Chemical composition of Ocimum basilicum, Syzigium aromaticum and Eucalyptus globulus essential oils and their larvicidal activity on two important mosquitoes (diptera: culicidae)

The extensive use of synthetic insecticides has led to insecticide resistance in mosquito vectors such as Culex pipiens L. and Aedes aegypti L. (Diptera: Culicidae). This study aimed to assess the chemical composition and larvicidal potential of essential oils (EOs) from Ocimum basilicum, Syzygium aromaticum, and Eucalyptus globulus. EOs were extracted via hydro-distillation and analyzed using GC-MS. Major compounds identified were estragole (45.03%) in basil, eugenol (78.70%) in clove, and spathulenol (29.29%) in eucalyptus. Larvicidal activity was evaluated against fourth instar larvae, revealing LC₅₀ values of 13.13–84.27 ppm for C. pipiens and 25.11– 168.65 ppm for A. aegypti. Basil oil showed the highest efficacy. Enzyme assays on larvae exposed to LC₅₀ doses indicated increased activity of GSTs, α-/β-esterases, ALP, and ACP, while AChE and cytochrome P450 activities decreased, suggesting oxidative stress and neurotoxic effects. These results highlight the potential of the tested EOs, particularly O. basilicum, as eco-friendly alternatives for mosquito control through both direct toxicity and biochemical disruption. KEY WORDS: GC-MS analysis, Sweet basil, Clove, Tasmanian blue gum, Bioassay, Enzyme activity Bull. Chem. Soc. Ethiop. 2026, 40(1), 237-251 DOI: https://dx.doi.org/10.4314/bcse.v40i1.19