Hickory Borer
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Hosts
Hickory, pecan. Commonly attacks water, mockernut, and bitternut hickories (Beal and others 1952, Solomon 1974). Other hickories are probably susceptible, and evidence of attack on black walnut has been observed. Occasionally infests grafted pecan. Oak species have been reported as hosts (Dillon and Dillon 1941), but this seems questionable.
Range
Occurs from southern Canada through the central and eastern United States (Solomon 1974). Common in the South, but populations vary greatly among localities.
Description
Adult
Robust longhorn beetle, ranging from 17 to 25 mm long and 5 to 8 mm wide with long antennae. Prominent spine midway along each side of pronotum. Body pale brown to grayish yellow ground color; elytra banded with darker brown across base and just beyond middle (Knull 1946, Dillon and Dillon 1941).
Egg
Yellowish white, parchment-like, elongate, averages 4 mm long and 1 mm in diameter.
Larva
Mature larva slightly robust, fleshy, generally cylindrical, legless, and 18 to 28 mm long. White to yellowish except for prominent dark brown mandibles and amber spiracles.
Pupa
White to greenish initially but becomes yellowish at maturity, with eyes, mandibles, and appendages darkening considerably before adult emergence (Solomon 1974).
Biology
Adults emerge in west-central Mississippi from early May to early June (Solomon 1974); in Ohio, adults have been observed on foliage in June and July (Knull 1946). After they feed on tender twigs, leaf petioles, and leaf midribs, adults begin mating and egg laying. To oviposit, females chew oval niches in the bark, then force the ovipositor through the opening, downward between the bark and sapwod to deposit 1 egg per niche. Females are known to deposit up to 14 eggs each, but probably deposit many more. Eggs are usually deposited singly, but clusters of two or three niches may be found. Adults live 11 to 32 days. Newly hatched larvae produce small irregularly shaped mines of 1 to 2 cm in diameter under the bark before tunneling into the sapwood. This behavior differs from that of the closely related species Goes tigrinus and G. pulverulentus, whose larvae bore directly into the sapwood after eclosion. During late fall and early spring of the final year of development, mature larvae construct pupal chambers by closing the uppermost portion of galleries with plugs of long excelsior-like fibers. Pupation lasts 15 days during mid-April to early May. The new adults chew circular emergence holes through the bark. The life cycle is completed in 3 to 5 years.
Injury and Damage
Earliest indications of attack are egg niches 4 to 8 mm in diameter made by egg-laying females (Solomon 1974). Egg niches are most common on the sunny aspect of the trunk; they frequently occur in branch crotches (Craighead 1923). As young larvae begin to reach the outer sapwood, oozing sap from the point of attack darkens the bark. In succeeding years, the stain becomes slightly bleached or yellowish brown. Frass extrudes from the entrance hole and falls to the ground. As larvae reach maturity, the frass changes to excelsior-like wood fibers 8 to 12 mm long. Larval galleries extend horizontally or obliquely upward 2 to 5 cm from the point of entry into the wood, rise vertically another 6 to 12 cm, then turn horizontally back to the surface. Active galleries often are partially filled with frass, particularly along the innermost wall. Small diverticula tightly packed with frass sometimes occur at the junction of the horizontal and vertical tunnels of the gallery. Completed galleries are 9 to 16 cm long and 1.0 to 1.3 cm in diameter. Each borer leaves two holes, an elongate entrance hole and a 7-mm-diameter round exit hole. As these wounds heal, bark scars at entrance sites appear as slightly sunken slits, with a small bulge around the periphery. The exit holes heal to form circular scars resembling overgrown branch stubs and are visible for several years. Borer attacks are most common on main stems 7 to 11 cm in diameter. Trunk diameters at point of attack average less for pecan and water hickory than for mockernut and bitternut hickories. Tree trunks are most commonly attacked between 1.5 and 2.3 m above groundline, but occasionally attacks may occur from the tree base to heights of 4.8 m. Attacks on large trees are restricted usually to the upper trunk and branches. On trees of poor vigor, whose borer injuries are slow to heal, galleries serve as nesting sites for ants and also permit stain and decay fungi to be established. Trunks weakened by borer galleries and woodpeckers excavations may be broken by wind. Borer holes, stain, and decay degrade the wood for handlestock, furniture, and other commercial uses (Solomon 1974).
Control
Heavy sap-ooze at oviposition sites kills many eggs and early instar larvae (Solomon 1974). Woodpeckers are major predators of borers that survive beyond the first year; up to a third of the larvae have been destroyed by woodpeckers in some localities. No parasites have been reported. In forest stands and woodlots, the removal of brood trees during stand improvement operations is silviculturally plausible. In shade trees and other valuable trees, this pest can be controlled mechanically with knife and wire of by injecting commercial fumigants into galleries. Attacks can be prevented with trunk sprays of an insecticide during the oviposition period.
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.
