Chrysolina fastuosa (Scopoli, 1763)
Dead-nettle Leaf Beetle
The only member of the morphologically distinct subgenus Fastuolina Warchalowski, 1991, this is a generally common species throughout Europe and east through Asia Minor, Kazakhstan and Siberia to Japan, four regional subspecies are described from southern Europe and many colour varieties have been named; ab. callichloris Bechyne, 1950 is uniformly green, ab. revyi Kaszab, 1962 is entirely cupreus, and ab. inexplicabilis Brancsic, 1910 is uniformly dark violet, the typical form with longitudinal stripes of colour to the elytra is widespread, extending to northern Europe including the UK. Here it occurs throughout the mainland although very sporadically and there has been a decline over recent decades, at least in the south. Typical habitats are river margins, ditches, woodland glades and edges, fens, willow carr and dune slacks where the diurnal adults are easily seen. Host plants include various Lamiaceae; dead nettles (Lamium spp.), hemp nettles (Galeopsis), self-heal (Prunella vulgaris L.), woolly hedge-nettle (Stachys byzantia Koch.), motherwort (Leonunus cardiac L.) and hedge nettle (Stachys palustris L.), and they often occur on common nettles (Urtica). Adults occur year-round but are most prolific from June to September and there is a single generation each year. The beetles emerge during April or May and feed on emergent foliage for a while before mating, they usually strip the leaves along veins or sometimes produce small holes as they feed from the upper surface and mating proceeds through May and into June. Oviposition occurs during July and August; eggs are laid singly or in small numbers on the underside of leaves, usually near the edges where the larvae will begin feeding. Larvae emerge after a week or so and develop rapidly, passing through four instars by September; they feed at night high up on the plant and hide among seed-pods during the day, when fully grown they descend the plant and burrow 3-5cm into the soil and construct a chamber in which they pupate. Adults eclose in the autumn and feed for a while before entering tussocks or moss etc. to overwinter, on the continent both larvae and pupae are known to overwinter and this may also be the case in the UK. Adults become active from April, depending on the year.
This species is distinct among the European fauna and immediately recognized by the form of the apical tarsomere which bears a pair of teeth under the apex. The typical form is very strikingly coloured; bright metallic green, the elytral suture and lateral margins blue and a broad reddish or golden longitudinal band runs through the disc. All appendages metallic-green. 4.8-7.0mm. Head usually metallic green, sometimes red, sparsely and finely punctured and with a well-impressed frontoclypeal suture and large convex eyes. Pronotum strongly transverse and broadest about the middle, finely punctured on the disc, becoming strongly so towards the margins, sub-lateral impressions weak or absent. Elytra with a mixture of fine to strong punctures, randomly arranged but tending towards striae on the disc and generally much finer on the apical third. Across the entire range the beetle varies from completely blue or green to entirely black and many named forms will be found but it is always distinctive on the form of the apical tarsomere.