INDUCED DEFENSE REACTION IN SCOTS PINE FOLLOWING STEM ATTACKS BY TOMICUS-PINIPERDA

The induced defence reaction of Scots pine Pinus sylvestris to stem attacks by the common pine shoot beetle, Tomicus piniperda (Col., Scolytidae), was studied by inducing natural attacks on young Scots pine trees of different vigour. Pruned trees were more heavily attacked by T. piniperda than unpruned ones. Vigorous trees successfully contained the attacking beetles within resinous lesions, whereas less vigorous trees failed to defend themselves. The content of resin acids increased dramatically in the lesions on all trees, and the resin acid composition differed somewhat between some treatments. Starch accumulation in the inner bark of the main stem was lower in pruned trees than in unpruned ones, and starch reserves were depleted in the most heavily attacked trees. All but one of the unpruned trees survived the attack, whereas most of the severely pruned ones died following attack by beetles at densities exceeding c. 300 egg galleries m-2.