Sevin dust has been used for many years.. Coop, boxes, Birds... The Spinosad you can also apply to the birds and area. Here is a study done on the Spinosad. It kills them fairly rapidly.
http://www.mapress.com/zoosymposia/content/2011/v6/f/v006p282-287.pdf...
The DE does not work to well, Get some Sevin and treat the birds and the coop, you can also spray the coop with a pyrthrin spray, if you want to stay organic you can use this http://www.amazon.com/Monterey-Spinosad-Organic-Garden-Insect/dp/B000BWY3OQ. I use it on my birds when mites are seen...