Rhopalosyrphus Giglio-Tos

Reemer, Menno & Stahls, Gunilla, 2013, Generic revision and species classification of the Microdontinae (Diptera, Syrphidae), ZooKeys 288, pp. 1-213 : 61-63

Rhopalosyrphus Giglio-Tos Figs 332-355

Rhopalosyrphus Giglio-Tos, 1891: 189. Type species: Holmbergia guentherii Lynch Arribalzaga, 1891, by subsequent designation of Giglio-Tos (1892: 2).

Holmbergia Lynch Arribalzaga, 1891: 196. Type species: Holmbergia guentherii , 1891: 195, by monotypy. See Weems et al. (2003) and Cheng and Thompson (2008) for synonymy.

Description.

Body length: 9-15 mm. Slender flies with long antennae and petiolate abdomen. Head a little wider than thorax. Face more or less convexly produced on ventral half; narrower than an eye. Lateral oral margins produced. Vertex flat, entirely pilose. Occiput ventrally narrow, dorsally strongly widened. Eye bare. Eye margins in male converging at level of frons, with mutual distance 1-2 times width of antennal fossa. Antennal fossa about 1.5 times as wide as high. Antenna longer than distance between antennal fossa and anterior oral margin; basoflagellomere longer than scape, oval; bare. Postpronotum pilose. Scutellum semicircular; with or without calcars, if present, then small and with mutual distance small. Anepisternum convex or with weak sulcus; entirely pilose. Anepimeron entirely pilose. Katepimeron flat to weakly convex; with wrinkled texture; bare, partly pilose or entirely pilose. Wing: vein R4+5 with posterior appendix; vein M1 perpendicular to vein R4+5; postero-apical corner of cell r4+5 widely rounded to rectangular, with or without small appendix; crossvein r-m located between basal 1/8 to 1/4 of cell dm. Abdomen elongate, more than three times as long as wide, constricted, with narrowest point between halfway tergite 2 and transition between tergites 2 and 3. Tergites 3 and 4 fused. Sternite 1 pilose or bare. Male genitalia: phallus furcate near apex, with dorsal process long and whip-like, ventral process very short; epandrium with ventrolateral ridge.

Diagnosis.

Vein R4+5 with posterior appendix. Abdomen petiolate. Vertex flat, entirely pilose. Postpronotum pilose. Mesonotal transverse suture incomplete. Tergites 3 and 4 fused. Anterior margin of tergite 2 at least twice as wide as posterior margin. Rhopalosyrphus s.s.: katepimeron pilose. Rhopalosyrphus s.l.: katepimeron bare.

Discussion.

Previous authors have defined this genus more strictly than is done in the present paper. Weems et al. (2003) and Cheng and Thompson (2008) only included species with a pilose katepimeron. A number of additional species are known from the Neotropical region which are similar to Rhopalosyrphus auct. in most characters, but which have a bare or almost bare katepimeron. In Rhopalosyrphus robustus sp. n. the katepimeron is only narrowly pilose along the anterior margin. In all other characters, this species has the diagnostic characters of Rhopalosyrphus as described by Weems et al. (2003): abdomen petiolate, antenna longer than face, scape and basoflagellomere elongate, face produced ventrally (variable), occiput strongly widened dorsally, metasternum developed, hind tibia flared apically. The male genitalia of Rhopalosyrphus robustus are very similar to those of Rhopalosyrphus auct., with an apically furcate phallus, of which the dorsal process is very long and whip-like (Figs 352-355).

Microdon abnormis Curran, 1925 is also similar to Rhopalosyrphus in the characters mentioned above, but has a bare katepimeron. In the analysis of morphological characters by Reemer and Ståhls (in press), a closely related species ( Rhopalosyrphus abnormoides sp. n.) is placed within Rhopalosyrphus .

Based on the results of the phylogenetic analyses and the (subjective) evaluation of external and genitalic characters, Rhopalosyrphus is here extended to include also the species with a bare or almost bare katepimeron, which includes species previously grouped in the abnormis group (see account of Pseudomicrodon in Cheng and Thompson 2008), as well as Microdon cerioides Hull, 1943. Species with a pilose katepimeron are included in Rhopalosyrphus s.s., while the other species are treated as Rhopalosyrphus s.l.

The inclusion of Rhopalosyrphus oreokawensis sp. n. in this genus is to be regarded as preliminary. Unlike the other species included in Rhopalosyrphus , this species has very short antennae, an oblique vein M1 and a more slender tergite 2. Analysis of its morphological characters ( Reemer and Ståhls in press) resolves its phylogenetic position near Rhopalosyrphus . Possibly, it would be better to erect a new genus for this spe cies. This is nevertheless not done here, in awaitance of a better understanding of the relationships of the taxa included in the ' Rhopalosyrphus- clade’.

Diversity and distribution.

Described species: 9. Mainly Neotropical, with two species in southern parts of the U.S.A. (Arizona, Texas, Florida).