|Lim, Eu Gene|
|Roh, Hyun Sik|
|Coudron, Thomas - Tom|
Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/11/2011
Publication Date: 4/1/2011
Citation: Lim, E., Roh, H., Coudron, T.A., Park, G. 2011. Temperature-dependent fumigant toxicity of some essential oils and their main constituents against two-spotted spider mite, Tetranychus urticae. Journal of Economic Entomology. 104(2):414-419. Interpretive Summary: Methyl bromide, a soil fumigant extensively used to control pests in a wide range of agricultural crops, is being phased out due its negative affect on the stratospheric ozone layer. The application of natural substances is one replacement strategy for the use of methyl bromide. This strategy is currently being tested where methyl bromide has been used as an insecticide and miticide. One example is the control of spider mites on fresh commodities, such as paprika, apple, pear, rose, strawberries, and sweet persimmon. The results of this study have demonstrated two new concepts: characterization of the active ingredient within natural substances that is lethal to adult and/or eggs of spider mites; and the effectiveness of the active ingredient at varying temperatures. Oil extracted from cinnamon, geranium, common thyme and lemongrass all had significant miticidal activity. Oil from common thyme and thymol, the active ingredient in common thyme, had the added advantage of miticidal activity at low temperatures, making them attractive for use during shipping. These findings demonstrate to the fresh commodity industry that a viable substitute for use of methyl bromide during pre-shipment and shipment phases may be plant oils and/or their active ingredients for the control of spider mites.
Technical Abstract: Fumigant toxicity assays of 34 commercial essential oils were conducted on female adults and eggs of the two-spotted spider mite (TSM) at 3 temperatures (5, 15, 25 deg C). Common thyme and cinnamon oils resulted in > or = 90% mortality of adults at 5 and 10 uL/L air at 25 deg C. At 15 deg C, lemongrass and peppermint resulted in > or = 90% mortality of adults at 10 uL/L air and only lemongrass was relatively active at 5 uL/L air. In tests on eggs, only common thyme at 5 uL/L air at 25 deg C had ovicidal activity. Among the main components of common thyme and lemongrass oils, citral was lethal to TSM adults at all tested temperatures. Thymol and carvacrol caused >91% inhibition of egg hatch at 25 deg C, whereas citral caused 64.8% inhibition of egg hatch at 15 deg C. Citral may be the better substance to use as a fumigant against TSM on agricultural products harvested throughout growing season. It resulted in mortality of TSM adults and eggs at all temperatures tested.