Mixogaster Macquart

Reemer, Menno & Stahls, Gunilla, 2013, Generic revision and species classification of the Microdontinae (Diptera, Syrphidae), ZooKeys 288, pp. 1-213 : 49-50

Mixogaster Macquart Figs 241-248

Mixogaster Macquart, 1842: 14. Type species: Mixogaster conopsoides Macquart, 1872: 14, by original designation.

Myxogaster Kertész, 1910: 351. Misspelling.

Myxogaster Shiraki, 1930: 8. Misspelling.

Description.

Body length: 9-15 mm. Slender flies with constricted abdomen, wasp-like. Head wider than thorax. Face convex or almost straight in profile; about as wide as an eye or narrower. Lateral oral margins not produced. Vertex flat. Occiput narrow, except slightly widened dorsally. Eye bare. Eyes in male not or hardly converging at level of frons, with mutual distance 4 to 5 times as large as width of antennal fossa. Antennal fossa about as wide as high. Antenna longer or shorter than distance between antennal fossa and anterior oral margin; basoflagellomere shorter to longer than scape, oval; bare. Postpronotum pilose. Scutellum semicircular; without calcars. Anepisternum with weak sulcus; entirely bare or pilose anterodorsally, or pilose anterodorsally and along posterodorsal margin. Anepimeron entirely pilose or bare on ventral half. Katepimeron convex; bare. Wing vein R4+5 without posterior appendix. Vein M with small anterior appendix into cell r4+5. Vein M1 either straight or with anterior part directed outward, with one or two angles, whether or not with small inward appendix and /or small outward appendix. Postero-apical corner of cell r4+5 angular. Crossvein r-m located betwee basal 1/4 to 2/5 of cell dm. Abdomen constricted at base, with tergite 2 varying in length and width. Tergites 3 and 4 not fused. Male genitalia: phallus unfurcate, bent dorsad, with either lateral or dorsal combined with ventral lamellae, sometimes with apical spines; hypandrium with bulb-like base and apical part consist ing of separate lobes, or hypandrium entirely consisting of two separate parts, which are not interconnected; epandrium without ventrolateral ridge; surstylus of varying shape.

Diagnosis.

Vein M with small anterior appendix into cell r4+5. Abdomen constricted. Metapleura connected, postmetacoxal bridge complete.

Discussion.

An important diagnostic character of Mixogaster , the anterior appendix of vein M, is also found in Spheginobaccha de Meijere, 1908 and certain specimens of Aristosyrphus primus . These taxa also share the character of the apical part of the hypandrium consisting of two separate lobes. See genus account of Aristosyrphus for discussion.

The morphology of the male genitalia is remarkably diverse in this genus, much more so than in other groups of Microdontinae (except perhaps Aristosyrphus / Eurypterosyrphus ). Some species have characters not known from any other Microdontinae . Some examples are illustrated in Figs 245-248. In Mixogaster breviventris Kahl, 1897, the phallus has wide dorsal and ventral lamellae (Fig. 245). This type of genitalia is found in all Nearctic species, which also have a straight vein M1 in common. In Microdon thecla Hull, 1954 (Fig. 247), the hypandrium consists of two separate lobes, which are not interconnected ventrally to envelope the phallus, as is the case in all other studied Microdontinae . Besides, the subepandrial sclerite is strongly developed in this species, and produced well beyond the epandrium in lateral view. In an undescribed species (Fig. 248), the phallus is asymmetric in ventral view, with wide lateral lamellae, which are apically densely occupied with irregular spines. This is the only known case of asymmetric genitalia among Microdontinae . The spinose phallus is also a unique character.

The keys to the species by Hull (1954) and Carrera and Lenko (1958) (Brazilian species only) work reasonably well, but the existence of several undescribed species makes it necessary to check original descriptions or, preferably, type material in order to verify identifications. Considering the large interspecific variation in the male genitalia, these characters should be further explored in future (re)descriptions of species.

Diversity and distribution.

Described species: 21. Mainly Neotropical, with three species in the Nearctic. At least one Nearctic and several Neotropical species are undescribed.