Chemical composition and Larvicidal efficacy of Ficus sycomorus leaf extract against major malaria vector Anopheles coluzzii

Abstract

Resistance to synthetic insecticides used in control of malaria vectors is a major threat to malaria control globally. Natural insecticides of plant origin provide environmentally safe alternativess. This study characterized the phytochemical contents of the Ficus sycomorus leaves and insecticidal activities of its methanolic extract on Anopheles colluzzii larvae. The active secondary metabolites from methanol extract of F. sycomorus leaves were characterized using gas chromatography - mass spectrometry (GC-MS). A modified WHO standard protocol for larvicidal bioassay was used to determine the activity of methanol extract of the F. sycomorus. Molecular species identification showed that 75 % of the larvae were Anopheles coluzzii (Coetzee & Wilkerson); 6.25 % Anopheles arabiensis and 12.5 % Anopheles gambiae s.s. The extract reduced the survival of An. coluzzii larvae by approximately 52 % at LC50 of 0.225 mg/ml (95% CI: 0.197-0.234; R2 = 0.9445) after 24 h, and the mortality was dose dependent (with highest mortality of 51.67 % at 1 mg/ml). Phytochemical screening revealed the presence of alkaloids, flavonoids, tannins, saponins, terpenoids, phytosterols and phenols, with alkaloid and flavonoids having the highest concentration in the extract. The GC-MS revealed that the extract contained: tetrapentacontane, 66.6 %; stigmasterol, 2.81 %; squalene, 1.01 %; bis(2-ethylhexyl) phthalate, 4.04 %; and 4,8,12,16-tetramethylheptadecan-4-olide, 0.51 %. The toxicity of the extract may be due to different insecticidal phytochemicals, probably working independently, synergistically, or additively. Overall, the F. sycomorus leaf extract is a promising larvicide against malarial vector An. coluzzii and should be exploited as an alternative, environmentally safe larvicide.