Aclypea Reitter, 1884
POLYPHAGA Emery, 1886
CUCUJOIDEA Latreille, 1802
SILPHINAE Latreille, 1806
A. opaca (Linnaeus, 1758)
A. undata (Müller, O.F., 1776)
Aclypea is a small Holarctic genus with two species in North America and twelve in the Palaearctic region, only one species, A. opaca, is Holarctic and the European fauna includes four species of which the two most widespread extend to the UK. In appearance they are typical of the Silphinae; medium sized, broadly-oblong and flattened, dark coloured with the forebody smooth and densely punctured and the elytra variously sculptured, all have the clypeus deeply emarginate and the temples parallel or outwardly-curved (although they are usually retracted into the prothorax in set specimens) and not constricted towards the base and so there is no distinct neck. Among our UK fauna they are superficially similar to species of Thanatophilus Leach, 1815 but here the temples are strongly constricted behind the eyes and so the base of the head forms a distinct neck. All species are phytophagous and polyphagous and a few are occasionally serious agricultural pests, the general life cycle is outlined below. They arereadily distinguished as follows:
-Dorsal surface of the elytra pubescent.
-Dorsal surface glabrous or virtually so.
A Holarctic species although only sparsely distributed in the Nearctic region, the main centre of its distribution is the western Palaearctic. In the U.K. there are records scattered through England, Wales and Scotland including the Western Isles. As with other species of the genus it is phytophagous, feeding on various Gramineae and Brassicaceae, preferring various Amaranthaceae (Chenopodioideae), and has at various times been a serious pest of beet crops on the continent. Adults occur from early spring and the typical habitats are meadows, wasteland and arable land where the adults, although mainly nocturnal, may be seen walking during the warmer months. Adults overwinter among tussocks and litter etc. on field margins and emerge in the spring when their food source is germinating. Females lay batches of eggs in the soil at a depth of seven or eight cm around the base of host plants and larvae emerge within a week or so, the egg laying period extends into the summer and so larvae in all stages of development may be present in a crop and large populations of adults may build up. Eggs are very sensitive to soil humidity and die off in dry soil and so outbreaks tend to occur in years with a moderately dry spring and damp summer. Fresh larvae emerge from the soil and feed on low foliage, they often remain on the soil surface and consume any hanging leaves but as they grow they feed voraciously and ascend the stems to access fresh foliage and it is older, almost fully-grown larvae that do most damage, they develop very rapidly, passing through three instars, and are fully developed within two to three weeks. At this stage descend the stems and move into the soil to pupate in a cell at a depth of one to five cm. Adults eclose between ten and fifteen days later, and after a period of hardening and pigmentation, leave the soil and begin to feed on the plants, mostly eating away the edges of leaves, but not so extensively as the larvae which may completely strip plants of foliage. Adults enter a summer diapause but may continue feeding through late summer and autumn but they do not become sexually mature until they have overwintered and spent time maturation feeding during the following spring. Adults generally pass the winter under debris or among leaf litter rather than in the soil and they may become active during mild spells. The entire cycle from egg to adult takes about a month and there is a single generation each year. The larvae are of the normal silphine type but typically have pale margins, a distinguishing feature of the genus, although all dark specimens occur and the defining character of the genus is the presence of a ventral as well as a mesal serrate edge to the mandibles.
9-12mm. An elongate and rather depressed species; black to dark brown and with fine, pale and recumbent pubescence which is dense on the head but otherwise even and diffuse. Antennal segments 1-3 elongate, 4-7 only slightly so, and 8-10 form an indistinct club. Labrum deeply emarginate. Eyes relatively small and without erect setae along the posterior margin. Temples convex. Pronotum distinctly shaped; laterally rounded and without borders, anterior margin straight and hind margin produced backwards. Surface punctured although there may be smooth areas anteriorly either side of the middle and occasionally others near the midline. Scutellum large, with angled lateral margins and acute apex. Base of elytra narrower than the base of the pronotum, each elytron with four longitudinal ridges distinct to the apical third. Punctures on the elytra shallow and separated by at least their diameter. Pronotum and elytra with distinct isodiametric microsculpture. Tibiae with longitudinal carinae and fine spines on the external margins; male hind tibiae with a fine curved spine at the apex. Claws red. Male-pro tarsi dilated.
Aclypea opaca (Linnaeus, 1758)
This is a mostly southern and central European species which extends north sporadically to the south of Finland and Sweden, and east into the Caucasus, Syria and Iran. Here it was formerly a very local and rare species known from a few localities in central England and coastal Wales but has not been recorded since the early 20th century and is now presumed to be extinct. On the continent it occurs from lowlands to low mountain altitudes in a variety of habitats including forests, open grassland and agricultural land. The life cycle is very similar to the previous species; it is similarly polyphagous and an occasional pest of beetroot crops.
Easily distinguished from A. opaca by the virtually glabrous pronotum and elytra; among the UK species by the transverse head, smoothly-rounded pronotum which is almost straight across the centre of the anterior margin, and the elytra which have strong and very irregular raised areas, these sometimes confluent and forming cells, especially towards the base. 11-15mm. Entirely black; the raised elytral areas sometimes shiny and contrasting against the rest of the dorsal surface. Head moderately convex and transversely-raised between relatively small and only weakly-convex eyes, clypeus deeply emarginate, and vertex finely punctured and pubescent. Antennae inserted laterally in front of the eyes, the second segment distinctly longer (up to 2X) than the third. Pronotum finely and densely punctured throughout, basal margin strongly bisinuate, lateral margins evenly curved, with a narrow and unpunctured margin, anterior angles absent. Scutellum large, punctured as the pronotum and broadly-triangular with the lateral margins distinctly angled towards the base. Each elytron with three incomplete longitudinal carinae which vary in strength and are sometimes partly or largely obliterated by the ground sculpture. Surface with broad and irregular raised ridges or tubercles between the carinae, these are smooth and contrast with the otherwise finely and densely punctured cuticle, lateral margins explanate and weakly raised. Legs long and robust; middle and hind tibiae with raised longitudinal carinae and two unequal apical spurs, front tibiae with a single long apical spur. Male pro-tarsal segments dilated.