Fumigant activity of 34 commercial essential oils was assessed on female adults and eggs of twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) at three temperatures (5, 15, and 25°C). Common thyme, cinnamon, and lemongrass oils were equally effective on twospotted spider mite adults showing 85.8–100% mortality at 5 and 10 µl/liter air at 25°C. At a lower temperature of 15°C, lemongrass and peppermint resulted in ≥90% mortality of adults at 10 µl/liter air. Only lemongrass was relatively active at 5 µl/liter air, at 15°C. At 5°C, lemongrass and peppermint caused significantly higher adult mortality than controls but only at 10 µl/liter air. Common thyme oil showed the highest ovicidal activity at 5 µl/liter air at 25°C. Among the main components of common thyme and lemongrass oils, citral was lethal to twospotted spider mite adults at all tested temperatures. Carvacrol, thymol, and citral caused the same inhibitory effects on the hatch of twospotted spider mite eggs at 25°C. However, citral was more active than other compounds to twospotted spider mite eggs at 15°C. Therefore, we conclude that citral has the best potential for development as a fumigant against twospotted spider mite on agricultural products harvested late in the growing season.
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Vol. 104 • No. 2