Ecology

The biology of many species from warmer climates is only poorly known but is understood to be very diverse; most species are associated with a narrow range of plant species but more generally they can be very specialized e.g. some Neotropical species develop in fungi while members of the south east Asian genus Orchidophilus Buchanan, 1935 feed on orchids; they sometimes occur among plant cargos and have become widely established under artificial conditions, similarly some Mexican species of Stethobaris LeConte, 1876, also orchid feeders, have spread along with horticultural stock and become established in the United States. A few species have been tried as biocontrol agents e.g. Acuthopeus cocciniae to control ivy gourd, an invasive species in tropical areas. Adults of many species, especially within the Madopterini, are diurnal and frequently visit flowers, giving rise to the common name of ‘flower weevils’. More generally the vast majority feed on vascular plants, both as adults and larvae, and this includes numerous associations with monocotyledons, especially grasses, sedges and palms. They occur in a very wide range of habitats, even in temperate northern regions where many species are associated with wetlands; mostly in marginal situations, salt marshes, damp woodland and floodplains etc. and a few are semi-aquatic, conversely many occupy drier habitats such as dunes, cliffs or calcareous grassland and, at least in Europe some may be found in parks and gardens. The majority of larvae feed on stems and leaves, rather fewer develop in roots or tubers etc, and pupation typically occurs in the soil at the end of the summer, producing adults that will overwinter and become active in the spring. Most species are oligophagous and few are strictly monophagous; a wide range of herbaceous plants are used as hosts but many are associated with various Brassicaceae, Asteraceae and Resedaceae.

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Description

It is quite pointless to try to describe the morphological variety exhibited by the group in tropical regions because they are so very diverse e.g. many species of the Apostasimerini resemble cossonids or even scolytids and some e.g. the Neotropical Azygides testaceus Hustache, 1940 might be mistaken for Anommatus or even elongate Colydiidae; they vary from long and parallel-sided to almost circular, from flattened to very strongly convex and any combination of colour and pattern may be found including many brilliantly metallic species. Among the most interesting, or bizarre, are members of Cylindrocerus Schönherr, 1825, brilliantly coloured weevils in which males have long, forwardly-pointing and upturned horns on the prosternum (giving rise to the common name of elephant weevils), and the colourful Pteracanthus smidtii (Fabricius, 1801), from Ecuador, which has the elytral humeri and apices produced into sharp horns and which mimics a flesh fly in order to escape predators. More sanely many species superficially resemble members of the Erirhininae Schönherr, 1825 (Brachycerinae Billberg, 1820), and there is a much morphological overlap, but that group is distinguished by the structure of the aedeagus; here the tectum and the pedon are separate and the tegmen is at least as long as the aedeagus in the present subfamily the tectum and pedon are fused and the tegmen is shorter than the aedeagus. For this reason the baridine weevils are usually keyed out among other groups on gross morphology, and because they are very diverse group, and because the limits of the group are not yet well-defined, they tend to appear in higher-order keys at several points. The majority of temperate species can be distinguished by the following combination of characters. Funiculus 6- or 7-segmented. Mesepimeron ascending and abbreviated by the elytral humeri, in most this is clearly visible behind the pronotal base from above, if sometimes only narrowly. All tibiae with a well-developed and usually large hook-like tooth produced from either the external apical angle, along the apical margin or the internal apical angle. Tarsi pseudotetramerous, claws single or paired. In most a prosternal rostral channel is absent but in some-which have a longer and more cylindrical rostrum-this may be well-developed and extend behind the front coxae or even into the mesosternum. Species of Ceutorhynchinae also have the combination of ascending mesepimera and a prosternal channel but here the form is generally less elongate, more convex and the pygidium is exposed. These baridine features are common to our UK species which are of a rather characteristic (though by no means definitive) elongate-oval or elliptical appearance, drab black, bluish or bicoloured black and red, and share the following features. 2.3-4.5mm. Glabrous or with a vestiture consisting of fine hair-like setae or (in Cosmobaris) with unevenly distributed and rather patchy pale and dark scales. Rostrum long and cylindrical, without any median or subapical thickening, usually delimited from the frons by a transverse impression and with the antennae inserted towards the apex. Funiculus 7-segmented.  Pronotum quadrate or nearly so, curved laterally and narrowed to the anterior margin which is narrower than the basal margin. Elytra elongate and near-parallel or only weakly curved laterally, only slightly wider than the pronotum, continuously rounded apically and covering the pygidium. Femora not toothed internally, front and hind tibiae with a strong internal apical tooth. Tarsi pseudotetramerous, claws paired, simple and not fused at the base.

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Distribution

The majority of the European fauna, and that of the western Palaearctic generally, includes species of the Baridini Schönherr, 1836 and 3 other tribes are only poorly represented. Apostasimerini Schönherr, 1844 is very diverse in the New World with about 35 Nearctic genera but only 2 occur in the Palaearctic region and one of these, Linogeraeus Casey, 1920, is recorded only as an accidentally introduced genus from Spain. The other, Limnobaris Bedel, 1885, is a truly Palaearctic genus of 11 species; it is most diverse in the east and Japan and some extend into south east Asia but only 2 species occur in Europe and both extend to the UK (see below). A few more species from Africa and the New World are sometimes included in the genus but will need to be transferred. Formerly included in the Curculioninae and sometimes classified in the following tribe, the Palaearctic Neosharpini Hoffmann, A., 1956 includes 5 species of 3 genera, they are mostly of very restricted distribution and include species endemic to India, Kazakhstan, Japan and Tajikistan, but Eumycterus albosquamulatus Boheman, 1838 is widespread in southwest Asia and North Africa and occurs in Greece. The group is otherwise not represented in Europe. Madarini Jekel, 1865 includes 12 Palaearctic genera but most occur in the east, including Japan, and many extend into the Oriental region where the group is diverse, the Nearctic region is also diverse with at least 8 genera. Only 2 genera occur in Europe; Arganthonus Alonso-Zarazaga, 2005 (2 spp.) occurs in Morocco and the Iberian Peninsula and the monotypic Cucubaris Alonso-Zarazaga, 2005 is widespread but does not extend to the UK. Baridinini is a large cosmopolitan tribe, the members of which display a huge and dazzling morphological diversity, especially in tropical regions, it is by far the most diverse tribe in northern temperate regions and this is reflected in the European fauna although by comparison they are a rather drab and ordinary-looking group of weevils. The UK fauna includes species of 4 genera which are otherwise speciose and widespread. Aulacobaris Desbrochers, 1892 is a mostly western Palaearctic genus, extending into the Middle East and North Africa; it includes almost 60 species and subspecies, of which more than 30 occur in Europe. Most have a restricted distribution and several are endemic to particular countries, especially in southern areas, but about 10 are widely distributed and generally common and 2 of these extend to the UK. Baris Germar, 1817 is a huge cosmopolitan genus of about 650 species and is diverse in the northern hemisphere; about 90 are known from North America, about 70 are Palaearctic, 44 are known from the Oriental region and17 occur in Europe, most Palaearctic species have a restricted distribution; only 2 are widespread in Europe and of these only one extends to the UK. Cosmobaris Casey, 1920 includes 2 widespread Palaearctic species of which one extends north to the UK, and a third, the type species and a notorious pest of sugar beet (the Sugar beet petiole borer), C. americana Casey, 1920 from North America. Many other species will be found in the literature but most of these have been synonymised with the European species. Melanobaris Alonso-Zarazaga & Lyal, 1999 is a Western Palaearctic genus of about 40 species, 17 of which occur in Europe and others are present in North Africa and the Middle East but only a single species, and the most widespread member, extends to the UK.