Aphthona nonstriata (Goeze, 1777)
This is a widespread and generally common species occurring throughout Europe and Asia Minor, much of the Middle East and extending east through Ukraine and Kazakhstan to central Asia and China. Here it is common and often abundant throughout England and Wales, becoming scattered further north and scarce in Scotland although there are plenty of records from the west and Western Isles. Habitats include anywhere the host, Iris pseudacorus (yellow iris), grows in abundance, basically wetlands but also permanently damp soil in woodlands, parks, gardens, wasteland, dunes and shingle beds etc. Adults occur year-round, overwintering among leaf-litter, moss and tussocks etc. and becoming active early in the year; during mild days in the winter but more generally from March or April, peaking in abundance from May to July and remaining common into the autumn. Overwintered adults feed in the spring, consuming strips of epidermis parallel to the leaf margins and leaving conspicuous pale lines, before mating and ovipositing on the host foliage. These adults will survive into the summer and appear alongside the new generation leading to very large local populations in the summer. Larvae appear from late May and live within the leaves, mining long tunnels towards the leaf tips and leaving characteristic pale marks; they are fully grown within a month and enter the soil to pupate in an earthen cell. New generation adults appear from July to September or October and in the UK the species is univoltine. Adults are usually obvious on the food-plant and are easily swept or picked-off; they also occur in flight interception and Malaise traps and in wetlands are often the most common chrysomelid.
At 2.5-3.0mm this is the largest member of the genus and this large size coupled with the darkened anterior and intermediate femora (in UK specimens) is usually sufficient to identify the species; specimens taken from the host will provide comparative material. Elongate-oval, females are generally broader and have more rounded elytra, and entirely dark blue or green, sometimes with a weak bronze reflection. Vertex of head convex and finely punctured, with distinct transverse convexities behind the antennae, anteriorly smooth and unpunctured, eyes large and convex, Antennae 11-segmented and pale, becoming dark beyond the base. Pronotum smooth and shiny, without basal impressions or with only indistinct fovea and gently curved laterally, anterior margin slightly broader than the posterior margin and the anterior angles expanded laterally. Scutellum and underside black. Elytra randomly punctured, with convex and distinct humeral angles. Legs yellow with the hind femora black and the anterior and intermediate femora and all tarsi variously darkened. Metatibiae with a long groove on the dorsal surface towards the apex, a smooth outer margin and a single spur at the inner apical angle. Basal metatarsomere shorter than half the length of the tibia. Claws smooth and with an obtuse tooth towards the base.