Well, I never knew fiddle bows had such problems! Mites that chomp on the hairs, indeed!
A garden magazine I get had recommended some herbs to a reader who had a problem with a lorrikeet with feather mites - place sprigs of mite-repelling herbs in its cage. Suggested were tansy, rue and wormwood. The reader has reported back that the herbs had worked very well, and the mites are gone, and the bird no longer looks moth-eaten and dull. Worth a try in your fiddle case, can't do it any harm.
AMC