Oak timberworm
Arrhenodes minutus (Drury)
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. Oak, elm, poplar, beech. Attacks trees in red and
white oak groups (Solomon and others 1987). Upland oaks, especially black
and scarlet oaks, are particularly susceptible (Buchanan 1960). Elm,
poplar (Shenefelt and Benjamin 1955), beech, and aspen (MacAloney and Ewan 1964)
have also been mentioned. Clusters of adults found under loose bark of
boxelder and honeylocust suggest that other hardwood species are probably
susceptible.
Range.Southeastern Canada throughout the eastern United States
to the Gulf Coast (Sanborne 1983, Solomon and others 1987).
Description
Adult. Shiny, very elongate snout beetle, varying from 7 to 25
mm long (Buchanan 1960, Shenefelt and Benjamin 1955, Solomon and others
1987). Reddish brown to brownish black with elongate yellowish spots on
elytra. Females have long slender snouts; male mouthparts are broad and
flattened and noticeably larger than those of females.
Egg. Round, less than 1 mm in diameter, and translucent
initially, but gradually becomes opaque.
Larva. White, elongate, cylindrical, and curved with three pairs
of two jointed, thoracic legs, and one pair of prolegs at end of abdomen.
Full-grown larvae 12 to 24 mm long.
Biology. Adults present from early May to August over most of
its range (Buchanan 1960); attracted to sap spots for feeding and sometimes
congregate under loose bark at wound sites (Sanborne 1983). Fresh wounds
are most attractive for oviposition, but some as old as 2 years are
chosen. To oviposit, females chew cylindrical hair-sized holes in large
wood vessels on wood surfaces shaded from direct sunlight. One egg is
deposited in each hole; most holes are plugged with a sticky secretion and
frass. In Ontario, there are two periods of oviposition, from mid-June to
late July and from early to mid-September (Sanborne 1983). Egg incubation
requires from a few days to 3 weeks, depending on temperatures. Newly
hatched larvae bore directly into the wood. The diameter of the tunnels at
first is sufficient for movement of the larvae through them but is enlarged in
time (Hopkins 1903). Typically, tunnels are bored nearly straight across
the wood grain with little up or down slope. Tunnels go almost to the
opposite side of the tree, make a sharp U-turn, and go back across the wood
grain toward the entrances. Larvae keep the tunnels clean by pushing the
frass outside. Pupation occurs near the tunnel exit from which the adults
emerge. The life cycle is generally 3 years, but some individuals develop
in 2 years and a few require 4 years (Buchanan 1960).
Injury and Damage. Attacks are usually associated with previous
injuries. Most attack sites are at wounds that expose sapwood (Buchanan
1960). White, powdery frass at egg sites on exposed wood or at large
vacated borer entrances provide evidence of infestation (Donley and Terry
1977). Holes are often found around large red oak borers galleries.
Small round tunnels 0.2 to 4.0 mm in diameter lead from the egg sites into the
wood. In sawn lumber, damage is characterized by mostly horizontal tunnels
extending in many directions. Dying trees and green fresh-cut logs are
sometimes attacked. Economically damaging losses are primarily to standing
timber grown for wood products (Hopkins 1903). In particular, losses
result form the small wormholes made by feeding larvae. Lumber cut from
infested logs may be unfit for special uses as tight cooperage or flooring (MacAloney
and Ewan 1964). Factory grade lumber is sometimes substantially reduced in
grade. Also, this borer has been reported to attack fresh-cut stave bolts,
large pieces of unseasoned lumber, and squared timbers, resulting in substantial
losses (Hopkins 1903). During peak larval activity from spring to
midsummer, incidence of attack in blazed trees in the Missouri Ozarks ranges
from 50 to 78% (Buchanan 1960). Defects are most prevalent in upland
forests of the central United States, east to Kentucky, Ohio, and West
Virginia. Oak timberworm can also vector the oak wilt fungus (Buchanan
1957).
Control. Trees should be protected against wounds and injuries,
including those caused by large borer species (Solomon and others 1987).
In areas with a history of serious timberworm damage, extra precautions during
harvesting and other woods operations are needed to minimize bark injuries to
residual crop trees. Infestation can also be minimized by promptly
removing dying and felled trees (Hopkins 1903). No natural enemies have
been reported. Chemical and other direct controls have not been
investigated.
Adult(s) female. James Solomon,
USDA Forest Service. |
Adult(s) male. James Solomon,
USDA Forest Service. |
Damage oak timberworm holes in oak lumber. James Solomon,
USDA Forest Service. |
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