Cionus tuberculosus (Scopoli, 1763)

This widespread western Palaearctic species occurs throughout Europe from Spain to Greece and north to the UK and southern provinces of Fennoscandia, it extends east through Asia Minor and Russia into Western Siberia and is present on many of the Mediterranean islands but absent from North Africa, it is generally common throughout this range and across most of Europe it is among the commonest members of the genus. In the UK it is common across England north to Nottingham and in South Wales though generally absent from the West Country and further north although there are older records from southern Scotland. Adults occur from April until October, typically in damp habitats; open deciduous woodland, parkland, grassland, coastal dunes and wetland margins, in the UK the usual hosts are figworts, Scrophularia nodosa L. and S. umbrosa Dumort, 1827, and adults occasionally occur on Buddleja although this may not be a host plant, and on the continent also Limosella aquatica L. (Scrophulariaceae). Mating occurs in the spring after a period of feeding and females chew small but deep holes into the ventral surface of mid-ribs and insert small batches of eggs, the holes are then sealed with abdominal secretions and they wander off to find further sites, this behaviour extends over a month or so and each will produce several hundred eggs. Larvae emerge from early May, they eat through the plant tissue and emerge onto the upper side of the leaf where they will feed, producing small round holes in the leaf at first but as they grow these become larger and merge to form large holes around the veins and petioles, they develop rapidly, passing through three instars and becoming fully grown by early August. Mature larvae spin silken cocoons on the under surface of leaves or under flower buds and pupate within, this stage is brief and adults emerge by cutting a small flap into the base of the cocoon, they immediately begin to feed on the ventral surface of the leaf and soon produce large holes, they may also feed on petioles, stems and seed heads, this continues into the autumn when they enter the soil beneath the host to overwinter. Adults are easily sampled by sweeping or beating suitable host material, they will usually occur in numbers and during the summer the larvae may also be present, they are smooth and dark, resembling tiny slugs as they lack legs and the only obvious detail is the heavily sclerotized head, they may not be recognized as beetle larvae as they secrete a slimy brown mucus which covers the body and deters predators and parasites.