John Carr wrote:
The keys I have are based on wings. In the key to Neoempheria in Insects of Connecticut (Shaw and Fisher 1952) it goes to nepticula (Loew) or impatiens Johannsen. In Johannsen (1910) it goes to nepticula Loew. The two species are very similar. One key character is the position of the sc-r crossvein ("Sc2") relative to the base of Rs. Your fly has opposite character states on opposite wings.