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There are somw confusion about lapponicus that P. GROOTAERT and M. DE MEYER worked throw in the paper On the taxonomy and ecology of Nephrocerus ZETTERSTEDT (Diptera, Pipunculidae) with a redescription of N. lapponicus and a key to the European species. 1986 Bull. Inst. R. Sci. Nat. Belg. : Entomologie 56, 85-91.
I will comment that i have lapponica with only smal yellow markings on abdomen.
The best caracter for scutellaris and lapponica is probably the size of antenna wich a can't see

third antennal segment rather small (a quarter of the height of the eyes ; male with distinct anteroventral bristles on hind femora; larger
species -> N. scutellatus
third antennal segment rather large (a third of the height of the eyes in male, about a quarter in female); only short bristles on the hind femora smaller species. -> N. lapponicus

It's not flavicornis that have a fringe of bristle in the end of hind tibia.