I just got some on sale for like five bucks. Just in case.I usually spray my coop with permethrin 10 once a month in summer to keep flies and other insects away. It is safe for chickens, but do not use if you raise bees. Mix it 37 ml per gallon of water in a garden sprayer or spray bottle. A pint is $8 at TSC and other feed stores.
https://www.tractorsupply.com/tsc/product/gordons-permethrin-10-livestock-and-premise-spray-32-oz