Isorhipis melasoides (Laporte, 1835)

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POLYPHAGA Emery, 1886

ELATEROIDEA Leach, 1815

EUCNEMIDAE Eschscholtz, 1829

MELASINAE Fleming, 1821

MELASINI Fleming, 1821

Isorhipis Lacordaire, 1835

This is a mostly southern and central European species; it is locally common across the south from Spain to Greece and the Near East, and more sporadic and scarce further north to Germany, Poland and, recently, from Lithuania, it is absent from the other Baltic countries but it occurs further north in parts of western Russia. It has only recently been added to the UK list, from specimens found breeding in a Berkshire woodland , but is known from bronze age fossils which might suggest it has survived here undetected ever since, but these recent specimens are more likely to be from recently introduced material. Typical habitats are broadleaved woodland and wooded parkland; this may be old-established or recent as the species is very active and noted for dispersing and colonizing new areas. Adults are active in June and July although specimens have been found much earlier and later than this, they are sometimes active in the evening or at night but are primarily diurnal, spending most of their time on fallen wood or trunks; they are generally very active, running and flying readily in bright sun, especially in the afternoon. Mating occurs through their short season and females oviposit in hard, damp wood, usually in crevices or old bark beetle emergence holes etc, and often in relatively small branches on standing dead trees or in trees that have died young. Larvae have been recorded from a wide range of trees including Beech (Fagus sylvatica L.), Lime (Tilia L.), Hornbeam (Carpinus L.), Poplar (Populus L.), Elm (Ulmus L.), Alder (Alnus glutinosa L.) and, less frequently, oak (Quercus L.) and very probably other species as well. The mycophagous larvae bore into dead xylem, producing tunnels perpendicular to the grain, they develop into the autumn and overwinter deep in the wood, then resume feeding in the spring and pupate in situ during May and adults eclose after about ten days. Adults emerge over a short period; they leave the wood through round emergence holes which may be detected by the presence of accumulated fine wood pulp.

Isorhipis melasoides 1

Isorhipis melasoides 1

© Lech Borowiec http://www.cassidae.uni.wroc.pl/Colpolon/index.htm

7.8-11.0 mm. Elongate and fusiform, body dark grey to dark chestnut-brown, sometimes with the forebody and elytra contrasting, with golden pubescence throughout, appendages pale brown. Superficially similar to many elaterids but distinguished by the form of the antennae; the basal segment is long and curved and the small second segment is inserted eccentrically on the basal segment. Head hypognathous with large but weakly convex eyes and short, diverging temples, vertex and frons evenly convex and densely punctured, clypeus broadened anteriorly, antennae inserted in deep lateral incisions in front of the eyes; separated by the length of the basal segment in the male, a little less in the female. Antennae strongly dimorphic; in the female strongly serrate from the fourth segment, in the male strongly pectinate with the third segment strongly expanded from the base. Pronotum quadrate or slightly transverse, broadest about the middle (female) or across the posterior angles (male), lateral margin sinuate and finely bordered, apical margin weakly curved, surface densely punctured, confluently so in places and with a median longitudinal impression from the base extending onto the disc, posterior angles produced backwards but not very strongly so, basal margin strongly bisinuate; indented at the centre and produced into two small teeth that flank the scutellum. Scutellum rounded in the female, triangular in the male. Elytra broadest behind the shoulders and narrowed to separately rounded apical margins, basal margins strongly rounded, surface finely punctured and granulate throughout, with finely impressed striae which fade towards the apex. Legs long and slender, all tibiae with fine apical spur, basal segments of all tarsi very long, fourth segment bilobed. Claws smooth and without a basal tooth. Among our UK fauna this species might only be confused with Microrhagus pygmaeus (Fabricius, 1792).

Similar species
  • Smaller (3.5-6.0 mm)

  • Antennae less developed in both sexes

  • Antennal insertions placed closer together

  • Basal pronotal margin not produced into teeth that flank the scutellum

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