Cold tolerance in the redbay ambrosia beetle (Xyleborus glabratus)

The invasive redbay ambrosia beetle (Xyleborus glabratus Eichoff) (Coleoptera: Curculionidae: Scolytinae) was introduced from Asia into the southeastern United States in 2002. The beetle carries Raffaelea lauricola T.C. Harr., Aghayeva, & Fraedrich, a newly described fungal symbiont responsible for a wilt disease that affects most lauraceous species of North America. Since introduction into the southeast U.S., the beetle and its associated fungal pathogen have devastated redbay (Persea borbonia (L.) Spreng.) and swampbay (Persea palustris (Raf.) Sarg.) populations along the Atlantic and Gulf Coastal Plains. More recently, laurel wilt has spread into sassafras in Alabama, Florida, and Mississippi; populations of sassafras range into southern Ontario, Canada. Additionally, very little is known regarding the physiology of the beetle or the effects of low temperature on its invasive potential into northern forests of North America. To understand physiological limitations of low temperatures on X. glabratus, the supercooling point (SCP), low temperature injury/mortality, and biochemical analysis was experimentally determined on field-collected and artificially cold hardened specimens. Field-collected beetles were trapped in Jackson County, Mississippi using Lindgren funnel traps baited with manuka oil lures. The mean supercooling point of field collected X. glabratus was -21.7 ºC ±0.5 ºC (±SE). Artificially cold hardened X. glabratus were reared from redbay bolts in June of 2012 and artificially cold hardened in a low temperature incubator at a thermo-photoperiod of 7ºC:2ºC (10L:14D) for 31 days. Artificially cold hardened X. glabratus supercooled to a mean temperature of -23.9 ±0.4ºC (±SE), significantly lower than that of field-collected beetles. Beetle size and weight had no effect on the SCPs of either field-collected or artificially cold hardened beetles. Prolonged periods of low temperatures are showing mortality above both mean SCPs and biochemical analysis has elucidated mechanisms involved in cold hardening and chill injury. Based on the mean SCPs and mortality from prolonged periods of low temperatures on X. glabratus, laurel wilt disease could theoretically impact Lauraceae throughout most of North America.