On the topic of mites and lice: I normally use DE, but only for treatment of bad cases, where I dust the birds in the bin and sprinkle it in dust-bathing areas every few days until the problem is under control. The last time I had to open my bin was over two months ago.
I did have a small hen earlier this year who was badly affected by lice due to stress, and the DE just wasn't doing it for her. (Two dunkings about a week apart typically do the job, but not this time.) I resorted to my safe-for-kittens flea treatment: mayonnaise. Starting at the orifices, slather on mayo being sure to cover every square millimeter of skin and feathers, then slather on more until you have a wriggling glob of slimy animal in your hands. Leave sit for ten minutes (the patient won't go far - mammals will start licking it off, but the chicken just sat in the sink confused!) and then wash off. Done. It's been months and I haven't seen a single louse make an appearance on her, and her feathers grew back smoother and healthier than the were before she lost them! (She was molting at the time of her infestation, too.) Obviously mayo isn't practical to treat a whole flock, but for an emergency, safe, one-shot complete treatment you can't beat it! It works because it smothers the bugs and their eggs, suffocating them; fleas will try to escape, but can't jump away in the thick goo.