Thank you, I really enjoyed coming up to Oregon and will be there again for the NW Fall Beekeeping Conference.
Turns out, powdered sugar does not harm brood at all. There has been studies down here http://www.bioone.org/bioone/?request=get-document&issn=0022-0493&volume=097&issue=02&page=0171
and here is a quote from Michael W during a discussion if I should try rye flour on Beesource.com. (OTC is an antiboitic that they were mixing with various dusts including powdered sugar).
'In the study they tested without the OTC also to see if the dusts alone would injure the hives. They found that powdered sugar did NOT but many other things did. They defined "mortality" by bees removing larvae. In Ellis's experiement, if adults were removed from the experiment, adult bees wouldn't have been there to remove the larvae. Adult bees may have removed the larvae due to a foreign substance in the cell that was not actually harming the brood. They dusted directly into cells so anything your applying to top bars may or may not end up in cells to a degree to matter.
They made a square on the frame of brood and dusted each dust directly into the cells to see what would happen. There are pictures of this in the study where the bees go back and remove the brood in the area of the square but no where else. The bees did NOT remove brood from the squares dusted with powdered sugar. They said this may be due to the fact that the sugar is very similar to the nectar they are already feeding to the larvae.'
We have found no damage in any of our hives. We have done 3 major treatments on all of our hives, and now we have two hives with large mite loads that we are treating with powdered sugar separately. There is no brood damage, no queen damage and the bees seem very happy with it. It also seems to increase their hygenic actions, now we see them grooming themselves all of the time on the landing boards, way after we have used powdered sugar.
You do have to monitor a lot to know the mite load and if its increasing. Your larger booming hives will have more mites. What is amazing is how many the sugar knocks down. On a very infested hive, the first treatment will yield over 700 mites, and the second treatment a week later showed about 300 mites. I need to do one more.
Our plan of action is to dust all hives in November when the queen stops laying to capture phorectic mites living on the bees (No brood to hide in).
I have pictures posted on www.countryrubes.com
Thanks for your input,