Ambrosia beetles are tiny beetles that bore into the heartwood of trees. Adults are generally small, reddish brown to nearly black, cylindrical beetles from about 1/8- 3/16 inch (3-5 mm) long. Larvae are small, white, legless grubs similar to bark beetle larvae.
While some species are associated with dying trees, some will attack healthy trees and shrubs and can kill nursery stock. Damage appears as wilting then terminal dieback. The beetles generally attack the tree within 3 feet of the ground. Strands of frass or boring dust, resembling fine pencil lead, protrude from tiny holes in the bark. There may also be sap oozing from the holes, which stains the bark.
As the beetles bore into the heartwood, they inoculate the galleries with fungi. They feed on this symbiotic fungus, which blocks the xylem vessels (transports water and nutrients from roots to stems and leaves) and may be partly responsible for the death of the plants.
The beetles can also transmit or create entry points for plant pathogenic fungi. Fusarium cankers have been associated with this beetle.
Source: Rutgers, University of Maryland Extension, NC State Extension, USDA/ARS
