Ditto, the only time I use Sevin is when there's clearly already an infestation. Their regular dust bathes naturally keep pests in check. Infestations are usually caused by other critters (wild birds, rodents, ect) sharing their coop. DE (Diatomatious Earth- the food grade kind) is fabulous as long as its kept dry. It cuts open the insects exoskeletons and dries them out. Wood ash is fantastic as well, mix some into their normal bathing holes, they'll love it. Otherwise, just let them throw some dirt around and they should be alright. With regular, normal dust bathes I've never had a mite or lice problem with my Silkies. Good luck.
Nikki