Olugbenga A Ojo* and Abidemi E Ojo
The aim of this present investigation is to evaluate and isolate larvicidal principles in leaves of Melia azedarach using the fourth instar larvae of An. gambiae. Larvicidal activity was evaluated by exposing 4th instar larvae of Anopheles gambiae to serial concentrations (0.625-10 mg/mL) of extracts, fractions and compounds of Melia azedarach. Larval mortality was recorded after 24h of exposure and 50% lethal concentration (LC50) values determined. L Results were compared to those of larvae exposed to N, Ndiethyl-m-toluamid (DEET), the reference insecticides and untreated groups. Larvicidal activity of the crude methanol extract of both leaves and stem bark of M. azedarach were 5.80 and 7.59 mg/mL respectively. The hexane soluble fraction of M. azedarach leaf displayed highly lethality at 0.625 mg/mL with LC50 of 0.025 than the remaining fractions. Similarly, larvicidal activity of DEET was significantly low (LC50=1.09 mg/mL) than the hexane fractions (p<0.05). Fractionation and purification of the active fractions led to isolation of three compounds. Fraction 35-49 (designated as ‘F’) of M. azedarach showed larvicidal activity on larvae with LC50 of 0.017 mg/mL. Two compounds were isolated from fraction ‘F’ using preparative thin layer chromatographic. Compound 2 and 3 had Rf values of 0.75 and 0.63 respectively on silica gel G using CH3Cl3 -CH3OH (9.5:0.5) and CH3Cl3 -Acetone (9:1) respectively. Compounds 2 and 3 showed positive test for the presence of triterpenoids after spraying with anisaldehyde/H2SO4 . The presence of triterpenoids may be responsible for the insecticidal activity observed in the two compounds isolated from the leaves of M. azedarach. The leaves of M. azedarach showed potent anti larvicidal activity. Compounds from this plant may serve as sources for the development of malaria vector control compounds.
