Incidence, Dispersal, and Risk Assessment of Walnut Twig Beetle, \u3ci\u3ePityophthorus juglandis\u3c/i\u3e, on Black Walnut in Appalachian Forests

The native range of walnut twig beetle (WTB), Pityophthorus juglandis Blackman, includes Arizona, California, New Mexico, and parts of Mexico. In 2010, WTB was found in the eastern United States, the native range of black walnut, Juglans nigra L. Although WTB is not believed to kill black walnut, it carries a fungal pathogen, Geosmithia morbida M. Kolařík et al., which was identified as the causal agent of thousand cankers disease (TCD). This disease complex has killed millions of trees in the United States. Studies have documented the movement of WTB in urban settings; however, its movement in forested systems is not well understood. The goal of this research is to understand the role of forests in TCD epidemiology and the risk of WTB to black walnut resources. This project will emphasize three research objectives, which are to: 1) document incidence and distribution of WTB on black walnut in Appalachian forests, 2) assess dispersal of WTB in forests, and 3) determine the dispersion pattern of WTB in black walnut orchards.Pheromone-baited funnel traps (n= 33) were deployed and monitored from April through November at 14 locations in eastern Tennessee and western North Carolina. Trap collection numbers suggest a low incidence of WTB in forests. To measure the dispersal of WTB in forests, a study was initiated in Morgan County, TN, using equally spaced traps along three transects from a central release point. No significant trends in dispersal were identified, as beetles were recovered at a range of distances and directions. Dispersion patterns of WTB were assessed in two black walnut orchards, in Anderson and Knox Counties. Analysis of trap collections revealed a clumped distribution of WTB at sites in both counties. Findings from this research can be used to inform risk assessments of WTB in forests, and to enhance current knowledge of TCD epidemiology in the native range of black walnut