Hickory timber beetle
Xyleborus celsus Eichoff
From: 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.
Hosts. Hickory. Reported in black, water, and pignut
hickories, but undoubtedly attacks other hickory species (Gagne and Kearby 1979,
Wood 1982).
Range. 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).
Description
Adult. 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.
Egg. Oval, smooth, white, 0.9 mm long by 0.4 mm wide (Gagne and
Kearby 1979).
Larva. White with amber head and mandibles, legless, C-shaped
body, 2.5 to 4.7 mm long.
Pupa. Exarate, white.
Biology. 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.
Control. 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).
Galleries in stems: cross-sections. James Solomon,
USDA Forest Service. |
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