A survey of antennal responses by five species of coniferophagous bark beetles (Coleoptera : Scolytidae) to bark volatiles of six species of angiosperm trees

Using Porapak Q traps, we collected the bark volatiles of six angiosperm tr ees native to British Columbia: black cottonwood, Populus trichocarpa Torr. & A. Gray (Salicaceae), trembling aspen, P. tremuloides Michx. (Salicaceae ), paper birch, Betula papyrifera Marsh. (Betulaceae), bigleaf maple, Acer macrophyllum Pursh (Aceraceae), red alder, Alnus rubra Bong. (Betulaceae), and Sitka alder, A. viridis ssp. sinuata (Regel) A. Love & D. Love (Betulac eae). Utilising coupled gas chromatographic-electroantennographic detection analysis, the captured volatiles were assayed for antennal responses in fi ve species of coniferophagous bark beetles (Coleoptera: Scolytidae), sympat ric with most or all of the angiosperm trees: the Douglas-fir beetle, Dendr octonus pseudotsugae Hopkins, the mountain pine beetle, D. ponderosae Hopki ns, the spruce beetle, D. rufipennis (Kirby), the western balsam bark beetl e, Dry-ocoetes confusus Swaine, and the pine engraver, Ips pini (Say). The identities of 25 antennally-active compounds were determined by coupled gas chromate graphic-mass spectroscopic analysis, and co-chromatographic compa risons with authentic chemicals. The compounds identified were: hexanal, (E )-2-hexenal, (Z)-3-hexen-1-ol, 1-hexanol, heptanal, alpha -pinene, frontali n, benzaldehyde, beta -pinene, 2-hydroxycyclohexanone, 3-carene, limonene, beta -phellandrene, benzyl alcohol, (E)-ocimene, salicylaldehyde, conophtho rin, guaiacol, nonanal, methyl salicylate, 4-allylanisole, decanal, thymol methyl ether, (E)-nerolidol, and dendrolasin. A number of these compounds a re known semiochemicals that are active in the behaviour of other organisms , including bark beetles, suggesting a high degree of semiochemical parsimo ny. Antennally-active compounds ranged from seven in A. viridis to 17 in P. trichocarpa. The fewest number of compounds (9) were detected by I. pini a nd the largest number (24) were detected by D. pseudotsugae. Six compounds excited the antennae of all five species of bark beetles. The large number of antennally-active compounds detected in common by numerous bark beetles and present in common in numerous nonhost trees supports the hypothesis of olfaction-based recognition and avoidance of nonhost angiosperm trees durin g the process of host selection by coniferophagous bark beetles.