The toxicity and physiological effect of essential oil from Chenopodium ambrosioides against the diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae)

- The research describes the potential of the oil for alternative control diamondback moth.
- The oil showed both contact and fumigant toxicity to diamondback moth.
- The oil had 30-fold more potent toxicity than either α-terpinene or p-cymene.
- The oil treatment decreased leaf consumption by larvae and inhibited the pupation.
- Some larval endogenous enzymes were affected by the essential oil treatment.

In this study, the bioactivities of the essential oil of Chenopodium ambrosioides L. and its two main components, α-terpinene and p-cymene, were evaluated against the diamondback moth (DBM), Plutella xylostella (L.). The contact and fumigant toxicity of the essential oil significantly decreased as the DBM larval instar increased. The essential oil had 30-fold more potent toxicity against third-instar larvae than either α-terpinene or p-cymene. With respect to antifeedant activity, treatment with C. ambrosioides essential oil dose-dependently decreased leaf consumption by third-instar larvae, and the median antifeedant concentration (AFC50) was 66.81 mg/L at 24 h and 78.24 mg/L at 48 h after the treatment. Development of pupae was also inhibited, and the median concentrations of pupae weight inhibition (PWIC50) and percentage inhibition of pupation (PIC50) were 176.5 mg/g leaf and 111.6 mg/g leaf, respectively. In general, contact treatment with the essential oil significantly inhibited the activities of insecticide detoxifying enzyme, including carboxylesterase and glutathione-S-tranferases, whereas, fumigant exposure only altered carboxylesterase activity. At nearly all the tested concentrations, the essential oil induced the activities of superoxide dismutase, peroxidase, and catalase; however, peroxidase activity was inhibited by contact treatment. Thus, the essential oils from C. ambrosioides showed potential as new control products to combat field crop-infesting insect pests, and it may function as fumigant, insecticide synergist, antifeedant, or insect growth regulator.