Insects of Britain and Ireland: the families of Coleoptera

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L. Watson and M. J. Dallwitz


Including Dacnidae, excluding Languriidae.

Pleasing Fungus-beetles.

General appearance. 2.5–7 mm long. Body length/maximum body width 1.15–2.87. Elytral length/pronotal length 2–5.75. Base of prothorax not or scarcely narrower than the combined elytral bases. Greatest prothoracic width not narrower or only slightly narrower than the greatest elytral width. Beetles oval to elongate; convex beneath; not necked; not waisted to somewhat waisted; often with a bright yellow and black pattern, or metallic colour; exhibiting bright ‘warning colours’, or without ‘warning colouration’. Upper surfaces of body glabrous or subglabrous, or non-glabrous; exhibiting stiff, erect, dark bristles, or not bristly; with neither scales nor scale-like setae.

Detailed morphology. Beetles without a rostrum; prognathous. Inclination of the head slight. Eyes strongly protuberant, or not strongly protuberant; not accommodating the antennae in a notch; bristly, or without bristles. The labrum at least partly visible in antero-dorsal view; labrum mostly moderately to heavily sclerotized. Mandibles with a well developed mola; with well developed prosthecae, or without prosthecae. The mandibular apices 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, or somewhat expanded and truncate to subtriangular. The apical segment of the labial palps more or less expanded apically, or not expanded apically. Antennae short; 11 segmented. Antennal scape not swollen. Antennae clubbed. Antennal clubs 3 segmented (flattened). Antennal insertions visible from above, or hidden from above; not in fossae.

Cervical sclerites present. Prothorax shorter than wide. Pronotal length/maximum pronotal width 0.25–0.97. The pronotum with lateral keels (pronotal carinae); keels complete. Prothorax at its widest not markedly narrower than the adjoining part of the abdomen. Prothorax without notopleural sutures. Scutellum conspicuous, or highly reduced; when applicable, elevated above the mesoscutum in lateral view, or not elevated; anteriorly simple; posteriorly broadly rounded or obtusely angulate. The prosternal process present; complete; slightly overlapping the mesoventrite, or moderately or strongly overlapping the mesoventrite. Metaventrite without a transverse groove. The fore-leg coxae countersunk in ‘procoxal cavities’. The fore-leg coxal cavities closed behind externally; narrowly closed, or broadly closed; quite widely separated; slightly transverse, or circular to longer than wide; without lateral extensions; internally open. 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 moderately to widely separated; not or scarcely oblique; closed laterally. Hind-leg coxae contiguous or narrowly separated (Dacne), or widely separated; not markedly extended laterally; not shaped posteriorly to receive the femur. Tarsal segmentation formula 5, 5, 5, or 4, 4, 4. The tarsi exhibiting bilobed segments; with a tiny penultimate segment hidden by distal lobing of the fourth and fused to the fifth, or without ‘hidden’ segments (but the fourth segment usually small). Front tarsi with as many segments as the mid-tarsi; 5-segmented. Mid-leg tarsi 5-segmented; pentamerous, or pseudotetramerous; the penultimate segment not distinctly shorter than the antepenultimate one (Dacne), or distinctly shorter than the antepenultimate one. The claws of the mid-leg tarsi not appendaged. The claws of the mid-leg tarsi simple; without an associated empodium. Hind tarsi with as many segments as the mid-tarsi, or with one segment fewer than the mid-tarsi; 4-segmented, or 5-segmented.

Elytral length/maximum width across the elytra 1–2.2. Elytra covering most to all of the abdomen; exposing no more than part of the terminal tergite; non-glabrous, or 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, 6–7, or 8 to 10. Scutellary striole present (Dacne), or absent. Elytra with epipleura. Elytral epipleura reaching to the tips of the elytra. Wings well developed, or absent or much reduced. Wings with an anal lobe, or without an anal lobe. Wings with a medial fleck; the medial fleck not bisected by a vein. Abdominal sternites 5; all articulated and moveable, or comprising both fused and moveable components. Basal abdominal sternites immovably joined when present, 2. Abdominal segment 8 apparently without functional spiracles. The male external genitalia cucujiform.

Adult habitat, ecology. Under bark and associated with fungi (often associated with agaric fruiting bodies on trees); mycetophagous.

Larvae. Mature larvae minute (less than 3 mm long), or small to medium-sized. The larvae elongate and more or less parallel-sided. Body circular in cross-section, or somewhat flattened. Vestiture restricted to fine hairs or setae. The larvae dorsally heavily pigmented or sclerotized, or dorsally only very lightly pigmented or sclerotized; ventrally only very lightly pigmented. The antennae 3 segmented. Stemmata present; on either side of the larval head 5, or 6. The frontoclypeal suture between frons and clypeus indistinct or absent. The labrum and head capsule separated by a complete suture. Apices of the mandibles bilobed or bidentate, or trilobed or tridentate. The maxillary palps 3 segmented. The labium with a short ligula between the palps. Labial palps present and segmented; 2 segmented. Mesothoracic legs present and segmented; 5 segmented; with 1 moveable claw. Visible abdominal segments 10. Tergum 9 of the abdomen extending to the underside. The abdomen having functional spiracles on anterior segments (annularbiforous); with anterior and 8th-segmental spiracles borne at the ends of a series of spiracular tubes, or without spiracular tubes. The abdominal apex without a respiratory chamber. Abdominal tergum 8 without amature. The last abdominal segment with cerci.

Larvae under bark and associated with fungi (on trees); mycetophagous (on fleshy fungi).

The larvae subcylindric, whitish to pale brown, with well developed legs and segmental sclerites bearing spines; head hypognathous with 5 or 6 pairs of ocelli and long, 3-segmented antennae.

Classification. Suborder Polyphaga; Superfamily Cucujoidea.

Representation in Britain and Ireland, and worldwide. Genera at least 100. 7 species in Britain; genera in Britain 3; Dacne, Triplax, Tritoma. E.g., Tritoma bipustulata.

General comments. Ovoid or elongate beetles associated with fungi, the tibiae flattened and expanded.

Illustrations. • Triplax aenea: B. Ent. 706. • Triplax aenea: B. Ent. 706, legend+text. • Triplax aenea: B. Ent. 706, text cont.. • Tritoma bipustulata (Double-spotted Tritoma: B. Ent. 498). • Tritoma bipustulata (details, B. Ent. 498). • Tritoma bipustula: B. Ent. 498, legend+text. • Tritoma bipustula: B. Ent. 498, text cont.. • Tritoma bipustulata (Rye & Fowler XV4). • Dacne bipustulata and D. rufifrons, with Coccinellidae and Endomychidae: Fowler 3, 83 (1889). • Fowler 3, 83 (1889): original legend.. • Triplax aenea, T. russica,, and Tritoma bipustulata (with Colydiidae): Fowler 3, 84 (1889). • Fowler 3, 84 (1889): original legend.. • Triplax lacordairii and T. scutellaris, with unrelated taxa: Fowler Suppl. 12, 1913. • Fowler Suppl. 12, 1913: original legend..

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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.’.