Donacia semicuprea Panzer, 1796
This is a very local though often abundant species occurring across central and southern England north to Yorkshire and west to Somerset with only occasional records further west and from South Wales. The European distribution extends from France eastwards to the Balkans and north to Southern Scandinavia and Western Russia. The adults may be found on a range of marginal plants but in the U.K. the host is usually reed sweet-grass, Glycera maxima, or sometimes plicate sweet-grass, G. notata, and although localized by the food-plant they are usually common. Typical habitats are beside open and shallow, still or slow-moving water where the host forms extensive growths; canals, reservoirs, gravel-pits and lakes etc. They appear early in the year, late March or April, and by mid-May are abundant and obvious on the host; they feed on the upper surface of the leaves, stripping the epidermis and leaving characteristic wrinkled and translucent strips parallel to the central rib, and during wet or overcast conditions when they are inactive, they are the easiest way to detect the presence of the species. They are active in warm weather and easily seen among the foliage; they fly well and are easily sampled by sweeping. The females lay small batches of 20 to 30 eggs on the inner surface of submerged leaves from May to August, and the larvae have been recorded feeding within the roots of the host from mid-June; they may take 2 seasons to fully develop as the life cycle is thought to take 3 years to complete. Pupae have been recorded in cocoons during September and October and the adults probably eclose at this time and overwinter within the cocoons.
6-9mm. overall metallic bronze with green overtones; when viewed from above the elytra appear green laterally. Head, scutellum and underside with fine grey pubescence; body otherwise glabrous, or nearly so. Head finely and densely punctured, generally more sparsely so over the vertex, with a well-defined longitudinal impression on the vertex, frons convex and smooth; without a furrow beside the eyes. Antennae usually entirely dark. Pronotum quadrate with strong and dense punctation which is generally not confluent; the cuticle smooth and shiny. The median longitudinal groove joining a strong basal and a weaker apical fovea is unique to this species, at least among the U.K. fauna. Elytra with prominent shoulders, broadest near the middle and obliquely truncate apically, with the first interstice nearly as broad as the second. Surface rather convex with any impressions shallow and indistinct, the striae are narrower than the interstices which are shagreened and transversely wrinkled. Elytral suture simple to the apex, c.f. Plateumaris. Legs dark metallic, the base of the femora pale although this is not always visible from above, and the tibiae may be lighter at the base, the mid- and hind tibiae sometimes extensively so. Hind femora not toothed, and the hind tibiae smooth along the ventral edge. In the female the elytra are generally broader.
Donacia semicuprea 1
Donacia semicuprea 2
Donacia semicuprea 3