Characterization of volatile compounds associated with thousand cankers disease and walnut twig beetle in northern California black walnut, Juglans hindsii

Thousand cankers disease is a serious threat to walnut trees, Juglans sp., in the western U.S, and has the potential to spread throughout the eastern U.S. The disease is associated with the walnut twig beetle (WTB) Pityophthorus juglandis, which carries the fungal spores of Geosmithia morbida. The beetles introduce the fungus into the phloem when they tunnel into the tree to construct their galleries. The infection results in numerous cankers that eventually kill the tree. In northern California black walnut, Juglans hindsii, branches are initially colonized by male WTB, which then release at least one main pheromone component that is attractive to both sexes. Arriving females may also contribute to the aggregation pheromone. We characterized the chemical composition of volatiles released from male and/or female WTB feeding on J. hindsii branches; from branches inoculated with G. morbida with no WTB present, and from uninfested branches. We also re-evaluated the response of flying WTB to various combinations of males and females in these branches.