Entomological Potencies of Extracts of the Weaver Ant (Oecophylla smaragdina) against Anopheles spp

Abstract

The endemicity of mosquito-borne diseases in more than 100 countries recently, as a result of mosquito complex behaviour dynamics coupled with the challenges of costs, environmental toxicity and most especially insecticide resistance associated with indiscriminate chemical vector control Therefore this study aimed to elucidate the mosquito larvicidal efficacies of crude and fractionated extract of the weaver ant against Anopheles mosquito spp. The entomochemical composition of the crude methanolic extract was analyzed following standard procedures. The larvicidal activities of both the crude and fractionated extract of the weaver ant against 4th instar larvae of Anopheles mosquito spp. were carried out using slightly modified WHO standard protocols and larvae mortality were recorded after 24 h exposure period. Graded concentrations, ranging from 0.1-1.2 mg LG1 of both the crude and fractionated extracts were tested against 20 batches of healthy 4th instar larvae of Anopheles mosquito spp. The entomochemical screening revealed the presence of saponins and cardiac glycosides in the crude methanol extract. Percentage larvae mortality was directly dependent on extract concentration in both the crude and fractionated forms. All the tested extract concentrations showed moderate to high larvicidal activities. However, the lowest lethal concentration was recorded with the n-hexane fraction, followed by the ethyl acetate fraction. The LC50 and LC90 of n-hexane and ethyl acetate fraction were recorded as 0.03, 0.34 and 0.463, 0.718 mg LG1 , respectively. There was strong correlation between larvicidal activities of the crude methanolic extract and n-hexane fraction is an indication of similarity in their mode of larvicidal action. The findings of this study concluded that bioactive metabolites from weaver ants is a promising source alternative highly potent and perhaps, eco-friendly insecticidal agents for sustainable malaria vector control and, hence should be thoroughly investigated for that purpose.