Effect of host and non-host plant volatiles on pheromone- mediated orientation in the beech bark beetle Taphrorychus bicolor

Broadleaf-feeding bark beetles remain far less studied than conifer-infesting species, particularly with respect to their semiochemical orientation and host selection. Here, we investigated the responses of the beech bark beetle Taphrorychus bicolor to host- and non-host-derived volatile organic compounds (VOCs) using field trapping experiments and electrophysiological analyses conducted in the Voděradské bučiny National Nature Reserve (Central Bohemia, Czechia). Pheromone-baited traps were supplemented with plant material from the host Fagus sylvatica or the non-host species Picea abies and Taxus baccata , and relative trap catches and male proportions were evaluated using generalized linear mixed-effects models. Traps baited with pheromone alone captured the highest number of T. bicolor (122,342 individuals), whereas the addition of P. abies branches significantly reduced trap catches and resulted in the lowest proportion of males (14%) among all treatments, suggesting a potential repellent effect of spruce-derived cues. Branches of F. sylvatica and T. baccata did not significantly affect beetle captures compared with the pheromone-only control, indicating the absence of an attractive effect of host-derived volatiles under the experimental conditions used. VOCs emitted by host beech and non-host spruce were collected using dynamic headspace sampling and analyzed by GC–EAD and GC × GC–TOF–MS. Antennal responses in beech samples were elicited by eucalyptol, γ-terpinene, and terpinolene, whereas in spruce samples two unidentified compounds elicited antennal responses, with host identity explaining 41.2% of the variation in antennal response profiles (R 2 = 0.412, p < 0.001). No antennal responses were detected to abundant monoterpenes in either VOC blend. This study provides the first evidence of differential antennal responses to host- and non-host-derived VOCs in T. bicolor , together with behavioral evidence of a potential repellent effect of non-host volatiles, with implications for mixed forest management strategies aimed at reducing bark beetle pressure on beech stands under ongoing climate change.