Two pheromones of coniferophagous bark beetles found in the bark of nonhost angiosperms

Volatiles from fresh bark of black cottonwood, Populus trichocarpa: trembli ng aspen, P. tremuloides; paper birch, Betula papyrifera; bigleaf maple, Ac er macrophyllum; red alder, Alnus rubra; and Sitka alder, Alnus viridis, we re collected on Porapak Q and subjected to coupled gas chromatographic-elec troantennographic detection analyses by utilizing the antennae of several s colytid beetles (Dendroctonus pseudotsugae, D. rufipennis, D. ponderosae, I ps pini, and Dryocoetes confusus). Among the antennally active volatiles id entified by coupled gas chromatographic-mass spectroscopic analysis were fr ontalin, 1,5-dimethyl-6, 8-dioxabicyclo[3.2.1]octane, in the two Alnus spec ies and conophthorin, (E)-7-methyl-1,6-dioxaspiro[4.5]decane, in the other four species. Field trapping experiments demonstrated that conophthorin had a significant disruptant effect on the response to a pheromone-host kairom one blend by both Dendroctonus psendoaugae and D. ponderosae. Our results, and the recent identification of other scolytid pheromones in various tree species, pose major questions regarding the evolution and ecological roles of these semiochemicals, including the possibility of Batesian mimicry by t he beetles. They also suggest a need for comparative studies on the biosynt hetic pathways for these compounds.