Swellings on winter stems of leaf-cup, Polymnia

The swelling on the right and the one on the left were both empty and hollowed-out inside, with a tunnel leading from the swelling down through the stem below it. I only collected a small portion of the stem so I don't know how far down the rest of the plant the tunnel went, or whether the tunnel-maker was at the end of it. The middle swelling contained frass-like powdery black material surrounding a dead wasp that seemed to be halfway between the pupa and the adult stage; also, there was no tunneling in the stem above or below this swelling. In its shape and in having powdery black material, the middle swelling reminded me of these galls


A similar-looking gall on Polymnia here in northeastern Iowa, from which MJ Hatfield reared two wasps: