I have found that diatomaceous earth is better painted on as a slurry. Get a few handfuls of food grade diatom, mix with a water so it becomes like a runny paint and paint your coop. When dried, your coop will become grey, but one application will last for around a couple of months and mites just cannot survive, after a few days they will be gone. I had an infestation by the time I found the mites and I had nothing to hand but this. At first I just sprinkled the powder but it was not very effective and I had to do it almost everyday as it just falls to ground. Not to mention it was dusty, bad for chickens breathing. But as a slurry, it is not dusty, seems to eliminate mite and only need to do a couple of applications over the summer. I would be interested to know if it kills of these flea type things also.