Aulonium Erichson, 1845
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POLYPHAGA Emery, 1886
TENEBRIONOIDEA Latreille, 1802
COLYDIINAE Billberg, 1820
COLYDIINI Billberg, 1820
T. ruficorne (Olivier, 1790)
T. trisulcus (Geoffroy in Fourcroy, 1785)
This is a small genus of about 40 species, most of which occur in the New World; 5 have been recorded in the United States, about 25 from Central and South America, and a further 3 are known from the Palaearctic region. They are elongate, near parallel-sided and rather depressed beetles of a very characteristic appearance; all are small, <10mm, drab coloured beetles; black to light or dark brown or variously bicoloured, glabrous and somewhat shiny. Within the family they might be mistaken for Colydium but here the striae are raised over the elytral declivity and there are 2 groups of long setae on the apical margin of the terminal abdominal ventrite. In any case, within the limited European fauna, all species of both genera are distinctive and will soon be recognized with a little experience. The following description represents the genus as a whole. Head quadrate to transverse with large, weakly convex eyes and short temples; vertex generally convex and smooth although some species are sexually dimorphic with males having one or two strong tubercles, clypeus expanded laterally to form a canthus over the antennal insertions, and weakly produced forward to a rounded, truncate or emarginate anterior margin. Vertex sometimes obliquely depressed in front of the eyes but without a distinct frontoclypeal suture, the surface generally microsculptured and relatively strongly punctured. The eyes are oval, emarginate anteriorly and coarsely faceted. Antennae 11-segmented with an abrupt 3-segmented club, palps short with the terminal segment pointed. Pronotum almost quadrate to distinctly elongate, usually almost parallel but in some Neotropical species widest anteriorly and tapering to the base, the surface usually with median and/or sub-lateral or lateral carinae or grooves which tend to be distinct for each species, all margins strongly bordered, the anterior margin sometimes with sub-lateral tubercles which may be dimorphic. Anterior angles perpendicular or projecting, posterior angles perpendicular or nearly so, and the basal margin usually weakly sinuate. Prosternum long in front of round or oval pro-coxae which are narrowly closed behind, the process broad and raised, sometimes strongly so, and rounded apically. The meso-coxae are oval
and separated by less than a coxal width, the meta-coxae transverse and reaching the elytral epipleura. Abdomen with 5 free ventrites; the basal segment long and lacking post-coxal lines. Elytra completely covering the abdomen and rounded apically, the striae punctured , distinct and usually complete to the apex, the interstices flat to weakly convex, never raised or carinate, microsculptured and finely punctured. The legs are robust and relatively short; the tibiae sinuate externally and gradually broadened to the apex, the meso- and meta- tibiae usually with stiff spines along the lateral margins, and all with a short and stout spur on the inner apical angle. Tarsi 4-4-4; without bilobed segments.
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All species are saproxylic, occurring and developing under bark or among decaying heartwood of various coniferous and hardwood trees. Larvae of some species occur in scolytid galleries and are known to be predators e.g. in the United States those of A. ferrugineum Zimmermann, 1869, are known to predate the eggs and larvae of The Southern Pine Beetle, Dendroctonus frontalis Zimmermann, 1868, but it is thought that many species are primarily fungivores and only facultative predators. Of the European species, A. sulcicolle Wollaston, 1864 is a Canary Islands endemic, A. trisulcus (Geoffroy in Fourcroy, 1785) is widespread extending to Iran in the south and The U.K. in the north, and A. ruficorne (Olivier, 1790) occurs throughout, extending to Scandinavia and Ukraine; it has been recorded in the U.K. but its modern status is unknown.
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The 2 species included on the U.K. list are readily identified as follows:
Body uniformly pale to dark brown. Frons smooth; without any swellings. Central furrows on the pronotum parallel in the anterior half then diverging behind the middle. Punctures in the elytral striae much stronger.
A. trisulcus (Geoffroy in Fourcroy, 1785)
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Body dark brown to black with the anterior clypeal margin and the basal two-thirds of the elytra pale. Frons with tuberculate swellings. Central furrows on the pronotum parallel from the base to the middle then diverging in the apical third. Punctures in the elytral striae much finer.
A. ruficorne (Olivier, 1790)
Aulonium trisulcus (Geoffroy in Fourcroy, 1785)
This is a widely distributed though very local and generally scarce species occurring throughout northern and western Europe, extending east to western Russia and south through Greece to northern Iran. In the U.K. it is local in central southern England extending north to Leicestershire and west to Gloucester; it was first recorded near London (Enfield) in 1904, probably from adventives imported with elm (etc.) logs from the continent, and during the 20th century its abundance seems to have fluctuated in line with outbreaks of Dutch elm disease, and following the devastating spread during the 1970’s it has remained local throughout its range. The typical habitat is woodland and wooded parkland and gardens etc., the species is saproxylic and both adults and larvae occur under the bark of a range of broadleaved trees e.g. we have recorded adults under damaged lilac bark in a Watford town centre garden, but especially elms (Ulmus procera and U. glabra). It has sometimes been considered a specialist predator of elm bark beetles but it is more likely a facultative predator, attracted to the conditions generated by the feeding scolytid larvae; they commonly occur in galleries under elm bark produced by Scolytus multistriatus (Marsham, 1802), the European elm-bark beetle, and S. scolytus (Fabricius, 1775), the Large European elm-bark beetle, but also with other species e.g. Hylesinus varius (Fabricius, 1775) under Fraxinus bark, and they also occur in cambium where these galleries are absent. Adults remain under loose bark or in crevices during the day and become active on the surface at night, they can run fast and they fly well, being strongly attracted to m.v. light, they occur from April until September but are most abundant in the spring. Larvae have been recorded from January to September, and pupae, which also occur in scolytid galleries, from April until July.
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A very distinctive species; among the U.K. fauna only Colydium is similar. In the field it might casually be mistaken for Rhizophagus but is very different in detail. 4.5-7mm. Elongate, parallel and rather flattened, entirely dull testaceous or, often, with the head a little darker. Head densely punctured and finely reticulate, the clypeus produced in front of the eyes, expanded over the antennal insertions, densely pubescent and emarginate anteriorly. Antennae inserted laterally, in front of the eyes; 11-segmented with a 3-segmented club. Pronotum subquadrate, the surface finely and diffusely punctured, and all the margins strongly bordered. Longitudinal furrows distinct; the median furrow diverging from the centre to the base, and the sub-lateral furrows parallel. Scutellum transverse with curved edges. The elytra completely cover the abdomen, each with 9 complete and punctured striae, an abbreviated scutellary striole and a deeply impressed but impunctate stria reaching from below the humerus almost to the apex. Apices rounded. Tarsi 4-4-4; the terminal tarsomere as long, or nearly as long, as the others combined. Claws long and curved; smooth internally and weakly toothed at the base.
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Aulonium ruficorne (Olivier, 1790)
Aulonium ruficorne is included on the British list on the strength of specimens found in Gloucestershire in the 1920’s under the bark of pine logs imported from the continent. It is considered as a doubtfully established introduction.