Here is a photo from Stéphane Brule in French Guiana. Could anyone confirm whether I have guessed the correct family ... and possibly add any more information?
Well, it does look a bit like some of our Platycheirus spp. but the abdomen has an odd shape and I think there must be different (perhaps related) genera in the neotropics
This is a male of Ocyptamus gastrostactus, a common species in tropical America. Larvae are aphid predators on various plants, incuding Phragmites and tobacco.
