Evaluation of Effect of Ocimum Gratissimum (Lamiaceae) Extracts on Nasutitermes Termite, Cocoa Pests in Côte d'Ivoire

Abstract

The misuse of synthetic pesticides in agrosystems has led to many problems including insect resistance and environmental pollution. To solve this problem, scientific research is increasingly focused on plants with insecticidal properties. Thus, this study has the general objective of evaluating the effectiveness of the various extracts (crude extract, fraction of extract, and essential oil) of Ocimum gratissimum on termites of the genus Nasutitermes, pests of cocoa trees. The crude extracts were obtained by the maceration of the dried leaf powders; the extract fractions by fractionation of the crude hydro-ethanolic extract and the essential oil by hydrodistillation. The tests, repeated four times, were carried out at the Animal Biology Laboratory of Félix Houphouët-Boigny University. Thus, 50 workers deposited in Petri dishes of termites were exposed to different doses of extracts of this plant and the effect of the extracts on termites as compared to the negative control. The results have shown that all the tested concentrations have scored the highest rate of mortality (100%) after 3 hours of exposure. This toxicity would be linked to the monoterpenes which constitute 80% of the compounds of this extract. However, by fumigation, the essential oil is effective at high concentrations (5 and 10 mg/l). Regarding extracts and fractions of extracts, only the acetate extract fraction showed a toxicity for termites. Nevertheless, this extract acts after 48 hours of exposure and at high concentrations.