Synergistic Activity of a Mixture of Lantana camara and Ocimum gratissimum Leaves Extracts against Aedes aegypti Larvae (Diptera: Culicidae)

Abstract

Due to the continuous and misuse of synthetic insecticides which led to development of insecticide resistance, the present study was to determine the mosquito larvicidal activity of Lantana camara and Ocimum gratissimum leaf extracts in individual and combined forms to explore eco-friendly plant extracts that have potentials to suppress mosquito larval population. Recommended WHO mosquito larval bioassay method for insecticide was used. Four concentrations ranging from 0.25 to 2 g/L were performed for all extracts and fractions in single and combined forms. In single form of L. camara , the LC 50 values of solvent extracts and fractions were ordered as follows: 0.62>0.72>0.96>2.20>3.36 g/L for ethyl acetate, hexane, methanol crude, chloroform and methanol, respectively. For O. gratissimum the following order of LC 50 values was observed: 0.37>0.60>0.97>1.60>3.23 g/L for hexane, methanol crude, ethyl acetate, chloroform and methanol, respectively. Methanol crude extract, hexane and ethyl acetate fractions were selected to form five combinations in 1:1 ratios. The combination of the two plants’ hexane fraction and hexane ( L. camara ) + ethyl acetate ( O. gratissimum ) showed assumed synergistic actions. However, the two plants’ ethyl acetate and ethyl acetate ( L. camara ) + hexane ( O. gratissimum ) exhibited assumed antagonistic effects. In Conclusion, identifying these possible synergistic compounds within mixtures may lead to the development of more effective biopesticides in reducing the Ae. aegypti population, especially in the areas where surveillance and supervisory mechanism are poor as Nigeria.