Larvicidal activity of leaf extracts and seselin from Clausena anisata (Rutaceae) against Aedes aegypti

• Hexane leaf extracts of Clausena anisata cause A. eagypti mosquito larval mortality.
• The larvicidal activity is partially attributed to the pyranocoumarin, seselin.
• The hexane leaf extract retains larvicidal activity after 2 months of storage.

The Aedes aegypti mosquito is a vector of various diseases in both humans and livestock. Mosquito control focuses on reducing the longevity as well as the population of mosquitoes to lessen their damage on human and animal health. It entails several strategies such as environmental management, insecticide treatments, and molecular entomological approaches. Environmental management centres on elimination of breeding sites, however mosquitoes can breed in sites that cannot be eliminated. Resultantly, focus is turned onto mosquito larvae control. The objective of this study was to evaluate the larvicidal activity of extracts and compounds from Clausena anisata against A. aegypti. The World Health Organization guidelines for testing of mosquito larvicides were used. The acetone, dichloromethane and hexane crude leaf extracts were evaluated in a preliminary screening for larvicidal activity at the concentrations of 12.5, 25, 50, 100 and 200 ppm. Batches of 25 third-instar larvae were transferred into cups each containing test solutions and larval mortality was recorded 24 h and 48 h after exposure. Acetone was used as the solvent control whilst permethrin was used as a positive control. Only the n-hexane extract caused mortality at the tested concentrations, thus it was further tested at 40, 60, 80, 100, and 120 ppm and had LC50 values of 68.30 and 59.65 ppm after 24 h and 48 h respectively. A stored hexane extract, of 2 months, was also evaluated under simulated field conditions to establish stability of extract. It caused about 90% mortality when tested at 100 ppm. The n-hexane extract was subjected to open column chromatography on silica gel to isolate the active compound. The isolated compound was identified as the pyranocoumarin, seselin. Dose dependent mortality was observed in the larvae exposed to seselin. The LC50 values at 24 and 48 h were 13.90 and 9.96 ppm respectively. Results obtained from this study indicate a potential of the incorporation of C. anisata extracts into the control of mosquito populations.