Oak Stem Borer
Solomon, J.D. 1995. Guide to Insect Borers in North American Broadleaf Trees and Shrubs. Agriculture Handbook 706. Washington, DC. United States Department of Agriculture, Forest Service. 735 p.
Oak, chestnut. White oak preferred but black, southern red, blackjack, post, willow, and water oaks have also been listed as hosts (Beal and others 1952).
Eastern United States from Pennsylvania south to Florida and west to Oklahoma (Linsley 1963). Collected most often in the Appalachian Mountains from Georgia northward.
Very narrow, extremely elongate longhorn beetle, 15 to 18 mm long and only about 3 mm wide (Knull 1946, Linsley 1963). Beetles generally light brown to reddish brown with semierect brown pubescence. Tips of elytra notched and bispinose. Antennae slightly shorter than body in females, slightly longer than body in males, and equipped with single short spines on third and fourth segments.
Very slender and cylindrical, with body thickly covered with fine, white setae that become golden on thorax. Grown larvae yellowish except for light brown mandibles and tergal plates; up to 18 mm long.
Head and thorax glabrous; posterior half of abdomen has prominent spines.
Adults emerge late May through July and deposit eggs at leaf bases, mostly on small twigs near the tops of seedlings and sprouts (Knull 1946, Linsley 1963, USDA FS 1985). Newly hatched larvae burrow into the twig and tunnel within the branch toward the main stem. Larvae make tiny round holes in a straight line to eject frass. As the larvae grow, they consume and hollow out the woody part of the stem, often cutting the stem off or causing it to break off in sections. During late summer and fall, larvae typically make their way to the base of the plant and enter the root collar and upper roots to overwitner. They usually cut off the main stem just above groundlines and plug the open gallery tightly with fibrous frass. During spring, they prepare pupal chambers between two wads of frass within the gallery and pupate (Champlain and others 1925). New adults chew through the upper wad of frass to emerge. There is one generation per year (Beal and others 1952, Craighead 1923).
Injury and Damage
Attacks usually begin in a small branch near the top of the plant but sometimes in a small twig on a side branch. Seedlings and sprouts 20 to 70 cm tall and 6 to 25 mm in diameter at the root collar seem most susceptible. Larvae tunnel in the twig down to the main stem or trunk and then to the root collar or below. Examination reveals a single straight row of small round holes 3 to 6 mm apart along the branch or twig and down the main stem to the groundline. Frass is extruded through these holes and can be found in small piles at or near the base of the plant. Larvae hollow the stem, sometimes cutting or girdling portions so that sections break. A stem may be completely hollowed, leaving only a shell. Browning foliage and dying terminals, branches, or entirely dead seedlings are quite noticeable during the growing season. Dying leaves remain attached to the plant as flags of continuing infestation. Occasionally, this borer becomes abundant and kills a high proportion of the oak regeneration in parts of the Southeast (USDA FS 1985).
Little is known of natural enemies. Some evidence of woodpecker predation has been observed. No direct controls have been investigated.