Cionus Clairville, 1798
This is a medium sized Palaearctic genus of 61 species distributed throughout Europe, Asia and North Africa although a single common and very widespread species, C. scrophulariae Linnaeus, 1758, has escaped and become established in North America. The European fauna includes 29 species although some of these are very restricted in distribution or are endemic to certain areas e.g. C. canariensis Uyttenboogaart, 1935 and C. griseus Lindberg, 1958 from the Canaries, C. inexpectatus Tempere, 1961 which is endemic to France or C. bulgaricus Angelov, 1959 which is endemic to Bulgaria, many occur on the Mediterranean islands and some of these are endemic e.g. C. distinctus Desbrochers, 1872 in Corsica, in general the greatest diversity is in the south but a good number are widespread and of these six species extend north into the UK.
Species of Cionus are very distinctive, even among the Cionini, and especially among our UK fauna where the only species likely to cause confusion is C. pulchellus (Herbst, 1795) which, beyond a superficial resemblance, is abundantly different. The Cionini Schönherr, 1825 includes more than one hundred species in five genera and is restricted to the Old World. Four genera are represented in Europe. Cleopus Dejean, 1821 includes two species, both of which are widespread but C. solani (Fabricius, 1792) is more southern and does not reach the UK. Cionellus Reitter, 1904 includes the single species C. gibbifrons (Kiesenwetter, 1851) which is restricted to warmer regions of Southern Europe. Stereonychus Suffrian, 1854 includes a single widespread species, S. fraxini (De Geer, 1775) which extends from North Africa to the Baltic countries including Finland but does not reach the UK, two further species are restricted to Southern Europe and another is endemic to the Canaries. The UK fauna is therefore relatively simple to deal with although some of the species can be difficult to identify. The species are easily recognized by their overall appearance and there should be no need to key out the genus; they are characterised by the narrow forebody and large, almost quadrate elytra, our species are distinctively patterned, either by the series of transverse dark markings to the elytra (C. alauda) or by the presence of dark discal and subapical maculae coupled with alternate light and dark markings to some of
the interstices. While the general body shape is universal among the species, the elytral pattern is not so clearly obvious in some European species; in the widespread C. olivieri Rosenschold, 1838 the elytra can be uniformly pale but for the dark maculae and any chequered pattern is restricted to the lateral margins or the apical half, and the widespread and very variable C. olens Fabricius, 1792 can be entirely white but for the dark elytral maculae. Nonetheless our UK species are very obvious among our fauna. A general description is as follows. Head evenly convex, narrow between convex eyes which occupy most of the visible margin and with short diverging temples. Rostrum moderately long, curved and near parallel-sided, scrobes situated laterally and not visible from above, apex in side view rounded or sabulate. Antennal scape long and narrow, funiculus 5-segmented, club long, narrow and pointed. Pronotum broadest across the base and converging to a narrow apical margin, smoothly convex and without structure. Scutellum triangular. Elytra quadrate or nearly so, with widely-rounded shoulders and a continuous apical margin which leaves the abdomen partly exposed. Femora usually strongly toothed below. Tarsi pseudotetramerous; the third segment widely bilobed and the fourth diminutive. Claws fused at the base and lacking a basal tooth, unequal in length, more so in males. In many species the male rostrum is shorter than that of the female.
The life cycle of most, including all our UK species is rather constant; adults emerge from overwintering in the spring and feed on host foliage before mating. Females oviposit on foliage, stems or flowers and the slug-like larvae feed externally on stems, leaves or, commonly, among flower parts. Larvae are covered with a sticky secretion which is distasteful to predators and is ultimately utilized, in part, to construct a cocoon in which pupation will take place. New-generation adults occur from mid-summer and these may become active and feed before entering litter etc. to overwinter although it is likely that adults developing later remain inactive until the following spring. Beyond this some species e.g. the widespread European C. olens Fabricius, 1792, have pseudo leaf-mining larvae that are more typical with a segmented body, they scrape at the upper epidermis of leaves and consume the mesophyll, the lower epidermis remains intact while the upper layer folds over the ‘mine to conceal the larva. When fully grown they pupate within a cocoon on the leaf surface as is usual for the genus. So far as is known all species feed on various Scrophulariaceae, particularly Mulleins (Verbascum L.) and Figworts (Scrophularia L.), but adults of some species also occur on various species of Buddleja L. (also Scrophulariaceae)and Cape figwort (Phygelius E. Mey) although here specific host associations are not understood.
Our UK species are keyed out as follows:
Elytra distinctly patterned, typically the basal macula is irregular, usually transverse and covering three interstices, often reduced but with a dark mark at the base of the third interstice. Interocular distance almost equal to the rostral width at the base. Appearance white or very pale grey with dark grey or black markings. 2.8-3.5 mm.
Elytra with discal and subapical round or oval maculae. Interocular distance much less than the width of the rostral base. 3.3-5.0 mm.
Overall appearance dark; the sutural elytral interstice with two contrasting patches of pale scales next to the round maculae and separated by mostly black scales, the odd-numbered interstices with very dark grey scales throughout and the even numbered interstices mottled dark grey or black and pale creamy.
Overall appearance light grey; the sutural and odd-numbered interstices with pale greyish scales and the even-numbered interstices mottled pale and dark grey.
Pronotum covered with pale scales except for sometimes a small patch of dark scales in the middle of the base. Front femoral tooth clearly smaller than the hind femoral tooth. 3.5-5.0 mm.
Pronotum with dense brown or yellowish scales laterally and strongly contrasting dark scales across the disc. Front femoral tooth larger, about the same size as the hind femoral tooth. 3.4-4.2 mm.
Rostrum clearly narrowed from the middle to the apex in side view. 3.8-4.6 mm.
Rostrum evenly broad and rounded apically in side view.
Eyes more convex and prominent, rostrum broader. Discal elytral macula round and about as large as the subapical macula, even-numbered interstices usually less distinctly tessellated. First elytral stria more strongly curved around the discal macula where it closely approaches the second stria. On average larger, 4.1-4.7 mm. [Modern records only from East Anglia]
Eyes less convex; more closely following the outline of the head, rostrum narrower. Discal elytral maculae usually smaller and more oval when compared with the subapical macula, even-numbered elytral interstices more distinctly tessellated. First elytral stria less strongly curved around the discal macula, the first and second striae well separated and almost parallel throughout. On average smaller, 3.6-4.3 mm. [Widespread but very local and scarce in the south.]