Oak Timberworm

Taxonomy

Domain	Eukarya
Kingdom	Animalia
Phylum	Arthropoda
Subphylum	Hexapoda
Class	Insecta
Subclass	Pterygota
Infraclass	Neoptera
Order	Coleoptera
Suborder	Polyphaga
Infraorder	Cucujiformia
Superfamily	Curculionoidea
Family	Brentidae
Subfamily	Brentinae
Tribe	Arrhenodini
Genus	Arrenodes

Scientific Name

Arrenodes minutus

Scientific Name Synonyms

Eupsalis minuta

Arrhenodes minutus

Common Name

oak timberworm

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.

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.