Acaricidal activities of the essential oils from several medicinal plants against the carmine spider mite (Tetranychus cinnabarinus Boisd.) (Acarina: Tetranychidae)

A screening for pesticidal activity of plant extracts with some known medicinal attributes could lead to the discovery of new agents for pest control. In the backdrop of recent revival of interest in developing plant-based insecticides, the present study was carried out to find an alternative to synthetic miticides currently used in the control of the devastating greenhouse pest, carmine spider mite (Tetranychus cinnabarinus Boisd.) (Acarina: Tetranychidae). The acaricidal activities of essential oils obtained from medicinal plants such as oregano (Origanum onites L), thyme (Thymbra spicata L subsp. spicata), lavender (Lavandula stoechas L. subsp. stoechas) and mint (Mentha spicata L.) were evaluated against the adults of T cinnabarinus under laboratory conditions. Chemical compositions of the essential oils were also determined by GC-MS analysis. Carvacrol was the principal compound present in the essential oils of thyme and oregano (70.93% and 68.23%, respectively), whereas alpha-thujone (65.78%) and carvone (59.35%) were the major constituents in lavender and mint essential oils, respectively. Volatile phase effects of different concentrations of the essential oils used were determined. Laboratory bioassay results indicated that all essential oils caused complete mortality of spider mites at different concentrations that are not phytotoxic to the host plant. Although all essential oils show acaricidal activities in a dose-dependent manner, essential oils of thyme and oregano have a marked acaricidal activity against carmine mite adults (at 5.0 and 7.5 mu g ml(-1) air concentrations, respectively). The mean lethal concentrations (LC50) of the essential oils of thyme, oregano, mint and lavender were 0.53, 0.69, 1.83 and 2.92 mu g ml(-1) air, respectively. The results of the present study concluded that plant essential oils could be useful in promoting research aiming at the development of new agent for pest control from the plants with medicinal values. (C) 2009 Elsevier B.V. All rights reserved.