My avian vet is dead set against cedar shavings in chicken coops. Now, he is also not crazy about any kind of shavings . . . even the kiln-dried Aspen I use in mine. I prefer Aspen over pine, and I would not use cedar for chickens because of the cedar oils. Aspen is expensive, though.
For my nest boxes, I clean them out thoroughly at least 4x a year (seasonally) when I clean out my coops, and when they are empty I lay a sprinkle of either Prozap Poultry Dust (Pyrethrin) or Sevin (Carbaryl) and a bit of diatomaceous earth before I lay fresh shavings down on top. I use only a tiny amount of these powdered insecticides, and I am careful to rotate them bi-annually so the buggies do not build immunity. Keeping a bit of the insecticide near the nooks and crannies works great.
The other thing that has helped me is caulking all the cracks in my coops. Yes, all of them - - every single nest box, too. Good times. Anyhoo, once it is done there are very few places for tiny mites to live.
Checking my birds at least once a month is the third thing I do to keep tabs on their condition. I pick up each and every one and check their faces, eyes, bottoms of feet, and their little bums.
Hope that info helps. Good luck!