Olfactory and feeding preferences of Cryptorhynchus lapathi among hosts and nonhosts

In British Columbia, native willows (Salix spp.) (Salicaceae) and, to a lesser extent, black cottonwood (Populus trichocarpa Torr. & Gray) (Salicaceae) are frequently attacked by the poplar and willow borer, Cryptorhynchus lapathi (L.) (Coleoptera: Curculionidae). Red alder (Alnus rubra Bong.) (Betulaceae), trembling aspen (Populus tremuloides Michx.), and bigleaf maple (Acer macrophyllum Pursh) (Aceraceae) are not attacked. We studied olfaction and feeding preferences in the laboratory and feeding, oviposition, and emergence in the field. Female C. lapathi preferred Scouler's willow (Salix scouleriana Barratt ex Hook.) over all other species by olfaction, but males did not discriminate between Scouler's willow and black cottonwood or trembling aspen. All species elicited at least some attraction in no-choice situations. Willow was generally preferred for feeding, but black cottonwood and red alder were also acceptable, unlike trembling aspen or bigleaf maple. In field caging experiments, adult weevils emerged from willow, black cottonwood, and red alder. We conclude that olfaction and feeding preferences are sufficiently powerful to mediate the frequent attack observed on native willows, the intermediate levels of attack on cottonwood, and the absence of attack on red alder. Successful development on red alder suggests that C. lapathi could expand its host range to include this species.