In Hawaii there are mosquitoes everywhere, year round, including in the chicken coop (inevitably). I and my chickens have grown up accustomed to dealing with mosquitoes. The chickens don't seem very bothered by them (along with all the other birds, and animals outside, farm animals, pets, and wild). I've never even seen fowl pox in twenty-some years (although it does exist here), or had any other epidemics for that matter, let alone mosquito-born ones. Obviously, it's up to you to use your own judgment in this particular case, but it's easy to overreact to these types of things, and if I were you I'd try to be sure you have a real issue on your hands, before busting out the heavy insecticides. That stuff is pretty nasty--do you really want traces of those toxins polluting your food, etc? Sometimes the cure is worse than the disease, especially if the "disease" isn't doing any harm in the first place...