Synthetic blend of larval frass volatiles repel oviposition in the invasive box tree moth, Cydalima perspectalis

Abstract

Insects find their oviposition sites using visual, contact and olfactory cues. Volatile stimuli emitted by an intact or herbivore-occupied host plant, non-host plants or the herbivore itself can all influence the final decision of females concerning where to lay eggs. Volatile substances surrounding larval excreted pellets, i.e., frass of the invasive box tree moth (Cydalima perspectalis Walker) were collected, and the physiological activity was investigated by coupled gas chromatographic–electroantennographic detection. Based on structural elucidation, two aromatic derivates and one terpene alcohol were identified to be physiologically active on the antennae of the adults: guaiacol, (±)-linalool and veratrol. For all compounds, antennal responses were found to be dose dependent with EAG amplitudes being the highest at the highest dose levels. Females were also more sensitive to all three compounds compared to males. Single sensillum recordings on mated female antennae revealed that these frass compounds triggered 22% of the tested olfactory sensory neurons housed in trichoid sensilla. Behavioral bioassays indicated that the blend of these compounds had an oviposition-repellent effect on conspecific females: individuals laid significantly fewer eggs on boxwood plants equipped with dispensers loaded with the synthetic blend compared to those treated with natural frass or the control plants. This difference likely originated from the measured rapid changes in the volatile profile of larval excrement when exposed to the air at room temperature. Our findings have the potential to unravel the complex ecology of this invasive moth species characterized by rapid range expansion and extensive damage in Europe.