I wonder if the sevin dust could be irritating their air system. I haven't used anything in a dust form before on my birds, yet we have mites/lice off and on also. I just check the birds periodically and if I notice the bugs, I put a drop of neem oil behind the neck and one under the tail above the vent. If it's a bad infestation, I sometimes put a drop under each wing also. It kills the bugs within 1 day - great stuff! It's from Rose Mountain Herbs and the small size will last you a long time. Just use a medicine dropper to get some out and put it on the birds. I even use it on babies and it doesn't hurt them as long as you just do a drop or two. That way you could avoid the dust which could be irritating their air sacs and causing congestion (just a guess!)
