July 16 -- MJ Hatfield was kind enough to take two other guests and I on a tour and collecting trip at her hill prairie in Allamakee Co. While there I came across a black knot gall on a young cherry (Prunus sp.). Insects were decomposing the gall. Elsewhere on BG, Maryann Whitman (here
) and Charley Eiseman and John Maxwell (here
) have noted signs of insect feeding in black knot. Some of this particular gall had already been converted to clumps of frass. Upon cutting into this and one other gall, I noticed small whitish larvae -- looked like fly larvae. In her post linked to above, Maryann Whitman reports similar small larvae in black knot galls. Some of the frass in the galls I opened looked too big to have been produced by the fly larvae...curious... In hopes of rearing the mystery fly larvae, I collected one gall.
Mid-July thru mid-August -- Gall set up in plastic ziplock with a few holes punched in it, similar to rearing technique suggested by MJ, Charley Eiseman, and Charley's partner Julia. Gall developed white fungus on exterior, which eventually died off or disappeared. Larva(e) continued to feed, expelling copious frass, which accumulated inside and beneath the gall.
August 16 -- Surprise! Adult clearwing moth found in bag; exuviae protruded from the gall. A significant portion of the gall had been "processed" into frass (a similar result is noted here
-- see Figure 14). No sign yet of pupae or adults of the fly larvae. I am hopeful some of the larvae have survived but I have not recently seen any signs of them.