Ambrosia beetles

Unlike native ambrosia beetles, which bore tunnels into dead and dying trees, non-native species taking hold in this area attack living trees, especially trees with some level of stress, as from drought. Ambrosia beetles are of the weevil family and most do not eat the wood from excavating their tunnels, but push it out of the tunnels as frass. Ambrosia beetles culture symbiotic fungi in the tunnels to provide their food. The fungi in the tunnels also accelerate decomposition of dead trees to enrich the soil.

Ambrosia frass on a Goldenrain tree


Two invasive ambrosia beetles are active in central Maryland: Xylosandrus germanus (black stem borer) and Xylosandrus crassiusculus (granulate ambrosia beetle). Drought conditions from 2006 through 2008 put trees under stress, and may have contributed to the increase in these Asian beetles. In 2009, the beetles were again responsible for tree damage in the area. With expectation of more invasive ambrosia beetle damage in 2010, the University of Maryland Extension is assessing populations with traps and can be contacted for advice on control.

Andrusgermanus male female is larger one on right

Credit: US Forest Service - Bob Rabaglia

The appearance on tree bark of frass, the wood bits like sawdust that the beetles push out of tunnels they construct, is often the first indicator of ambrosia beetle activity. The two invasive species in this area do not have natural predators, and pesticides are often used for control.

Article by FCFCDB

Nature Notes for 4/11/2010