Laurel Wilt

Insect Vector

The insect carrying the laurel wilt fungus (Raffaelea lauricola) is a very small beetle named the redbay ambrosia beetle or Xyleborus glabratus . This beetle is a member of a group of insects, known as ambrosia beetles, which carry fungi ("ambrosia") necessary for their young to develop. The beetles bore into wood, usually recently dead trees, to create tunnels or galleries where they lay their eggs. While boring in the wood, the tunnels are infected with fungi carried in special pouches in the head near the base of the beetles' mandibles. The larvae that hatch from the eggs live in the tunnels where they feed on the fungi growing on the wood.

The pouches or mycangia (arrows) in the head of a redbay ambrosia beetle where they carry the wilt fungus (Photo by Mike Ulyshen).

The redbay ambrosia beetle measures only about 1/16 th inch (2 mm) long, it is dark brown to black in color, and cylindrical in shape. It can be separated from other similar beetles found in or on redbay trees by looking at the tip of the abdomen which is somewhat V-shaped and pointed. It is also glabrous or shiny and without hairs.

Adult redbay ambrosia beetle (Photo by Mike Thomas)

Adult beetles can be found year-round along the coast but they occur at low numbers from late fall to early summer. They are most abundant from late-June until late-September.

Numbers of adult beetles captured in traps on infected trees at Hunting Island State Park, SC.

Normally ambrosia beetles are considered beneficial because they accelerate the decay process in dead trees, which is important for nutrient cycling in healthy forests. The redbay ambrosia beetle is native to Asia and was only recently introduced into the U. S. Although a number of other ambrosia beetles have been accidentally introduced into our country, they generally don't kill trees in forests. Unfortunately, the redbay ambrosia beetle and the associated wilt fungus have become tree killers.

The redbay ambrosia beetle is strongly attracted to redbay trees, particularly trees that have been wounded in some way such as through construction damage. Why redbay trees are so attractive is unclear but these trees are probably related to the beetles' natural hosts in its native countries.

Stopping redbay ambrosia beetle and laurel wilt will not be easy, and may not be possible. Unlike many other insects that feed on trees and require hundreds or thousands of individuals to cause serious harm, only one redbay ambrosia beetle is necessary to inoculate and kill a tree. So traditional approaches to insect control, such as preventative insecticides, will only reduce the chances of a tree being infected. But with large numbers of beetles and enough time, the chance that a beetle will find a place on the tree not covered by insecticide and successfully bore into the wood becomes increasingly likely.

Additional Information

• Redbay Ambrosia Beetle Biology, Attractants and Traps, James Hanula, US Forest Service, Southern Research Station, Laurel Wilt Conference 27-Feb-09 (Slideshow 2.1 MB).

• Host Chemistry and Redbay Ambrosia Beetle Attraction, Lissa Leege and Norman Schmidt, Georgia Southern University, Laurel Wilt Conference 27-Feb-09 (Slideshow 1.3 MB).

• Hanula, J.L. and B. Sullivan. 2008. Manuka oil and phoebe oil are attractive baits for Xyleborus glabratus (Coleoptera: Scolytinae), the vector of laurel wilt. Environmental Entomology 37(6): 1403-1409. [PDF 343 KB]

• Hanula, J.L., A.E. Mayfield, III, S.W. Fraedrich, and R.J. Rabaglia. 2008. Biology and Host Associations of the Redbay Ambrosia Beetle, (Coleoptera: Curculionidae: Scolytinae), exotic vector of laurel wilt killing redbay trees in the southeastern United States. Journal of Economic Entomology 101(4): 1276-1286. [PDF, 160 KB]

• Laurel Wilt: Insect Vector - Xyleborus grabratus, Stephen Fraedrich, USDA Forest Service 1/19/2007 [PDF, 146 KB]

• Non-native Bark and Ambrosia Beetles - Robert J. Rabaglia, USDA Forest Service , 1/19/2007 (Abstract, 11 KB) (Slideshow, 515 KB)

• Beetles and Their Emergence Patterns from Dead Redbay Trees - John L. Foltz, University of Florida (retired), 1/19/2007 (Slideshow, 839 KB)

• Redbay Ambrosia Beetle Biology and Host Attraction - James Hanula, Robert J. Rabaglia, and Stephen W. Fraedrich, USDA Forest Service, 1/19/2007 (Slideshow, 924 KB)

• Fungal-Ambrosia Beetle Interactions; Influences on Vectoring - Eric Ott, LSU Agricultural Center, 1/19/2007 (Slideshow, 437 KB)

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USDA Forest Service - Forest Health Protection, Southern Region
Last Modified: Friday, 17 May 2013 at 12:04:07 EDT