Our bees got through the winter pretty well and had a big population build up in March and April. When we took off the bottom board it was easy to see the mites that had dropped during winter, and I started noticing a lot of dead bees under the hive and bees unable to fly because their wings were mis-shaped or missing.  Decided that we should treat for mites, and still not wanting to use chemical treatments I decided to go for the powdered-sugar treatment. A few bees inevitably get crushed when we start moving boxes around, but the bees seemed okay with the sugar treatment -- their first reaction looked like "hey, what are you doing?" and the second one seems like "oh, it's sugar...sugar is goood!"  It took them just a few minutes to calm down after we put the hives back together -- they all were inside grooming each other and knocking off mites and putting away some of the good stuff. Though I'm not happy about the cornstarch in the sugar -- undoubtedly GMO corn as even I am not insane enough to use organic powdered sugar to dump by the cupful on my bees.