Insects of Britain and Ireland: the families of Coleoptera

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L. Watson and M. J. Dallwitz


= Monotomidae (Rhizophaginae and Monotominae).

General appearance. 1.5–6 mm long. Body length/maximum body width 3–3.4. Elytral length/pronotal length 2.1–2.35. Base of prothorax distinctly narrower than the combined elytral bases. Greatest prothoracic width not narrower or only slightly narrower than the greatest elytral width. Beetles elongate; conspicuously necked to not necked; conspicuously waisted; decidedly short-legged. Upper surfaces of body glabrous or subglabrous; not bristly; with neither scales nor scale-like setae.

Detailed morphology. Beetles prognathous (and the heads of males sharply constricted behind the eyes). Inclination of the head slight. Eyes strongly protuberant; finely facetted, or coarsely facetted. The labrum at least partly visible in antero-dorsal view, or concealed beneath the clypeus; labrum mostly moderately to heavily sclerotized, or mostly membranous or only very lightly sclerotized (some Rhizophaginae). Mandibles with a well developed mola; with well developed 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 very short to short; 10 segmented. Antennal scape not swollen. Antennae clubbed. Antennal clubs 2 segmented (tight, spherical). Antennal insertions hidden from above; not in fossae.

Cervical sclerites present, or absent (some Monotominae). Prothorax shorter than wide to about as long as wide. Pronotal length/maximum pronotal width 1–1.07. The pronotum with lateral keels (pronotal carinae), or without lateral keels (some Monotominae); keels when present, complete. Prothorax at its widest not markedly narrower than the adjoining part of the abdomen. Prothorax without notopleural sutures. Scutellum conspicuous, or highly reduced (some Monotominae); when applicable, not elevated; anteriorly simple; posteriorly narrowly rounded or acute, or broadly rounded or obtusely angulate. 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; quite widely separated; strongly transverse (Rhizophaginae), or circular to longer than wide; without lateral extensions; internally open, or internally closed by a slender bar. 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; open laterally. Hind-leg coxae contiguous or narrowly separated, or widely separated; not markedly extended laterally; not shaped posteriorly to receive the femur. Tarsal segmentation formula 5, 5, 5, or 5, 5, 4. The tarsi without bilobed segments; without ‘hidden’ segments (the penultimate segment small, the basal two broad with long setae). Front tarsi with as many segments as the mid-tarsi; 4-segmented (males), or 5-segmented (females). Mid-leg tarsi 4-segmented (males), or 5-segmented (females); pentamerous, or pseudotetramerous, or tetramerous; the penultimate segment not distinctly shorter than the antepenultimate one, or distinctly shorter than the antepenultimate one (some Monotominae). The claws of the mid-leg tarsi not appendaged. The claws of the mid-leg tarsi simple; with an empodium between them (this with no more than two setae). Hind tarsi with as many segments as the mid-tarsi, or with one segment fewer than the mid-tarsi; 4-segmented (males), or 5-segmented (females).

Elytral length/maximum width across the elytra 2–2.25. Elytra meeting along the length of the mid-line; covering most to all of the abdomen; exposing no more than part of the terminal tergite to at least one but fewer than three complete abdominal tergites; truncate; glabrous; punctate- striate. Elytra with six or more longitudinal lines of punctures, or with six or more impressed striae, 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 11. Scutellary striole absent. Elytra with epipleura. Elytral epipleura falling short of the elytral tips. Wings well developed. Wings without an anal lobe. Wings with a medial fleck, or without a medial fleck; the medial fleck if present, not bisected by a vein. Abdominal sternites 5; all articulated and moveable. Abdominal segment 8 apparently without functional spiracles. The male external genitalia cucujiform.

Adult habitat, ecology. Not predacious (perhaps not exclusively?); mainly in rotting wood and under bark; consuming decaying plant material, or consuming rotting wood, or mycetophagous (primarily saprophagous and fungivorous?).

Larvae. Mature larvae minute (less than 3 mm long), or small to medium-sized. The larvae elongate and more or less parallel-sided. Body somewhat 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 present; on either side of the larval head 4. 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. 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 (these nnular-biforous); without spiracular tubes. The abdominal apex without a respiratory chamber. Abdominal tergum 8 without amature. The last abdominal segment with cerci.

Larvae not predacious (exclusively?); in decaying plant material, in rotting wood, under bark, and associated with fungi (Rhizophagus often inhabiting the galleries of bark beetles, Monotominae often in grass piles and compost heaps or within ascomycete fruit bodies); consuming decaying plant material and mycetophagous.

Classification. Suborder Polyphaga; Superfamily Cucujoidea.

Representation in Britain and Ireland, and worldwide. About 220 species worldwide; genera about 20 (?). 21 species in Britain; genera in Britain 3; Cyanostolus, Monotoma, Rhizophagus. E.g., Rhizophagus bipustulatus.

Illustrations. • Rhizophagus bipustulatus: B. Ent. 579. • Rhizophagus bipustulatus: B. Ent. 579, legend+text. • Rhizophagus bipustulatus: B. Ent. 579, text cont.. • Rhizophagus (4 spp.) and Monotoma (3 spp.), with Trogossitidae, Merophysiidae, etc.: Fowler 3, 91 (1889). • Fowler 3, 91 (1889): original legend.. • Cyanostolus aeneus and Rhizophagus oblongocollis, with unrelated taxa: Fowler Suppl. 13, 1913. • Fowler Suppl. 13, 1913: original legend.. • Rhizophagus bipustulatus (Janson 136).

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.’.