10/03/2011 MJ Hatfield collects a spherical stem gall on leafcup, Polymnia, that produces two wasps; C. Eiseman mentions that one of these (the one in her BG post, below) is likely a parasitoid torymid



02/14/2017 I collect similar spherical swellings on winter stems of Polymnia, each with a medium-sized fly puparium inside. Two puparia retained for rearing; one kept in my rearing collection, other one given to a coworker with a budding interest in bugs



06/13/2017 Puparium I kept turns out to be inviable...or maybe spent...anyway, it's empty and apparently was when I collected it. Hence the gray color to the puparium, I suppose. Nothing ever emerged from my coworker's puparium either.

07/05/2017 Galls on living Polymnia plants, finally; they look to be of the same type as those found previously by MJ and me. Three galls collected for rearing

07/11/2017 OK, you know what, who knows if this rearing will succeed or fail; it's high time we at least knew what the inside of one of these galls looks like...so I cut open one of my 3 galls. Result is shown in this series

Fairly large fly larva inside; easily one of the largest fly larvae I've seen inside a living plant stem to date. Seems like the sort of thing that would give rise to a medium-sized adult fly, something around the size of a house fly, perhaps.

My current hypothesis is that (1) this fly is the gallmaker; (2) it pupariates in the gall and then emerges as an adult at some point between now and the end of the growing season (rather than overwintering); and (3) the gall tends to split open at some point, perhaps at just the right time for the adult to emerge through the split, perhaps later in the season.

Rearing in progress

Ruler units in this photo are sixteenths of an inch