Detection of Geosmithia morbida on Numerous Insect Species in Four Eastern States

Thousand cankers disease is caused by the coalescence of numerous Geosmithia morbida cankers on branches and stems of Juglans species, leading to branch dieback and eventual tree death. The fungus sporulates in galleries of the walnut twig beetle (Pityophthorus juglandis), allowing for acquisition of pathogen propagules and its subsequent transmission to other branches or trees following adult emergence. Recently, G. morbida has been isolated from Xylosandrus crassiusculus and Xyleborinus saxesenii collected in Ohio and Stenomimus pallidus collected in Indiana. These beetles are known to colonize diseased Juglans nigra in these states. In this study, an operational trap survey for ambrosia beetles, bark beetles, and other weevils was conducted in four eastern states, and captured beetles were assayed to detect G. morbida using both culture and PCR-based methods. A new primer pair (GmF3/GmR13), based on the β-tubulin region, was designed for G. morbida DNA detection. The pathogen was detected on 18 insect species using molecular methods, and live cultures were isolated from two species. This is the first report of the pathogen in Illinois and Minnesota.