CRYPTORHYNCHINAE Schönherr, 1825
Represented by six species in Britain, all of which are nocturnal and saproxylic. Although some species are widespread they are elusive and seldom seen.
POLYPHAGA Emery, 1886
CURCULIONOIDEA Latreille, 1802
The latest UK checklist includes this group as a distinct subfamily, our species being included within the single tribe Cryptorhynchini Schönherr, 1825, and to avoid confusing the situation we are presenting the group here accordingly, but it is often included as a tribe of a very broadly-defined Molytinae Schönherr, 1823 (although molecular studies suggest otherwise). Even when considered as a distinct subfamily i.e. in a narrow sense, the group is very large; with more than 7000 described species it is the second largest subfamily of the Curculionidae Latreille, 1802. The classification is poorly understood and many systems will be found but It is often divided into seven tribes (and lots of subtribes), some of which e.g. Psepholacini Lacordaire, 1866 are probably monophyletic while others e.g. Cryptorhynchini are almost certainly not. The group has a worldwide distribution and is by far most diverse in warmer regions of South America, Australasia and Oceania, by comparison northern temperate regions are relatively poor as both the Nearctic and Palaearctic faunas include less than 500 species. Psepholacini is a large group of about 40 genera, they occur in the Neotropics, Australasia and the Oriental region, extending into Japan and India but generally absent from northern temperate areas, some southern hemisphere countries have very diverse faunas e.g. about 20 species of 6 genera occur in New Zealand (a fauna which otherwise includes more than 300 species of about 40 genera of the Cryptorhynchini). Sometimes considered as a tribe of the Molytinae and equally ranked alongside the Cryptorhynchini, Aedemonini Faust, 1898 includes about 35 genera, it is widespread in Australasia, southeast Asia and the Oriental regions and is represented in the Palaearctic region by 5 genera and about 50 species, mostly from India, China and Japan. Camptorhinini Lacordaire, 1866 is a widespread Old World tribe of 8 genera; it is most diverse in Africa and includes several genera endemic to Madagascar. The European fauna includes 2 species of Camptorhinus Schönherr, 1825, a genus otherwise widespread the Old World. Gasterocercini Zherikhin, 1991includes 18 genera and, with the exception of Africa, is diverse in tropical areas around the world, several genera are endemic to the Neotropical region and some extend north into temperate regions e.g. Canada and Mongolia, and while Australasia and South America have diverse faunas the African region is virtually devoid of species. Only a single species, Gasterocerus depressirostris (Fabricius, 1792), occurs in Europe; it is widespread but does not extend to the UK.
Sophrorhinini Lacordaire, 1866 includes about 20 genera, it occurs in tropical areas worldwide and is diverse in Australia and Africa, many genera are of very restricted distribution e.g. 5 are endemic to Madagascar and there are endemics in French Guiana, Jamaica, India and Namibia. No species are established in Europe. Torneumatini Bedel, 1884 is a small tribe of 3 genera which occur in the western Palaearctic region. The 3 species of Paratorneuma Roudier, 1956 are endemic to the Canary Islands, Somodytes Gonzales, 1970 is represented by a single species in Spain, and Torneuma Wollaston, 1860 includes about 20 species, most of which are of very limited distribution in the south or on Mediterranean islands. The vast majority of species are classified among three subtribes of the Cryptorhynchini and most are restricted to warmer regions worldwide. Mecistostylina Lacordaire, 1866 is the smallest of the subtribes with about 15 genera, it occurs in warmer regions worldwide but the greatest diversity is in Australasia, no genera extend into northern temperate regions. Tylodena Lacordaire, 1866 includes almost 250 genera and is cosmopolitan with a large generic diversity in Australasia, the Nearctic fauna includes 13 genera and about 30 occur in the Palaearctic region, the European fauna includes almost 200 species of 10 genera, of which only 4 species of 3 genera occur in the UK. The group includes the large and cosmopolitan genus Acalles Schönherr, 1825 which (though acknowledged to be artificial and a ‘dumping ground’ for many awkward species) includes almost 600 species; 12 occur in North America and more than 80 in Europe though only 2 extend to the UK. Cryptorhynchina Schönherr, 1825 includes about 200 genera it is very diverse in tropical areas worldwide but particularly so in Australasia and the Oriental regions, 10 genera occur in the Nearctic region and 16 in the Palaearctic but the European fauna includes only the single species Cryptorhynchus lapathi (Linnaeus, 1758) which extends north to the UK. The undoubtedly artificial genus Cryptorhynchus is otherwise cosmopolitan and includes almost 500 species. The UK list also includes the unlikely Achopera alternata Lea, 1910, a member of a genus found otherwise only in Australia and Chile, it seems to be established in a single UK locality (our local park) and occurs nowhere else in the northern hemisphere, its method of arrival remains a mystery.
The vast majority of species are associated with dead or decaying trees and shrubs both as adults and larvae, the larvae are generally endophytic while adults occur more generally among wood and on foliage. Adults generally spend the day under bark or in crevices to avoid predation and are more active at night but many species may be collected during the by beating foliage near to areas of decaying wood, especially in the spring when they may swarm, albeit usually in modest numbers, at night on trunks etc. In temperate regions they often occur under loose dry bark with plenty of wood debris and spider webs and there seems in general to be little host-specificity although some prefer Gymnosperms or Angiosperms and in a few cases are associated with particular plant genera, but further afield many occur in leaf-litter and species have been recorded from rhizomes, avian nest cavities, mosses, lichens and among decaying seaweed. The biology of most is unknown but it seems that associations with living plant material is rare, exceptions to this are some tropical species that mine leaves as larvae. Among the more unusual lifestyles are some Australian species that feed on herbivore dung and a Central American species that will feed on psyllid larvae. Because the majority of are associated with dead wood there are very few pest species but where the larvae feed on living tissue they may become a problem e.g. larvae of the poplar-and-Willow Borer, Cryptorhynchus lapathi (Linnaeus, 1758), feed in the bark of trunks and stems of young trees and may girdle stems causing them to die and exposing dead wood to further infestation. More generally it is thought that many species act as fungal vectors between damaged trees.
Distinguishing features of this subfamily are the prosternal and (variously developed) mesosternal groove into which the rostrum is accommodated in repose, and the production of the outer apical margin of the protibiae into a curved hook-like process, these features will distinguish most members, and they apply to the northern temperate fauna generally, but some exotic species (notably among the Psepholacini) have the prosternal groove reduced and the mesosternum smooth. Most members of the subfamily are small or medium sized beetles, <10mm but many are <5mm, they are generally drab-coloured and variously patterned with brown, grey and while, often with parts of the body tessellated, which renders them cryptic against bark etc. and many superficially resemble debris, frass or bird droppings. The general form is broadly elongate and discontinuous in outline with the head visible from above and narrower than the pronotum, the pronotum is transverse to quadrate and usually narrower across the base than the base of the elytra, the elytra vary from parallel-sided with well-developed shoulders to almost circular and lacking shoulders and the legs are usually long and robust. The dorsal surface is usually densely scaled, often giving a velvety appearance, and the pronotum and/or elytra often have patches or rows or erect or semi-erect broad truncate or spatulate scales which confuse the outline in lateral view and add to the cryptic appearance. The head is generally transverse and rather flat with convex eyes that are visible from above and an elongate rostrum with lateral scrobes, the length or curvature of the rostrum and the site of the antennal insertions are often sexually dimorphic; generally nearer the apex in males. The antennae are usually short with the scape gradually thickened and only a little shorter than the seven-segmented funiculus and in most there is a distinct three-segmented club. The pronotum is transverse or quadrate, usually convex and sculptured with furrows, fovea and tubercles, the lateral margins vary widely from simply straight or rounded to strongly angled and in many there is a subapical constriction, the basal margin is generally straight or nearly so and the apical margin gently curved. The prosternum is deeply channelled between round and projecting coxae and the apical margin of this channel is usually produced forward into lobes which variously cover the ventral margin of the eyes, laterally the channel is carinate; these may be simple and continuous with the apical lobes or there may be several which terminate either side of the lobes. The mesosternum is short with widely separated and usually circular coxal cavities, between which the anterior margin is variously excavate for the reception of the rostral apex. The metasternum is usually flat or weakly concave and in many there is a median pit or longitudinal depression, the coxal cavities are usually relatively small and widely separated and many species are sexually dimorphic with respect to the degree of concavity between the middle and hind coxae. The scutellum may be concealed beneath the elytral base or exposed, in which case it is usually small. The elytra typically have broad and well-defined shoulders and are variously constricted before a continuously curved apical margin, they otherwise vary from elongate and parallel-sided to almost circular, well-impressed and punctured striae usually merge with the basal margin and continue to the apex and the interstices vary widely in width and convexity, in many cases the striae are obscured by areas of dense scales or there may be raised and glabrous tubercles. In many cases the lateral elytral margins are reflexed ventrally, with or without distinct epipleura, and cover the margins of the mesonotum, metanotum and abdomen. Abdomen with 5 visible sternites; the first moderately long and variously produced between the metacoxae, the often as long as the third and fourth, and the terminal ventrite long and rounded apically. The legs are usually well-developed with long trocanters obliquely attached to the internal apical margin of the femora, the femora are robust, they are unarmed but have a well-developed furrow extending variously along the ventral margin for the reception of the tibiae. The tibiae are straight or sinuate before the base and apex, they are usually only weakly expanded from the base and the apex is always smoothly produced into an external curved process, this is not a tooth or spur but rather a continuation of the tibial cuticle. Tarsi 5-segmented and pseudotetramerous, the terminal segment often long and curved and bearing two claws which are separated across the base.
The two most obvious morphological features which define the group (although neither is unique to the subfamily) are the ventral rostral channel and the form of the tibial apex and these two features, combined with the normally developed hind femora and widely-separated eyes, will distinguish our species which in any case are otherwise distinctive in general appearance. Our UK species are seldom encountered because they are nocturnal and cryptic, they may be found by searching very carefully among dead or decaying trees by powerful torchlight or by beating low foliage in likely situations, they also overwinter among dead wood or under bark and so may appear in extraction samples. When beating or sweeping foliage at night they must be looked for with great care as when disturbed the adults will retract the rostrum and appendages into the body, drop to the ground or into the net and remain motionless for some considerable time, resembling fragments of bark or detritus. For these reasons our species may be more common than records suggest. Achopera alternata Lea, 1910 has been recorded from a single site in Wales and is thriving at a single site in southern England. Cryptorhynchus lapathi (Linnaeus, 1758) occurs on various willows throughout England, Wales and southern and central Scotland but is very local and rare. Our two species of Acalles, A. misellus Boheman, 1844 and A. ptinoides (Marsham, 1802) are widespread and though not generally common should be expected with patient searching. Kyklioacalles roboris (Curtis, 1835) is also widespread but generally sporadic and scarce. Onyxacalles gibraltarensis (Stüben, 2002) is a recent addition to our list which so far seems to be established at a single site in the southeast (Telfer , M.G. and Stüben, 2006).