There is no doubt Sevin works on bugs however it is being taken out of the market gradually, for both plants and critters. It's proven to be highly carcinogenic and a long residual nerve toxin as well as highly water toxic for a very long time. Many people that thought it safe for years and used it now have tremors and even seizures from the lasting effects building up. If you check it's status on the PAN info site you will see most of the licenses to produce it are now canceled.
Enter Sevin here. If you go to
an individual product like this one you can read the risks and studies under each warning about it.
Depending on where you are Sevin could already be restricted for use in poultry, we can't use it here. And even when it was approved there is a withdrawal time for all concentrations, and it could never come in contact with eggs as they are too porous. So check to make sure your using the up to date information on this product.
Sadly the alternatives are not being approved fast enough so for a bad outbreak we still may have to resort to Sevin. I agree DE works great if you can keep it up, and if the chickens will help by using the dust box themselves.
Rotenone is being phased out as a dust too, and it was the other very effective choice for mites. However they have linked that to Alzheimer's disease.
For just a few birds I have bathed them in dog shampoo for fleas and ticks, that works totally, and you don't have to worry about any rehatch. However that is totally unapproved in that product form, but the ingredients are approved for use here as a poultry spray, I just don't want to buy a 5 gallon bucket of the concentrate that makes 500 gallons of spray for my few birds.
PAN is just one good site, others are around but for sure check your local regulatory body to get the update for your district/state/country.