Your coop may prove difficult to treat with only the dust.
Here is a very good article (not poultry specific) on INERT DUSTS (ash DE etc) and their efficacy in dealing with mites etc.
http://www.oznet.ksu.edu/grsc_subi/...ure_slides/GRSC651_lect_20(1)_Inert_Dusts.pdf
ETA: Sorry but I cant seem to be able to get the link to work (google INERT DUSTS and oznet.ksu.edu)
a small excerpt from this excellent article:
" ..1.6 Advantages and limitations
The advantages and limitations outlined below apply mostly to DE dusts that are now becoming commercially acceptable by the grain and food industry. Fields (2000) described some of the advantages and limitations in detail. Advantages Inert dusts have low mammalian toxicity (e.g., DE rat oral LD50, >5000 milligrams per kilogram of body weight (Subramanyam et al. 1994)). They are stable on the grain, and
provide protection as long as the dusts remain dry. Unlike organophosphate grain protectants, they do not leave toxic residues. It was thought that insects may not be able to develop resistance to inert dusts (Ebeling 1971), although it now appears that such a development is likely (Korunic and Ormesher
2000)...
..........Inert dusts are ovicidal (El Halfawy et al. 1977), and such an action may be of value when they are applied as a surface treatment to empty storage facilities, warehouses, and mills. The hatchability of eggs of T. castaneum, O. surinamensis, the cadelle, Tenebroides mauritanicus (L.), R. dominica, and C. chinensis was reduced when the eggs were exposed to Petri dishes lightly dusted with 0.5 grams of each of 12 inert dusts. The hatchability of untreated eggs ranged from 94-100%. Across all 5 species, about 35-85% of eggs exposed to diatomaceous earth hatched.
The hatchability of eggs exposed to kaolin clay was 20-52%. The exact mode by which hatchability is reduced following exposure to an inert dust is unclear. The reduced progeny production, to some extent, may be due to the eggs failing to hatch on inert dust-treated grain. ....... "
