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Monoterpene hydrocarbons from the xylem oleoresins of Pinus tropicalis, P. caribaea var. caribaea, P. cubensis and P. maestrensis growing in Cuba were investigated. A large number of oleoresin samples from trees, attacked and unattacked by the moth Dioryctria horneana , as well as from trees growing in different localities, were analyzed. In each sample, the relative amounts of the volatiles and the enantiomeric compositions of six chiral monoterpene hydrocarbons were determined using a two-dimensional gas chromatographic (2D-GC) system. The GC-data were evaluated using two methods for multivariate data analysis, PCA (principal components analysis) and PLS-DA (projections to latent structures-discriminant analysis). PC-plots based on the relative amounts of the monoterpenes present in the volatile oleoresin fractions analyzed, showed that P. tropicalis and P. cubensis formed one group, separated from P. caribaea , while pines belonging to the species P. maestrensis were found in both groups. The species P. tropicalis and P. maestrensis , both of which are resistant to D. horneana , and the subgroups within the species P. caribaea and P. cubensis , that had not been attacked by D. horneana , showed no signs of constituting a chemical subgroup. No significant difference was found between the attacked and the unattacked P. cubensis trees. In P. caribaea , on the other hand, the composition of volatiles in attacked trees was significantly different from that in unattacked trees. However, an influence of monoterpenes on the oviposition of D. horneana was not proved. |
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