Ecology

The biology of the group is very varied, there are many terrestrial species and some are hypogean, some live among maritime or freshwater shingle and many live among leaf-litter or other accumulated debris, but the majority are associated with trees and shrubs and have larvae that develop among dead wood or decaying plant debris, there are species whose larvae develop within stem and root phloem and many that develop among conifer foliage or cones. Some are stem or leaf miners and some larvae feed within fruits, seeds or other reproductive parts of plants. Many are oligophagous and some are monophagous, thus some have been trialled as biocontrol agents against invasive plants and, especially in the tropics, many have become economic pests to both native and introduced plants e.g. the Australian elephant weevil, Orthorhinus cylindrirostris (Schönherr, 1825) develops naturally in various species of Eucalyptus but has become a very damaging vineyard pest.

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Description

Any attempt to define the group in morphological terms would be futile as they are very varied and exhibit the full range of weevil morphology, they are mostly grouped together due to a curved extended process on the apex of the hind tibiae, or bear various modifications to the hind tibiae related to the development of this process, and the other tibiae are commonly developed along similar lines. Extremes of development are seen in many tropical groups e.g. the very convex, rounded and tuberculate Elephant weevils (Orthorhinus Schönherr, 1825) of Australia, or the elongate, flattened and parallel-sided Lixodes Pascoe, 1882 (which resembles Lixus) of South America, but the majority are small to medium sized weevils and rather drab in appearance and within the general variation it is not difficult to find genera that closely resemble members of the other subfamilies of weevils. Within the broad scope of these weevils that share modified tibial apices the other morphological characteristics vary widely and continuously; the eyes may be large and convex, diminutive and flat or missing altogether, the anterior coxae may be contiguous or widely separated, a prosternal rostral channel may be absent or weakly to very strongly developed, bordered by sharp ridges or simple, and short or extending between the coxae or onto the mesosternum. In most the rostrum is well-developed and long, the scrobes extending to the eyes or converging ventrally, and the antennae 11-segmented, geniculate and distinctly clubbed although the scape may be very short and various funicular segments fused. The legs may be very long and flattened, this is exemplifies by the spider weevils (species of Arachnobas Boisduval, 1835 that not only superficially resemble spiders but also mimic their movement and behaviour) of New Guinea where the femoral and tibial margins are fringed with dense long setae (these are known to be fungal-spore brushes used in defence against entomophagous fungi), the femora and tibiae may be toothed or have ventral series of tubercles or spines and the tarsi are very variable, from simply pseudotetramerous to having all segments narrow and unmodified, and the claws may be fused or connate and smooth to strongly toothed. Because of this variation the genera tend to be keyed out individually or in groups among the weevil subfamilies, but identification among limited faunas such as those of the European countries tends to be straightforward, at least to the generic level, as the following account will show.

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Classification

Syagrius intrudens C. O. Waterhouse, 1903 is our only member of the Phrynixini Kuschel, 1964 and is so far known only from the UK; it is associated with a range of introduced and native ferns including bracken, Pteridium aquilinum (L.). The genus is otherwise endemic to eastern Australia and the tribe is otherwise more or less restricted to Australasia with 25 of the 34 genera endemic to New Zealand and a single genus occurring in Chile. Adults have been found during the summer in a few widely scattered locations including Cornwall, South Wales and County Dublin in Ireland where it was first discovered and from where it was described, it is established at a single site in East Sussex and has been recorded from Guernsey but is otherwise unknown from Europe. Larvae develop in stems and roots with pupation occurring within the larval galleries and it is thought the species, though so far unknown in that country, was thus introduced with horticultural material imported from Australia. This medium sized weevil. 4.5-7.2mm, is distinct among our fauna due to the dark colour, overall shape and the dense blunt tubercles covering the pronotum and elytra.

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Hylobiini Kirby, 1837 includes about 50 genera, it is mostly tropical with only a few genera either extending into or restricted to temperate regions, the greatest diversity is in South America and the group is largely absent from Australasia. The European fauna includes 7 species of Hylobius Germar, 1817, of which 2 extend to the UK, a Holarctic and Oriental genus of about 40 species that display a wide range of host associations but many are specialist conifer feeders and several are serious pests of commercially grown trees. H. abietis (Linnaeus, 1758), the large pine weevil, is a generally common pest of pine plantations across Europe including most of the UK. H. transveresovittatus (Goeze, 1777) is a very rare species associated with Purple-loosestrife (Lythrum salicaria L.); it occurs locally across central Europe but is very rare in the UK and known only from the Somerset Levels. More widely it has become established and widespread in northern parts of North America since being introduced in 1992 to help control Lythrum which is an invasive introduction from Europe. Larvae burrow within stems and roots or, in the case of arboreal species, tunnel under bark and enter the xylem, in all cases causing serious damage to the host. They may be recognized by their size, 7.5-13.5mm, dark brown or black colour and patchy yellow elytral pubescence; present on the humeral prominence in transverseovittatus but absent from the humerus in abietis. In both the antennae are inserted towards the rostral apex, the pronotum is strongly and rugosely punctured, the femora are bluntly toothed ventrally and all tibiae have a sharp and very strong apical tooth.

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Trachodini Gistel, 1848 is represented in Europe by 2 species of Trachodes Germar, 1824; T. heydeni Stierlin, 1881 is endemic to Romania and Croatia while T. hispidus (Linnaeus, 1758) is widespread across central Europe and extends to the UK where it occurs locally across England, Wales and South West Scotland. Adults are active over a long season from early spring until the autumn and are associated with various deciduous trees, particularly oaks, where they occur under bark or among nearby leaf-litter. Larvae develop among damp decaying wood. Adults are small, 2.5-4.0mm, and distinctive in appearance; they may be distinguished by the broad semi-erect scales and protective setae on the odd-numbered elytral interstices, ventrally toothed femora and sinuate internal margins to the tibiae. The outer apical margin of all tibiae is produced into a narrow sharp tooth.

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Typoderini Voss, 1965 includes a single UK species, Anchonidium unguiculare (Aubé, 1850). In Europe this species is restricted to Spain and France and here it is very rare and known from only a few localities in The West Country, adults occur among leaf-litter in oak forests and on cliffs but little is known of the biology. Adults are small, 2.2-3.0mm, and entirely reddish brown in colour, the femora lack ventral teeth and the elytra have a single row of erect setae on the raised odd-numbered interstices.

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Our only representative of the Lepyrini Kirby, 1837, the widespread European Lepyrus capucinus (Schaller, 1783) was formerly known from a few grassland sites in the south of England but has not been recorded since the 19th century and is thought to be long extinct. Adults are large, 8.5-11.0mm, and distinctive; the dorsal surface is clothed in dense elongate pale grey and creamy scales which produce a mottled effect on the elytra, especially towards the margins, and there is a longitudinal strip of paler scales towards the lateral pronotal margins. The elytra are smoothly convex and lack erect scales or setae and the femora are toothed ventrally.

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Pissodini Gistel, 1848 is represented by 3 widespread central and northern European species of Pissodes Germar, 1817. All are associated with pine woodland where the larvae develop in dead wood or cones; the widespread P. castaneus (De Geer, 1775) and P. pini (Linnaeus, 1758) are occasional plantation pests while P. validirostris (C. R. Sahlberg, 1834) is a very local and generally rare species restricted to central Scotland. They may be recognized by the large size, 5.0-9.5mm, elongate and parallel-sided form and dark red colour mottled with patches of pale scales; they differ from similar sized species in having the antennae placed towards the apex of the rostrum, the tibial apices smoothly rounded from the external margin and produced into a sharp tooth and the femora without a ventral tooth.

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Our remaining species are currently classified within 3 subtribes of the Molytini Schönherr, 1823. All are distinguished by the sloping humeri, mostly glabrous body, smoothly convex elytra with regular punctured striae (except in Liparus Olivier, 1807) and antennae placed towards the rostral apex. Our 2 species of Liparus are associated with various apiaceae (cow parsley and hogweed etc.), the larvae developing in the roots and adults occurring among the soil around the hosts. Both are very local and generally rare; L. germanus (Linnaeus, 1758) is known from a few sites in Sussex and Kent while L. coronatus (Goeze, 1777) is more widespread in England and Wales. Both are large, at least 10mm, have toothed femora and rugose elytra that bear small patches of recumbent scales. Mitoplinthus caliginosus (Fabricius, 1775) is associated with various herbaceous plants and also occurs in decaying wood, it was formerly much more common and an occasional pest of hops, but is now a very local and rare species of South and Central England. Adults are distinguished by the size, 6.0-9.0mm, elongate and sub-parallel habitus, and the form of the elytra; the striae are very strongly punctured and alternate interstices are raised. The pronotum is strongly punctured, about the same as the elytral striae, all tibiae have a strong apical tooth and the dorsal surface has sparse short pale setae. Of our 3 species of Leiosoma Stephens, 1829, L. deflexum (Panzer, 1795) is widespread and generally common, L. oblongulum Boheman, 1842 is also widespread but is very local and generally rare, and L. troglodytes Rye, 1873 very local and restricted to south east from Hampshire to Kent. All are associated with various Ranunculaceae (buttercups etc.) with larvae developing within the roots. They are small weevils, 1.8-3.0mm, with smoothly convex and regularly striate elytra; L. deflexum has toothed femora while in the others it is smooth; L. troglodytes is smaller at 1.8-2.4mm while L. oblongulum is at least 2.5mm.