If they are fruit flys is it possible they hatch, fly around, return to the bin and die? I never see any bodies. So as long as none are breathed in it is ok. They seem more attracted to the vinegar if it is placed at the apex of something above the bin. The leaves were a great move. Maybe stop feeding the bin until they disapear. They probably have a short life.

Put a piece of fabric down over your pile and put rocks or bricks in place to keep it covered for a few days, they will leave it alone after that.
Always bury your waste or cover with 3-4 inches of bedding/browns.
Liz

Yellow Sticky fly paper

Have any one tried Bacillus thuringiensis (var. israeli)?
They are supposed to kill any diptera larvi and do not affect other creatures (suppousedly)
Is there any brave vermicomposter willing to try?
I chicken out because I am a newby.