Are you sure there are no mites? I had some birds that I thought were molting but discovered they had mites. Some mites only come out at night so my suggestion would to be check the birds after they roost. I use a headlamp so I have both of my hands free to inspect the birds. I had no luck with DE. I had some luck with Sevin. I had my best luck with permethrin. With any insecticide one treatment isn't enough. repeat weekly treatments for 3 or 4 weeks works, at least it has for me. Nothing kills the pest eggs so repeat treatments are necessary. One bonus with permethrin is that there is no egg withdrawal period as there is with most other insecticides. I treated inside my coops thoroughly. Initially I sprayed the birds too. I even bathed them with people lice shampoo that you can buy most anywhere. I also use poultry dust in the nest boxes. Good luck...