Spotworm Borer
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Hosts
Oak. White and overcup oaks are specific hosts (Donley and others 1974, Morris 1964). Other white oaks probably also serve as hosts. Adults have been collected from the foliage of birch, poplar, and hazelnut, but it is doubtful that they are larval hosts (Fisher 1928).
Range
Widley distributed from Maine south to Florida and and west to Texas and Colorado (Fisher 1928, Mutchler and Weiss 1922). Also reported from Ontario, Quebec, and Newfoundland.
Description
Adult
Slender to moderately robust beetle, slightly flattened (Fisher 1928). Feebly shining, dark blue to black with less distinct greenish tinge. Antennae extend to about middle of pronotum on male; slightly shorter on female. Adults 7.5 to 12.7 mm long.
Larva
Slender, white, and extremely elongate, ranging from 25.4 to 33.0 mm (Morris 1964). Body noticeably flattened, with prothorax slightly wider than body.
Biology
Adults emerge in May and June and sometimes through July (Chittenden 1900b, Morris 1964). Females deposit eggs in bark crevices on host trees (Morris 1964). Larvae bore through the bark and excavate patches of the inner bark about 13 mm in diameter. They soon enter the cambium and tunnel spirally, primarily in the outermost growth ring. Gallery lengths have not been measured adequately, but individual galleries are at least 1 m or more in saplings and small trees. Larvae pupate in enlarged chambers in the tunnels, and new adults emerge in late spring and early summer. A generation requires 2 years.
Injury and Damage
Trees growing on river bottomlands subjected to backwater flooding from December through June are most apt to be infested. Larvae cause injuries by tunneling the outermost growth ring of the sapwood (Morris 1964). By cutting away the bark of infested saplings, one can observe larval feeding sites. Galleries are long, crooked (occasionally spiralling around the stem), flattened, and packed tightly with frass. Adults leave small D-shaped emergence holes in the bark, but there is little other evidence of infestation on the bark surface. Ends of fresh-cut logs usually show irregular lines of stained wood where the spots are exposed. On large sawlogs, the stains resemble scribbled handwriting on log ends, and woodsmen read them as a sign of infestation and poor-quality wood. Cross sections of small stems may reveal tiny frass-packed galleries surrounded by dark stain. In sawn lumber, spotworm damage is characterized by dark stains, oval to diamond or spindle shaped in cross section and about 25.4 to 43.2 mm long with a 1.5-mm frass-packed hole in the center of the stain. Larvae tunnel the outer sapwood of host trees, leaving defects called "grease spots" or "worm spots." Lumber with heavy spotworm defect is graded as Sound Wormy or No. 3A Common, which is worth about $60 less per thousand board feet than lumber without the defect (Morris 1964). Defect has been reported as particularly prevalent in overcup oak from river bottoms of the lower Ouachita, White, Arkansas, Alabama, and Pearl Rivers and in smaller river bottomlands in Alabama, Arkansas, Louisiana, and Mississippi. Lumber degraded by spotworm defects has been suggested for use as character-marked paneling that could help lumbermen recover some of the losses from degrade (Solomon 1986).
Control
Evidence of woodpecker predation has been observed, but no other natural controls have been recorded. Direct controls have not been investigated.
Gallery
 Photo by James Solomon, USDA Forest Service, 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.
