I had flys and mosquitos BAD and sprayed the grass and trees in the pens with permethrin 10%(Animal friendly) and haven't seen a bug in them for several days now. It's pretty resonably priced if you shop around. I also sprayed all the grass and soaked the trees around the outside with tempo(not to be sprayed in pens), it lasts for along time(couple weeks or so unless it rains) and the flys usaully hang out in the shade of the trees during the day. The deer are loving it! Make sure the permethrin is 10% and not the 1% that is sold in most stores, 1% is an actual drench dilluted to put right on the animal but by the time you dilute with water for a spray mix it's too diluted. You may have to order it off the internet. It's the same stuff the guys who have the timer foggers use. If you spray down the grass in the area they like to bed in it works great, gets right on them. I wish I would have done it a month ago. Good luck
Cody Warne