On June 13 a friend brought me some sprigs of her grape vine that were covered with succulent swellings. They seemed like a good match for the drawing in Gagné (1989)* for Janetiella brevicauda, but this statement made me want to double-check:
Although placed in Dasineura or Janetiella . . . the species responsible for [irregular, succulent swellings or indehiscent leaf spots or blisters] on grape form a monophyletic group. A separate genus will eventually be erected for them. It is now very difficult to associate any of the described species with particular galls.
With a little online searching I found this 2009 paper, in which Dr. Gagné placed these species in the genus Vitisiella. Meanwhile, little bright orange midge larvae were popping out of the galls, and by the end of the day the bag was full of them. So I put the bag in the fridge and wrote to Dr. Gagné for advice.
He confirmed that my photo was of Vitisiella brevicauda galls, and he described how to raise midge larvae that want to burrow into the ground to pupate. Some gall midge species have multiple generations per year, and others have only one, with the larvae overwintering in the ground. He didn’t know which was the case for this species, but his method allowed for the possibility that the adults wouldn’t emerge until next spring. So on June 15 I transferred the 84 larvae to a jar of moist peat. As I was doing so I found a tiny wasp in the bag. It may have emerged from one of the galls, or it may have been on the plant when it was put in the bag; in either case I think it is likely that it is a parasitoid of V. brevicauda.
On June 17 there were another 79 larvae to transfer to the jar of peat, and I think there were a few more after that. June 25 I left for Vermont, and when I returned on July 3 I found that about two dozen adult midges had emerged. They are continuing to emerge today. I wrote to Dr. Gagné that this species does in fact have more than one generation a year, and he said he will be sure to add this information in the second edition of his book. (He had mentioned to me previously that he now knows of 22% more galls made by gall midges and much more about their biology, in addition to having to change many of their names, so I’m looking forward to this revision.)
Metamorphosis is an amazing thing… the orange tinge is the only feature of the adult that bears any resemblance to its immature form.
* Gagné, Raymond J. 1989. The Plant-feeding Gall Midges of North America. Ithaca, NY: Comstock Publishing Associates. 356 pp.