Effects of plant essential oils on immature and adult sweetpotato whitefly, Bemisia tabaci biotype B

Effects of essential oils derived from garden thyme, Thymus vulgaris L., patchouli, Pogostemon cablin (Blanco) Benth., and lemon-scent gum, Corymbia citriodora (Hook.) K. D. Hill & L. A. S. Johnson, on mortality of eggs, first-instar nymphs, and pupae, and on adult oviposition, of Bemisia tabaci (Gennadius) biotype B were determined under laboratory conditions. Three concentrations of essential oils, 0.125%, 0.25% and 0.5% (v/v), were applied in contact toxicity experiments. In separate experiments, 0.5% essential oil treatment was tested for repellency. Greater mortality was observed with increasing dose of essential oils. No phytotoxicity was observed on plants treated with these essential oils. First-instar nymphs were more sensitive to essential oil treatments, compared with eggs and pupae. The greatest effect was found with essential oil extracted from T. vulgaris, which reduced the survival rate of B. tabaci by 73.4%, 79.0% and 58.2% after treatment of eggs, nymphs and pupae, respectively, as compared with controls. In no-choice tests, the cumulative survival rates of B. tabaci females treated with T. vulgaris, P. cablin and C. citriodora were 46.4%, 38.8% and 26.8% lower, respectively, as compared with controls. In choice tests, the mean numbers of eggs laid on P. cablin, T. vulgaris and C. citriodora oil-treated plants were 74.5%, 59.0% and 48.0% fewer, respectively, than on control plants. Based on this study, essential oil derived from T. vulgaris possessed the greatest contact toxicity, while P. cablin oil exerted the strongest repellency to B. tabaci. Hence, these two oils could be used as effective and environmentally sustainable bio-insecticides for the control of B. tabaci.