SILVANIDAE | uk beetles

SILVANIDAE Kirby, 1837

Grain Beetles

At least some saproxylic species should soon be found under bark, whereas the stored product pests are very sporadic, and rarely encountered outside of commercial premises.

POLYPHAGA Emery, 1886

CUCUJOIDEA Latreille, 1802

2-7mm

Suborder:

Superfamily:

Subfamilies:

Genera:

Species:

Size:

Introduction

This cosmopolitan family includes about 500 described species in about 60 genera and 2 subfamilies although the arrangement has varied widely with up to 4 subfamilies being recognized; major groups such as Psammoecinae and Cryptomorphinae are now treated as tribes of the Sylvaninae Kirby, 1837. Although many variations will be found the Brontinae Erichson, 1845/Blanchard, 1845 now includes 10 genera and about 40 species and is not divided into tribes; former tribes include Hyliotini Reitter, 1879 and Uleiotini Gistel, 1856. At one time the Brontinae included the Telephanini LeConte, 1861 to accommodate the genus Telephanes Erichson, 1845, a large pantropical group of about 110 species, the distinction being the form of the anterior coxal cavities; open in Brontini and closed in Telephanini, but the group is now included in the Silvaninae. Species of the Brontinae are distributed throughout the Holarctic, Oriental and Australasian regions and several occur in Madagascar but only a single species, Parahyliota africanus Grouvelle, 1889, occurs in Africa, and two are Neotropical, a single species of Australohyliota Thomas, 2004, the other member of the genus occurring in Australia, and the only member of the genus Microhyliota Thomas, 2004; M. Integricollis (Fairmaire, 1860). Silvaninae is a cosmopolitan group of about 50 genera included in 3 tribes. Cryptamorphini Casey, 1884 includes about 30 species of Cryptamorphus Wollaston, 1854, 17 of which occur in Australia and/or New Zealand and the remainder in southern Asia or Indonesia. C. redtenbacheri (Reitter, 1876) is doubtfully recorded from Chile and C. desjardinsi (Guérin-Méneville, 1844) is cosmopolitan. Psammoecini Reitter, 1829 includes 5 genera, 2 of which are large; Psammoecus Latreille, 1829 with more than 80 species is a widely distributed old world genus with the greatest diversity in southeast Asia and Australia, and Telephanus Erichson, 1845, with more than 100 mostly new world species with the greatest diversity in the Neotropical region where many are localized or Island endemics e.g. T. dentatus Nevermann, 1937 from Haiti and the Dominican Republic, and T. darlingtoni Nevermann, 1937 from Jamaica. With one exception the remaining genera

are monotypic; Pseudochrodes suturalis Reitter, 1876 is Neotropical, Indophanus dakshinus Pal, 1982 is Indian, Psammaeochidius spinicollis Fairmaire, 1869 is Madagascan, and Megapsammoecus Karner, 1995 includes a species from China and one from India. The cosmopolitan tribe Silvanini Kirby, 1837 includes the majority of the genera, some of which are localized or Island endemics e.g. Acathartus insignus (Grouvelle, 1895) from Sumatra, Metacorimus mroczkowskii Halstead, 1997 from Cameroon or Astilpnus reflexicollis (Motschulsky, 1868) from Egypt. Cathartosilvanus tropicalis (Van Dyke, 1953) occurs on the Galapagos Islands. Some larger genera have interesting distributions e.g. Austronausibus Halstead, 1980 includes 6 Australian species while Eunausibius Grouvelle, 1912 includes 5 Neotropical species, and Airaphilus Redtenbacher, 1858, with about 36 species is mostly Palaearctic but with a single species from India, 3 from South Africa and one from Ethiopia, there are also several Island endemics e.g. A. nubigena (Wollaston, 1863) from Tenerife and A. vaulogeri Grouvelle, 1912 from Tunisia. Many species have become dispersed through trade etc. e.g. Eurausibius salutaris Parsons, 1974, native to Brazil and Guyana, is now established in the United States, and Silvanus lateritius Broun, 1880 is native to Australia but also occurs in South Africa, Hawaii and Madeira.

The central European Silvanid fauna includes 17 species of 12 genera of which 8 are synanthropic while the Nearctic fauna includes 32 species in 14 genera. Among the U.K. fauna the family is most closely related to the Cucujidae although more generally there is a closer phylogenetic relationship with the Passandridae Erichson, 1845.

Adults of some species of the Brontinae can reach 15mm but the majority of Silvanids are less than 10mm in length. The habitus is generally elongate and near parallel-sided and most species are to some extent flattened, often strongly so, and some e.g. species of Dendrophagus or Uleiota superficially resemble cerambycids while others e.g. species of Telephanus or Psammoecus resemble carabids but most will be recognized, with a little experience, from the overall form. Most are drab coloured, black to pale brown although several genera include maculate or patterned species e.g. Psammoecus or Monanus and the Nearctic Telephanus atricapillus Erichson, 1846 is among the most attractive. In general the Brontinae are larger, less compact and have longer antennae and in some species the mandibles of the male are modified. Members of Brontinae and the silvanine genus Telephanus have inverted male genitalia, open procoxal cavities and mandibular mycangia; structures adapted for the transportation of symbiotic fungi. The remaining genera of the silvaninae lack these characters.

Description

The head is very variable; prognathous with the labrum usually visible and well-sclerotized. The mandibles are visible from above, with bidentate or bilobed apices and the inner edge simple or with a single tooth. The apical segment of the labial and maxillary palpi is usually cylindrical, never securiform. The eyes vary from large and convex e.g. Ahasverus to small and relatively flat e.g. Oryzaephilus, the size of the facets is also variable and in some species the eyes are finely pubescent. The antennae are vary widely; from distinctly clubbed e.g. in Silvanoprus Reitter, 1911 to filiform e.g. in Psammoecus and they are sometimes very long as in most Brontinae but the longest, proportional to the body, are probably seen in the Neotropical species Australohyliota chilensis (Blanchard, 1851). The insertions are sometimes visible from above. The vertex is variously punctured and to some extent convex although often depressed behind the labrum and sometimes sculptured e.g. the Australian Nepharinus goudiei (Lea, 1904) has a very elongate head with short and thick filiform antennae and raised ridges to the head, pronotum and elytra. The temples may be short and constricted towards the base as in Psammoecus or variously expanded and even toothed e.g. in Silvanus. In many species the width of the head, measured across the eyes, is equal to or a little narrower than the anterior margin of the pronotum. The form of the pronotum is very variable, generally quadrate to elongate and from convex e.g. in Ahasverus to flat as in Uleiota, the surface is variably punctured and sometimes has raised sculpture or depressions. The lateral margins may be smooth and almost parallel-sided e.g.in Ahasverus longulus (Blatchley, 1910) or sinuate e.g. in species of Dendrophagus but in general they are dentate and this is a good indicator of the family; common among members are laterally or anteriorly produced anterior angles which vary from smoothly rounded to sharply acute and lateral margins varying from being finely denticulate to having unequally spaced larger teeth e.g. in Oryzaephilus surinamensis (Linnaeus, 1758); sometimes the entire margin is toothed e.g. in Austronausibius aemulus Halstead, 1980 with 4 or 5 large teeth, and sometimes there are various irregular lateral projections and teeth e.g. in species of the New Zealand genus Brontipriscus Sharp, 1886, Megahyliota feae (Grouvelle, 1892) from Thailand or species of Macrohyliota Thomas, 2004 from southeast Asia and Australia but perhaps most developed in species of Brontoliota Thomas, 2004 from Queensland. The scutellum is usually obvious. The elytra tend to be subparallel or weakly rounded laterally and evenly rounded apically to cover the entire abdomen although in some tropical species they vary from obliquely truncate to separately produced. In some the surface is smooth or weakly carinate, especially in temperate Brontinae, but most species have between 6 and 10 well-formed and punctured striae and in some there is also a scutellary striole. The interstices are variously punctured and sculptured and in some there are longitudinal carinae, in many, or even most, they are finely pubescent. The legs are usually robust and relatively long with the femora much wider than the tibiae. The pro- and mesocoxae lie in depressions; the pro coxae are circular with the cavities open or closed, and well separated, the mesocoxal cavities are open laterally and the metacoxae only weakly transverse, if at all. The tarsi are usually 5,5,5 although sometimes appear to be 4,4,4 due to the tiny basal segment, with the segments variously lobed beneath, in some Telephanus strongly so, and the last segment elongate. The claws are generally smooth and lack appendages.

As with most groups of beetles the various characters can become exaggerated in tropical or subtropical species and in the present family some examples of this can be seen in Telephanus gomyi Thomas, 1992 or T. allaudi Grouvelle, 1899 in which there are long erect setae to the pronotum and elytra, or perhaps most spectacularly in the Madagascan T. spinosus Grouvelle, 1890 with huge mandibles, massively developed hind femora which are toothed on the inner margin, very long metatibiae which bear a large internal tooth, and widely bilobed tarsal segments.

Ecology

The majority of species of the Silvanidae are thought to be fungivores and most are saproxylic, occurring beneath the bark of damaged or fallen trees and logs etc. Most temperate species occur under the bark of deciduous trees especially oak, beech and hornbeam but a few occur under conifer bark and some have a wide host range e.g. Silvanus muticus Sharp, 1899, a native Nearctic and Neotropical species recently imported into Europe, occurs beneath both deciduous and coniferous bark. In tropical regions they occur under the bark of a wide range of species e.g. Ficus and in the case of S. lateritius Broun, 1880, Eucalyptus. Species of Cryptamorpha Wollaston, 1854 have been recorded on Corynocarpus (New Zealand Laurel), Dracophylum (Australian ‘Grass Trees’) and the monocotyledon Cordyline. Some species are known to be predacious e.g. Cathartus quadricollis (Guérin-Méneville, 1844), The Square-necked Grain Beetle, has been found inside coffee beans feeding upon larvae of the coffee bean borer weevil, Hypothenemus hampei (Ferrari, 1867) (Scolytinae) and in macadamia nuts feeding upon the tropical nut borer weevil H. obscurus (Fabricius, 1801) in Hawaii. Species of Brontoliota Thomas, 2004 occur on the outside of fallen branches etc. in wet forest areas of Queensland, and Protodendrophagus antipodes Thomas, 2004 occurs under rocks in alpine areas of New Zealand. Adults of many species of the very diverse Neotropical genus Telephanus Erichson, 1845 occur on decaying leaves of a range of woody and herbaceous plants especially Heliconaceae (vines.) Outside temperate regions many silvanids occur in the soil and among leaf litter and several genera e.g. Nepharus Laporte, 1869 or Nepharinus Grouvelle, 1912 have become inquilines in ant nests in Australia. The genus Coccidotrophus Schwarz & Barber, 1921 includes 2 Neotropical species both of which are adapted to live among the foliage of ant-plants (Tachigalia sp.), feeding upon the honeydew produced by mealybugs (Pseudococcidae.) At least one species of Eunausibius Grouvelle, 1912 is thought to have a similar lifestyle.

Several genera have been transported along with commercial timber and foodstuffs and now have a cosmopolitan or near-cosmopolitan distribution e.g. Monanus Sharp, 1879, Cryptamorpha Wollaston, 1854, Silvanus Latrielle, 1804, Ahasverus des Gozis, 1881 and Oryzaephilus Ganglbauer, 1899. Among these are several species which have become serious pests of stored products; the most economically important being 2 species of Oryzaephilus; O. Surinamensis (Linnaeus, 1758), The Saw-toothed Grain Beetle, and O. mercator (Fauvel, 1889), The Merchant Grain Beetle. Both are cosmopolitan and most prolific in tropical climates and both are secondary pests of stored grain, feeding upon fungal infections of damaged seeds and spreading spores although a wide range of other products may become infested e.g. oilseed, cereals of all kinds, nuts, copra, confectionary and any kind of milled products. Ahasverus advena (Waltl, 1834), The Foreign Grain Beetle, feeds upon moulds among damaged grain and milling refuse etc. and Cathartus quadricollis (Guérin-Méneville, 1844), The Square-necked Grain Beetle, is one of the commonest Nearctic pests of stored corn while also attacking developing plants in the field.

UK Species

The U.K. list includes 12 species in 10 genera although many others have been recorded among imports.

Ahasverus des Gozis, 1881 is a mostly new world genus of 10 species although A. advena (Waltl, 1834) has become cosmopolitan through trade and is now established in the U.K.
Uleiota Latreille, 1796 is a Holarctic genus of 8 species saproxylic beetles. U. planata (Linnaeus, 1761) is widespread through England and Wales, occurring beneath the bark of a range of deciduous trees.
Dendrophagus Schönherr, 1809 includes 3 species; D. cygnaei Mannerheim, 1846 is Nearctic, D. longicornis Reitter, 1889 occurs in Japan and the type species, D. crenatus (Paykull, 1799) is Palaearctic. D. crenatus occurs very locally under the bark of fallen pine trees and logs in the Scottish Highlands.
The widespread old world genus Psammoecus Latreille in Cuvier, 1829 includes more than 80 species, most of which occur in tropical regions and several of which are island endemics. The single European species P. bipunctatus (Fabricius, 1792) occurs throughout England and Wales north to Yorkshire; it is a wetland species and may be especially common in reed beds, often swarming on summer evenings.
Cathartus quadricollis (Guérin-Méneville, 1844), the only member of the genus, is a cosmopolitan pest species regularly imported into the U.K. in stored products.
Cryptamorpha Wollaston, 1854 includes about 30 species, most of which occur in the Austalasian region. Desjardins’ Flat Beetle, C. desjardinsii (Guérin-Méneville, 1844) is native to tropical Asia but is now cosmopolitan through trade; it occurs throughout Europe and is regularly imported into the U.K. in stored fruits etc.
Nausibius Lentz, 1857 includes 12 species; 11 are Neotropical and one, the pest species N. clavicornis (Kugelann, 1794) is cosmopolitan and has become established in the U.K. following introductions in stored food products.
Oryzaephilus Ganglbauer, 1899 includes 15 species occurring mostly in old world tropical regions. The two cosmopolitan pest species; O. surinamensis and O. mercator occur regularly in the U.K. in stored grain, the former species being the more common.
Silvanoprus Reitter, 1911 includes about 20 old world species although they are absent from Australia and New Zealand. The European S. fagi (Guérin-Méneville, 1844) occurs very locally in southern England; there are records from Hampshire and around the Thames estuary.
Silvanus Latreille, 1804 includes about 20 species of saproxylic beetles occurring throughout the world with the exception of the Neotropical region. Two species occur in the U.K. S. unidentatus (Olivier, 1790) is a widespread Palaearctic and Nearctic species while S. bidentatus (Fabricius, 1792) is more widespread; Holarctic and also recorded from India, Thailand and Hawaii.