Family EUCNEMIDAE

Euryptichus porosus

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Family EUCNEMIDAE

Click Beetles, Eucnemids

Compiler and date details

31 December 1996 - Andrew A. Calder, CSIRO Entomology, Canberra, Australian Capital Territory, Australia

Introduction

The Eucnemidae (= Melasidae) are a cosmopolitan family found mainly in tropical regions and contains about 190 genera and 1200 species (Lawrence 1982). The Australian fauna consists of 35 genera and 90 species arranged in four subfamilies and 17 tribes. The first catalogue of the Australian species by Masters (1886) listed nine genera and 16 species. Four decades later the world fauna was catalogued by Schenkling (1928) who listed 24 genera and 71 species from Australia. The Australian fauna is currently under revision by Jyrki Muona and the arrangement followed in this Catalogue is detailed in Muona's phylogenetic analysis of the family (Muona 1993). Synonynies and occurrences first published in the Zoological Catalogue (Calder 1998) but deriving J. Muona's studies on eucnemids are accredited to him.

Eucnemids were first recognised formally as the group Melasidae, by Fleming (1821). However, this work and thus correct name for the family was ignored by nearly all subsequent workers on the group. Eschscholtz (1829) erected the tribe Eucnemides, which has become the name that has since gained universal acceptance. Lacordaire (1857) divided the Eucnemides into three groups: Melasides, Eucnemides vrais and Perothopides following the work of Guérin-Méneville (1843). Bonvouloir (1871, 1872, 1875) monographed the family as Eucnemides also including Balgus Fleutiaux and its allies (the thylacosternine genera), which have been moved either to the Elateridae (Lameere 1900; Calder 1996) or alternatively to the Throscidae (Crowson 1955; Muona 1993, 1996). Another two small genera, Potergus Bonvouloir and Subprotelater Fleutiaux, have since been correctly placed in the Throscidae and Elateridae respectively by Cobos (1959, 1961). Cobos (1964) provided the first major work on the classification of the Eucnemidae since 1950 and recognised five subfamilies: Gastraulacinae, Eucneminae, Melasinae, Dirhaginae and Perothopinae. Muona (1993) attempted to find a more natural classificatory system that relied on finding characters that demonstrate sister group relationships. This work recognised 30 tribes arranged in eight subfamilies—Perothopinae, Phyllocerinae, Pseudomeninae, Palaeoxeninae, Phlegoninae, Melasinae, Eucneminae, and Macraulacinae. Of these, only four subfamilies and 17 tribes are represented in the Australian fauna.

The first eucnemid to be described from Australia was Galbodema mannerheimii, by F.L. de Laporte, Comte de Castelnau (Laporte 1835), from the collection of Gory. However, another species, Galbites marmoratus (as Galba), now known to occur in Queensland, had previously been illustrated from specimens from Indonesia (Guérin-Méneville 1830). Castelnau (1840) described Galba hagenbachii from unknown provenance, a species now synonymised with Galbodema mannerheimii, and Montrousier (1855) decribed another Galbites, Galba tomentosa. In his monograph of the family, Bonvouloir (1871, 1872, 1875) was responsible for describing another 20 species from Australia, two of which are synonyms. Macleay (1872) described Hemiopsida mastersii and an eucnemid Acroniopus pubescens, as an elaterid, both from Gayndah, Queensland. The latter was ascribed to the eucnemid genus Nematodes Berthold by Lea (1920). Blackburn (1892a, 1892b, 1895, 1900) described 11 species and Lea (1895, 1916, 1919, 1929) another 42 species among which only three are recognised as synonyms. Fleutiaux (1896, 1912, 1931) described four species from Australia and Schwarz (1902) described Lycaon atra (= Hemiopsida atra) from an unknown Australian locality. More recently, Cobos (1964, 1979) described eight new species and the genera Janczykia and Pseudofornax now synonymised with Entomosatopus and Discaptothorax respectively and Freyiola, from specimens collected in Queensland. Recently, Muona (1993) described four new species and five genera as a result of his phylogenetic studies on the family. Most of the Australian eucnemid species so far known were described during the Macleayian Period of Australian entomology (Musgrave 1930) with 86 species being characterised. Only four species were described during the Westwoodian Period, and 13 species during the recent Musgravian Period (Whitley 1961). Between 1871 and 1929, Lea and Bonvouloir described most of our species, amounting to a total of 60% of the known Australian fauna.

The eucnemid fauna of Australia contains several endemic genera. These include
Anabalodes Strand, Dictyeucnemis Lea, Discaptothorax Blackburn, Echthrogaster Blackburn, Freyiola Cobos, Jenibuntor Muona, Myall Muona, Onya Muona, Orodotes Bonvouloir, Pinaroo Muona, Pseudomenes Fleutiaux and Yanga Muona. The genera Galbites Fleutiaux, Dromaeoloides Cobos, Heterotaxis Bonvouloir and Hylis des Gozis, are shared with New Guinea. Agalba Broun and Dromaeolus Kiesenwetter are shared with New Zealand. Widespread genera include Arrhipis Bonvouloir, Dromaeolus Kiesenwetter, Entomophthalmus Bonvouloir, Euryptychus LeConte, Fornax LaPorte, Heterotaxis, Macroscython Fleutiaux, Microrhagus Dejean and Nematodes Berthold, and are shared with several other zoogeographic regions.

Eucnemids are common in forested and woodland regions where they breed in decaying wood. Adults are secretive in habits and are rarely encountered in general collecting, being fairly rare in museum collections. Both adults and larvae can be found in decaying logs while many adults are attracted to light. Hammond (1990) and Penny & Arias (1982) have shown that the Eucnemidae form a major group of beetles in lowland closed forests in Indonesia (Sulawesi) and Brazil, respectively. Most adult eucnemids are capable of clicking like elaterids by a mechanism which also involves a prosternal process and mesosternal cavity. However, this jumping action is rarely employed as a mechanism for righting themselves, but rather is a means to startle predators. Muona (1993) has observed three species of eucnemid producing a series of rapid clicking sounds while at the same time attempting to escape predators (or disturbances) by running away.

Eucnemid larvae are inhabitants of dead wood and are possibly liquid feeders. Lawrence & Britton (1994) suggested that the larvae possibly digest wood fibres extraorally, but they may also feed on slime mould plasmodia or other available nutrients resulting from fungal decay in the wood. Muona (1993) provided a review of the biology of this family, summarising the literature and providing many original observations on the habits and development of numerous species.

Diagnosis

Adult eucnemids are elongate, cylindrical to slightly flattened beetles covered with a fine pubescence. They are small to medium sized beetles that range in length from 2 to 18 mm. The head is hypognathous and the labrum is concealed beneath the frontoclypeal region. A frontal ridge is absent. The eyes are usually large; the antennae are inserted some distance from the eyes and in some species are received into hypomeral grooves. The antennae are often more elaborate and elongate in the males. Antennomeres 3–11 have sensory pegs. The pronotum has acute hind angles and a prosternal process which is received in a mesosternal cavity similar to that found in elaterids. All five abdominal ventrites are connate. The tarsi are usually simple but have membranous appendages on segments 2–4 in Galbites Fleutiaux. The first tarsomere of the fore leg usually has a sex comb. The aedeagus is of the trilobed polyphagan type and has undergone extensive modification in this family. The parameres of the aedeagus often form a tube surrounding the median lobe. The ovipositor can be well sclerotised without apical styli or weakly sclerotised with apical styli. Paired colleterial glands are absent and the spermathecal gland is attached to the spermathecal capsule. The bursa copulatrix lacks sclerotised structures that are so typical of most of the elaterids (Lawrence 1982; Lawrence & Muona 1993; Britton 1994).

Larval eucnemids are elongate, slightly to strongly flattened and are either lightly or strongly sclerotised. The head is prognathous, depressed, with reduced maxillae and labium and non-opposable mandibles, that are narrowed anteriorly in lateral view, sometimes forming a sharp wedge. The antennae are vestigial or reduced to a 2-segmented rudiment. The legs are highly reduced or absent. Tergite 9 may or may not possess fixed urogomphi and segment 10 is reduced and fused with segment 9. The spiracles are biforous and have a closing apparatus. Two main types of eucnemid larvae are known: the first resembles a buprestid larva with a subcylindrical, lightly sclerotised body that has an enlarged prothorax bearing rod-like sclerotisations and dorsally exposed mouthparts that is found in Trigonopleurus and its relatives; the second has a depressed, parallel-sided, distinctly sclerotised body, with a sclerotised wedge-like head with mouthparts not exposed dorsally and is characteristic of Fornax and its allies (Becker 1991; Lawrence & Britton 1994).