Larvicidal efficacy of Ocimum basilicum extracts and its synergistic effect with neonicotinoid in the management of Anopheles stephensi

Abstract

ObjectiveTo evaluate the larvicidal activities of different combinations of synthetic nicotinoid insecticide, imidacloprid with an insecticidal plant, Ocimum basilicum (O. basilicum) against malaria vector, Anopheles stephensi, with reference to the impact of most potent combination on some non-targets, Anisops bouvieri (A. bouvieri) and cyclop. MethodsThe larvicidal activity was determined against mosquito larvae in various concentrations, 1:1, 1:2 and 1:4 under laboratory conditions. These experiments were conducted according to WHO standard procedure. ResultsIn bioassays, binary mixtures of different combinations of synthetic insecticide (imidacloprid) with crude petroleum ether leave extract of O. basilicum and then with most potent 4th fraction of it, produced promising results. Therefore, ratio 1:1 of all the binary mixtures was most effective as compared to 1:2 and 1:4 against mosquito larvae and showed synergism in all cases. The combinatorial ratio 1:1 of imidacloprid and most potent 4th fraction of petroleum ether extract of O. basilicum with LC50 value 0.010 and 0.007 ppm; LC90 value 0.033 and 0.023 ppm for anopheline larvae after 24 and 48 h of treatment, respectively, showed high toxicity. This effective ratio was found safe to aquatic mosquito predator, A. bouvieri and other aquatic non-target cyclops with the respective LC50 values 12.351 and 5.290 ppm after 24 h of exposure. ConclusionsIt is, therefore, concluded that the tested combination is more effective than its individual constituents. Further, this formulation is cost-effective and ecofriendly to the aquatic fauna.