Abstract

Objective: To investigate insecticidal properties of organic solvent extracts of Clerodendron inerme (C. inerme) leaves against larval stages of Aedes aegypti (Ae. aegypti) and Culex quinquefasciatus (Cx. quinquefasciatus) mosquito species. Methods: The sundried leaf powder of C. inerme was subjected for extraction using organic solvents viz. methanol, chloroform, petroleum ether and hexane extract, and were tested against third/fourth instar larvae of Ae. aegypti and Cx. quinquefasciatus species in accordance with WHO standard methods. Experiments were conducted in four replicates with control group containing water alone and positive control group containing respective solvent (dimethylsulfoxide/acetone) used for dissolving the extracts. Results: Among the four solvent extracts, hexane extract has effective growth disruptive activity against Ae. aegypti, and showed positive tests for presence of four groups of phytochemical constituents viz. tanin, phytosteriod, terpenoid and cardiac glycoside. The hexane extract was tested against field collected filarial vector Cx. quinquefasciatus larvae for growth disruptive activity. Adult emergence inhibition values for 50 percent suppression (EI50) of the tested population for methanol, chloroform, petroleum ether and hexane extracts treated against third instar larvae of Ae. aegypti were found to be 37.45, 14.79, 2.56 and 1.96 mg/L respectively, while hexane extract treated against Cx. quinquefasciatus was found to be equally effective with EI50 value of 3.74 mg/L. Hexane extract treated against fourth instar larvae of Ae. aegypti and Cx. quinquefasciatus showed EI50 values of 8.07 and 19.55 mg/L respectively in comparison with that of standard insect growth regulator methoprene demonstrating EI50 value of 0.05 mg/L. Besides, the hexane extract was also found to possess toxic effect against non-target organism Gambusia affinis (a bio-control agent), however, the lethal concentration (LC50=172.7 mg/L for 24 h) against Gambusia affinis was much higher in comparison with that of tested concentrations against Ae. aegypti and Cx. quinquefasciatus. Conclusions: We conclude from the present investigation that the hexane extract of C. inerme has positive implications for its consideration in integrated control of dengue/filarial vectors due to their ecological distinctness in comparison with non-target organism and further due to ecofriendly nature of the extract in terms of easy biodegradability.

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