From: Stephen B. Bambara, Extension Entomologist
Samples of the Asian ambrosia beetle have been arriving in the Plant Disease and Insect Clinic at North Carolina State University these past weeks. This pest is spread most often by movement of plant material. It is first noticed by the curved toothpick-like strands of frass pushed out the holes of the excavating females. This beetle attacks wounded, stressed, and also healthy trees. It is suspected that the mild winter and a build-up on Hurricane Fran injured trees and cut stumps has created a larger than normal problem this Spring.
This scolytid bark beetle, Xylosandrus crassiusculus, was introduced from southeast Asia. It is sometimes called the Asian ambrosia beetle. It was first found near Charleston, South Carolina, in 1974 in peach trees. It also attacks cherry, Chinese elm, fig, golden rain tree, magnolia, pecan, persimmon, plum, shumard oak, sweetgum, redbud, cherry, crape myrtle and even sweetpotato. Female beetles bore into stems of young trees. Visible symptoms include wilted foliage and strings of boring dust that may protrude from the bark as tiny sticks or tooth picks. These strands may reach 1.5 inches if wind and rain do not break them off. The beetles are present most of the year, but Clinic records indicate Asian ambrosia beetles are most active in March. Eggs, larvae and pupae are found together. There are no individual egg niches, larval tunnels or pupal chambers. High humidity is required for successful reproduction. Adults and larvae feed on a mold-type of fungus known as ambrosia that the beetles introduce as they tunnel into the sapwood and sometimes heartwood of trees and logs. The fungus grows on the walls of the tunnel. With this species, the beetles bore galleries straight into the wood from 1 to 3 cm or more. The tunnels then branch one to six times in the same plane following an annual ring. In small trunks and branches, the galleries go straight in or spiral upward from the point of attack around the stem or limb, branching upward or downward from the spiral gallery. The Asian ambrosia beetle seems to attack trees and shrubs more aggressively than native ambrosia beetles that attack mostly dead, dying or heavily stressed plants. Because most of the boring is done in the sapwood or heartwood rather than the cambium, it is sometimes possible to save plants infested with Asian ambrosia beetles.
Most plant death occurs from the point of green-up until leafing
out. It is recommended that dead wood be pruned out and dying
plants be destroyed. Chemical sprays of lindane, Dursban or Thiodan
during female flight season, may be directed at the bark and trunks
of trees 1-2 inches in diameter. This protectant spray does not
kill beetles already in the tree and has only been mildly
successful, at best. We do not have complete biological information
on this pest, and it is difficult to predict how long the threat
from the beetles lasts.
Web page last updated on April 16, 1998 by Stephen J. Toth, Jr..
