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Hi Christophe
This is not Dioctria - the very curved hind tibia and the form of the genitalia are not right. It is a species of Choerades, and the one it fits best is dioctriaformis! :)
The author, Meigen, clearly thought the same as you - you're in good company! :D
It's not a common species in France, according to Seguy - a very good find!