Coniferophagous bark beetles are host-specific. The mountain pine beetle, Dendroctonus ponderosae attacks lodgepole and other pines, the Douglas-fir beetle, D. pseudotsugae attacks Douglas-fir, the spruce beetle, D. rufipennis attacks spruce and the western balsam bark beetle, Dryocoetes confusus attacks subalpine fir. Gas chromatographic-electroantennographic detection analyses (GC-EAD) of captured volatiles from the bark and foliage of trees, against the antennae of all four species of beetles followed by gas chromatography-mass spectroscopy (GC-MS), revealed that the beetles perceived 13 volatile monoterpenes present in all four tree species. To determine the qualitative and quantitative variation of these compounds among the four tree species, we sampled bark and foliage from 10 trees per species in three geographic locations in British Columbia. Solvent extraction and gas chromatographic analyses of bark and foliage revealed substantial differences in monoterpene profiles indicating a potential basis for olfactory discrimination among sympatric hosts. In bark, predominant compounds were:
(+)-alpha-pinene and (-)-beta-pinene in Douglas-fir; (-)-beta-phellandrene and (-)-beta-pinene in lodgepole pine; (+)-3-carene and (-)-beta-phellandrene in spruce; and (-)-beta-phellandrene, (-)-beta-pinene and (-)-limonene in subalpine fir. In foliage, predominant compounds were: (-)-alpha-pinene, (-)-camphene, (-)-sabinene, (-)-beta-pinene and
(-)-bornyl acetate in Douglas-fir; (-)-alpha-pinene, (-)-beta-pinene and (-)-beta-phellandrene in lodgepole pine; (-)-alpha-pinene, (-)-camphene, myrcene and (-)-bornyl acetate in spruce and (-)-alpha-pinene, (-)-camphene, (-)-beta-pinene, (-)-beta-phellandrene, (-)-limonene and (-)-bornyl acetate in subalpine fir. For bark and foliage volatiles, subalpine fir had five and three times more extractable material respectively compared to the next nearest species. Synthetic blends simulating the volatile profiles of the four conifers are being field tested to test the hypotheses that 1) beetles are preferentially attracted in flight to host odors and 2) are repelled by nonhost odors.
Species 1: Coleoptera Scolytidae Dendroctonus ponderosae (mountain pine beetle)
Species 2: Coleoptera Scolytidae Dendroctonus pseudotsugae (Douglas-fir beetle)
Species 3: Coleoptera Scolytidae Dendroctonus rufipennis (spruce beetle)
Keywords: monoterpene, variation
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