Cold tolerance and invasive potential of the redbay ambrosia beetle (Xyleborus glabratus) in the eastern United States
Native Lauraceae (e.g. sassafras, redbay) in the southeastern USA are being severely impacted by laurel wilt disease, which is caused by the pathogen Raffaelea lauricola T. C. Harr., Fraedrich and Aghayeva, and its symbiotic vector, the redbay ambrosia beetle (Xyleborus glabratus Eichhoff). Cold temperatures are currently the only viable limitation to the establishment of X. glabratus in northern populations of sassafras. The observed lower lethal temperature of X. glabratus (- 10.0 °C) is warmer than its supercooling point (- 22.0 °C), indicating the beetle is a freeze intolerant and chill susceptible species. Empirically derived X. glabratus lower lethal temperature thresholds were combined with host distribution and microhabitat-corrected climate data to produce species distribution models for X. glabratus in the eastern USA. Macroclimate data (30-year mean annual minimum temperature) were corrected (- 1.2 °C) to account for thermal buffering afforded to X. glabratus while living inside sassafras trees. Only 0.1% of the current US sassafras spatial extent experiences sufficiently harsh winters (locales where mean annual minimum winter temperatures ≤ - 6.2 °C for ≥ 12 h) to exclude X. glabratus establishment in our species distribution model. Minimum winter temperatures will likely cause some X. glabratus mortality in * 52% of the current spatial extent of sassafras, although current data do not allow a quantification of X. glabratus mortality in this zone. Conversely, * 48% of the current spatial extent of sassafras is unlikely to experience sufficiently cold winter temperatures to cause any significant impediment to X. glabratus spread or establishment. A modest climate change scenario (RCP4.5) of + 1.4 °C would result in 91% of the current spatial extent of sassafras in the eastern USA occurring where winter minimum temperatures are unlikely to cause any mortality to X. glabratus.