I have found Diatomous Earth completely eradicates and prevents red mite and lice and it's non-toxic, in fact the birds can eat it and it helps condition! The stuff, called Diatom, is tiny diatoms which damage the outer layer of mites and lice so they die in a couple of days. I dust a small quantity round the henhouse each time I clean it and haven't had a problem with mites since I started. It's not cheap but goes a long way...not sure if I'm allowed to give you the supplier on the Forum but mail me if you'd like it. The supplier has won awards and sends lots of info about the product and does other environmentally friendly stuff as well.
Good luck!
Judi