Curculio betulae (Stephens, 1831)
This species is locally common from the Mediterranean north to the UK and middle provinces of Fennoscandia, it extends east through the entire northern Palaearctic region to the far east of Russia and Japan but is generally absent from southern regions including China and North Africa. In the UK it occurs sporadically across central and southeast England and Wales and there are scattered records from western Ireland; adults may sometimes occur in numbers where found but it is otherwise very local and scarce. Adults occur from June until (exceptionally) October, peaking in abundance during July, but specimens occasionally occur following mild spells in January or February, typical habitats include wet forest margins, carr, peat bogs and drier parts of fens and marshes. In the UK the usual host plant is Birch, Betula pendula Roth, and it is only occasionally found on Alder but through much of northern Europe the usual hosts are Grey Alder, Alnus incana (L.), and Black Alder, A. glutinosa (L.) and it only occasionally occurs on Birch and, much less frequently, adults are sometimes found on willows, Salix L., and various species of Prunus L. including Blackthorn and cherry. Mating occurs early in the season following a period of feeding on host foliage and females lay groups of three or four eggs in developing female catkins. Larvae feed into the summer, passing through three instars and completely hollowing-out the catkins, when fully-grown they leave the catkin, fall to the ground and burrow a few cm into the soil where they construct a pupal chamber; the pupal stage is probably brief as adults are sometimes found during the winter but the majority will remain in situ until the late spring, emerging when the catkins are at the right stage of development for oviposition. Adults are usually found by chance sweeping or beating suitable foliage.
Curculio betulae 1
© Lech Borowiec
Curculio betulae 2
© Mark Gurney
3.0-4.3 mm. Distinguished among our UK species by the form of the scutellum and femora; body pale to dark red or reddish-brown with decumbent yellowish or pale grey scales, pronotum with lateral and medial lines of broader and paler scales, and elytra with patches of pale scales that tend to be confused about the base and form a more-or-less complete transverse band at the apical third, legs pale brown, often yellowish, rostrum and antennae reddish-brown. Head transverse, almost semi-circular from above, with weakly convex eyes that follow the outline and rather long diverging temples, surface evenly convex and without impressions, rostrum long and slender, female antennae inserted behind the middle, male in front of the middle. Antenna; scape abruptly thickened just before the apex, funicular segments elongate and club elongate and narrow. Pronotum transverse, broadest towards the base and narrowed to a weak sub-apical constriction, apical margin weakly curved, basal margin bisinuate and surface evenly convex. Scutellum quadrate or nearly so and clothed with dense pale scales. Elytra broadest just behind the shoulders and narrowed to a continuously curved apical margin, striae narrow and punctured, usually obvious among the scales, and interstices broad and flat. Legs long and robust, all femora broadened about the middle; front femora without a ventral tooth, middle femora with a fine ventral tooth and hind femora strongly toothed. Third tarsomere strongly bilobed, claws free, smooth and with a distinct basal tooth.