The genus Eosphaerophoria is recognized among the syrphines (subfamily Syrphinae, tribe Syrphini) by this combination of characters: 1) nearly vertical apical vein M1; 2) subtriangular scutellum; 3) male narrowly dichoptic; 4) slightly narrowed abdominal base in males; and 5) reduced alula and anal lobe.
Vockeroth (1969) considered this genus the most aberrant of the Syrphini based on the presence of uncommon morphological characters, such as wing venation and dichoptic males, but noting also the asymmetry of the superior lobes of the male genitalia. This character cannot be considered diagnostic because there are species with symmetrical superior lobes too, as pointed out by Vockeroth (1969).
Small slender species with male narrowly dichoptic, mesonotum bright yellow laterally, scutellum usually subacute or acute apically, abdomen of male very slightly petiolate, abdomen of female slightly broadened from base to near apex. Length from 4.9 mm to 6.8 mm.
Head. Eye bare. Face slightly broadened below, yellow, with or without medial black vitta, with a tubercle small but well defined, rather compressed in male. Antenna short, less than head width; scape about as broad as long; pedicel broader than long; basoflagellomere oval to slightly elongate, not more than 1.3 times as long as broad; arista dorsobasal, bare. Frons of male very narrow, at antenna about 1/5 head width, narrowed to 1/8 to 1/10 head width a little below anterior ocellus, then very slightly broadened to vertex; frons of female broader, narrowed gradually to posterior ocellus, then parallel-sided to vertex. Ocellar triangle, especially in male, well before posteromedian angle of eye; anterior ocellus separated from eye by much less than its diameter.
Thorax. Scutum black, with postpronotum, broad presutural stripe (notopleuron) and narrower postsutural stripe yellow; black dorsomedial area usually with opaque margin and shining or sub-shining centre. Postpronotum bare. Notopleuron with posterolateral angle sometimes produced postero-laterad into a strong blunt tubercle which extends distinctly caudad of suture (Fig. 28). Scutellum with basal black triangle and yellow margin, subtriangular in outline with apex bluntly rounded, subacute, or produced into a short, acute, sometimes upcurved tubercle. Subscutellar fringe very short and present only laterally or entirely absent. Pleura yellow (propleuron, ane- pisternum, anepimeron, katepimeron and katatergum), except katepisternum black with a dorsal yellow macula and meron black. Thoracic pile extremely short and sparse. Katepisternum with dorsal and ventral pile patches broadly separated, the pile in the dorsal patch extremely short or absent, scarcely distinguishable. Metasternum bare. Legs. Simple; metafemur near apex sometimes with a ventral row of short strong black spine-like setae. Wing. Vein M2 short, perpendicular or nearly so to M1; vein M1 (apical crossvein) straight or slightly sinuate, meeting R4+5 at approximately a right angle at more than half its own length from wing base (see Figs 22 and 23); posterior margin without black sclerotized puncta. Alula narrow, narrower than cell BM, anal lobe greatly reduced. Wing partially bare basomedially: 2nd costal cell bare; cells R1, R2+3, R4+5, DM, CuA1 and CuP bare basally; cells BM and R bare; anal lobe sparsely microtri- chose distally; alula usually microtrichose (see Fig. 22). The proportion bare on each cell can vary slightly between species.
Abdomen. Abdominal pattern variable; terga without marginal sulcus; in male very slender and slightly to rather strongly narrowed on segments 2 and 3, 2nd abdominal tergum narrower than thorax; in female broader, narrowest near base of segment 2. Male genitalia. Usually large reaching the posterior margin of 4th sternum; typical syrphine form; cercus elongate oval; surstylus elongate, broad basally; lingula absent; aedeagus two-segmented, with apical segment flared apically; superior lobe variable, articulated with aedeagal base and with lateral surface covered with short black blunt bristles.
Eosphaerophoria Frey, 1946: 169. Type-species, marginata Frey (original designation). Vockeroth 1969: 134, map 26 (distribution), Figs 11 (wing), 89 (male genitalia) (key reference, description, distribution); Knutson et al. 1975: 313 (catalog cita- tion); Thompson and Vockeroth 1989: 443 (catalog citation); Ghorpadé 1994: 3, 5 (citation, key); Mengual et al. 2009: 7, 8, 23 (citation, morphological characters, phylogenetic analysis).
Tambavanna Keiser, 1958: 202. Type-species, dentiscutellata Keiser (original designation). Synonymy by Vockeroth (1969: 134).
No closely related taxa have been previously proposed. Mengual et al. (2008a) analysed the current tribal classification of the subfamily Syrphidae, but Eosphaerophoria was not included due to the absence of suitable material for DNA extraction. Mengual et al. (2009) in their cladistic analysis of Allograpta using morphological characters, included representatives of Episyrphus, Meliscaeva, Anu, Citrogramma, Exallandra, Giluwea, Sphaerophoria and Eosphaerophoria based on adult morphological similarity. Eosphaerophoria was resolved in a polytomy with the Allograpta subgenera Antillus, Allograpta, Costarica and Rhinoprosopa in the strict consensus tree. Consequently, its phylogenetic position remains incognito but if the overall morphological similarity with Sphaerophoria is taken under consideration, the genus might be a member of the Allograpta-Sphaerophoria clade recovered by Mengual et al. (2008a, 2008b).
Ghorpadé (1994: 5) placed together Rhinobaccha de Meijere, 1908 and Eosphaerophoria in couplet 13 of his identification key.
unless otherwise stated