Comparison of the effects of extracts from three Vitex plant species onAnopheles gambiae s.s. (Diptera: Culicidae) larvaeMokua

Abstract

tAcetone and methanol extracts of different parts of three Vitex species (leaves and stem bark of Vitextrifolia, leaves, stem bark and root bark of Vitex schiliebenii and stem and root bark of Vitex payos) wereevaluated for their potential to control Anopheles gambiae Giles s.s. larvae (Diptera: Culicidae). The extractsgave different levels and rate of mortality of the larvae. Some (methanol extract of V. trifolia leaves, acetoneextracts of stem bark and leaves of V. schiliebenii, acetone extract of root bark of V. payos) caused 100%mortality at 100 ppm in 72 h, with those of V. schiliebenii and V. payos showing faster rate of mortality(LT50= 8 h) than that of V. trifolia (LT50= 14 h). At lower doses of these extracts (≤50 ppm), most of thelarvae failed to transform to normal pupae but gave larval–pupal intermediates between 4 and 14 days ofexposure. Some pupated normally but the adults that emerged appeared to be weak and died within 48 h.Extracts of the stem bark of V. payos showed interesting effects on the larvae. Initially, the larvae wererelatively hyperactive compared to those in control treatments. Later, the ones that did not transform tolarval–pupal intermediates became stretched and inactive and died and floated in clusters on the surface.These observations suggest some interesting growth-disrupting constituents in the plants, with possibleapplication in the practical control of mosquito larvae in aquatic ecosystems.