Sphaeroderma testaceum (Fabricius, 1775)
This widespread and generally common western Palaearctic species occurs throughout Europe, except for the extreme west, it extends north into the UK and southern Fennoscandia and east into Russia, Ukraine and Azerbaijan, it is also present on many Mediterranean islands, it extends south to Tunisia and Israel and, following accidental introductions has become established western Canada. Here it is widespread and common throughout England and Wales, widespread but very local and mostly coastal in Ireland, and sporadic and rare in Scotland. Host plants include a range of Asteraceae, mostly various thistles (species of Carduus L, Carlina L, Cirsium Mill, Onopordum Vaill. Ex L. and Cynara L.) but also occasionally knapweed (Centaurea nigra L.) and it can be a nuisance, if not a pest, of commercially-grown artichokes. Typical habitats include grassland, arable land, verges, wooded borders and hedgerow margins etc, wherever the host has become established, the adults fly well and may quickly arrive at new sites or in gardens and they may be especially common on disturbed land. Adults occur throughout the year, at least some overwinter in tussocks or litter etc. and become active early in the spring, they are generally abundant from June until September and may be found into November. Reproduction occurs in early summer and oviposition continues from July until October or November, several eggs are laid beneath both fresh and mature leaves, generally away from large veins and usually several to a leaf, and larvae emerge within two weeks. Fresh larvae immediately bore into the leaf and begin to mine, they produce a long curved mine, often following the edge of the leaf, containing very little frass and with the margins unevenly eaten out so that in places it has a blunt saw-tooth appearance, often several mines will run parallel near the edge and sometimes they form irregular loops. Larvae pass through three instars and are present in various stages of development during the autumn but all will go on to overwinter and it is likely that a winter diapause is necessary before pupation can occur, younger larvae will continue to develop in the spring and pupation occurs from March until July, the first new-generation adults appear from May and it is probably some of those that eclose late that will go on to overwinter. Sampling is straightforward, host material may be swept and adults occur in flight-interception traps etc, but a certain degree of dexterity will be needed as they hop readily when alarmed and seem to vanish, sweeping in cool weather or at night will overcome this. Both adults and larvae may be detected by their feeding signs; larval galleries will soon become familiar in thistle leaves, and adults produce numerous small holes in the foliage as they feed.
Sphaeroderma testaceum 1
Sphaeroderma testaceum 2
Sphaeroderma testaceum 3
2.5-4.2mm. Elongate-oval and very convex, slightly discontinuous in outline with the base of the pronotum narrower than the base of the elytra, entirely orange with only the eyes darker. Head transverse and very finely punctured, usually substantially concealed from above, eyes large and convex, antennae 11-segmented and inserted in front of the eyes, separated by about the length of the basal segment, all segments narrow and elongate. Pronotum transverse, broadest at the base and narrowed to a rounded anterior margin, surface coarsely punctured, especially towards the base, otherwise smoothly convex, without basal fovea or furrows. Elytra broadest in front of the middle, with sloping shoulders and a continuously-rounded apical margin, surface randomly and moderately coarsely punctured. Legs long and robust with femora visible in normal setting, hind femora much larger than the middle femora. Tibiae weakly broadened to an obliquely-truncate apex, slightly sinuate and produced apically to a blunt external tooth, each with a small spur and a series of short, stiff setae about the external apical angle. Tarsi pseudotetramerous, the third segment widely bilobed, male with the basal pro-tarsomere dilated.