Bark colonization of kiln-dried wood by the walnut twig beetle: effect of wood location and pheromone presence
The walnut twig beetle (Pityophthorus juglandis Blackman) (Coleoptera: Curculionidae) is a regulated pest in the United States due to its causal role in thousand cankers disease of walnut trees, including the commercially valuable eastern black walnut (Juglans nigra L.). Several state quarantines designed to limit spread of P. juglandis regulate movement of kiln-dried walnut lumber that contains bark. Previous research demonstrated that P. juglandis will enter and re-emerge from bark of kiln-dried, J. nigra slabs subjected to extreme beetle pressure (baited with a pheromone lure and hung in infested J. nigra trees). This study evaluated P. juglandis bark colonization of both kiln-dried and fresh J. nigra slabs, varying the presence of aggregation pheromone and relative proximity to a beetle source.Wood treatment, slab location, and pheromone presence all significantly affected P. juglandis colonization, as assessed by subsequent beetle emergence. When placed on the ground directly beneath infested trees, kiln-dried slabs were not colonized, and fresh slabs were colonized only when baited with the pheromone lure (6/14 replicates). When placed in crowns of infested trees, kiln-dried slabs were colonized only when baited with pheromone (3/14 replicates), whereas fresh slabs were colonized with and without pheromone (14/14 and 1/13 replicates, respectively). Timing of emergence indicated that beetles did not reproduce in kiln-dried bark. Results suggest that the risk of kiln-dried walnut bark becoming colonized by the P. juglandis during movement of commercial wood products is very low. This information may be
useful to government agencies that administer quarantines regulating the transport of walnut lumber.