Wood-Infesting Insects

COMMON NAME: Buprestids, flatheaded and metallic wood borers

SCIENTIFIC NAME: Various

CLASS/ORDER/FAMILY: Insecta/Coleoptera/Buprestidae

METAMORPHOSIS: Complete

INTRODUCTION. The common name of flathead comes from the larva whose thorax is greatly enlarged and flattened, metallic because the adults almost always have a metallic luster, and wood borers because the larvae bore through wood. They are primarily nuisance pests indoors and are commonly brought in with firewood, but their damage must be recognized because wood previously damaged by the larvae is often used as structural timbers. Of concern are log homes with bark left on the logs, and the golden buprestid, buprestis aurulenta Linnaeus, in the western states because of its long life cycle. Over 700 species are found in the United States and Canada, and over 11,300 worldwide.

RECOGNITION. Depending on the species, adults mostly about 3/16-3/4” (5-20 mm; range 2-40 mm) long; hard-bodied, compact, somewhat flattened; hairs (setae) present or absent. Color nearly always metallic or bronzed, especially ventral surface, some species marked with red or yellow. Antenna usually short, sawtoothed (serrate); threadlike/comblike in some species. Elytra (wing covers) usually deeply grooved or pitted, with sides nearly parallel, and apices/tips often pointed. Tarsi 5-5-5.

Depending on the species, mature larvae usually 3/16-1 15/16” (5-50 mm; range 2-100 mm) long, legless; body elongate with thorax (especially prothorax) greatly enlarged and flattened, abdomen parallel-sided, straight, and slightly flattened; color whitish or cream.

BIOLOGY. Adult females lay their eggs in bark or wood crevices, or under bark at the edge of wounds. The 1^st instar larvae first bore under the bark, then into the sapwood, and then sometimes into the heartwood. Larvae usually require 1-2 years to mature. Pupation takes place in an elongated pupal cell near the surface of the wood. Emerging adults cut their way to the surface.

Larvae of the golden buprestid usually require 2-4 years to complete their development, but this may be greatly lengthened if infested wood is incorporated into wood products. There are cases of adults emerging up to 50 years after the initial infestation. Adults live 3-5 months.

COMMON NAME: Anobiid, deathwatch beetle

SCIENTIFIC NAME: Various

CLASS/ORDER/FAMILY: Insecta/Coleoptera/Anobiidae

METAMORPHOSIS: Complete

INTRODUCTION. Anobiids are the most commonly encountered of the powderpost beetles, lyctids and bostrichids being the other 2 groups. They get their common name of anobiids from the beetle family to which they belong. For some species, the name of deathwatch beetle comes from the tapping they make by striking their mandibles (jaws) against the wood surface of their tunnel as a mating call. Heard in the quiet of the night when people were sitting up with an ill person, this tapping was superstitiously believed to indicate that death was near. They are worldwide in distribution, with about 310 species occurring in the United States.

RECOGNITION. Depending on the species, adults about 1/32-3/8” (1.1-9 mm) long but those attacking buildings range from 1/8-1/4” (3-7 mm) long. Shape variable but usually elongate, cylindrical. Color reddish brown to nearly black, sometimes with lighter areas of pale hairs (setae). Prothorax hoodlike, nearly always enclosing head, concealing it when viewed from above. Antennae with club not symmetrical, last 3 segments nearly always lengthened and expanded or simply lengthened; sometimes serrate (sawtoothed) or pectinate (comblike). Punctures/pits on elytra (wing covers) I or not in rows.

Depending on the species, mature larvae range up to about ½” (11 mm) long. Color nearly white. Form C-shaped but with thorax enlarged/swollen. Antennae short 2-segmented. Posterior (rear most) spiracle not enlarged. Legs 4-segmented, hairy.

BIOLOGY. Female anobiid beetles lay their eggs (usually 20-60; maximum 121) on wood under surface splinters, in cracks, or in old exit holes. After hatching, the larvae bore straight into wood for a short distance, and then make a right-angle turn and bore with the wood grain. As they bore, the larvae pack their frass and fine wood fragments into the tunnel behind them. If a softwood (conifer/evergreen) is being attacked, this loosely packed mixture feels gritty due to the lemon or bun-shaped fecal pellets whereas, if a hardwood (broadleaf tree) is being attacked, this mixture is tightly packed and does not feel gritty. Each time the larva molts, the tunnel is made larger in diameter. When larval development is completed, the immediate tunnel is often enlarged for pupation. When the adult is ready to emerge, it bores straight to the wood’s surface and exits/emerges. In other species, the mature larva bores almost to the wood surface and creates its pupal chamber there, and when the adult is ready to emerge, it bites through the thin outer surface and exits/emerges. Adults usually emerge in the spring or early summer and do not feed, but actively seek a mate. Under very favorable conditions, developmental time (egg to adult) may require only 1 year, but it usually requires 2-3 years indoors and sometimes longer. Although most anobiids are strong fliers, females tend to lay their eggs on the wood from which they emerged. Based upon those studied, anobiids can digest wood cellulose with the aid of yeast cells in their digestive tracts; bostrichids and lyctids cannot digest cellulose.

COMMON NAME: Lyctid or powderpost beetle

SCIENTIFIC NAME: Various

CLASS/ORDER/FAMILY: Insecta/Coleoptera/Lyctidae

METAMORPHOSIS: Complete

INTRODUCTION. Lyctids are commonly known as (true) powderpost beetles because their larvae produce a very fine, powderlike frass in their galleries (vs. bostrichids/false powderpost beetles and anobiids, whose larvae produce coarser frass which also contains fine wood fragments or pellets respectively). They are worldwide in distribution, with about 11 species occurring in the United States.

RECOGNITION. Depending on the species, adults about 1/32-1/4” (1-7 mm) long. Body elongate, narrow, flattened, almost parallel-sided; head pronotum, and elytra (wing covers) about equal in width; pronotum somewhat wider at front; head and often mandibles visible when viewed from above. Color reddish brown to black. Antennae with abrupt 2-segmented club. Elytra (wing covers) often with rows of hairs (setae). First abdominal segment ventrally much longer than other segments.

Depending on the species, mature larvae up to about ¼” (6 mm) long. Color nearly white. Body C-shaped but with enlarged thorax. Antennae short, 4-segmented. Spiracle of 8^th (last) abdominal segment 3 times larger than other abdominal spiracles. Legs 3-segmented, ending with a long claw. However, 1^st instar larva straight-bodied, white, and bears a pair of small spines at rear end.

BIOLOGY. Female lyctids lay their eggs (15-50) in exposed wood pores, cracks, or crevices. Eggs are never deposited in/on waxed, polished, painted, or varnished surfaces. The larvae tunnel only in the sapwood and usually tunnel with the wood grain. As they bore, the larvae loosely pack their tunnels with very fine powderlike dust (like talcum powder or flour). After several molts requiring 2-9 months, the mature larva bores to near the surface and constructs a pupal chamber and pupates. When the adult emerges, it bores straight to the wood’s surface and exits/emerges. Indoors, adults usually emerge in late winter or early spring and with little feeding, mate. Under very favorable conditions, developmental time (egg to adult) usually requires 9-12 months, but may be as short as 3-4 months or as long as 2.5-4 or more years. Although some lyctids are strong fliers, most tend to lay eggs in the wood from which they emerged. Since lyctid larvae cannot digest cellulose, they feed only on the cell contents which is primarily starch, but also sugar and protein.

Black Polycaon

COMMON NAME: Bostrichid, false/large powderpost beetle, branch-and-twig borer

SCIENTIFIC NAME: Various

CLASS/ORDER/FAMILY: Insecta/Coleoptera/Bostrichidae

METAMORPHOSIS: Complete

INTRODUCTION. Bostrichids are commonly known as the false powderpost beetles. This distinguishes them from the lyctids which were the first to be called powderpost beetles because of their powder-fine dustlike frass. The common name of branch-and-twig borer comes from their habit in nature of infesting the dead and dying branches of trees. Bostrichids are worldwide in distribution, with about 60 species occurring in the United States.

RECOGNITION. Depending on the species, adults mostly about 1/16-1” (2-24 mm) with 1 western species about 2” (52 mm) long, but those typically found indoors range from 1/8-1/4”(3-6 mm). Color reddish brown to black. Antennal club of 3-4 segments, often enlarged to 1 side. First abdominal segment ventrally about equal in length to other segments. Two body forms present: (1) most species elongate and cylindrical, elytra (wing covers) parallel-sided, pronotum with rasplike teeth at front, prothorax as wide as head but not enclosing it, head directed downward and usually not visible from above; and (2) a few species with body flattened, head clearly visible from above, pronotum without rasplike teeth.

Depending on the species, most mature larvae about ¼-3/8” (5-8 mm) long. Color nearly white. Body C-shaped but with thorax enlarged. Antennae 3- or 4-segmented. Posterior (rear most) spiracle not enlarged. Legs 4-segmented, hairy.

BIOLOGY. Female bostrichids differ from anobiids and lyctids in that they bore into wood to prepare for egg laying. Eggs are laid into wood pores exposed by these cross-grain tunnels. Most species develop in the sapwood and as the larvae bore, they tightly pack their meallike frass in the tunnel behind them. After several molts, the mature larva bores a little nearer to the surface, sometimes constructing a pupal chamber, and pupates. When the adult emerges, it bores straight to the wood’s surface and exits/emerges. The developmental period (egg to adult) varies with the species, but is usually about 1 year. Adults are usually seen from spring through autumn. The bamboo borer only requires about 51 days developmental time, so there may be several generations per year. Developmental time for some species which lay eggs in partially seasoned wood my be lengthened from 1 year to up to 5 years if the wood dries rapidly, but the black polycaon beetle has been found emerging from wood about 20 years old. Since bostrichid larvae cannot digest cellulose, they feed on the cell contents which is primarily starch, but also protein and sugar.

Bostrichid, Lead cable borer

This is a reddish-brown beetle, 1/5 to 1/4 inch in length. This bostrichid is known to bore through the lead covering of aerial telephone cables. The holes are 1/10 inch in diameter and may extend into the insulation. The attack is usually made where the suspending ring supports the cable. Most damage occurs from June to August, when the beetles are emerging in greatest numbers. Rivers (1886) reported this species damaging wine casks in California. Ebeling and Reierson (1973) reported that in Oregon this beetle damaged plasterboard, plaster casts, hardwood paneling, and floors. They are known to be injurious to living trees and plastic conduits.

Burke et al. (1922) reported the adult female bores into solid wood and lays her eggs. Eggs hatch in about three weeks and the larvae feed in the wood. The larval stage lasts about nine months and the pupal period lasts about two weeks. The adult beetles may remain in the wood for 30 days before emerging. Usually one generation per year occurs.

COMMON NAME: Cerambycids, longhorned beetles, roundheaded wood borers

SCIENTIFIC NAME: Various

CLASS/ORDER/FAMILY: Insecta/Coleoptera/Cerambycidae

METAMORPHOSIS: Complete

INTRODUCTION. The common name of longhorned comes from their antennae which are very long, often much longer than the body, roundheaded comes from the larvae which have a fairly cylindrical thorax and bore round to slightly oval holes in wood, and wood borers because the larvae bore through wood. With the exception of the old house borer, Hylotrupes bajulus (Linnaeus), and the flat oak borer, Smodicum cucujiforme (Say), these beetles do not reinfest seasoned wood and are therefore nuisance pests, although some can cause minor/cosmetic damage by adult emergence through various materials. About 1,200 species occur in the United States and Canada. This section will be restricted to those species which attack wood used in structures or are commonly brought into the structure in firewood.

RECOGNITION. Depending on the species, adults usually about 3/8-1” (10-25 mm; range 2-60 mm) long; usually oblong or elongate and somewhat cylindrical, some flattened with only prothorax cylindrical. Head with compound eyes notched on inner margins. Antenna very long, usually exceeding body length, and inserted into eye notch so that base is partially surrounded by eye; usually 12-segmented (range 10-25+ segments). Elytra (wing covers) usually covering abdomen, a few species with short elytra. Tarsi apparently 4-4-4 (5-5-5 with 3^rd bilobed and surrounding small 4^th segment).

Depending on the species, mature larvae about 3/8-3 1/8+” (10-80+ mm) long; body elongate, cylindrical, parallel-sided except thorax enlarged/swollen, and segments distinctly separated; color whitish or cream; ocelli 0-5 pairs; antenna short, 3-segmented; and legs absent, or very short and 5-segmented with spinelike tarsus.

BIOLOGY. Females lay their eggs in wood or bark crevices during the spring, summer, or early autumn. Eggs are laid singly or in small groups. Larva hatch in a few days. After finding a suitable entry point, they feed near the surface at first where the protein is in greatest concentration. As they grow, they bore deeper into the wood. The larval stage may last from a few months to several years, being prolonged by a low nutritional value of the wood and any decrease in moisture such as caused by the wood being sawed into lumber. Pupation takes place in a cell near the wood surface. The time of adult emergence depends on the species and environmental conditions. Outside, they mate, lay eggs, and die. Indoors, the only 2 species that can reinfest dry, seasoned wood are the old house borer and the flat oak borer.

The new house borer requires at least 2 years to complete its life cycle (adult to adult), the old house borer at least 3 years, the flat oak borer 1-2 years, and the pine sawyers (Monochamus spp.) require 2 years in the more northern parts of their range.