Changes in volatile organic compounds (VOCs) content in resistant and non-resistant forest trees in response to bark beetle attack

The response offorest trees tobark beetle attack involves substantial changes interpene content, which varies between resistant and non-resistant species. Terpenes serve ascrucial chemical defences against pests, and their production can beinfluenced byprior attack history, water stress, and biotic interactions. Moreover, the effectiveness ofterpenes inresisting bark beetle attack isinfluenced bytheir chemical composition. Different tree species produce different types and amounts ofterpenes that can affect their overall resistance levels. Inconifers, acyclic and cyclic monoterpenes and sesquiterpenes were significantly present inall samples. Acyclic monoterpenes, ketones, aldehydes, monocarboxylic acids and their esters, and aromatic and cyclic compounds have been identified inbeech. Astatistically significant decrease ofcompounds ininfested trees was determined inpine (<i>cis</i>-β-ocimene, neo-allo-ocimene, terpinene-4-ol, and δ-cadinene), and fir (acetophenone, benzonitrile, phenol, and zonarene). Inaddition, increased benzaldehyde production was observed. However, ininfested beech trees, only increased production ofsome aliphatic and aromatic compounds (2-butanone and 3,5-octadien-2-one, 2-methyl-4-pentenal and 2,4-hexadienal, octanoic acid, nonanoic acid, 3,4-dimethyl-2,5-furandione, acetophenone, benzeneacetaldehyde, 2-ethyl-1H-pyrrole, β-ionone-5,6-epoxide, β-cyclocitral, and geranyl acetone) was found. Weinvestigated the changes inthe terpene composition ofsurviving trees inbark beetle-infested stands ofbeech (<i>Fagus sylvatica</i>), pine (<i>Pinus sylvestris</i>), and fir (<i>Abies alba</i>). Our data showed that the distribution of different groups of volatile compounds varied according to the tree species.