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 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.
SIMILAR GROUPS:
(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, antenna! club large,
flat, 1-segmented. (5) Deathwatch beetles (Anobiidae) with hoodlike prothorax,
concealing head from above, last 3 antenna! segments lengthened and/or
expanded.
DAMAGE AND SIGNS OF INFESTATION:
Exit holes are round, and depending
on the species, range from 1/32-1/16" (0.8-1.6 mm) in diameter. Another
indication of an infestation is the accumulation of piles of very fine
powderlike 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).
REPRESENTATIVE SPECIES:
From an economic viewpoint, the 2 most
important Iyctids in the U.S. can be briefly characterized as follows:
- Southern Iyctus 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.
- Velvety powderpost beetle,
Trogoxylon parallelopipedum (Melsheimer).
Adults rusty red-brown to black, densely covered with short yellowish
hairs not arranged in rows; antenna! 10th segment not wider
than long; lateral margins of prothoax converge behind (towards wing
covers); length about 1/8" (2.5-4.3 mm); found throughout the United
States.
BIOLOGY:
Female Iyctids 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 Iyctids are strong fliers, most tend to lay eggs in
the wood from which they emerged. Since Iyctid larvae cannot digest cellulose,
they feed only on the cell contents which is primarily starch, but also sugar
and protein.
HABITS:
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.
CONTROL:
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.
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