Are you attempting to get rid of the larva or the mama fly? Once the egg is laid inside the leaf you cannot get to it in any way except by squishing the bugger. Later when that larva falls out of the leaf to pupate in the soil you might be able to control them there. There is a wasp that lays its egg in that larva so doing stuff, or in some cases not doing stuff, to encourage that type of wasp to hang around is good.
