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Chemical determinants of tree susceptibility to mountain pine beetle (Dendroctonus ponderosae Hopkins) Syed, Akbar

Abstract

Volatile constituents of bark from the two species of pine hosts of the mountain pine beetle, (Dendroctonus ponderosae Hopkins) were investigated as postulated factors in host tree discovery and selective attack by the insect. The anemo-olfactory, klinokinetic and klinotactic responses of pedestrian adult flown females to odors of different aged pines of the species Pinus ponderosa Laws, (ponderosa pine) and Pinus monticola Dougl. (western white pine) were used as criteria to test for evidence as to possible involvement of host tree volatiles in host selection. Volatile substances from pine bark were collected through sublimation under vacuum from frozen state. The volatile extracts were analyzed by Gas-Liquid Chromatography. Total volatile extracts and their ether soluble fraction from mature pine trees were "attractive" to beetles, whereas those from saplings were "repellent." No qualitative differences were found in the ether-soluble fraction of mature trees and saplings respectively, but proportions of individual constituents in the extracts differed. Ethanol at various concentrations caused arrestance of the anemo-olfactory response of pedestrian beetles. As a constituent of trees under stress ethanol may thus play an important role in the programme of responses which lead ultimately to attack. Problems encountered during the storage of tree samples and their extracts have been discussed.

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