Abstract
In 1970, 280 lodgepole pines between 8 and 140 years old, in the east Kootenay region of British Columbia, were inoculated with Europhium clavigerum. The resinous response of the tree to this inoculation was used as a measure of potential resistance to bark beetle attack. Trees between 31 and 50 years old had the greatest frequency of potentially resistant individuals. The following year, 250 trees between 10 and 120 years old were inoculated on June 11, July 5, and July 23, with similar results. The youngest (10–30) and oldest (91–120) trees had a greater decrease in frequency of resistant individuals, as the summer progressed, than the intermediate age classes. Trees rated as potentially resistant from all three inoculations had faster growth rates and thicker phloem than those rated nonresistant.

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