Electroantennogram and behavioural responses of Plutella xylostella to vola host plant Mentha spicata

Plutella xylostella Linnaeus (Lepidoptera: Plutellidae) is one of the most important pests of cruciferous vegetables. Mechanically damaged Mentha spicata Linnaeus (Lamiales: Lamiaceae) strongly repels P. xylostella adults; however, the repellent mechanism remains unclear. In this study, the repellent mechanism was explored based on the electroantennogram (EAG) and behavioural responses of P. xylostella to volatiles from the damaged M. spicata. First, the active volatile compounds in the headspace volatiles of damaged M. spicata were identified by gas chromatography-electroantennographic detection (GC-EAD) and gas chromatography-mass spectrometry (GC-MS). Furthermore, the EAG and behavioural responses of P. xylostella to these compounds were investigated. The GC-EAD results indicated that four compounds, 2,4-dimethylheptane, 4-methyloctane, 2-methylnonane, and myrcene induced EAG responses in female antennae. 2-methylnonane and myrcene elicited strong dose-dependent EAG responses starting at a dose of 1 mu g/mu L. Choice tests in a four-arm olfactometer showed significant repellent effects of the four compounds on P. xylostella adults at 100 mu g/mu L, and the repellent indices of 2,4-dimethylheptane, 4-methyloctane, 2-methylnonane, and myrcene were 70.0%, 76.7%, 66.7%, and 73.3% to mated females, respectively. Finally, oviposition repellence assays showed that female adults were significantly repelled by these compounds, and the oviposition repellent index for myrcene was 23.9%. 2,4-dimethylheptane, 4-methyloctane, 2-methylnonane, and myrcene mediate the repellence of wounded M. spicata to P. xylostella adults, suggesting that the four compounds contribute towards developing behavioural regulators of this important pest.