| Abstract: | Summary. Host selection in tree-killing bark beetles(Coleoptera: Scolytidae) is mediated by a complex of semiochemicalcues. Using gas chromatographic-electroantennographicdetection (GC-EAD) and GC-mass spectrometricanalyses, we conducted a comparative study of the electrophysiologicalresponses of four species of tree-killing barkbeetles, the Douglas-fir beetle, Dendroctonus pseudotsugae,Hopkins, the mountain pine beetle, D. ponderosae Hopkins,the spruce beetle, D. rufipennis Kirby, and the western balsambark beetle, Dryocoetes confusus Swaine, to volatilescaptured by aeration of 1) bole and foliage of four sympatricspecies of conifers, Douglas-fir, Pseudotsuga menziesii(Mirb.) Franco, lodgepole pine, Pinus contorta var. latifoliaEngelm., interior spruce, Picea engelmannii x glauca, andinterior fir, Abies lasiocarpa x bifolia, and 2) con- andheterospecific beetles at three stages of attack. We identified13 monoterpenes in the conifers and nine compounds in thevolatiles of beetles that elicited antennal responses. Therewas no qualitative difference in the terpene constitution ofthe four species of conifers and very little difference acrossbeetle species in their antennal response to compounds fromconifers or beetles. The lack of species-specific major orminor components in conifers suggests that beetles wouldneed to detect differences in the ratios of different compoundsin conifers to discriminate among them. Attraction tohosts and avoidance of nonhost conifers may be accentuatedby perception of compounds emitted by con- and heterospecificbeetles, respectively. The 22 compounds identifiedare candidate semiochemicals with potential behaviouralroles in host location and discrimination. |
