Lyctus Fabricius, 1792
POLYPHAGA Emery, 1886
BOSTRICHOIDEA Latreille, 1802
LYCTINAE Billberg, 1820
L. brunneus (Stephens, 1830)
L. linearis (Goeze, 1777)
Lyctus brunneus (Stephens, 1830)
The origins of this species are unclear; it is native to either Asia or South America but has been established in Europe, where it is now widespread, for at least 150 years. The beetles are transported with both processed and unprocessed wood and are now more or less cosmopolitan, being especially abundant in tropical regions, in the UK it is established and widespread, occurring sporadically and locally across England north to the Scottish border though generally rare or absent from western areas. The natural habitat is open deciduous or mixed woodland with a good supply of fallen timber but the species can also utilize processed timber of all kinds from ornamental to structural and it can develop in a range of stored dry seeds and spices etc., in tropical region it can infest bamboo and large populations can become serious pests of a range of stored dry products. The susceptibility of processed timber depends on its starch content; cut wood that is still alive and moist dead wood tend to become depleted and so are ignored by the beetles, but dead wood that is slowly dried or seasoned tends to retain some of its starch and so is susceptible to attack, hence naturally seasoned wood or that from drier or warmer climates may contain larvae that go undetected. In warmer climates the beetles develop in a very wide range of trees and shrubs while in temperate areas they infest mostly hardwoods such as walnut, oak, elm, alder, ash and eucalyptus etc. In northern temperate regions they univoltine and adults are active from April until August or September, they swarm and mate throughout the season and disperse by flight over long distances so may suddenly appear in well-worked sites. On warm nights they may be observed in numbers running around on fallen timber, females sample the wood to ensure sufficiently high starch content before ovipositing; the ovipositor is long and nimble and they deposit eggs into pores, crevices or open scolytid galleries etc., each will lay between 50 and 75 eggs either singly or in small batches. At this time the moisture content is also important, when above 30% or below about 8% the wood is ignored, the optimum being between 12 and 15%, and the ideal temperature for larval development is around 26°C, hence in warmer climates they may be continuously brooded and the entire life-cycle may be completed within 4 months. The eggs are cylindrical and very small and so are deposited readily in wood with larger pores while some species with smaller pores such as
Lyctus brunneus 1
Lyctus linearis 1
© Lech Borowiec http://www.cassidae.uni.wroc.pl/Colpolon/index.htm
Lyctus linearis 2
© U.Schmidt https://www.kaefer-der-welt.de/index.htm
beech and horse chestnut are ignored and others, with pores just large enough, on average, to accommodate the eggs such as willows, cherry and apple, are only rarely attacked. Larvae emerge after about 2 weeks and immediately begin to feed and bore into the wood, they generally develop through the year and overwinter to pupate within the wood and produce adults the following spring and summer but various constraints such as moisture or starch content may slow their development and they may take 2 or 3 years to become fully-grown. Lyctus galleries are narrow, 1-2mm, and extend mostly along the direction of the grain, they resemble those of Anobium but the frass is powdery and dry, not forming pellets, and they tend to run just below the surface. Fully-grown larvae construct cells and pupate just below the surface during the spring or early summer and adults eclose after about 4 weeks. Adults emerge through circular holes between 2 and 3mm in diameter, in furniture they will also chew through any covering materials such as leather or card, and they have been recorded boring through silver and lead. Larvae are pale grey to white, enlarged anteriorly, C-shaped and up to 6mm long, they have tiny legs and may be identified (to the generic level) among other wood-borers by the presence of an enlarged spiracle either side of the eighth abdominal segment. The damage caused tends to be characteristic and extensive, the xylem may be completely destroyed and reduced to dust, leaving a thin surface layer of wood-hence the common name of ‘powder post beetles’-and because the surface remains intact an infestation may go unnoticed until a structural failure occurs. Adults and larvae are preyed upon by various clerids and in the wild they often occur alongside Tillus elongatus.
2.7-6.0mm. Adults are elongate, parallel-sided and weakly convex, entirely pale to dark brown, usually with the forebody darker, and the entire dorsal surface is very finely pubescent. Head transverse from above, narrowed in front of large convex eyes and evenly and smoothly convex, vertex and frons coarsely punctured and mandibles robust and curved. Antennae slender, 11-segmented with a 2-segmented club (which is a good diagnostic character as it is rare among our fauna, e.g. see Teredus); penultimate segment expanded towards the apex and terminal segment short and rounded. Pronotum broadest behind the rounded anterior angles, lateral margin sinuate and appearing finely denticulate, surface flat and densely and moderately strongly punctured. Prosternum long in front of round and well-separated coxae, mesosternum short and narrow, the process extending about half way between the round and well-separated coxae. Metasternum very long, shiny and very sparsely punctured and pubescent, metacoxae transverse and very widely separated, reaching the elytral margin. First abdominal ventrite much longer than the others and all ventrites sparsely punctured and pubescent. Elytra parallel-sided and very long, at least 2.5:1, entirely covering the abdomen and continuously rounded apically, with narrow epipleura behind rounded and almost perpendicular shoulders. Elytral surface with fine punctures that often form distinct rows but are generally random, especially near the suture, distinct striae usually obvious towards the lateral margins. Tarsi 5-segmented although they appear 4-segmented due to the tiny basal segment, terminal segment long, curved and widened apically. Claws robust and curved, smooth and without a basal lobe or tooth.
Lyctus linearis (Goeze, 1777)
Originally native to tropical regions and possibly also the Western Palaearctic region this species is now more or less cosmopolitan, having been transported around the world with timber and timber products over the past few centuries e.g. it was first noticed in the United States in 1896 and is now established across the Nearctic region. It is locally common throughout lowland Europe except for the far north, occurring in a range of deciduous trees as well as in processes timber and timber products and is an occasional serious pest of furniture and structural timber although it is rarely recorded in the UK and may not be established in the wild. In northern temperate regions the life-cycle is much the same as L. brunneus; univoltine with eggs laid in the spring and larvae developing through the year and pupating the following spring to produce a new-generation of adults from April or May. Host choice and larval development depend on the moisture and starch content of the wood and the size of the pores as eggs are inserted into the vascular bundles, and females are careful in their choice of host when laying eggs but in adverse conditions larval development can be prolonged over several seasons, making this a difficult species to detect in processed wood. Adults are nocturnal, they mate throughout the season and disperse by flight and so might appear in any suitably wooded situation.
2.5-5.5mm. Adults are similar to those of the previous species but are lighter and more uniformly brown in colour, the pronotum is more parallel-sided and densely punctured and the elytra are more regularly striate; the first stria consists of an irregular double row of punctures and the rest, for the most part, consist of a single row of round and flat punctures separated by less than their diameter.