Studies on larvicidal and pupicidal activity of Leucas aspera Willd. (Lamiaceae) and bacterial insecticide, Bacillus sphaericus, against malarial vector, Anopheles stephensi Liston. (Diptera: Culicidae)

Abstract

The efficacy of whole plant extracts of Leucas aspera and Bacillus sphaericus has been proven against larvicidal and pupicidal activities of the malarial vector, Anopheles stephensi. The present study investigated the larvicidal and pupicidal activity against the first to fourth instar lavae and pupae of the laboratory-reared mosquitoes, A. stephensi. The medicinal plants were collected from the area around Maruthamalai hills, Coimbatore, Tamil Nadu, India. L. aspera whole plant was washed with tap water and shade dried at room temperature. The dried plant materials were powdered by an electric blender. From the powder, 100g of the plant materials was extracted with 300ml of organic solvents of ethanol for 8h using a Soxhlet apparatus. The extracts were filtered through a Buchner funnel with Whatman number 1 filter paper. The crude plant extracts were evaporated to dryness in a rotary vacuum evaporator. The plant extract showed larvicidal and pupicidal effects after 24h of exposure. All larval instars and pupae have considerably moderate mortality; however, the highest larval mortality was the ethanolic extract of whole plant L. aspera against the first to fourth instar larvae and pupae values of LC(50) = I instar was 9.695%, II instar was 10.272%, III instar was 10.823%, and IV instar was 11.303%, and pupae was 12.732%. B. spaericus against the first to fouth instar larvae and pupae had the following values: I instar was 0.051%, II instar was 0.057%, III instar was 0.062%, IV instar was 0.066%, and for the pupae was 0.073%. No mortality was observed in the control. The present results suggest that the ethanolic extracts of L. aspera and B. sphaericus provided an excellent potential for controlling of malarial vector, A. stephensi.