Thousand cankers disease: Influence of girdling on volatile organic compounds released from black walnut genotypes

Thousand cankers disease (TCD) has caused widespread death of black walnut trees throughout the West and was recently detected in Tennessee, Virginia, Pennsylvania and North Carolina. This disease complex is caused by a Geosmithia fungus vectored by the walnut twig beetle (WTB), Pityophthorus juglandis (Coleoptera: Curculionidae: Scolytinae).  Male WTB locate suitable black walnuts by orienting to host odors and, once on an appropriate tree, release volatile aggregation pheromones that coordinate mass attack and mating.  Currently, monitoring and detection efforts for WTB rely on a pheromone lure that is effective from a distance of only ~20 m. Overall goals of this research are to develop a kairomone-based lure for WTB and determine the influence of genotypic variation and girdling on the attraction of adult beetles to black walnut. In this project, we performed olfactometer bioassays to test the attraction of adult WTB to volatiles released from twelve different cultivars of black walnut and found significant variation in their attractivity to the beetles. Additionally we tested the influence of girdling on the release of volatile organic compounds (VOCs) and found that those released from girdled branches are more attractive to adult beetles than VOCs from ungirdled branches. This work may lead to the development of a kairomone lure that may enhance current detection and monitoring efforts.