Factors affecting Xyleborus glabratus attack and host utilization in sassafras and redbay in the Carolinas

The laurel wilt disease complex is a destructive combination of a non-native beetle vector [redbay ambrosia beetle (RAB), Xyleborus glabratus Eichhoff (Coleoptera: Curculionidae: Scolytinae)] and a symbiotic fungus (Harringtonia lauricola (Ophiostomataceae) T.C. Harr., Fraedrich & Aghayeva), which serves as a pathogen in the host trees infested by RAB. The complex originated from Asia and was first discovered in the United States near Savannah, GA in 2002, and has rapidly made its way across the southeastern US, causing mortality for redbay and other important Lauraceae species, including sassafras, giving this disease complex the potential to have far-reaching ecological effects across North America. Our goal with this study was to examine the spatial distribution of RAB attacks in redbay and sassafras trees along the leading edge of disease progression. RAB attacks were clustered in both tree species, with attacks being most concentrated on the south side of the tree in sassafras, and with RAB clustering more with other RAB attacks on redbay. When comparing bolts that produced adult RABs, the average number of RABs emerged was higher in redbay compared to sassafras. Entrance hole density, RAB emergence, and moisture content were higher near the base of the stem compared to stems sections higher on the bole of both tree species. Our results suggest that physiological differences, such as size and structure of vessels, between these tree species may drive beetle attack patterns and, therefore, affect the progression and spread of disease throughout sassafras and other Lauraceae.