Ambrosia beetles

Natural History
Dust from beetle tunnels piled at base of tree
Photo credit: USDA Forest Service

"Ambrosia beetles" is the common name used collectively for a group of wood-boring insects in a number of related genera. These insects, which are found throughout the southern United States, share a common habit of tunneling through the bark into the wood of trees. Ambrosia beetles may cause significant damage to green logs and unseasoned lumber, and occasionally to dead, dying, or severely stressed trees.

As the adult beetle chews through the bark and into the wood, it creates a series of winding tunnels called "galleries." The wood debris from the galleries can appear as either a series of thin, white tubes pushed out of the bark or as fine sawdust piling up at the base of the tree. The insect does not use the tree xylem as food, but uses the galleries that are created as a place for a fungus to grow. The fungus becomes the source of food for the insects. Interestingly, because of this dependence on the fungus, the insect carries spores of the fungus with it as it moves from one tree to another. This transportation of spores guarantees that, no matter where the ambrosia beetle may go, it will always be able to produce a steady food supply.

Here in the southeastern United States, the redbay ambrosia beetle (Xyleborus glabratus) is a species of special concern because it transmits the fungus that causes laurel wilt disease. The disease primarily affects redbay (Persea borbonia) but it can also damage or kill other members of the laurel family, including avocado. The redbay ambrosia beetle is not directly responsible for the widespread death of redbay trees, but by transporting the fungus from tree to tree it is the vector that allows the disease to spread.


Identifying Characteristics

Identifying the injury: Ambrosia beetle attack can be recognized by piles of fine, whitish dust found around the 1/16" entrance holes or at the base of the tree. In lumber, the fungus darkly stains the galleries and these stains can easily be seen.
Identifying the insect: Adult beetles are long and thin, usually about 1/4" long. They are reddish brown in color with sharp spines at the back end of their bodies. Fully-grown larvae and pupae are the same size as the adult beetles but are yellowish white in color.
Susceptible trees: Ambrosia beetles attack most tree species. The beetles target very weakened, dying trees, green logs, and unseasoned lumber. The beetles will only attack trees and logs with high moisture content.



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