Metadon Reemer

Reemer, Menno & Stahls, Gunilla, 2013, Generic revision and species classification of the Microdontinae (Diptera, Syrphidae), ZooKeys 288, pp. 1-213 : 38-40

Metadon Reemer gen. n. Figs 163-175

Type species:

Microdon wulpii Mik, 1899: 143. Type locality: Indonesia, Sumatra. Replacement name for Microdon apicalis Wulp, 1892: 29 (preoccupied by Walker, 1858).

Description.

Body length: 7-21 mm. Slender to moderately broadly built flies with oval abdomen and long antennae. Head slightly wider than thorax. Face almost straight to convex in profile; narrower to wider than an eye. Lateral oral margins produced or not produced. Vertex flat. Occiput ventrally narrow, dorsally widened. Eye bare. Eye margins in male converging at level of frons, with mutual distance 2-3 times as large as width of antennal fossa. Antennal fossa about as wide as high. Antenna longer than distance between antennal fossa and anterior oral margin; basoflagellomere shorter than scape; bare. Postpronotum pilose. Scutellum semicircular; with or without calcars. Anepisternum sulcate; entirely pilose, except sometimes with small bare part ventrally (only known exception: Metadon bifasciatus , in which anepisternum is bare on entire ventral half). Anepimeron entirely pilose. Katepimeron flat to somewhat convex; smooth or with wrinkled texture; not pilose, but often with rows of microtrichia. Katatergum with oblique rows of microtrichia. Wing: vein R4+5 with posterior appendix; vein M1 more or less straight, perpendicular to vein R4+5; postero-apical corner of cell r4+5 angular to widely rounded, with or without appendix; crossvein r-m located between basal 1/7 and 1/4 of cell dm. Abdomen oval, 1.5-2.5 times as long as wide. Tergites 3 and 4 fused. Sternite 1 pilose. Male genitalia: phallus projecting not or little beyond apex of hypandrium (except projecting well beyond apex of hypandrium in Metadon bifasciatus ), bent dorsad, furcate in apical half, with both processes about equally long (except ventral process much longer in Metadon bifasciatus ); epandrium with or without ventrolateral ridge; surstylus unfurcate, sometimes with long posterior process.

Diagnosis.

Body never metallic green or blue. Vein R4+5 with posterior appendix. Abdomen oval, longer than wide but less than 2.5 times as long as wide. Postpronotum pilose. Anepisternum with bare part limited to ventral half, or entirely pilose. Antenna longer than distance between antennal fossa and anterior oral margin. Basoflagellomere shorter than or as long as scape. Tergite 1 short: length/width ratio 1:25 or less.

Discussion.

All included species (except the ones here described) were originally described in the genus Microdon . However, the morphology of Metadon is distinct. Characters that separate these taxa in all examined species (except Metadon bifasciatus , see below) are: anepisternum (almost) entirely pilose; phallus projecting not or only little beyond apex of hypandrium; aedegus furcate in apical half. Additional characters for distinguishing Metadon from Microdon (that may not work for all species) are: katepimeron more or less flat, with wrinkled texture; katatergum with oblique rows of microtrichia. In general, the abdomen of Metadon species is more elongate than that of Microdon species.

The East Palaearctic species Metadon bifasciatus Matsumura, 1916 is aberrant in certain characters. In this species the bare part of the anepisternum reaches up to about half the height of the sclerite. In addition, the genitalia are aberrant as the ventral aedeagal process is much longer than the dorsal process (Fig. 172), a character not known from any other species of Microdontinae . Nevertheless, this species is placed in Metadon because of the elongate abdomen and the oblique rows of microtrichia on the katatergum. This is supported by the results of Reemer and Ståhls (in press). As the Chinese species Microdon brunneipennis Huo, Ren & Zheng, 2007 and Microdon pingliensis Huo, Ren & Zheng, 2007 and Microdon spuribifasciatus Huo, Ren & Zheng, 2007 are similar to Microdon bifasciatus , the characters as mentioned may also be valid for those species.

Metadon is erected as a new genus distinct from Microdon in order to facilitate distinction between these apparently monophyletic groups. Results of phylogenetic analyses by Reemer and Ståhls (in press) support this decision.

Diversity and distribution.

Described species: 42. About half of the species (22) are described from the Oriental region. Several undescribed species from this region were seen by the first author in different collections. From the Afrotropical region, 14 species are described, remarkably none of which is from Madagascar. Four species are known from the Palaearctic region. These seem to form a closely related species group, all related to Microdon bifasciatus , restricted to eastern China, Korea and Japan. Two species are known from the Aru Islands off the southwest coast of New Guinea (these were collected by Alfred Russel Wallace in 1857, to be described by Walker 1858). These are the only known records of this group from the Australian region.

Etymology.

The generic name is a combination of the ancient Greek words meta and odon, with the latter used as a suffix derived from Microdon . The prefix meta is used in the sense of ‘near’ or ‘close’, in order to indicate the resemblance in habitus to Microdon s.s. It is a masculine name.