frass tubes from ambrosia beetles

​​​​​​​Frass tubes or boring dust caused by ambrosia beetle infestation.

Updated: February 28, 2023

About ambrosia beetles

  • 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, sweetgum, magnolia, ash, beech, birch, elm, linden, oak, planetree, tuliptree, willow, and azalea.
  • This is primarily a pest in nurseries where it can kill nursery stock. It is also a pest in home landscapes where sometimes infested trees can recover. 
  • 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 (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.
ambrosia beetle damage
Strands of frass or boring dust, resembling fine pencil lead, protrude from tiny holes in the bark


  • 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.
  • Infested trees should be removed and disposed of.

Additional resources

Bark Beetles and Ambrosia Beetles: the Big Picture | Ohio State University

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