Abstract
Winter honey bee losses were evaluated during the two overwintering periods of 2009/2010 and 2010/2011. The research included dead bee workers that fell on the hive bottom board (debris) and the ones that flew out of the hive. Differences were observed in the number of bees fallen as debris between the two periods, whereas the number of bees flying out was similar in both years. No differences were found between the numbers of dead bees in strong and weak colonies. The percentage of bees flying out of the colony increased in the presence of Nosema spores, Varroa infestation, increased average air temperature, and insolation during the day. In addition, both the presence of Nosema and insolation during the day had an impact on the number of bees that died and fell on the hive board.