Thank you for noting DE is toxic. Give a bird dirt for dust baths. That is their normal way to handle parasites. Works.If it kills insects, it's toxic! That's what it's for, and handling anything requires reading and following directions. Inhaling DE is really toxic!
Used as directed, permethrins are an excellent product for the chickens and their housing. There aren't 'non-toxic' insecticides!!!
Carbaryl is not approved for chickens in the USA, and it's 'more toxic' than permethrin anyway.
Cats don't manage pyrethrins well at all, so they need to be away from it until it's totally dry.
Mary