Merodon aureus, FABRICIUS, 1805

Merodon aureus View in CoL B in Milankov et al. (2008).

Redescription: MALE ( Figs 10, 11, 12A, B): Length of body 6–10 mm, of wing 6–8 mm (N = 120). Head ( Figs 11A, C, 12B): Antenna brown; basoflagellomere reddish-brown to dark-brown, 1.3–1.5 times longer than pedicel [length of basoflagellomere as on fig. 5 in Marcos-García et al. (2007)], dorsal margin concave between the arista and the apex, apex rounded; arista yellow basally, as long as pedicel and basoflagellomere together; face and frons shiny black with olive lustre, covered with long pale-yellow pile and indistinct scarce brownish microtrichia, most visible along eye margin; ventral part of face bare, with black lustre; vertical triangle isosceles, shiny black, predominantly covered with long, pale pile, except at anterior end with black ones; eye contiguity more than 20 ommatidia long; ocellar triangle equilateral; eye pile long, black in the upper half or more and lower corner, paler between; occiput shiny, silver-green, covered with whitish microtrichia and pale-yellow pile. Thorax ( Fig. 11A, B, D): Mesonotum brown with olive-green reflections, rough punctate, covered with long, dense, erect yellow to orange pile; scutum with three weak vittae of dark brown microtrichia; posterior anepisternum, anepimeron and dorsal part of katepisternum with long yellow pile. Wing: Hyaline, with dark-brown veins; calypteres brownish; halteres with brown pedicel and dark brown capitulum. Legs: Femora black with brown apex; pile on pro- and mesofemur predominantly yellow, except black pile medially; metafemur predominantly covered with yellow pile, except short, black ones in the apical quarter medially; tibiae and tarsi black, except dark brown basis of tibiae, covered with yellow pile with some intermixed black ones; metatrochanter with inner spine ending in two angular points (one corner more protruded). Abdomen ( Fig. 11A, E): Oval, slightly longer than mesonotum; black with olive-green reflections; terga completely covered with yellow to orange pile; sterna shiny black, covered with long, light yellow pile. Male terminalia: Similar to all other species of the M. aureus group ( Fig. 10). FEMALE ( Figs 13A, 14): Similar to the male except for normal sexual dimorphism. Head: Frons shiny black; vertex mostly covered with black pile, except for posterior end covered with yellow ones. Legs: Metatrochanter without spine. Abdomen: Shiny black, with pairs of white microtrichose fasciae on terga 2–4; on tergum 2 these fasciae are subparallel to the anterior margin of the tergum, whereas on terga 3–4 these fasciae are oblique; terga partly covered with pale pile; black pile present in medial parts of posterior half of tergum 2, all of tergum 3 and on anterior half of tergum 4, except on mictrotrichose fasciae; tergum 5 covered with yellow pile with some intermixed black ones.

Diagnosis: Eye pile black at least in upper half ( Fig.12A,B) (all white in M.unicolor ); pile on metafemur whitish yellow ( Fig. 11B); similar to Merodon pumilus from which it can be separated by eye contiguity longer than 16 ommatidia, approximately as long as vertical triangle (eye contiguity in M. pumilus 5–10 ommatidia); in female ocellar triangle equilateral or isosceles, if isosceles then two lateral sides longer than basal ( Fig. 13A), while in M. pumilus isosceles, two lateral sides shorter than basal ( Fig. 13B); distance between two posterior ocelli (in Fig. 13A: pink line) comparing distance between posterior ocellus and eye margin shorter in M. aureus (in Fig. 13A: yellow line), while in M. pumilus distance between two posterior ocelli (in Fig. 13B: pink line) comparing distance between posterior ocellus and eye margin longer (in Fig. 13B: yellow line).

Material examined: Type material: Syrphus aureus Fabricius, 1805: 198 . Type locality: Germany. Described based on unspecified number of specimens. There are two specimens in the collection considered here as syntypes. Lectotype, designated here, deposited in Copenhagen Museum – ZMUC, with two wings and part of thorax remains on pin, with handwritten label ‘aureus’ (see Fig. 15). Other syntype is even more destroyed, but still with wings and small part of thorax, designated as paralectotype.

Merodon aeneus Megerle View in CoL in Meigen, 1822: 367. Type locality: Austria. Type material presumably lost. Neotype (designated here) ♂ AUSTRIA, Lower Austria, Josefsthal   GoogleMaps , 1856, 48.962132N 15.013034E, Mann leg. (NHMW).

We chose the specimen from Austria as a neotype of M. aeneus View in CoL based on type locality designated in the original description ( Austria). The neotype is the property of the Naturhistorisches Museum Wien, Vienna, Austria ( NHMW), which maintains a historical collection, with proper facilities for preserving namebearing types, and that makes them accessible for study .

Notes: Speight (2018) reported: “In the Biosystematic Database of World Diptera ( Thompson & Brake, 2005) , Merodon aeneus is given as a synonym of M. aureus Fabricius , but without providing any justification for this supposed synonymy.” Speight (2018) also discuss the type of M. aureus : “Unfortunately, since Fabricius' description of M. aureus is inadequate to decide the identity of the species to which it applies and the type material of M. aureus is reduced to a remnant comprising, according to Zimsen (1964), ‘only wings’, there is no basis for establishing this synonymy, unless a neotype can be designated for M. aureus (assuming this would be a valid act in the circumstance that there remains a fragment of the original type material, however useless) and a redefinition of M. aureus can be provided, that permits its separation from the other Merodon taxa to which it is closely related and which have recently been either re-established as species or described as new species (see Marcos-García et al., 2007). No such actions have been taken in any publication produced to date and, until and unless some meaningful basis is established for the claim that M. aeneus is a synonym of M. aureus , that synonymy is here regarded as unproven. These problems are confounded by the reality that the description of M. aeneus cannot be used to separate it from other segregates of the aeneus complex now recognised as distinct species and the type material of M. aeneus cannot be found.”

Descriptions of M. aureus and M. aeneus are relatively poor with information, but some key characters can be extracted. Fabricius (1805) described males from Germany under the name Syrphus aureus and provided some useful characters: small species with orange head and dark antenna, body shining, pile orange (golden), thorax orange, without spots, abdomen black, legs dark, femora black, thickened, with dentate plate. Meigen (1822) described M. aeneus based on a single female from Austria with only few characteristics that can be used in the identification of this taxon: metallic dark-green species, with yellow pilosity and brown antenna.

There is only one species morphologically in accordance with both descriptions ( aureus and aeneus ) in Central Europe from where the type material from both names originated ( Germany, Austria, also in Switzerland). Concerning this, we believe that both names refer to the same species. Using the remaining fragment of the M. aureus type, we were able to identify this specimen as conspecific with populations cited here under this name. Scutum and coloration of pile perfectly match the M. aureus complex and the wing in our geometric morphometric analyses fit 99% to central European populations.

Among seven species known for Germany, M. aberrans , M. aeneus ( M. aureus ), M. armipes , M. equestris , M. moenium , M. ruficornis and M. rufus ( Speight 2018) , Fabricius (1805) lectotype of M. aureus fit to specimens from Germany until now identified as M. aeneus . Based on that we propose a designation of neotype for M. aeneus , and an establishment of correct synonymy.

We propose here a re-evaluation of a taxon present in high Central European (and Balkans) mountains under the name M. aureus , with the name M. aeneus as a junior synonym. The taxon presented by Milankov et al. (2008) under the name M. aureus B, is conspecific with the ‘real’ M. aureus .

Biology and preferred habitat: Preradović et al. (2018) described the pupa under the name of Merodon aureus . Molecular data presented here reidentified this pupa as an immature stage of Merodon calidus . Speight (2018) listed biological data under the name M. aeneus . Preferred environment: Open ground; unimproved, calcareous montane grassland. Adult habitat and habits: Flies fast and low over ground vegetation in open situations; settles on vegetation, bare ground and stones in the sun. Flowers visited: Apiaceae ; Anthericum ramosum L., Leucanthemum vulgare Lam. , Mentha , Ranunculus , Solidago , Taraxacum . Flight period: End of May to August. At higher elevations, the peak is in July/August.

Distribution: Distributed in high Central European (and Balkans) mountains: The Alps in France, Austria, Germany, Switzerland, Italy and Slovenia, the Apennine Peninsula and the Dinaric mountain range in Croatia, Bosnia and Herzegovina, Serbia and Bulgaria. Elevation range starts from sea level up to 2650 m ( Figs 7, 16).