RESEARCH ARTICLE Plant Essential Oils Synergize and Antagonize Toxicity of Different Conventional

Plant-derived products can play an important role in pest management programs. Essential oils from Lavandula angustifolia (lavender) and Thymus vulgaris (thyme) and their main con-stituents, linalool and thymol, respectively, were evaluated for insecticidal activity and syn-ergistic action in combination with insecticides against green peach aphid,Myzus persicae (Sulzer) (Hemiptera: Aphididae). The essential oils and their main constituents exerted simi-lar insecticidal activity when aphids were exposed by direct sprays, but were non-toxic by exposure to treated leaf discs. In synergism experiments, the toxicity of imidacloprid was synergized 16- to 20-fold by L. angustifolia and T. vulgaris essential oils, but far less syner-gism occurred with linalool and thymol, indicating that secondary constituents of the oils were probably responsible for the observed synergism. In contrast to results with imidaclo-prid, the insecticidal activity of spirotetramat was antagonized by L. angustifolia and T. vul-garis essential oils, and linalool and thymol. Our results demonstrate the potential of plant essential oils as synergists of insecticides, but show that antagonistic action against certain insecticides may occur