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Pentarthrum huttoni Wollaston, 1854







POLYPHAGA Emery, 1886

CURCULIONOIDEA Latreille, 1802

CURCULIONIDAE Latreille, 1802

COSSONINAE Schönherr, 1825

PENTARTHRINI Lacordaire, 1865

PENTARTHRUM Wollaston, 1854

Thought to have spread by trade from South America this tiny wood-boring weevil now occurs across Europe and North America; although specimens have been found among dead timber in the wild the species is generally synanthropic and associated with decaying timber in old buildings, its occurrence is sporadic and it is generally very local and scarce throughout its Western Palaearctic range e.g. it was first recorded from Poland in 2001 and was then absent until a second specimen was recorded in 2018, and the first Austrian record was from 2006. In the north it extends to the Netherlands and the UK where it is probably exclusively synanthropic, here it is has been recorded widely from southern and central England and Wales, it occurs among damp fungoid timber in houses and sheds etc and there may be an association with the Cellar fungus, Coniophora puteana (Shum,: Fr) P.Karst although this may simply be the most prolific species in conditions preferred by the beetle. Adults occur year-round and the first sign of their presence may be dead specimens below widow frames as they are attracted to light when dispersing but in general they remain near the host material and under the right conditions may be continuously breeding. About a week after mating females deposit single eggs in damp crevices or they may resort to gnawing holes in smooth surfaces into which they can leave an egg, they need very humid conditions and will not oviposit in dry timber, typical of the family they are not very fecund and each will lay about 30 eggs over a three month period.  Larvae emerge after two or three weeks and begin to bore into the host timber, they generally tunnel parallel to the surface but may produce random tunnels as they follow moisture gradients in the wood, they are capable of digesting cellulose and hemicelluloses but lignin is present in their frass suggesting that they develop on the products of fungal decay in the host, they pass through five instars and are fully-grown after six to eight months. Fully grown larvae are about 3.5mm long and a 1mm wide, they are legless, strongly convex and covered in dense pubescence and fine setae, they construct a pupal chamber lined with fungal hyphae just below the wood surface and the pupal stage lasts between two and three weeks. Adults cut small irregular exit holes between 1.5 and 2.0mm wide and mate and disperse soon after emergence.

Pentarthrum huttoni

Pentarthrum huttoni

© Lech Borowiec

Adults are small, 2.9-4.0mm, elongate and weakly convex species identified by the combination of 5-segmented antennal funiculus, characteristically shaped pronotum and distinctly bilobed third tarsomere; they differ from the very common Euophryum in lacking the raised keel near the apical elytral margin. Glabrous and shiny reddish-brown or with the head and pronotum darker. Head transverse with convex and prominent eyes, vertex convex and sparsely punctured, frons flat and densely punctured, rostrum broad, elongate, near-parallel sided and almost cylindrical. Antennae short, inserted just behind the middle of the rostrum, scape about as long as the head across the eyes, gradually thickened in the distal half, funicular segments progressively more transverse to a compact and oval club. Pronotum elongate, widely rounded in front of obtuse posterior angles and broadest about one third from the base, them straight and narrowed to a sub-apical constriction, basal margin straight and finely bordered, surface strongly and quite densely punctured, the punctures discrete throughout. Elytra with distinct shoulders, parallel-sided and constricted before separately rounded apical margins. Striae regularly and strongly punctured to the apex although this may be obscured by the convex interstices which merge randomly across the striae. Legs long and robust, femora almost fully visible from above (an effect produced by the very widely separated coxae), middle and hind tibiae sinuate and expanded apically into a broad and blunt external tooth, fore tibiae narrower, parallel-sided and produced externally into a curved hook-like tooth at the apex. Tarsi 5-segmented, the basal two segments short, the third quite strongly bilobed and enclosing most of the tiny fourth segment, the terminal segment long and gradually thickened to the apex, claws smooth and not fused at the base. Males differ from females in having a broader, more strongly punctured rostrum and having the antennae inserted slightly further from the base.

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