Chemical constituents and mosquito larvicidal properties of leaf extracts and fractions of <i>Quassia amara</i> linn against <i>Anopheles gambiae</i>

Abstract

This study evaluated the larvicidal efficacy of the crude methanol extract of the leaves of Quassia amara and the hexane, chloroform and ethyl acetate fractions partitioned based on their polarities, against the fourth instar larvae of Anopheles gambiae. Larvicidal studies were carried out on larvae collected from mosquito breeding sites, at concentrations ranging from 125 to 2000 μg/mL for the crude extract, 125 to 500 μg/mL for the partitioned fractions and 7.5 to 120 μg/mL for the sub-fractions. Larvae were exposed to extracts/fractions for 24 h. The percentage mortalities were calculated and the LC₅₀ values were obtained using GraphPad Prism, a nonlinear regression analysis. The  structures of compounds present in the active fractions were elucidated using spectroscopic techniques. The crude methanol extract was toxic to the larvae displaying 100 % mortality at 2000 μg/mL and an LC₅₀ of 640 μg/mL. Results were concentration dependent. The LC₅₀ values for the hexane and chloroform soluble fractions were 37.38 and 283 μg/mL respectively. The ethyl acetate fraction had a percentage mortality of <50 % at the highest dose tested. Further bioactivity led chromatographic separation of the hexane soluble fraction (LC₅₀= 17.84 μg/mL) obtained methyl gallate. Results obtained from this study suggest that Q. amara could serve as an alternative to synthetic larvicides.

Keywords: Quassia amara, Anopheles gambiae, larvae, extracts, methyl gallate, toxicity