University of Maryland Extension

Ambrosia Beetles - Trees

frass tubes on bark
Frass or boring dust caused by ambrosia beetle infestation

Ambrosia beetles (Xylosandrus germanus) are tiny beetles that bore into the heartwood of trees. Ambrosia beetles are generally associated with dying trees but this particular species attacks healthy trees and shrubs. They have a wide host range of trees and shrubs including styrax, ornamental cherry, pecan, peach, plum, cherry, persimmon, Japanese maple, holly, golden rain tree, dogwood, sweet gum, magnolia, ash, beech, birch, elm, linden, oak, planetree, tuliptree, willow, and azalea. 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 innoculate the galleries with fungi. They feed on this symbiotic fungus, which blocks the xylem vessels and may be partly responsible for 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.)

This is primarily a pest in nurseries where it can kill nursery stock. Infested landscape trees usually recover.

Management

These beetles are attracted to stressed trees so, it is important to maintain good tree health. Provide adequate water during dry periods. Insecticides are ineffective against beetles that have bored into the trees.

ambrosia beetle sticking out of hole in trunk
Beetle in boring hole

sap leaking from trunk
There may also be sap oozing from the holes
which stains the bark

closeup of frass
Strands of frass or boring dust, resembling
fine pencil lead, protrude from tiny holes in the bark

 

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