Microdon (Dimeraspis), Newman

Reemer, Menno & Stahls, Gunilla, 2013, Generic revision and species classification of the Microdontinae (Diptera, Syrphidae), ZooKeys 288, pp. 1-213 : 42-43

Subgenus Dimeraspis Newman Figs 181-186

Dimeraspis Newman, 1838: 372. Type species: Dimeraspis podagra Newman, 1838, by monotypy.

Mesophila Walker, 1849: 1157. Type species: Ceratophya fuscipennis Macquart, 1834, by monotypy. Syn. n.

Description.

Body length: 8-12 mm. Broadly built flies with oval to round abdomen and long antennae. Head narrower than to about as wide as thorax. Face convex in profile; narrower to wider than an eye. Lateral oral margins not produced. Vertex flat. Occiput ventrally narrow, dorsally widened or narrow (only in Microdon abditus Thompson, 1981). Eye bare. Eye margins in male converging at level of frons, sometimes only weakly so ( Microdon adventitius Thompson, 1981, Microdon fuscipennis (Macquart, 1834)) with mutual distance 2-5 times as large as width of antennal fossa. Antennal fossa about as wide as high. Antenna longer than or as long as distance between antennal fossa and anterior oral margin; basoflagellomere shorter to longer than scape; bare. Postpronotum pilose. Scutellum semicircular to trapezoid; without calcars, but large and blunt calcars may seem to be present due to strong apicomedian sulcus. Propleuron bare. Anepisternum without sulcus (or only a very weak one dorsally); pilose dorsally, extensively bare on slightly more or slighly less than ventral half. Anepimeron entirely pilose. Katepimeron more or less convex; smooth or with wrinkled texture ( Microdon fuscipennis ); bare. Katatergum uniformly microtrichose. Wing: vein R4+5 with posterior appendix; vein M1 more or less straight, perpendicular to vein R4+5, slightly recurrent; postero-apical corner of cell r4+5 rectangular, with appendix; crossvein r-m located between basal 1/7 and 1/4 of cell dm. Abdomen oval, 1-1.5 times as long as wide. Tergites 3 and 4 fused. Sternite 1 pilose or bare. Male genitalia: phallus projecting little beyond apex of hypandrium, bent dorsad, furcate apically, with both processes equally long; epandrium with ventrolateral ridge; surstylus with wide basal lobe and narrow posterior lobe.

Diagnosis.

Difficult to diagnose, because included species vary strongly in several key characters. See key and discussion.

Discussion.

This group was erected for the Nearctic Dimeraspis podagra Newman, 1838, a subjective synonym of Mulio globosus Fabricius, 1805 ( Thompson 1981b). This species differs from Microdon s.s. in the unsulcate anepisternum, the bare propleuron, the rectangular postero-apical corner of cell r4+5, and the male genitalia: phallus apically furcate, hypandrium with bulb-like base. Some other Nearctic (and one Cuban) species are very similar in morphology of the male genitalia: Microdon abditus Thompson, 1981, Microdon adventitius Thompson, 1981, Microdon fuscipennis (Macquart, 1834), Microdon marmoratus Bigot, 1883, and Microdon remotus Knab, 1917. Thompson (1981b) also regarded these species as related, with the 'globosus complex’ ( Microdon abditus , Microdon globosus , Microdon marmoratus ) as sister to the fuscipennis-group ( Microdon adventitius , Microdon fuscipennis , Microdon remotus ). These species are also similar in their overall brownish colouration and in the wing venation. The morphological similarities are here taken as a reason to include all species in Dimeraspis . Because of similarities in male genitalia this group might tentatively be considered related to Archimicrodon , Menidon or Serichlamys . However, because of considerable uncertainty, the group is here treated as a subgenus of Microdon .

Mesophila Walker, 1849 was erected for Ceratophya fuscipennis Macquart. As this species is here included in the older genus group Dimeraspis , Mesophila becomes a junior synonym of Dimeraspis .

Diversity and distribution.

Described species: 5. Nearctic (4 species) and West Indian (1 species from Cuba).