I had this same problem this past summer, if you go back thru my posts you'll find it. I got a lot of snark about it but clearly it's not just me. You're one of several that's had the same problem. I treated my birds more aggressively than it sounds like you want to just yet, but what I did was #1, treat every bird with a drop of puppy frontline, 1 drop under each wing and 1 by the gland on the tail. Then I dusted each with Sevin. Cleaned All of the bedding from the coop, sanitized, dusted everything in the coop with Sevin, replaced the bedding everywhere (nestboxes too) and sprinkled Sevin in all of that as well. I didn't have to redust, I didn't find a single bug the next day. The doves are still around, if it wasn't the chickens they'd still be in my garden beds.. but I just keep the girls up on the frontline (or revolution, it's a bit cheaper) and all is well.