The black bugs are mites, the white almost too tiny to see are lice.
Sevin is being taken off the market as it's been proven to be carcinogenic. Rotenone is being taken off the market since it's been linked to Parkinson's Disease. Both are still available only till the supply contract run out, use them if you wish. Both are dusted on and both will kill both bugs. You need to spray your coop as well since the black mites are generally the ones that only spend a short time on the bird, they live in the coop the rest of the lifespan. Red mites, if you ever get those are the ones that never leave the bird. For lice it's often a good idea to do anything that the birds spend time in contact with like perch and nest box. Livestock sprays with pyrethrin in them are still approved as are the dips.
Depeneding on how many chickens you have and the temps where you are you might want to take care of this with a pyrethrin shampoo, like dog or cat flea and tick shampoo, or a livestock lice/tick dip. Ask at your feed store what is available, what the cost is and how much you have to buy. If you have to buy a jug of dip that will treat 100 sheep your probably better off to get a bottle of shampoo that will bath one dog 4 or 5 times. However some of the dips have instructions on them for mixing to spray the barns as well, something a shampoo can't do for you.