PHYSIOLOGICAL ASPECTS OF LODGEPOLE PINE WOUND RESPONSES TO A FUNGAL SYMBIONT OF THE MOUNTAIN PINE BEETLE, DENDROCTONUS PONDEROSAE (COLEOPTERA: SCOLYTIDAE)

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Abstract
The acetone-soluble fraction of phloem tissue samples from 78 lodgepole pines was examined prior to and following artificial inoculation with Europhium clavigerum, a fungus transmitted by the mountain pine beetle. All trees showed quantitative increases in the concentration of extractives within 3 days after treatment. Further increases continued for at least 7 days. By this time qualitative changes in the chemical composition of the host tissue had also occurred.Trees were defined as resistant or susceptible depending on whether they survived beetle attack under natural conditions. The composition of the acetone-soluble extracts was similar for the constitutive tissue of resistant and susceptible trees, but the total quantity of acetone extractives of reaction tissue was higher in resistant trees.The ability of trees to respond to fungal inoculation is diminished by mass attack. Trees responded more extensively to inoculation prior to, than during, aggregation under field conditions. An experiment was conducted to simulate this relationship under controlled conditions by examining the effect of multiple fungal inoculations on the production of monoterpenes during the wound response. Individual trees showed a weaker quantitative response on stem sections administered high inoculation densities than on stem sections administered only a single inoculation. Those trees which responded most extensively to a single invasion by the pathogen were more responsive at all inoculum densities.