Chesnut Timberworm
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Contents |
Hosts
Chestnut, oak. American chestnut, before its demise, was the preferred host (Hopkins 1894); now found chiefly in white oak (USDA FS 1985).
Range
An eastern species, range corresponds closely with that of American chestnut in the eastern United States (Snyder 1927).
Description
Adult
Slender, elongate, chestnut brown beetle with deflexed head, clothed with fine, silky hair, 11 to 15 mm long (Herrick 1935, USDA FS 1985).
Larva
White to yellowish brown, smooth, elongate, and cylindrical with a large, yellow, rounded head partially covered by enlarged hood-shaped tergum of prothorax (Peterson 1960). Ninth abdominal segment enlarged and conspicuously armed with dark brown scooplike structure bearing many toothlike spines. Full-grown larvae 15 to 18 mm long.
Biology
Adults deposit eggs in cracks and crevices on the surface of wood, often at wounded sites (Hopkins 1894, USDA FS 1985). Young larvae bore directly into wood, forming tiny holes that are scarcely visible. As larvae grow, galleries are enlarged and extended for many centimeters through the sapwood and heartwood. Pupation occurs in cells constructed near the surface. New adults chew circular exit holes. The life cycle has not been established, but a generation probably requires several years.
Injury and Damage
Fine powdery frass may be found at tiny holes that initially are barely visible. Attack sites are found in both sapwood and heartwood and most often are associated with wounds and broken or decayed branches (Herrick 1935, Hopkins 1894); dying trees, stumps, and fresh-cut logs are also attacked. Holes in lumber are generally unstained or only slightly stained, round, and vary from 0.3 to 6.4 mm in diameter (Snyder 1927). Most American chestnut was killed by the mid-1900's by chestnut blight, a disease introduced from the Orient in the early 1900's (Clapper and Gravatt 1943). Diseased and dying trees were riddled by chestnut timberworms. Nearly every tree of merchantable size contained some injury. Lumber from such trees was downgraded to "sound wormy," resulting in sizeable losses. Today, affected lumber is considered character marked and sold as "wormy chestnut" for decorative purposes at handsome prices.
Control
Minimizing wounds from harvesting equipment, stand improvement work, wildfire, and other insect borers can help to reduce infestations and losses (Craighead 1950).
Gallery
 Photo by Ronald S. Kelley, Vermont Department of Forests, Parks and Recreation, Bugwood.org |  Photo by James Solomon, USDA Forest Service, Bugwood.org |
References
Solomon, J.D. 1995. Guide to insect borers of North American broadleaf trees and shrubs. Argic. Handbk. 706. Washington, DC: U.S. Department of Agriculture, Forest Service. 735 p.
