Pirapion immune (Kirby, 1808)
Following the recent (1990) removal of Protopirapion atratulum (Germar, 1817) from Pirapion the genus now includes only 2 species, both are European but the present species is the more widespread, occurring throughout Europe and extending south to Algeria and north to southern Scandinavia and the UK. The other member, P. kraatzii Wencker, 1859 occurs across southern Europe and northwest Africa. In the UK P. immune is locally common across England, Wales and Southern Scotland; it is likely to occur wherever the host plants are well-established and will generally be found in numbers. Here the usual host is Broom, Cytisus scoparius but also occasionally Gorse, Ulex sp. and on the continent it is recorded from Dyer’s greenweed, Genista tinctoria L. Adults have been recorded from January to September, peaking in early spring and again during August, mating occurs in the spring and eggs are laid in freshly developing stems where the larvae develop causing swellings, these may contain several chambers each containing a developing larvae and measuring up to 60mm long and 5mm wide. Pupation occurs within the stem and lasts for about 10 days; freshly eclosed adults emerge and feed in the summer before overwintering when they become active during mild spells.
A small, 2.0-2.8mm, entirely dark and characteristically-shaped species with the elytra broadly developed behind the middle, steeply declined toward the apex and with the shoulders obsolete. Entire dorsal surface with sparse and fine pale pubescence; head quadrate to transverse, with large convex eyes, densely and quite strongly punctured vertex and frons, and long parallel-sided and subcylindrical rostrum which is longer in the female; about as long as the head and pronotum combined. Antennae entirely dark or with the scape obscurely red towards the base, inserted within the basal third of the rostrum, club elongate-oval with all the segments obvious. Pronotum quadrate, evenly curved laterally and widest about the middle, surface strongly and densely punctured and with a short basal fovea which may be obscured by the punctures. Elytra fused; with deeply impressed and strongly punctured striae that are narrower than the flat or only weakly convex interstices; the sutural stria abbreviated before the apex of the scutellum. Legs long and robust; femora unarmed, basal tarsomere with a small ventral tooth in the male, simple in the female.
Distinguished from the superficially similar Protopirapion atratulum (Germar, 1817), which occurs on the same host, by the short pronotal furrow, the obviously striate frons and coarsely punctured vertex.