Chemical composition and evaluation of mosquito larvicidal activity of Vitex payos extracts against Anopheles gambiae Giles S.S larvae
AIM: The aim of this study was to evaluate the acetone and methanol root bark extracts of Vitex payos and different fractions thereof, following acetone extraction and column chromatographic separation, for their immediate toxicity and long term effects on Anopheles gambiae Giles sensu stricto larvae under simulated semi-field conditions. METHODS: In the present study, acetone and methanol extracts and acetone chromatographic fractions were investigated against late third/early fourth-instar larvae of laboratory reared A. gambiae. The tests were conducted according to the method of the World Health Organization (WHO) on guidelines for laboratory and field testing of mosquito larvicides. In addition, chemical compositions of the extracts were carried out using gas chromatography-mass spectrometry (GC-MS). The study was conducted in 2012. RESULTS: Acetone chromatographic fractions showed significant larvicidal activity against A. gambiae larvae with LC50 values ranging between 0.7 - 0.9 ppm. Dose-response relationships were established with the highest dose of 500 ppm causing over 85% mortality in all the test extracts. Long-term (11-14 days) post-exposure observations at lower doses showed that the extracts achieved over 90% adult growth inhibition with morphogenetic variations and behavioral changes. In acetone and methanol extracts, carbonyl compounds were determined as the main constituents with percentage compositions of 34.26% and 23.53% respectively. The other class of compounds determined was the phytoecdysteroids where gamma sitosterol (6.43%) was the major sterol in acetone extract while stigmasterol (2.83%) was major in methanol extract. CONCLUSION: Extracts and chromatographic fractions from V. payos possess larvicidal and/or insect growth regulatory (IGR) principles which can be used in aquatic ecosystems by the local communities where most of the people cannot afford synthetic larvicides.