Warf Borers

Wharf Borers

Wharf borers are found in very moist wood. Larvae form extensive galleries in piling, wharves, decaying support timbers of buildings, wet flooring, wet boxes, wood lying on damp ground such as in crawlspaces or cellars and wood buried under the soil. The presence of this insect often indicates unsatisfactory plumbing and rotting timbers. This insect may promote the extension of rot into wood, resulting in damage. Serious damage by wharf borers is debatable as the wood is already moist and decayed to a certain extent before feeding occurs. Adult beetles can emerge from wood in large numbers, creating a nuisance by their presence.

Adult wharf borers are narrow, depressed, about 1/2 inch long and brownish to reddish-yellow on top. The tips of the wings, eyes, sides of the thorax, legs and undersides are blackish. The body is covered with a dense, yellow pubescence, with the wing covers pointed at the tips. Each wing has four lengthwise raised lines.

Antennae are about half the body length. Mature larvae are about an inch long, cream-colored and covered with brown hairs. They have brown mouthparts that are almost black at the tips. Larvae bear a wart-like swelling on the upper side of the last two segments of the thorax and the first two abdominal segments.

The development time from egg to adult is about 12 months, and adults tend to emerge around June to late August. Eggs are deposited on wood surfaces where they are subjected to temperature extremes. Egg capsule longevity is reported to be 5-11 days. First instar larvae burrow about 1 cm beneath the surface of the wood after hatching, where soft-rot type degradation is evident. The larval stage is reported to last up from 2 months up to 2 years, during which time larvae digest cellulose and hemicellulose. Larvae produce the enzyme cellulase, which enables them to feed on rotting wood. Tunnels formed by larvae during burrowing through the wood can be 30 cm long. Pupae are reported to last 6-17 days, the exact amount of time being influenced by temperature and relative humidity. Adults are short-lived, non-feeding, free-living, able to fly and can locate wood via olfactory cues. They emerge from the resting pupal stage between May and September, though are more often observed in June. Adults live for about 2-10 days under laboratory conditions, during which time they mate and lay eggs. Females are not substrate specific when choosing an oviposition site. Wharf borers are known to infest both hardwood and softwood.

Adult beetles usually are observed in May and June in large numbers when emerging from wood. Beetles mate in rotten wood kept moist and deposit eggs, which hatch into larvae. Pupation and adulthood follow. The life cycle from egg to adult is usually completed in one year, but in cooler climates, several years may be required to reach adulthood. Larvae may occur in cellars or basements and overwinter, protected in the damp wood. Introduced from Europe, this insect has been found in wharf timbers between flooding and the high water level, especially which were in badly decayed, well-riddled wood. Annual swarming of adult beetles, especially into new structures, can disrupt business operations and annoy homeowners and apartment tenants.