Feeding-, settling-inhibitional and insecticidal activities of garlic and onion oils against Myzus persicae (SULZER) were investigated with an assay system consisting of EMIF (electronic measurement of insect feeding behavior), no-choice-, choice-tests and a toxicity test. No remarkable feeding inhibition activity by either oil was observed in EMIF. In the no-choice test, aphids rarely settled on the sealing film which covered the diet containing garlic oil and most of them died. The settling inhibition activity of onion oil was lower than that of garlic oil. In the toxicity test, both oils indicated toxicity, and the toxicity of garlic oil was higher than that of onion oil. Death of aphids in the no-choice test might have been caused by starvation and toxicity of both oils. In the choice test, both oils strongly prevented the aphids from settling. The volatile constituents of essential oils of garlic or onion may inhibit M. persicae from settling on these plants.It was shown that both oils have settling inhibition and insecticidal activity, but negligible antifeedant activity to this aphid. It was revealed that not all essential oils with settling inhibition or insecticidal activity had the feeding inhibition activity.
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