Shade Trees: Trunk

Ambrosia Beetles

Ambrosia beetles (Xylosandrus germanus) are tiny beetles that bore into the heartwood of trees. Ambrosia beetles (beetle in boring hole) 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.

Keywords: ambrosia beetle, tiny beetles, tiny boring beetles, pencil lead strands, fusarium

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Photo Gallery

Ambrosia beetles (beetle in boring hole) are generally associated with dying trees but this particular species attacks healthy trees and shrubs.

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

Fusarium cankers have been associated with this beetle.

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