Effects of Exposure to Differentially Stressed Pinus sylvestris Seedlings on the Susceptibility of Receivers to Feeding by the Large Pine Weevil

Plants release volatile organic compounds (VOCs) in response to herbivory or damage as part of an indirect defence strategy. These broadly defined damage-induced plant volatiles (DIPVs), include herbivore-induced plant volatiles (HIPVs). DIPVs elicit defence-related responses in neighbouring plants, which may influence herbivore behaviour. Although DIPVs have been studied in conifers, little is known about how they influence neighbouring plants and shape subsequent interactions with herbivores. We tested whether DIPVs released by damaged Scots pine (Pinus sylvestris) seedlings alter the susceptibility of undamaged receivers to feeding by the large pine weevil (Hylobius abietis). A two-stage experiment examined the effects of exposure to VOCs from mechanically damaged, pine weevil-damaged, sawfly-damaged, and undamaged seedlings on neighbouring receivers. In the first stage, receivers were exposed to VOCs for seven days. VOC emissions from receivers were collected and analysed using gas chromatography-mass spectrometry. Analyses revealed treatment-specific volatile profiles. In the second stage, weevil orientation was tested, and receiver susceptibility evaluated by quantifying bark damage area using digital photograph analysis and classification of feeding-damage type as superficial or deep. Weevils first oriented towards the control receivers most frequently before being found in greater numbers on receivers exposed to DIPVs from mechanically damaged and weevil-damaged neighbours. Towards the end of the experiment, they were found on receivers exposed to sawfly-induced DIPVs. The control group had more deep damage than superficial damage, whereas all DIPV exposure groups had more superficial than deep feeding spots, suggesting that prior VOC exposure may result in surface-level feeding. These findings show that DIPVs can trigger changes in receivers that influence pine weevil orientation and feeding behaviour.