Featured Bug

"Asian Ambrosia Beetle"

This month's insect feature is courtesy of Carma Robinson. At our last BAMGA meeting, Carma asked if I knew anything about the Ambrosia Beetle. She relayed that on March 11th, a research group had placed traps in an around Duis Nursery where she works. I knew of the beetle but not much more than that. Here is some of the information I discovered.

The Asian Ambrosia Beetle (xylosandrus crassiusculus) was first detected near Charleston, South Carolina in 1974. According to one source, it had infested peach trees in the area. Since then, it has spread to the Lower Piedmont Region and Coastal Plain to North Carolina, Louisiana, Florida and eastern Texas. It is now being spotted throughout Virginia.

The Ambrosia Beetle overwinters as adults in the Heartwood. They emerge in Spring, generally during the month of April, and fly to new hosts where the female bores tunnels and deposits her eggs.

A quick indication of an infestation is sighting tooth- pick-like spines protruding up to 1.5 inches from the trunk or limbs of the host plant. These spines are strings of boring dust produced by the female beetle. The group of tunnels are referred to as "galleries". The spines are easily knocked off by rain or wind. An individual host may be attacked by anywhere from one to 50 beetles.

This is a small beetle - less than 1/4 inch - with a stout, reddish brown body. It attacks the trunks of young and weakened trees and shrubs, tunneling into stems and constructing galleries where they raise their young.

What is most interesting is the beetle does not feed on the wood or pith of the host plant, but rather on a symbiotic ambrosial fungus which grows in the galleries the beetle has created. The adults carry spores of this fungus on their bodies and, once they have constructed the galleries, the fungus grows inside the galleries to create the fungus which then feeds both young and adults.

The Ambrosia Beetle is deadly to the host plants and is attracted to a wide range of trees and shrubs. Smaller diameter branches or stems, or smooth bark sections of the host plant are mainly infected. Peach, pecan and plum orchards have been attacked, along with nursery tree stock. Other hosts are cherry, persimmon, golden rain tree, Chinese elm, magnolia and sweet gum, and they have been found on river birch, zelkova, crape myrtle, dogwood, sugar maple, sweet bay magnolia and Styrax. Keep in mind, this beetle is attracted to trees that have been weakened due to drought, flooding, transplanting, disease, winter weather and/or injury; however, the beetle will, apparently, also attack healthy trees.

High humidity is required for reproduction. Control in the home landscape is tricky and not effective once the entry holes have been clogged by frass. But, Pyrethroids will control adult beetles if applied prior to this clogging. Late Winter-early Spring spraying is needed until suspected trees are leafed out. This should be done every 10-14 days. The primary effective control is to keep your trees and shrubs healthy. Watch for stresses such as drought and injuries (heavy pruning, weed trimmer).

Here is a project for you to try. To build your own Ambrosia Beetle trap, visit hortweb.tamu.edu/county/smith/industry/maketrap.html. Sources: Fluvanna County, VA Master Gardeners; Featured Creatures - University of Florida; Florida Forest Insects; Agriculture and Lands - British Columbia; University of Georgia - UGA Center for Urban Agriculture.

Jim Revell, Bedford Area Master Gardener