Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract

Recovery plan for laurel wilt on redbay and other forest species caused by Raffaelea lauricola and disseminated by Xyleborus glabratus.

Abstract

Laurel wilt is a highly destructive disease affecting members of the Lauraceae in the United States. The insect vector, the redbay ambrosia beetle (Xyleborus glabratus) was first captured in monitoring traps near Port Wentworth, GA, in 2002 and first reported associated with mortality of redbay (Persea borbonia) trees in 2003. Laurel wilt disease is initiated when X. glabratus introduces its fungal symbiont (Raffaelea lauricola) into the sapwood of host trees. The fungus is carried within specialized pouches (mandibular mycangia) near the beetle's mouthparts, where it lives in a budding, yeast-like state. The fungal spores are introduced into the xylem as the beetle bores into the stem, leaving typical evidence of ambrosia beetle attack (small holes and boring dust). Host trees react to the fungal invasion with the production of gums and tyloses, which block water transport and cause crown wilt. Upon dissection of infected wood, xylem discoloration is readily evident. Laurel wilt has now been detected in eight southeastern states (Alabama, Florida, Georgia, Louisiana, Mississippi, North Carolina, South Carolina, and Texas), causing significant mortality to redbay populations. Redbay serves an important ecological role in forests, and the loss of this species has had significant effects on forest composition. Several other lauraceous hosts [sassafras (Sassafras albidum), silk bay (Persea humilis), swamp bay (Persea palustris), pondspice (Litsea aestivalis) (state endangered), and pondberry (Lindera melissifolia) (federally endangered)] are susceptible to laurel wilt and have been affected by the disease to varying degrees. In addition, agricultural [avocado (Persea americana)] and ornamental non-native members of the Lauraceae within the United States are susceptible. Eradication of the vector and pathogen is improbable due to the ability of the vector to persist in small-diameter stems and of a few females to establish new populations. Currently, management options within a natural forest setting are limited and spread of the disease into new areas (e.g., California, Mexico, and Central and South America) remains a threat. For these reasons, it is essential to continue to monitor the spread of the disease and to continue to develop a better understanding of the biology of the beetle and pathogen as well as the epidemiology of the disease. In addition, further development of the following strategies may help to reduce the impact of laurel wilt in forests and urban settings, and limit the spread of the disease: * minimization of human-aided transport of firewood and unprocessed wood materials, a mechanism for long-distance movement of the disease; * utilization of chemical options (fungicides and possibly insecticides) for the protection of high-value trees; * continued development of resistant host-plant cultivars for landscape use and restoration; * collection and maintenance of germplasm of vulnerable hosts, especially rare species that may be in danger of extinction; * continued research on disease biology, vector chemical ecology, alternative disease pathways and vectors, management options, and natural enemies, and * continued efforts to educate the public about the potential cultural, economic, and ecological effects of laurel wilt.