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U. stylata always has the 2 apical crossbands fused,
U. affinis has the stigmal crossband more or less complete and the preapical crossband lesser washed at anterior margin and the apical crossband wider separated from it; in addition, this fly has longer oviscape (in affinis it is not visible beu\yond the wings.
And the final reason: it observes a flower bud of Carduus or Cirsium, but not Centaurea (Acrolophus), the host of affinis.