The primary host trees for Asian longhorned beetle (ALB) are maple (Acer sp.), birch (Betula sp.), elm (Ulmus sp.), willow (Salix sp.), and horsechestnut (Aesculus sp.). Look for these signs year-round on those trees:

(click on images to enlarge)

Oviposition Sites:

Round to oval pockmarks in the bark where an adult female has chewed a depression to lay an egg. One female lays up to 90 eggs, so many can be seen on a single tree.


ALB exit holes and egg-laying pits

Exit holes and oviposition (egg-laying) sites (Photo by Dennis Haugen, USDA Forest Service)

heavily attacked tree

Oviposition (egg-laying) sites (Photo by Michael Bohne, USDA Forest Service)

Exit Holes:

Round holes 3/8 inch in diameter on the trunk or branches where the adult beetles emerge. A pencil can be inserted at least an inch into an ALB exit hole.

Look for oviposition sites on the bark if you see a suspicious hole.

ALB exit hole with pencil

Exit hole (Photo by Rutgers University)

ALB exit holes

Exit holes (Photo by Kenneth R.Law, USDA APHIS PPQ)

Tunnels and Galleries:

Larval feeding tunnels meander towards the heartwood, where it will then pupate to complete development.

Look for these signs in split and cut wood.

ALB tunnels and pupal chambers

ALB larval tunneling and pupal chambers (Photo by Patricia Douglass, USDA APHIS PPQ)

ALB pupal chambers

Frass-filled pupal chambers (Photo by Joe Boggs,


Frass is sawdust-like material which the beetle larvae push out as it feeds in the tree. This may be found in oviposition sites, exit holes, branch junctions, or on the ground.


Frass coming out of oviposition site (Photo by Kenneth R.Law, USDA APHIS PPQ)

ALB and frass

ALB and frass on the ground (Photo by Michael Bohne, USDA Forest Service)


Updated: January 23, 2015