Ambrosia Beetle

   * July 2006 Update

   * May 2006 Update

On March 17, 2005, representatives from the Oregon Department of
Agriculture informed the Extension Office that in 2004 they had
trapped a number of exotic borer beetles at the Amerities
(Kerr-McGee) plant in The Dalles. The most disconcerting of the
species trapped was the granulate or Asian ambrosia beetle (GAB)
(Xylosandrus crassiusculus). In 2004 they had trapped 156 of these
insects in non-specific traps located around the tie plant.

It was believed that this beetle hitchhiked on raw ties imported from
the southeastern U.S. The beetle is originally from Africa and
southeast Asia and came to the United States a number of years ago
and has established widely in the southeast.

GAB is reported to attack over 200 species of plants, mostly hardwoods including cherries, pears, apples, grape, peach, plum, cottonwood, poplar and willow, along with many ornamental species.

GAB bores into wood but does not actually eat the wood. Adults and larvae feed on a symbiotic fungus (“ambrosia”) that the beetle introduces into the infested wood. The fungus plugs up the tree’s vascular system and can eventually kill the tree. Trees with a trunk diameter of 3 inches or less are often killed by as few as 5 GAB. Trees of this size are almost always killed by 10 or more GAB.

Once a tree is infested, no chemical controls will save it. Juvenile trees, up to three years old, are usually killed. Mature trees are more likely to survive but may serve as a staging base for the beetle to attack nearby younger trees. For this reason, the general control strategy is to cut down and destroy any infested trees immediately.

Apparently, healthy trees may be attacked. Trees with a diameter of 3 inches or less are preferred, but injured or stressed older trees can also be attacked. Newly transplanted trees are especially vulnerable and are usually attacked at the root collar.

GAB makes a perfectly circular entrance hole approximately 2 mm in diameter. Long toothpick-like strings of compacted sawdust may be found emerging from these holes. Unfortunately, other wood boring insects in Oregon cause similar damage.

Eggs are laid in a brood chamber, and larvae hatch and feed on the symbiotic fungus growing on the galley walls. A female may produce up to 100 offspring and several generations per year.

During the course of the ODA’s trapping program, other exotic ambrosia beetles have also been found in the same traps. These include three potential pests to the orchard industry: the apple wood stainer (Monarthrum mali), the hardwood platypus (Euplatypus compositus), and the oak platypus (Oxoplatypus quadridentatus). Other potentially injurious wood boring beetles foreign to Oregon have also been trapped.

Literature cited:
Anonymous (2005). Pest Alert: The Granulate
Ambrosia Beetle. Oregon Department of Agriculture.