You need 5% Sevin. It's an insecticide powder. Looks like you need to put it in a plastic bag, put the chicken in the bag with the head sticking out and shake it real good. Otherwise, turn the chicken upside down and sprinkle it under wings, around vent and other underbody areas, legs and work it in real good. Repeat in a week. You'll need to do this to all your birds.
You also need to pull everything out of your coop and nests, dust everything with the Sevin and put in all new bedding.