Shooting with a reversed 50mm on a prosumer before, I know how hard this shot was to make. Small manual focusing screen, having to steady hands like mad. I don't miss those days one bit, heh heh. :bsmilie:
Even at maximum aperture on the camera, your depth of field will be paper thin, so concentrate the focus on the eyes, not the body. Main focus should always be on the eyes of the subject when shooting a portrait, be it insects, animals or humans.