Colony Size, Rather Than Geographic Origin of Stocks, Predicts Overwintering Success in Honey Bees (Hymenoptera: Apidae) in the Northeastern United States

Honey bees (Apis mellifera L.) are key pollinators of agricultural crops. However, approximately 30% of managed colonies die each winter in the United States. There has been great interest in breeding for 'locally adapted stocks' which survive winter conditions in a particular region. Here, we evaluate the impact of geographic origin of stock on colony weight, population size, and overwintering survival. Comparing four different U.S. honey bee stocks (two bred in southern and two bred in northern regions) under standard beekeeping practices in three different apiary locations in central Pennsylvania, we examined possible adaptation of these stocks to temperate conditions. We confirmed the genotypic difference among the stocks from different geographic origins via microsatellite analysis. We found that stock or region of origin was not correlated with weight, population size, or overwintering success. However, overwintering success was influenced by the weight and population size the colonies reached prior to winter where higher colony weight is a strong predictor of overwintering survival. Although the number of locations used in this study was limited, the difference in average colony sizes from different locations may be attributable to the abundance and diversity of floral resources near the honey bee colonies. Our results suggest that 1) honey bees may use similar strategies to cope with environmental conditions in both southern and northern regions, 2) colonies must reach a population size threshold to survive adverse conditions (an example of the Allee effect), and 3) landscape nutrition is a key component to colony survival.