Galerucella lineola (Fabricius, 1781)

Generally common and often abundant, this species occurs across the entire Palaearctic region, from Europe through Russia and Asia Minor to Kazakhstan, Siberia, Mongolia, China and Japan, it is widespread in Algeria and Morocco and is also known from Iran. The European distribution extends from Portugal and Spain to Greece and Ukraine in the south and north to the Arctic Circle; it is yet to be reported from some parts of the Balkan Peninsula and the eastern Baltic region but the distribution is probably continuous throughout. The nominate subspecies occurs throughout while in Italy it is sympatric with ssp. solarii Burlini, 1942. In the UK it is common throughout England and Wales and the north of Ireland, including all the islands, and much more local and scattered further north to the Scottish Highlands and in the south of Ireland where it seems to be mostly coastal or near-coastal. The species is generally confined to lowlands and typical habitats are wetlands and permanently damp grassland e.g. alder and willow carr, floodplains, fens, marshes, and margins of ponds, lakes and rivers etc., but it occurs on a range of broadleaf trees and may also occur in drier areas where the hosts are common; moorland, calcareous grassland, coastal pasture and dune slacks. This is the only UK member of the genus associated with trees, and while adults sometimes occur on various herbaceous plants during spring and early summer, these are not considered to hosts. A wide range of host trees may be found in the literature, including some unlikely species such as False Acacia (Robinia pseudoacacia L.), but the usual hosts include various willows (Salix L.) and alders (Alnus Mill.), while adults often occur on Black Poplar (Populus nigra L.) and Silver Birch (Betula pendula Roth.) Adults occur year-round, they overwinter under bark, in dead umbel (Apiaceae) or willow herb (Epilobium L.) stems or in grass and sedge tussocks and are active over a long season from early spring until the autumn, peaking in abundance during May and June. Adults mate after a period of feeding when they nibble small holes in host foliage, these may become extensive and damage areas of leaves and, at least in Europe, the species is sometimes considered harmful to commercially grown saplings. Oviposition begins in early June and continues until late in July; eggs are laid in small batches on the underside of leaves and larvae emerge after a week or so. Larvae feed on lower epidermis, they pass through three instars and are fully developed within three or four weeks, at which time they fall to the ground and pupate in a subterranean cell. Larvae may be found until late August but new-generation adults appear from July until late in September, overlapping with the overwintered adults which persist into the summer. These new generation adults will not become sexually mature until they have overwintered and fed in the spring and so the two generations are unlikely to breed. Adults fly well and disperse between feeding sites during the spring but they have been found in flight-interception traps through the summer and so might suddenly appear in well-worked sites, they are easily sampled by sweeping or beating host foliage and they usually appear in numbers.