Chemical composition and larvicidal evaluation of Mentha, Salvia, and Melissa essential oils against the West Nile virus mosquito Culex pipiens

The volatile metabolites of wild-growing Mentha spicata, M. longifolia, M. suaveolens, Melissa officinalis, Salvia fruticosa, S. pomifera subsp. calycina, and S. pomifera subsp. pomifera from Greece were determined by gas chromatography and gas chromatography–mass spectrometry. The insecticidal properties of the analyzed essential oils were screened on Culex pipiens larvae. Additionally two of the main components of the essential oils, piperitenone oxide and 1,8-cineole were assayed against C. pipiens in order to define the affiliation between them and the larvicidal properties of the oils. The most effective oils were M. suaveolens (major constituent piperitenone oxide, 62.4%), M. spicata (piperitenone oxide, 35.7% and 1,8-cineole, 14.5%) and M. longifolia—Central Greece (piperitenone oxide, 33.4%; 1,8-cineole, 24.5% and trans-piperitone epoxide, 17.4%), which exhibited LC₅₀ values ranging from 47.88 to 59.33 mg l⁻¹. Medium activity revealed the oils of M. officinalis (terpin-4-ol, 15.8%; caryophyllene oxide, 13.2%; sabinene, 12.9%; β-pinene, 12.1%; and trans-caryophyllene, 10.2%), M. longifolia—Southern Greece (carvone, 54.7% and limonene 20.0%), S. pomifera subsp. pomifera (trans-caryophyllene, 22.5% and trans-thujone, 21.0%), S. pomifera subsp. calycina—West Southern Greece (trans-thujone, 56.1% and 1,8-cineole, 10.4%), and S. fruticosa—population 2 (camphor, 23.1%; α-pinene, 12.7%; and borneol, 12.6%), with LC₅₀ values ranging from 78.28 to 91.45 mg l⁻¹. S. pomifera subsp. calycina (Central Greece) essential oil (trans-thujone, 26.5% and cis-thujone, 12.0%) presented rather low activity (LC₅₀ values 140.42 mg l⁻¹), while S. fruticosa—population 1 (1,8-cineole, 31.4% and camphor, 22.6%) was the only inactive oil. Additionally, the constituent piperitenone oxide was found to be highly active (LC₅₀ values 9.95 mg l⁻¹), whereas 1,8-cineole revealed no toxicity.