Colombian Timber Beetle, Corthylus columbianus Hopkins

Leininger, T.D; Solomon, J.D.; Wilson, A. Dan; Schiff, N.M. 1999. A Guide to Major Insects, Diseases, Air Pollution Injury, and Chemical Injury of Sycamore. Gen. Tech. Rep. SRS-28. Asheville, NC: USDA Forest Service, Southern Research Station. 44 p.

Importance.-The Columbian timber beetle occurs from Massachusetts south to Florida and west to Kansas. Beetles bore into the trunks of trees of all sizes. Beetle attacks do not seem to affect tree health directly, but they provide entry points for canker and other diseases. Damage can degrade the lumber by as much as 25 percent.

Identifying the Insect (fig. 16a).-Adults are 3.6 to 4.0 mm long, reddish brown to black, cylindrical ambrosia beetles. Eggs are white, translucent, shiny, and oval. Larvae are white, legless, C-shaped, and about 4 mm long.

Figure 16a. - Adult of C. columbianus Photo by

Identifying the Injury (fig. 16b, c).-Sap and fine frass oozing out of small round entrance holes in the trunk are evidence of injury. Radiating brown stains in log ends are evidence of damage in sawlogs. In lumber and veneer, defects consist of small, black, round holes surrounded by elongated brown stains.

Biology.-Adults overwinter in bark niches around the base of host trees. Beetles emerge in May and June and begin excavating brood galleries on host trees. Completed galleries consist of primary, secondary, and tertiary channels with 1 to 20 brood cells (cradles). Eggs are deposited singly in each brood cell. Both larvae and adults feed on ambrosia fungi that grow on gallery walls. Brood emergence occurs in 6 to 7 weeks. There are two to three generations per year.

Figure 16b. - Tiny entrance hole with frass and stain. Photo by James Solomon, USDA Forest Service

Figure 16c. - Stained flagworm defects in lumber. Photo by James Solomon, USDA Forest Service

Control.-Few natural enemies have been identified, and no direct controls have been developed.