A few years ago, I bought some blown plastic hive bodies which came with screened bottoms for mite control. I've got eight hives and no mites at least at a problem causing level. I've lost two hives per winter the last two years...the two with the open bottoms! I know these hives are said to be just dandy for overwintering, but how can that really be true? Common sense says they're going to get frigid in the Pennsylvania winter and that killed them. Maybe it would be ok just to slip a piece of plywood inside the hive over the screen?