Unfortunately DE is not an effective treatment for a mite infestation.
You will want to break the cycle, so repeat treatment in 5-7 day intervals until the mites are gone.
There are different types of mites, that's true. Most mites have a life cycle (from egg to hatch) from 5-12 days...
You can find Permethrin Poultry Dust or Spray at your local TSC or feed store.
Treat your flock, clean out their housing and treat that too.
Repeat treatment in 5-7 day intervals.
There is no withdrawal period when using Permethrin.
Yes, your hens will preen, they may get a bit on their...