Hickory. Reported in black, water, and pignut hickories, but undoubtedly attacks other hickory species (Gagne and Kearby 1979, Wood 1982).
Vermont south to Florida and west to Texas and Kansas (Bright 1968, Wood 1982); probably occurs throughout the natural range of hickories (Beal and Massey 1945, Blackman 1922).
Reddish brown, cylindrical ambrosia beetle with head directed downward and hidden from above by pronotum (Beal and Massey 1945, Bright 1968, Wood 1982). One of the largest species of Xyleborus in North America; females 3.9 to 4.5 mm long, males 2.3 to 2.6 mm long and somewhat lighter colored. Pronotum slightly longer than wide, broadly rounded in front, roughened on anterior, and shiny and sparsely punctured on posterior. Elytra slightly wider than pronotum with sides parallel. Elytral declivity drops off abruptly and steeply and bears four large acute teeth and several acute granuals.
Oval, smooth, white, 0.9 mm long by 0.4 mm wide (Gagne and Kearby 1979).
White with amber head and mandibles, legless, C-shaped body, 2.5 to 4.7 mm long.
This beetle overwinters in adult stage in galleries of host trees. Hibernating adults emerge and are attracted to new susceptible host trees by their odors during March and April (Beal and Massey 1945, Chamberlin 1939, Gagne and Kearby 1979). Most attacks are in the lower trunk. Male beetles are rare in most populations. Females bore through the bark and straight into the wood. They often make cavelike excavations at the end of the straight entrance tunnel from which unbranched galleries radiate outward. This species does not deposit eggs in niches or cradles as do many scolytids, but lays them in groups of 1 to 16, mostly toward the ends of open galleries about 1.5 cm long. Eggs hatch in about 7 days. Larvae move freely in the gallery system and feed on the ambrosial fungi that grow on gallery walls; the fungus is transmitted from host to host by adult females. Larvae have three instars and develop from eggs to adults in about 35 days. New adults either emerge and seek new hosts or remain and extend the existing gallery system. The second generation of adults commences in early July, but most attacks are in late July and early August. There are two generations per year; second generation adults do not emerge and seek new hosts but overwinter in the galleries.
Injury and Damage
Weakened and dying trees are most susceptible, but this pest occasionally attacks fresh-cut logs and stumps (Beal and Massey 1945, Blackman 1922, Gagne and Kearby 1979). Trees under attack by Scolytus quadrispinosus are particularly susceptible to infestations. Attacks are common on the basal portion of the trunk within 1.5 m of the ground and in buttress roots. Large trees generally sustain a higher rate of infestation per unit area than small trees. White frass in bark crevices usually is the first sign of beetle attack. Dissection reveal palmate or simple, branched gallery system. Entrance tunnels extend straight into the bole 1 to 3 cm then branch up to six times. At the end of the entrance tunnel, beetles often make a cavelike excavation from which unbranched galleries radiate in a fanlike pattern in a single plane. Branch galleries are usually simple, but some have secondary branches and a few even anastomose or rejoin. Galleries may extend to depths of 6 cm or more. Those extended by second-generation beetles are longer and more complex. This insect causes rapid deterioration of dying hickories. The black-stained galleries degrade wood products sawn from infested logs.
Practices that keep trees healthy and prevent S. quadrispinosus attacks will largely eliminate problems with X. celsus. Prompt harvesting and milling of weakened trees and those infested by S. quadrispinosus will minimize losses from degrade by X. celsus (Beal and Massey 1945).
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.