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Many species of Hilara and Rhamphomyia (Megacyttarus) swarm low above water, but your fly is neither of those groups. Hilara and, as far as I know, Brazilian relatives, have forked R4+5.

If it is tribe Empidini it should be Porphyrochroa. Rhamphomyia has shorter first flagellomere. Macrostomus has a reduced anal lobe. If it is, you should find your species here: http://www.tandfo...0903437333. (I do not have access to the journal.)