Insects of Britain and Ireland: the families of Coleoptera

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L. Watson and M. J. Dallwitz



Powder-post Beetles.

General appearance. 2.7–6 mm long. Body length/maximum body width 2.45–3.65. Elytral length/pronotal length 2.6–3.25. Base of prothorax not or scarcely narrower than the combined elytral bases, or distinctly narrower than the combined elytral bases. Greatest prothoracic width not narrower or only slightly narrower than the greatest elytral width, or distinctly narrower than greatest elytral width. Beetles elongate; dorsally flattened; not necked; conspicuously waisted. Upper surfaces of body non-glabrous; not bristly; exhibiting scales or scale-like setae, or with neither scales nor scale-like setae.

Detailed morphology. Eyes strongly protuberant; without bristles; finely facetted. The labrum at least partly visible in antero-dorsal view; labrum mostly moderately to heavily sclerotized. Mandibles with a well developed mola, or with a reduced mola; with reduced prosthecae, or without prosthecae. The mandibular apices simple, or bidentate or bilobed. The incisor edges of the mandibles simple, or with a single tooth. The maxillae with distinct galea and lacinia apically to the palp. The apical segment of the maxillary palps cylindrical to fusiform. The apical segment of the labial palps not expanded apically. Antennae short; 11 segmented. Antennal scape not swollen. Antennae clubbed. Antennal clubs 2 segmented. Antennal insertions hidden from above (but head visible from above).

Cervical sclerites absent. Pronotal length/maximum pronotal width 0.8–1.16. The pronotum with lateral keels (pronotal carinae); keels when present, complete, or incomplete. Prothorax without notopleural sutures. Scutellum conspicuous to highly reduced; not elevated; anteriorly simple; posteriorly truncate. The prosternal process complete; slightly overlapping the mesoventrite. Metaventrite without a transverse groove. The fore-leg coxae countersunk in ‘procoxal cavities’. The fore-leg coxal cavities closed behind externally; broadly closed; narrowly separated to quite widely separated; slightly transverse, or circular to longer than wide; without lateral extensions; broadly closed internally. The mid-leg coxae countersunk in ‘mesocoxal cavities’; separated by less than the shortest diameter of the cavity, or more than the shortest diameter of the cavity. The mid-leg coxal cavities narrowly separated, or moderately to widely separated; not or scarcely oblique; closed laterally. Hind-leg coxae contiguous or narrowly separated, or widely separated; extending laterally to meet the elytra, or not markedly extended laterally. Tarsal segmentation formula 5, 5, 5. The tarsi without bilobed segments; with a tiny penultimate segment hidden by distal lobing of the fourth and fused to the fifth (pseudotrimerous), or without ‘hidden’ segments. Front tarsi with as many segments as the mid-tarsi; 4-segmented, or 5-segmented. Mid-leg tarsi 4-segmented, or 5-segmented; pentamerous, or pseudotrimeous; the penultimate segment not distinctly shorter than the antepenultimate one. The claws of the mid-leg tarsi not appendaged. The claws of the mid-leg tarsi simple. Hind tarsi with as many segments as the mid-tarsi; 4-segmented, or 5-segmented.

Elytral length/maximum width across the elytra 1.65–2.7. Elytra covering most to all of the abdomen; exposing no more than part of the terminal tergite; non-glabrous. Elytra with six or more longitudinal lines of punctures, or apunctate, irregularly punctate, or each with fewer than 6 longitudinal lines of punctures or impressed striae; the lines per elytron when more than five, 11, or 12 or more. Scutellary striole present. Wings well developed. Wings with an anal lobe. Wings without a medial fleck. Abdominal sternites 5 (the first almost as long as the second and third together); all articulated and moveable, or comprising both fused and moveable components. Basal abdominal sternites immovably joined when present, 2. Abdominal segment 8 with apparently functional spiracles. The male external genitalia bostrichoid.

Adult habitat, ecology. In rotting wood and in dried plant material (in dry herb roots, and in dead wood: associated with felled oaks); eating dried plant material or stored plant products (e.g., dried plant roots), or boring into dead wood.

Larvae. Mature larvae minute (less than 3 mm long), or small to medium-sized. The larvae oblong to ovate; C-shaped in lateral view. Body somewhat flattened to strongly flattened. Vestiture restricted to fine hairs or setae. The larvae dorsally only very lightly pigmented or sclerotized; ventrally only very lightly pigmented. The antennae 3 segmented. Stemmata absent. The frontoclypeal suture between frons and clypeus distinct. The labrum and head capsule separated by a complete suture. Apices of the mandibles with a single lobe or tooth, or bilobed or bidentate. The maxillary palps 3 segmented. The labium without ligula between the palps. Labial palps present and segmented; 1 segmented. Mesothoracic legs present and segmented; 5 segmented; with 1 moveable claw. Visible abdominal segments 10. Tergum 9 of the abdomen entirely dorsal. The abdomen having functional spiracles on anterior segments (these annular); without spiracular tubes. The abdominal apex without a respiratory chamber. Abdominal tergum 8 without amature. The last abdominal segment without cerci.

Larvae in rotting wood and in dried plant material (in dry herb roots, and in dead wood: associated with felled oaks, seemingly avoiding coniferous wood); eating dried plant material or stored plant products and boring into dead wood.

The larvae C-shaped, white, head partly buried in the prothorax, with 3-segmented antennae, the mouthparts directed forwards; the abdomen 10 segmented with the last one small.

Classification. Suborder Polyphaga; Infraorder Bostrichiformia; Superfamily Bostrichoidea.

Representation in Britain and Ireland, and worldwide. About 70 species worldwide; genera 4. 6 species in Britain; genera in Britain 2; Lyctus, Trogoxylon. E.g., L. brunneus, L. fuscus.

General comments. Small, parallel-sided, flattened beetles, the thorax sculptured, with longitudinal costae; notorious woodborers, destructively attacking wood products..

Illustrations. • Lyctus linearis (as canaliculatus) and L. brunneus, with Cisidae etc.: Fowler 4, 119 (1890). • Fowler 4, 119 (1890): original legend.. • Lyctus brunneus, Lyctus linearis.

To view the illustrations with detailed captions, go to the interactive key. This also offers full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, and distributions of character states within any set of taxa.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2003 onwards. Insects of Britain and Ireland: the families of Coleoptera. Version: 16th May 2016.’.