On the leaf of a Jerusalem artichoke, Gatineau Park, Quebec, near Luskville. These flies are very small, perhaps a couple of mm in size, and very attractive. They are also beneficial as one species feeds on common ragweed and one on giant ragweed. I'm not sure which species this one is, but it is one of the ragweed flies, and I'm leaning towards Euaresta festiva, the one that develops on giant ragweed.