Curculio rubidus (Gyllenhal, 1835)
This species has a rather restricted western and central European distribution extending sporadically east into Asia Minor and parts of western Russia and north to the UK and some of the southern Baltic countries, it occurs throughout the region except for alpine areas and is generally common in central areas but otherwise sporadic and scarce. It was recently discovered in the United States from specimens collected in Michigan in 2010, these are not native but from European introductions and the species is now established in the area. In the UK it is widespread though very local and rare across south and central England north to Nottingham though absent from the West Country and there are a very few records further north into Lancashire. Typical habitats are open woodland, commons and heaths with plenty of silver birch (Betula pendula Roth.); the species is generally monophagous on this host although in central Europe adults have been recorded from other birches and from the foliage of various willows (Salix L.) Adults occur from June to September, peaking in abundance early in the season, they reproduce in June and July and females oviposit in male flower buds. Silver birch has both male and female catkins on the same tree, female catkins appear in the spring along with emerging foliage but male catkins develop in the autumn and remain on the tree through the winter to open during April and May; they are longer and thinner than female catkins and so easily identified. Larvae begin to develop from August or September and overwinter in the catkins to finish their development in the spring, they are fully developed by May or June when they drop to the ground and burrow into the soil to pupate in a subterranean cell. The first adults appear in early June and in Europe teneral specimens have been recorded much later. Adults usually occur on the same trees as the developing larvae, they are generally sampled by beating or sweeping host foliage, especially from young trees and even saplings, and while they are very local and rare they may be common where they occur.
Curculio rubidus 1
Curculio rubidus 2
© Lech Borowiec
Curculio rubidus 3
2.8-3.8 mm. Elongate-oval with sloping shoulders that are much wider than the pronotal base, pale to dark reddish-brown, usually with the forebody darker than the elytra, appendages entirely brown, head and pronotum with evenly distributed pale scales, those on the elytra forming a variable pattern but typically rather dense across the base and forming a transverse band across the apical third and along the suture towards the apex. Head with large eyes that follow the outline and short diverging temples, surface finely and quite densely punctured throughout, rostrum long and narrow, the antennal insertions placed behind the middle in the female and at or in front of the middle in the male. Antennae long and slender, scape expanded and globular just before the apex, basal funicular segment long and expanded apically, the rest elongate and the club long and slender. Pronotum transverse, broadest before curved posterior angles and narrowed to a weakly-curved apical margin, surface evenly convex and with scales oriented obliquely from the mid-line. Scutellum quadrate, curved laterally and densely clothed with white or creamy scales. Elytra elongate, broadest behind the shoulders and narrowed to a continuously curved apical margin, with narrow punctured striae that are visible among the scales and broader roughly sculptured interstices. Legs long and robust; all femora smooth ventrally – this lack of ventral teeth will distinguish rubidus from our other species – and all tarsi with a strongly expanded third segment.