This appears to be a Cynipid wasp ovipositing into a cynipid gall that had been made by a different species. The gall is probably of Philonix nigra. Thanks to Charley Eiseman for his help with this photo.
Photo data: 9 September 1989. On Kodachrome film. The gall is on an oak leaf. Ruraldale, Upshur County, West Virginia.