Granulate Ambrosia Beetle: Another Exotic Pest of Ornamentals to Watch For

Published: February 1, 2011

It seems that there is a constant stream of exotic insect and disease pests that affect ornamental trees and shrubs. The Granulate Ambrosia Beetle is another one to watch for. This tiny insect (Xylosandrus crassiusculus) is native to Asia and arrived in the Carolinas on wooden packing crates in the early 1970's. It is now well established in the Gulf States and has been recently found in the Midwest, including Missouri. Ambrosia beetle has a wide hose range, including maples, peach, cherry, plum, dogwood, certain oaks, magnolia and black walnut and others. We have found it on the MU campus in yellowwood and goldenrain tree.

Despite its miniature stature (2 mm), Ambrosia Beetle kills trees by creating extensive feeding galleries for its young. The insect does not feed on plant tissue but on a fungus (Ambrosia fungus) that the female spreads within the galleries. A telltale sign of this pest is the presence of toothpick-like columns of frass that are pushed out of tiny holes in the bark during gallery excavation.

Unfortunately, Ambrosia beetle is difficult to manage because symptoms and signs may not be evident early in an infestation. The pest is easily spread by movement of infested nursery stock and may go undetected for some time in a new location. There is no effective treatment for eradicating the insect once it has entered the host. Therefore, the best management approach is to destroy infested plants and treat the trunks of nearby susceptible plants with insecticide.

So, if you see what appear to be toothpicks sticking out of the trunk of a tree, call your local Extension office to report your observation. It may be possible to eradicate the infestation before it becomes established.