Not CCD. What were your actual mite loads? Small cluster, few capped brood, heads in cells, I'd bet it's the cold snap with too small a population that did them in. The varroa mites really seem to build up in those large Fall hives (especially untreated) and dwindle the population over the winter. The cold snap invariably had them trying to keep too much brood warm with too few bees. Varroa are not to be underestimated. They are by far the major player in the failure of hives in overwintering or dying in early spring.I have been doing natural bee keeping.