Physiological Differences Between Lodgepole Pines Resistant and Susceptible to the Mountain Pine Beetle 1 and Associated Microorganisms 2

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Abstract
Lodgepole pines, Pinus contorta Douglas var. latitolia Engelmann, were assayed for traits associated with resistance to the mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Scolytidae). There was no relationship between resistance and the daily rate of resin flow, rate of resin crystallization, monoterpene content, monoterpene composition, or current growth rate. The major difference between trees which survived or died during exposure to naturally occurring high beetle populations was the extent of their active response to fungal invasion. Resistant trees responded to artificial inoculation with fungi vectored by D. ponderosae by forming greater quantities of resin than did susceptible trees. This wound response is general in nature, quantitatively variable, metabolically active, rapid, and localized. It appears to form the major line of defense to D. ponderosae and its associated fungi, and to be related to the general vigor of the tree. The wound response was greatest in those trees which had a periodic growth ratio greater than unity.

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