of An. stephensi registered lower LC(50) values than the susceptible strain. Among the three insecticides tested, thiacloprid was found more effective than the other two insecticides. Culex quinquefasciatus registered lowest LC(50) for imidacloprid than the other two mosquito species tested. In larval bioassays, the LC(50) values registered for imidacloprid were in the order of Cx. quinquefasciatus <An. stephensi (SS) <An. stephensi (RR) <Ae. aegypti. In case of thiacloprid, the order of efficacy (LC(50)) was Cx. quinquefasciatus <An. stephensi (SS) <An. stephensi (RR), whereas in case of thiamethoxam, the larvicidal efficacy was in the order of An. stephensi (RR) <An. stephensi (SS) <Cx. quinquefasciatus. INTERPRETATION & CONCLUSIONS: The present study indicated that insecticide resistant strains of mosquito species tested showed more susceptibility to the three neonicotinoids tested, and the possibility of using neonicotinoids for the control of resistant mosquitoes should be explored.