Common Name: Lyctid or Powderpost Beetle
Scientific Name: Various
Lyctids are commonly known as (true) powderpost beetles because their larvae produce a very fine, powder like 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.
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 1/4″ (6 mm) long. Color nearly white. Body C-shaped but with enlarged thorax. Antennae short, 4-segmented. Spiracle of 8th (last) abdominal segment 3 times larger than other abdominal spiracles. Legs 3 segmented, ending with a long claw. However, 1st instar larva straight-bodied, white, and bears a pair of small spines at rear end.
(1) Flat bark beetles (Cucujidae) with antennae usually long and threadlike/beadlike, sometimes short with 2-4-segmented club, elytra (wing covers) usually lack hairs. (2) false powderpost beetles (bostrichidae) usually cylindrical in form, pronotum with rasplike teeth at front, head usually not visible from above. (3) Bark and ambrosia beetles (Scolytidae) are cylindrical in form, antennae elbowed and clubbed. (4) Pinhole borers and ambrosia beetles (Platypodidae) cylindrical in form, antennal club large, flat, 1-segmented. (5) Deathwatch beetles (Anobiidae) with hoodlike prothorax, concealing head from above, last 3 antennal segments lengthened and/or expanded.
Exit holes are round, and depending on the species, range from 1/32-1- 1/16″ (0.8-1.6 mm) in diameter. Another indication of an infestation is the accumulation of piles of very fine powder like dust beneath the exit holes or on the wood. This dust/frass contains no pellets (like anobiid’s) and falls easily from the hole instead of being packed in (like anobiids and bostrichids).
From an economic viewpoint, the 2 most important lyctids in the U.S. can be briefly characterized as follows: 1. Southern lyctus beetle, Lyctus planicollis LeConte. Adults black; antennal 10th segment wider than long; prothorax usually with a median, broad, shallow depression; elytra (wing covers) with space between striae (longitudinal furrows) composed of 2 regular series of elongate punctures (pits) and separated by rows of fine, long hairs; length about 1/4″ (5 mm) but males much smaller; distributed throughout the United States. 2.Elvety powderpost beetle, Trogoxylon parallelopipedum (Melsheimer). Adults rusty red-brown to black, densely covered with short yellowish hairs not arranged in rows; antennal 10thsegment not wider than long; lateral margins of prothorax converge behind (towards wing covers); length about 1/8″ (2.5-4.3 mm); found throughout the United States.
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 powder like 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 tot he woods 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.
Lyctids attack the sapwood and only that of hardwoods, usually less than 10 years old. They attack both lumber and manufactured products; they also attack structural timbers but hardwoods are rarely used for this purpose today because of their cost. The wood moisture content required for beetle development is 8-32%, with greatest activity at 10-20%. Adults are active at night, readily fly, and are attracted to light. Lyctids are usually brought into structures in wood which contains their eggs and/or larvae. This wood is typically infested during drying time or storage. Finish on wood prevents egg laying. They usually attack oak, hickory, and ash, but will attack other native and tropical hardwoods. Lyctids often attack bamboo.
First, determine if the infestation is active. If it is, then prescribe replacement, localized pesticide application, or fumigation, whichever is the least expensive to achieve control.