Summary

Seasonal variation of the volatile terpenoids of Pinus pinea Ten and Pinus halepensis Mill, infested and uninfested by the caterpillar Marchalina hellenica, was followed by GC and GC-MS analyses of the pines cortical oleoresin. α-Pinene was found to be the dominant monoterpene in P. halepensis, while in P. pinea limonene was the most abundant compound. A significant decrease in the number of identified volatiles from winter to summer was observed and was more pronounced in the minor metabolites. Variation of the terpenoids according to the depth of the draining (drilling) holes in the trees was also determined. In addition, terpenoids were correlated with the results of cross feeding experiments designed for the study of the host preference of M. hellenica. All results revealed the dependence of M. hellenica on the secondary chemistry of the host. P. pinea, having a high content of limonene, appears to be more resistant to the caterpillar. Canonical discriminant analysis, in the discriminant space of the relative contribution of the ten major terpenes, separated P. pinea from P. halepensis, and infested from uninfested P. halepensis trees.