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Thanks for your remarks, i didn't notice this spot. Could be a really usefull character. I'll check for the curvation, not sure it is stable, but worth cheking!

Base of this questionning was this specimen (http://www.diptera.info/forum/viewthread.php?thread_id=73812), a female i first thought about R scolopaceus due to the large extension of the dark patch, but the shape of dark patch was in favour of R vitripennis, so i needed other opinion. That would be R vitripennis then.

You largelly answer my question, so thanks! :) (and thank if you check on other specimens, i tested it on only 10 vitripennis. Please tell me about the result)