Lixinae | uk beetles

LIXINAE Schönherr, 1823

Includes mostly rare and very local species, only Larinus carlinae and Rhinocyllus conicus being widespread in the south. Of our five species of Lixus, four are probably extinct while the recently discovered L. scabricollis has spread rapidly around the coasts of England and Wales.

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POLYPHAGA Emery, 1886

CURCULIONOIDEA Latreille, 1802

CURCULIONIDAE Latreille, 1802

4-17.5mm

Introduction

This large subfamily includes more than 1500 species of about 100 genera classified into 3 tribes, they occur worldwide and are very diverse in northern temperate regions; about 110 species occur in North America while more than 700, or almost half the total, occur in the Palaearctic region. Of the 3 tribes, Rhinocyllini Lacordaire, 1863 is the smallest and is sometimes included within the following tribe, it includes only 2 genera, both of which are naturally restricted to the western Palaearctic, including Mediterranean North Africa, but a single species of each is now established and widespread in North America, having been introduced to help control various invasive weeds. Lixini Schönherr, 1823 is a cosmopolitan tribe of about 15 genera, it is most diverse in the Palaearctic region but well-represented Africa and the Oriental region, 4 genera are represented in North America and most of the Neotropical fauna are members of large and cosmopolitan genera, only a single genus being endemic, and several genera are endemic to particular regions such as Australia and Madagascar. Cleonini Schönherr, 1826 is the largest tribe with more than 80 genera, it is most diverse in warmer and drier areas of Asia and the Oriental and African regions, and only poorly represented elsewhere e.g. 33 species of 5 genera occur in North America and this includes 2 introduced species, and it is almost absent from Australia and South America. The European fauna is very diverse with more than 265 species of 41 genera representing all 3 tribes although most occur in warmer southern regions and only 20 species of 10 genera occur in northern Europe where country faunas tend to be impoverished e.g. 14 species of 8 genera occur in Latvia, 23 species of 9 genera in Belarus, 13 species of 7 genera in Estonia and 12 species of 6 genera are recorded from the UK.

Although many temperate species are associated with woodlands and wetlands, the majority of species occur in dry habitats on light chalky or sandy soils and further south many occur in very arid environments; in general members of the Lixini are associated with wetlands or permanently damp environments while those of Cleonini inhabit drier habitats. Most species oviposit in the stems or about the flower heads of herbaceous plants and the larvae mine stems, roots or rhizomes although some develop within flowers. Adults are generally diurnal and may be sampled

by sweeping or searching stems, most are brachypterus and cannot fly and most occur in numbers when found. Hence some have been used as biocontrol agents against invasive weed species e.g. the Palaearctic Larinus carlinae (Olivier, 1807) was introduced into the United States during the 1960’s to help control invasive thistles (and has subsequently proved to be a nuisance as it also attacks some native species), and some have been accidentally introduced to other areas and have become widely established e.g. the Palaearctic Cleonis pigra (Scopoli, 1763), in North America since the early 20th century. The biology of most species is only poorly known but many are oligophagous or polyphagous and may use hosts from a range of families. Of the known hosts various species of Asteraceae are probably the most common, and many species develop in various species of thistle, but a range of families are known to host at least some species, these include Leguminosae, Rosaceae, Cruciferae, Polygonaceae, Chenopodiaceae and Zygophyllaceae. Outside the UK some species occasionally occur on cultivated plants or crops, especially of the Chenopodiaceae or Cruciferae but so far none have been classed as important economic pests.

Description

Adults are among our largest and often easiest weevils to identify but they vary widely in morphology and so, as with many weevil groups, are difficult to describe as a group; technically, though rather useless from a practical point of view, they may be recognized by two characters not known outside the subfamily, firstly the ventrally-situated, 3-segmented labial palps, the segments of which which can be retracted or ‘telescoped’ together, and secondly, in females the presence of paired symbiont sacs attached to the vagina near the base of the second gonocoxite. Adults of many species are covered pale powdery secretion which gives them an attractive appearance, especially in pubescent species, but this soon wears off and is very rarely seen in preserved specimens. Sexes are usually easy to distinguish; females are often larger and have a longer rostrum, the abdominal ventrites are usually convex and there is a single sclerotized tergum at the abdominal apex; males are often smaller and narrower, the rostrum is often shorter, the abdominal ventrites are flat or concave and there are 2 sclerotized terga at the abdominal apex though these may be difficult to appreciate without manipulating the abdomen. Very fortunately our UK species are distinctive enough to describe in general terms.

Our only species of Rhinocyllini, Rhinocylus conicus (Frölich, 1792) is easily distinguished among our weevils by its size, pubescent-mottled appearance and combination of short rostrum and straight (not geniculate) antennae. Rhinocylus was formerly a very scarce and local coastal species but it has expanded greatly in recent decades and is now generally distributed and locally common, it is associated with various thistles but will often be found near the flowers of Cirsium vulgare (Savi).

The remainder of our species may be distinguished among our weevil fauna by the following combination of characters. Size >4.0mm, rostrum at least twice as long as wide but at most as long as the pronotum, antennal funiculus 7-segmented, Prosternum without a rostral channel; the front coxae closely approximated, mesepimera not ascending and so not visible from above, tibiae without external teeth except for any apical spurs etc, tarsi pseudotetramerous though sometimes the third segment is very narrow.

Three genera of Cleonini are present on the UK list, two represented by a single species, and Coniocleonus Motschulsky, 1860 by two, they may be distinguished from species of Lixini by the dorsally flat rostrum which has well-developed longitudinal keels either above or laterally. All are large and easily recognized by their general appearance. Bothynoderus affinis (Schrank, 1781) is distinguished by the very elongate third antennal segment, it is otherwise large, 6.0-11.0mm, and very distinctively patterned and so should not be mistaken for any other species. It is associated with various Amaranthaceae on the continent, it occurred sporadically in Scotland and south east England during the 19th century and was last recorded near the New Forest in 1936, it is now thought to be long extinct. Cleonis pigra (Scopoli, 1763), the Large Thistle Weevil, has the third antennomere quadrate, it is also large, 9.0-15.0mm and very distinctive in appearance. It is associated with a wide range of Asteraceae but usually occurs on thistles in the UK, it is a local and mostly maritime species extending north to southern Scotland but generally absent from the West Country. Coniocleonus may be recognized by the two basal meta-tarsomeres being very elongate, the second almost twice as long as wide, both are large and very distinctive weevils. Of our listed species, C. turbatus (Fåhraeus, 1842) was last recorded in 1815 and is thought to be long extinct while C. nebulosus (Linnaeus, 1758) is a very local and scarce species associated with heather on sandy heathland at a few sites in the south.

Lixini is represented by two genera in the UK; they may be distinguished from the previous tribes by the relatively long and dorsally convex rostrum which has, at most, a very fine longitudinal keel along the middle of the dorsal surface. Two species of Larinus Dejean, 1821 appear on our list but one, L. turbinatus Gyllenhal, 1835, is known from only a single recent record from Kent and is unlikely to be established. L. carlinae (Olivier, 1807) is widespread across England and Wales though probably more coastal in the west, it is locally common and associated with Asteraceae, especially thistles. Both are medium sized beetles, 4.0-9.5mm, elongate and rather parallel-sided with a distinctive appearance suggestive of Rhinocyllus in the field but most obviously different in the form of the rostrum. Five species of Lixus Fabricius, 1801 appear on the UK list but only L. scabricollis Boheman, 1842 is likely to be found in the wild; first recorded from Kent in 1987 it is now widespread though local around the coasts of England and Wales, it is associated with Beta vulgaris ssp. maritima (L.) (Sea beet) and is usually common where it occurs. Our other listed species are almost certainly long extinct in the UK; L. paraplecticus (Linnaeus, 1758) has been long established here and was locally common in parts of Kent until the 1940’s but changes in land use caused a drastic decline and it was last recorded in 1958 from Somerset, L. pulverulentus (Scopoli, 1763) was last recorded from Sussex in 1928, L. iridis Olivier, 1807 is known from only 2 early 19th century records, and the last record of L. vilis (Rossi, 1790) was in 1905 from Kent. Lixus are easily recognized by the very elongate form and often large size, L. pulverulentus may reach 18mm, all occur in sandy or marshy habitats, often near the coast, and are associated with various Asteraceae, Geraniaceae or Apiaceae.