Attack rates of scolytids and composition of volatile wood constituents in healthy and mechanically weakened pine trees

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Abstract
The composition of volatile wood constituents in healthy (untreated) and injured (top‐cut or girdled) Scots pine trees, Pinus sylvestris L., was studied during three years using gas chromatography. The data were evaluated using PCA (principal components analysis) and PLS‐DA (projections to latent structures‐discriminant analysis), two methods for multivariate data analysis. Data from headspace analysis from the first and the third year revealed a significant difference in the composition of volatile wood constituents between untreated and top‐cut trees while GC analysis of extracts only revealed a significant difference for the first year. The higher proportions of ethanol and acetaldehyde in top‐cut trees were important in differentiating these trees from healthy ones. Differences in the monoterpene composition also seemed to be important in this respect. Untreated trees remained unattacked by the scolytid species. Hylurgops palliants (Gyll.) and Trypodendron lineatum (Oliv.) (Scolytidae) only attacked top‐cut trees, which were characterized by relatively high proportions of ethanol and acetaldehyde. Tomicus piniperda (L.) attacked both top‐cut and girdled trees, which were in some, but not all cases also characterized by relatively high proportions of ethanol and acetaldehyde.