Antifeeding, settling inhibitory and toxic activities of labiate essential oils against the green peach aphid, Myzus persicae (Sulzer) (Homoptera: Aphididae)

Labiate plants, such as spearmint, thyme and rosemary, inhibit the settling of Myzuspersicae (Sulzer) on them. The effects of their essential oils on the aphids' behaviors are little known thus far. In this study, the antifeeding, settling inhibitory and insecticidal activities of 10 labiate oils were investigated. On EMIF (electronic measurement of insect feeding behavior), 8 of the ten oils (rosemary and sage oils were exceptions) significantly reduced the total penetration time, average penetration time, and maximum penetration time, and increased the frequency of penetration. In the no-choice test, aphids rarely settled on the sealing film which covered the diet containing spearmint or thyme oil and most died. In the toxicity test, pennyroyal and thyme oils indicated relatively high toxicities while toxicities of the other oils were low. In the choice test, all 10 oils exhibited settling inhibitory activities. Spearmint, thyme, pennyroyal, mint and peppermint oils had especially high activities. Although the mechanisms of the settling inhibition differed among the oils tested, all the oils inhibited the aphids from settling under the choice condition. Labiate essential oils may play a role in deterring aphids from settling on these plants by effecting the aphids' gustatory and/or olfactory sense.