permethrin should never be used in proximity to eggs (egg boxes when chickens have access to lay in them)If you must use permethrin, it should not be allowed to contact the eggs. Fresh nesting materials or a clean pad should cover any permethrin used. Pyrethrin is safe and unfortunately less effective, to use in the nest boxes and on the chickens. I suggest people always thoroughly read the pesticide labels and err in favor of safety in regards to the food we eat! Permethrin dust is approved for use on chickens but not on eggs or eggs in  close contact with the dust, in regards to the dust treated surfaces. I use diatomaceous earth for larvae control and pyrethrin (natural safe insecticide derived from flowers) on  the birds and in their nest boxes. Used Proactively as a preventative, it controls mites ands lice and flys for me very well, used along with fly traps and good sanitation.