CEUTORHYNCHINAE Gistel, 1848
Among the largest of the UK subfamilies with many common and widespread species in a range of habitats, they occur on a wide range of host plants and some have become notorious pests of Brassica crops.
For convenience this group is here considered as a distinct subfamily, a status widely accepted and used in the literature, and as such it is generally classified into 11 tribes, but the group is also frequently considered as a supertribe of the Conoderinae Schoenherr, 1833 with a corresponding tribal classification. Other systems of classification will be found in the literature and until a genetic study has been completed the group is likely to remain fluid at all levels. The subfamily includes about 1400 described species in more than 170 genera and is almost cosmopolitan in distribution, being largely absent from New Zealand, many Pacific islands and southern parts of South America. The greatest diversity is in the Palaearctic region, followed by the Oriental, Nearctic and African regions. By far the majority of species are included in the predominantly Old-World Ceutorhynchini Gistel, 1848 but the tribal limits remain uncertain in many cases e.g. the Amalini Wagner, 1936, which includes a single widespread Palaearctic species, is often included in the Ceutorhynchini. Some tribes e.g. Mononychini LeConte, 1876 are very distinct but in general there are many overlapping morphological characters and the limits become vague; moreover with many the distribution also overlaps and so clearly-defined groups are difficult to appreciate; the Mononychini includes 11 species in 2 genera and is mostly Palaearctic but a single species is native to North America. While this is primarily an Old-World group, the large tribe Cnemognini Colonnelli, 1979, with >120 species of >30 genera is almost exclusively New World in distribution and is the only tribe to occur in the Neotropical region. Most Old-World groups are widespread but a few, e.g. the mostly Southeast Asian Egriini Pajni & Kohli, 1982 are more restricted. The Lioxyonychini Colonnelli, 1984 is endemic to Africa with about 15 species of 5 genera occurring from Ethiopia to South Africa. Hypohypurini Colonnelli, 2004 is a small Australian and African group with several species endemic to Madagascar. The Australian fauna includes about 15 species, mostly related to those of the Palaearctic and African faunas, and only a single species of the large and primarily Holarctic genus Rhinoncus Schoenherr, 1825 occurs in New Zealand. Oceanic islands are mostly unrepresented but many species are pests of agricultural products and are becoming established on many islands. The Nearctic fauna includes more than 160 species of 36 genera while that of Europe includes about 560 species of 60 genera, of which about 90 species of 30 genera extend to the UK. With about 300 species, the genus Ceutorhynchus Germar, 1842 includes more
© U.Schmidt 2006 www.kaefer-der-welt.de
© U.Schmidt 2006 www.kaefer-der-welt.de
than one-fifth of the subfamily, it has a Holarctic and Afrotropical distribution, although some pest species are now near-cosmopolitan, and is by far most diverse in the Palaearctic region; about 70 occur in the Nearctic region and about 150 in Europe, several species and groups of species have been removed and now form distinct genera, it is a very difficult genus and likely to be split further, it is also certain that many more species will be added. Most of our UK species form part of a much wider continental distribution and in most cases represent only a small part of much larger genera, the greatest diversity here is in Wales and the south of England and most habitats are likely to host at least some species.
Species within this subfamily are generally easy to recognize and with a little experience will be obvious; they have a distinct rostrum, usually at least twice as long as wide, and the apices of the mesepimera (in the vast majority of species, including all those occurring in Europe)are visible from above between the pronotal base and the elytral humeri. The rostrum can be held ventrally in a wide groove extending between the pro-coxae and in many species with a moderately long or very long rostrum the meso- and metasternum are also impressed between the coxae, these grooves are simple and do not have the raised margins or keels seen in the Cryptorhynchinae Schoenherr, 1825, another subfamily with a well-developed rostral channel. Size varies between 1.2 and 7mm although the majority are 1.5-3.5mm (among our UK fauna the largest is Mononychus punctumalbum (Herbst, 1784), reaching 5.1mm), but despite the small size most are robust and heavily-sclerotized, typically convex ventrally and rather flattened across the elytra, most are drab black, grey or brown but many have patterns of pale scales to the pronotum or elytra and a few are metallic green or blue. In many the entire ventral surface is clothed with broad pale scales, contrasting with the dorsal surface. The head appears small and transverse from above, with convex and usually transverse eyes placed anteriorly and divergent temples which are often retracted into the prothorax, the vertex is simply convex or may have a median impression and is usually densely punctured, in many it is clothed with scales but these may be confined to a median line or absent altogether. Rostrum long and thin, often more than 3.5X longer than broad; least so in Phytobiini Gistel, 1848, smoothly curved or angled with the vertex and with long lateral scrobes hidden from above, antennae long and thin with the scape often abruptly thickened before the apex, funiculus 6 or 7 segmented with at least the basal segments elongate, club 3-segmented and pubescent, often elongate and apically acute, insertions usually near or beyond the middle and often sexually dimorphic. Pronotum quadrate to transverse, broadest at or near the base and narrowed to straight or weakly curved anterior margin, lateral margins unbordered, anterior margin smoothly convex and closely approximated to the head, abruptly raised or finely channelled so appearing as a double margin from in front, usually smoothly curved but sometimes emarginate or with small teeth about the centre. The pronotal surface is usually densely and often strongly punctured although there may be a smooth median line, in many it is strongly sculptured with sub-apical or sub-basal constrictions or lateral tubercles, depressions or raised areas. In most temperate species the elytra are flattened and only slightly elongate, giving the group a distinctive broad-oval appearance, but in exceptional cases e.g. Poophagus sisymbrii (Fabricius, 1776) the form of the mesepimera and the rostral channel is diagnostic. Elytral base straight to strongly bisinuate, with broad shoulders and forming a distinct angle with the pronotum or (e.g. in Scleropterini Schultze, 1902) with sloping shoulders and more-or-less continuous in outline with the pronotum, elytra broadest behind the shoulders or in the basal half and narrowed to rounded or truncate apical margins, usually with well-impressed and punctured striae complete to the apex, interstices flat and simply punctured, tuberculate or raised. The elytral vestiture varies widely; they may be almost glabrous or completely scaled or have a pattern of while or contrasting scales, in many there are raised scales or fine setae obvious along the lateral margins and there is often a patch of pale scales common to both elytra behind the scutellum. In many the pygidium and propygidium are well-sclerotized and visible beyond the elytral apex. The prosternum is usually steeply convex with the anterior margin incised and at least as long as the posterior margin, the pro-coxae round and projecting and widely separated to accommodate a rostral channel. The meso- and meta-coxae are round or weakly transverse and weakly convex, both are widely separated but the meta-coxae may be very widely so. The legs are long and robust and with a little familiarity will be seen to be quite distinctive of the group. The femora are long, generally widest about the middle and curved overall, the front femora vary from smooth to very strongly toothed internally, the middle and hind femora are generally smooth although there may be small internal tooth and all are often constricted before the apex. The tibiae are very variable; usually long and widened gradually to the apex and variously toothed or modified apically or externally. The tarsi are pseudotetramerous, often with the basal and apical segment long and slender and the third segment widely dilated (although there are exceptions e.g. in Eubrychius velutus (Beck, 1817) the lobes are reduced and hardly discernible), and the vast majority have paired claws which are not fused and bear various basal teeth or appendages. Five tribes are recognized in the UK and are easily identified; Mononychini includes a single species, identified by having only one claw on each tarsus, in Phytobiini the rostrum is short and broad, the only exception being some Pelenomus Thomson, 1859 which are otherwise distinct in having two small teeth on the anterior pronotal margin. Rutidosoma globulus (Herbst, 1795), our only representative of the Scleropterini, is distinguished by the rounded elytra with obsolete humeral angles and the strongly tuberculate elytral interstices. Both Amalini and Ceutorhynchini are typical of the group, with well-developed humeri and lacking teeth on the pronotal margin; the only species of the former tribe, Amalus, is superficially very similar to several species of Ceutorhynchini but differs in having the anterior margin of the prosternum entire whereas in Ceutorhynchini it is deeply incised. Although the subfamily is large and specific determination can be very difficult, our UK fauna are, at least to generic and very often to the specific level, fairly straightforward to deal with, more especially so since the publication of the RES handbook by Mike Morris in 2008. Many species are capable of flight and dispersal over quite long distances and many can retract the rostrum and appendages into the body, resembling seeds, and display thanatosis when disturbed. A few e.g. some Rhinoncus Schoenherr, 1825 are able to jump although they do not have the greatly enlarged femora seen in various Rhamphini Rafinesque, 1815 and this tends to be rather feeble.
All species feed on plants both as adults and larvae; the majority are oligophagous and associated with various herbaceous species and only a few develop on trees; Coeliodes Schoenherr, 1837 and Coelodinus Dieckmann, 1972 on oak and birch, Rutidosoma globulus is associated with Poplar and Micrelus ericae (Gyllenhal, 1813) develops on heather and heaths. Mononychus punctumalbum is unique among our fauna in developing on monocotyledonous plants; various species of iris. The group as a whole includes many pest species but in the UK only a few species of Ceutorhynchus are of any concern; C. pallidactylus (Marsham, 1802), C. assimilis (Paykull, 1792), C. picitarsis Gyllenhal, 1837 and C. obstrictus (Marsham, 1802) remain serious pests of various Brassica crops and a great deal of research is continuing into their control. Several others remain serious pests on the continent but are insignificant in the UK; Calosirus terminatus (Herbst, 1795) attacks various root crops while Stenocarus ruficornis (Stephens, 1831) attacks poppies and a range of species feed on watercress e.g. Amalorhynchus melanarius (Stephens, 1831) and Drupenatus nasturtii (Germar, 1824). A few have been considered as biocontrol agents but so far they are not in widespread use, Stenocarus has been used against poppies grown for the illicit drug trade and various Hadroplontus Thomson, C.G., 1859 and Trichosirocalus Colonelli, 1979 have been used to control thistles in various parts of the world. The majority of species occur in terrestrial environments, often in dry areas and frequently on ruderal sites, the group as a whole includes many species associated with ‘weeds’ and early plant assemblages on recently disturbed land, but many species are associated with wetlands and some are adapted to a semi-aquatic lifestyle. Many species of Phytobiini develop on aquatic plants and the adults are able to move under water and walk on the surface, the most adapted among our fauna being Eubrychius velutus (Beck, 1817) which may pass the entire life-cycle under water and use plastron respiration as an adult. Among the Ceutorhynchini a few are associated with various cresses and may be common in marginal environments, these are partially adapted to an aquatic lifestyle, can survive immersion and will often be found among samples taken from open water, among these are Poophagus sisymbrii (Fabricius, 1777), Amalorrhynchus melanarius and Drupenatus nasturtii. Terrestrial species occur on a fairly wide range of plant families although host preferences tend to be narrow, among the UK species host families include Papaveraceae, Rosaceae, Urticaceae, Geraniaceae, Lythraceae, Resedaceae, Brassicaceae, Polygonaceae, Primulaceae, Boraginaceae, Plantaginaceae, Lamiaceae and Apiaceae. Many genera are confined to a single genus of plants e.g. Zacladus Reitter, 1913 on various Geranuim species, Rhinoncus on Polygonaceae and Mogulones Reitter, 1916 on various Boraginaceae, our largest genus, Ceutorhynchus, occur almost exclusively on various Brassicas, an exception being C. resedae (Marsham, 1802) which develops on Reseda luteola L. (Resedaceae). Sampling adults is straightforward and a knowledge of host associations will assist not only with finding them but also in their identification; Calosirus terminatus develops on various umbels and species of Datonychus Wagner, 1944 occur on various Lamiaceae while sweeping nettles will very often produce two of our most common and widespread species; Nedyus quadrimaculatus (Linnaeus, 1758) and Parathelcus pollinarius (Forster, 1771). In temperate northern regions most species are univoltine although further south there may be several generations in a year and in the tropics they may be continuously breeding, most of our species become active early in the year and peak in abundance during late spring or early summer, many may be found mating in the spring and adults of many species vanish during early summer, reappearing in late summer or autumn when mating may occur before they enter the soil etc. to overwinter. There are exceptions to this general life-cycle, the most notable being Ceutorhynchus picitarsis, here the adults occur through the year and oviposit through during the autumn and winter in stems of Brassicas, particularly in oilseed rape; larvae develop through the winter and produce adults in the spring. Larvae develop in various plant structures; the majority within fruits, feeding upon seeds, but wide range of strategies are included in the group. Stenocarus larvae feed within poppy roots and are one of the few root-feeding species, several Ceutorhynchini feed in stems and a few are leaf miners; larvae of Hadroplontus initially mine thistle leaves but as they grow move into the stems to feed, and some Ceutorhynchus induce galls on the stems or roots of various Brassicas in which they feed. Most larvae feed within various host structures but a few are ectophagous; among the UK fauna most notably the semi-aquatic species of Pelonomus. Fully grown larvae may descend the host stems to pupate in a subterranean cell or they may pupate at their feeding sites within stems or leaves. Adults of our few species associated with trees breed in the spring and larvae grow within developing plant structures; those of Coeliodes among the flowers and shoots of oaks and those of Coeliodinus in female birch catkins.