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I can also discard Mydaea nubila which is shorter than 7.7 mm and which also has darkened halteres

So it seems it is Mydaea ancilla. The mediotergite indeed appears shiny black and not pruinose (although I could not take a convincing pictures of this structure on my specimen as the wings were hiding it). Supporting criteria include:
- scutum with 4 very dark stripes
- posterior crossvein oblique
- prealar seta about 3/4 of posterior notopleural, although here pra is 85-91% of post nt (based on two measurements from different images)
- katepisternals 1 + 2
- fore tibia without posterior seta
- hind tibia with 2-3 anterodorsals and 2-3 anteroventrals