Test Your Knowledge - March

Frass tubes produced by granulate ambrosia beetles
Frass strands extending from entrance holes made by granulate ambrosia beetle
Byron Rhodes, University of Georgia, United States, Bugwood.org

The granulate ambrosia beetle (Xylosandrus crassiusculus) is a small, reddish-brown beetle that attacks many ornamental and fruit trees grown in South Carolina. The adults bore into the limbs and smaller trunks most commonly of peach, pecan, plum, cherry, persimmon, oak, elm, sweet gum, magnolia, fig, Bradford pear and crape myrtle, but other species may also be attacked.

Adult female granulate ambrosia beetle
Adult female granulate ambrosia beetle
J.R. Baker & S.B. Bambara, North Carolina State University, Bugwood.org

This Asian pest entered South Carolina in 1974, and since has spread throughout the state. The females typically bore into susceptible hosts in the early spring and lay eggs. The first visible symptom will be the insect frass strands (sawdust mixed with insect waste) which are pushed from the holes and protrude like 2- or 3-inch long fragile toothpicks (see top image).

Once the larvae hatch, they tunnel within the limbs and trunk, and feed not on the plant, but on introduced ambrosia fungi brought into the plant by the female. Not only are plants damaged by the extensive tunneling, but also by these introduced, pathogenic fungi. The xylem elements that conduct water movement within the tree become clogged by the fungi, and ultimately this disruption of water transport will kill all or parts of the plant.

When the larvae develop into adults, the new females leave the infested tree for a new host. Research in Tennessee has determined the life cycle is approximately 55 days from egg to adult. Therefore, once a beetle infestation has been observed, prompt removal and burning of these plant parts or the whole tree is necessary to stop their spread.

Other susceptible trees should be maintained as healthy as possible to reduce the chance of attack. Water trees weekly during periods of drought, and properly fertilize and mulch to reduce stress. Trees may become less attractive to these beetles once the leaves are fully expanded. Nearby susceptible trees may be protected by trunk and limb sprays of synthetic pyrethroids, such as in Bonide Borer-Miner Killer Concentrate, Green Light Borer Killer Concentrate, Green Light Conquest Insecticide Concentrate, or Astro.

It is possible that if the infestation is discovered early and before the female beetles have sealed their holes with frass, a trunk and limb spray of the synthetic pyrethroids may give some control on an infested plant.

Since the beetles and larvae are feeding upon the ambrosia fungi and are not consuming plant material, systemic insecticides, such as imidacloprid, are not effective.

For more information on the granulate ambrosia beetle, see the Clemson Entomology Insect Series Fact Sheet, EIIS/TO-22 Ambrosia Beetle.

Joey Williamson, Ph.D.
Home & Garden Information Center

Page maintained by: Home & Garden Information Center

This information is supplied with the understanding that no discrimination is intended and no endorsement by the Clemson University Cooperative Extension Service is implied. All recommendations are for South Carolina conditions and may not apply to other areas. Use pesticides only according to the directions on the label. All recommendations for pesticide use are for South Carolina only and were legal at the time of publication, but the status of registration and use patterns are subject to change by action of state and federal regulatory agencies. Follow all directions, precautions and restrictions that are listed.