Petiole borer (Diptera: Agromyzidae) in Calystegia

Each larva of this borer appears to inhabit just a single leaf, tunneling out the interior of the petiole and sometimes part of the midrib as well. The walls of the tunnel have a noticeably ragged look to them. The leaf may wilt or shrivel and turn yellow or brown, betraying the presence of a larva at work in the leaf stalk. Some larvae prepare an exit shaft to near the surface of the petiole and pupate there, leaving the epidermis intact except for penetrating it with the anterior spiracles. I located puparia in petioles during early- to mid-July. In 2022, I found petioles with completed tunnels but no culprits present, which suggested that these leaves' larvae may have exited the petioles and pupated externally, but I was unable to confirm this.