TITLE:
An Uncertain Future for American Lauraceae: A Lethal Threat from Redbay Ambrosia Beetle and Laurel Wilt Disease (A Review)
AUTHORS:
Paul E. Kendra, Wayne S. Montgomery, Jerome Niogret, Nancy D. Epsky
KEYWORDS:
Laurel Wilt; Lauraceae; Raffaelea lauricola; Redbay Ambrosia Beetle; Xyleborus glabratus
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.4 No.3A,
March
29,
2013
ABSTRACT:
Laurel wilt is a destructive vascular disease responsible for high mortality of
American tree species in the family Lauraceae, particularly
redbay (Persea borbonia) and swampbay
(P. palustris), two dominant
components of Coastal Plain forest communities in the southeastern United States.
The disease syndrome emerged as a result of establishment of an exotic
wood-boring beetle, Xyleborus glabratus,
now known as the redbay ambrosia beetle. During gallery excavation, females of X. glabratus introduce a
newly-described, obligatory fungal symbiont, Raffaelea lauricola. This fungus proliferates within the gallery
and provides food for the beetles, but it has proven to be pathogenic to
American lauraceous hosts, which have had no co-evolved history with R. lauricola. Presence of the foreign
fungus elicits secretion of resins and formation of extensive parenchymal
tyloses within xylem vessels. The extreme defensive response results in
blockage of water transport, systemic wilt, and ultimately tree death. The
beetle vector was first detected near Savannah, Georgia in 2002, and since has
spread throughout the Southeast to become established in six states. The
epidemic spread south through Florida more
rapidly than predicted and currently threatens commercial production of avocado
(Persea americana). Recent research indicates
that California bay laurel (Umbellularia
californica) can serve as a reproductive host for X. glabratus and is susceptible to laurel
wilt disease. Thus, the US Pacific coastal forest ecosystems (and the
California
avocado industry) would be negatively impacted should the vector become
established along the western coast. This review article summarizes our current
understanding of the insect vector, the mycopathogen, and the susceptible host
tree species. It also addresses elements of disease management and limitations
with our current detection methods for redbay ambrosia beetle, which rely
on manuka oil lures. Of the host-based attractants evaluated, cubeb oil shows
the most promise as a potential new lure for X. glabratus.