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Normally in Geomyza hackmani the subscutellum is normally darker. The abdomen in G. balachowskyi is normally more clearly banded.
I have seen a few specimens of G. hackmani with vaguely banded abdomen and not so dark subscutellum. To be sure which species you are dealing with, you should study the shape of sternite 8 (which is often not readily visibile).
My best guess would be female Geomyza cf. hackmani.