Lethal and Residual Effects of Lambdacyhalothrin, Deltamethrin and Cyfluthrin Insecticides on Adult Mosquitoes of Anopheles stephensi Liston(Diptera: Culicidae) on Different Surfaces

Background: Human malaria remains a major malady in Eastern Iran. Vector control interventions such as indoor residual spraying are used to fight with the disease. This study was undertaken to determine the lethal and residual effects of three different pyrethroid insecticides on adult mosquitoes of Anopheles stephensi on different surfaces in Iran, as part of a national program to monitor insecticide resistance in endemic areas. Methods: Two main endemic foci were selected as collection sites. Wild adult females of An. stephensi (mysoriensis strain) from the first focus were subjected to standard susceptibility tests, using lambdacyhalothrin, deltamethrin and cyfluthrin insecticides within holding tubes according to the method proposed by WHO. In Kazerun, the residual effects of these compounds were examined by conical bioassay tests of An. stephensi (type strain) on plaster and cement walls. Data were analyzed using Mann-Whitney test to determine the differences in susceptibility and residual effects of An. stephensi mosquitoes to these insecticides. Results: The susceptibility of females of An. stephensi to three concentrations of lambdacyhalothrin, deltamethrin and cyfluthrin insecticides culminated in full scale mortality at the highest diagnostic dose. The maximal residual time of these three insecticides on plaster and cement walls was estimated to be about three months. There was no significant difference in the mortalities of An. stephensi on different sprayed surfaces (P=0.653). Conclusion: All field-collected An. stephensi populations exhibit gross susceptibility to all diagnostic doses of the three evaluated insecticides. In endemic areas, lambdacyhalothrin reveals a slightly longer residual activity than the other two insecticides.