I had an egg today with mites on it...first of the year. How are you treating them?
I loathe having to do it, but the only thing that seems to really stop them for good (for awhile at least) is permethrin. I hate powdering them myself so I have storage bins full of dirt that I use for them to dust bathe in. I add a coating of permethrin to it and mix it in and when they dust bathe they basically treat themselves.