, Volume 24, Issue 9, pp 1551-1561

The Effect of Lignin and Bark Wounding on Susceptibility of Spruce Trees to Dendroctonus micans

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The effect of lignified stone cell masses (lignin) and mechanical wounding of bark on gallery formation and oviposition by the spruce bark beetle, Dendroctonus micans, was determined in plantations of Norway and Sitka spruce. When beetles were implanted onto trees that varied in bark lignin concentration, there was a significant negative relationship between lignin and adult gallery size. Only a few larval galleries were established, all of them on trees with a low lignin concentration. Results confirm the importance of lignin as a preformed defence in living trees. Adults excavated significantly larger galleries in wounded than unwounded bark. Most larval galleries were also established in wounded bark. The concentrations of nitrogen, carbohydrate, and resin and the moisture content of wounded and unwounded bark were measured at the beginning of the experiment. A number of significant changes were induced by wounding, including an increase in the concentration of nitrogen and starch, and decreases in the moisture content and the concentration of free sugars. There was no overall effect of wounding on resin content of bark, although concentrations were significantly lower in new than old wounds. An increase in the nutritional quality of bark following wounding appears to be the main factor influencing attacks on wounded trees by D. micans.