Activity of Trichilia megalantha Harms and Trichilia welwitschii CDC Extracts and Fractions on Anopheles gambiae Larvae

Abstract

Background: Lately, there is an increasing shift towards the use of environmentally friendly and biodegradable natural vector control of plant origin as agent for disease vector control. Objectives:  To determine the toxicity of extracts and fractions of T. megalantha and T. welwitschii on Anopheles gambiae larvae. Methods: The larvicidal activity of methanol extracts of leaf, stem bark and root bark of Trichilia megalantha and Trichilia welwitschii (Meliaceae) and fractions of stem bark of T. megalantha and root of T. welwitschii were evaluated on early 4^th instar Anopheles gambiae larvae. Larvae were exposed to various concentration of plant extracts and fractions. Dead larvae were counted after 24 h of exposure. The most active extracts of both plants were partitioned into hexane, dichloromethane (DCM), ethyl acetate and methanol and subjected to the same assay.  Ethanol (5%) was included as a negative control. The experiments were done in triplicate. Results were compared to those of larvae exposed to N,N-diethyl-3-methylbenzamide (LC₅₀ =1000.09 µg.mL^-1), the reference insecticide. Results: All tested extracts and fractions showed larvae mortality. Of the six crude extracts screened, T. megalantha stem bark showed the highest activity with LC₅₀ of 15.6 µg.mL^-1 while the leaf (LC₅₀ =496.1 µg.mL^-1) showed the least activity. The root of T. welwitschii was more toxic to the larvae (LC₅₀ =65.0 µg.mL^-1) while the leaf (LC₅₀ =232.0 µg.mL^-1) showed the least larvae toxicity. Conclusion: The results showed that the extracts and fractions of T. megalantha and T. welwitschii were significantly toxic to Anopheles gambiae larvae.  The promising activity demonstrated by the two plants in mosquito vector control could contribute significantly to malaria control

Keywords: Plant extract, Meliaceae, larvicidal, vector control