Rhizophagus aeneus (Richter, 1820)
POLYPHAGA Emery, 1886
CUCUJOIDEA Latreille, 1802
RHIZOPHAGINAE Redtenbacher, 1845
Formerly classified as a distinct genus, Cyanostolus Ganglbauer, 1899 is now included as a subgenus of Rhizophagus and includes only the present species. Seemingly very local and generally scarce throughout its range, this species occurs from the Pyrenees through northern Italy to Bulgaria in the south and north to the UK, Latvia and a few southern and central parts areas of Norway, where it is red-listed, and Finland, the eastern limit of its range being parts of eastern European Russia. The species occurs from lowlands to boreal and alpine regions but in many northern areas of Europe it is thought to have declined over recent decades due to water and forestry management. In the UK it is very local and rare across Wales and southern England, it was formerly much more widespread, extending into southern Scotland, but seems to have declined over the 20th century. Adults occur year-round, they overwinter under bark or among dead wood and are active over a long season from March until September, peaking in abundance during May and June. Typical habitats are river and lake margins, marshes and seasonally flooded woodland. Adults occur under dead bark on stumps and standing or fallen trunks and branches of a wide range of deciduous trees, always where it is damp and often where the wood is partly submerged, they prefer wet and slightly loose bark on soft wood but may also occur under dead but tightly fitting bark on fallen willows etc. Both teneral adults and fully-grown larvae have been observed late in July, both stages are thought to be predatory, although they are sometimes quoted as fungivores, on subcortical insects and their larvae, and adults have been observed attacking scolytid (species of Xyleborus Eichhoff, 1864) adults and larvae. Beyond this little is known of the biology. Adults may be found by searching under bark, the most likely places being damp or wet bark on recently dead trees that are subject to periodic inundation, but they are primarily nocturnal, they sometimes wander on bark and during warm summer nights they disperse by flight.
Rhizophagus aeneus 1
Rhizophagus aeneus 2
© Lech Borowiec
2.2-3.3 mm. Elongate, rather flat and discontinuous in outline with the elytra clearly wider than the pronotum, body black to dark brown, forebody without or with a faint blue or green metallic lustre, elytra more strongly metallic, antennae pale with dark clubs, legs brown or with darker femora. Head broadest across convex and prominent eyes, temples short and converging, surface without sculpture, finely punctured throughout. Antennae placed laterally in front of the eyes, 10-segmented and abruptly clubbed. Pronotum quadrate or slightly transverse, broadest about the middle and evenly curved to widely rounded angles, the margin finely crenulate, basal and apical margins weakly curved and very finely bordered, surface evenly and rather sparsely punctured throughout, a little more strongly so than the head, and with fine but distinct granular microsculpture. Elytra evenly curved laterally from rounded and extremely finely toothed shoulders to separately curved apical margins which do not completely cover the abdomen, each with nine punctured and weakly-impressed striae and weakly convex interstices, surface with granular microsculpture that is a little stronger than that on the pronotum. Legs long and slender. Femora unarmed, tibiae gradually widened from the base to truncate apices, margins without teeth or spines and each with a short external apical spur, the front tibiae also with a short and curved internal spur. Tarsi 5-segmented in females, 5-5-4 in males, in each case the terminal segment about as long as the others combined.