Rhagium inquisitor (Linnaeus, 1758)
POLYPHAGA Emery, 1886
CHRYSOMELOIDEA Latreille, 1802
LEPTURINAE Latreille, 1802
RHAGIINI Kirby, 1837
RHAGIUM Fabricius, 1775
This is the Only Holarctic member of the genus; it occurs North America from New Mexico to the northern boreal forests as the subspecies lineatum (Olivier, 1795) and is represented across the Palaearctic region by at least six subspecies. In many areas of Europe e.g. France, it was formerly restricted to mountainous regions and pine forests in the south but following the general and huge expansion of commercial conifer forests during the twentieth century it is now generally common from the Mediterranean to the north of Fennoscandia and the UK, extending east through central and northern Russia to the far east of Asia. In the UK it is native to the Scottish Highlands where it is widespread and locally common but it has also been recorded sporadically throughout the rest of the mainland from adventive and accidentally introduced specimens, no doubt transported with timber products. The typical habitat is coniferous woodland where it is associated with various trees e.g. larch and Fir and but more especially pine and spruce, it has also been recorded from oak and birch but this may depend on host availability. Adults occur a little later than other members of the genus, from late May or June until August and unlike the others do not visit flowers; mating occurs early in the season and females choose old trees, fallen timber or stumps in which to oviposit, often those infected with fungi, damaged by fire or with the bark damaged and sticky with resin. Larvae emerge after two or three weeks and develop under bark, preferring damp or sticky areas, and do not enter the xylem, they generally develop over two years, rarely extending to three depending on the condition of the bark and the temperature, producing galleries 10-20mm wide and loosely filled with shredded bark, wood and frass. They pupate in a distinctive subcortical cell, about 30mm long and composed of rings of wood fragments and fibres, during late summer or autumn or, very occasionally, in early spring. Adults eclose in the autumn and quickly become fully developed but they remain in the cell until the following spring when they will emerge from the wood en masse. This species attacks and may kill trees weakened by drought or fungi, it usually infests lower parts of the trunk and larvae may occur in large numbers in a single tree. Larvae are active and aggressive, they will bite when handled and when present in high density will control the larvae of other saproxylic species such as Tomicus piniperda (Linnaeus, 1758) or Hylobius abietis (Linnaeus, 1758).
Adults vary in length from 10-21mm; they are mostly black with the anterior margin of the pronotum and numerous irregular areas of the elytra pale; the overall impression of the elytra is a mix of grey and brown areas with two transverse glabrous dark bands, one in the anterior half and one behind the middle. Head with moderately long and weakly convex eyes and short temples (shorter than the eye length) that curve to a wide neck, vertex rather flat; often with a line of pale pubescence but without a longitudinal median groove. Antennae entirely dark with dense short and pale pubescence, relatively short and not, or only just overlapping the elytra at rest. Pronotum transverse, with a strong lateral tooth and curved anterior margin, posterior angles almost perpendicular and the basal margin weakly sinuate. Elytra with broad rounded shoulders and gradually narrowed to a continuously curved apical margin, each with three longitudinal raised keels from the basal third almost to the apex, colour and pattern variable, as above. Legs entirely dark or sometimes with the base of the tibiae variously pale to dark brown. Third segment of all tarsi strongly bilobed.