Bio-activity of Ocimum gratissimum Essential Oil on Aedes aegypti Mosquitoes Towards Vector Control

Abstract

Aedes aegypti mosquito is a notorious vector which transmits various diseases in Nigeria especially yellow fever virus. To that regards, the need to control the vector is not only crucial but urgent. Therefore the effect of varying concentrations of Ocimum gratissimum leaf-oil extract on Aedes aegypti larvae and adults was studied between January 2023 and June 2024. Essential oil from authenticated fresh samples of O. gratissimum leaves were extracted by steam distillation. Bioactive constituents of the oil were analyzed by gas chromatography. The extracted oil taken as 100% concentration was serially diluted to 20%, 10%, 5%, 2.5%, and 1.25% used for larval bioassays and adult repellency tests. Concentrations (20%, 10%, 5%, 2.5%, 1.25% w/w) of oil-based creams were formulated for repellency tests. Plain petroleum jelly and Odomos® (12% DEET) served as negative and positive controls, respectively. Aedes aegypti eggs from National Arbovirus and Vector Research Centre Enugu were reared to 4th instar larvae and adults for the study. Log-probit regression produced LC₅₀ and LT₅₀ while two-way ANOVA indicated significant differences (p<0.05) between mortality and repellency regarding concentrations and exposure times. Bioactive components of essential oil included ephedrine, tannin, flavonones, cardiac glycoside, ocimene, and decanal. In-vivo, 1.25% concentration caused 41.3% larval mortality (LC₅₀=2.4%; LT₅₀=7h). Simulated trails with encapsulated essential oils and oil-based creams exhibited comparable effects observed with pure essential oil. There was higher mortality and repellency effects at elevated concentrations. The essential oil of O. gratissimum has demonstrated larvicidal and adult repellency properties so that further research is urgently required to develop the oil for sustainable eco-friendly vector control.