Carbohydrate nutrition associated with health of overwintering honey bees.

In temperate climates, honey bees rely on stored carbohydrates to sustain them throughout the winter. In nature, honey serves as the bees' source of carbohydrates, but when managed, beekeepers often harvest honey and replace it with cheaper, artificial feed. The effects of alternative carbohydrate sources on colony survival, strength, and individual bee metabolic health are poorly understood. We assessed the impacts of carbohydrate diets (honey, sucrose syrup, high-fructose corn syrup, and invert syrup) on colony winter survival, population size, and worker bee nutritional state (i.e., fat content and gene expression of overwintered bees and emerging callow bees). We observed a nonsignificant trend for greater survival and larger adult population size among colonies overwintered on honey compared to the artificial feeds, with colonies fed high-fructose corn syrup performing particularly poorly. These trends were mirrored in individual bee physiology, with bees from colonies fed honey having significantly larger fat bodies than those from colonies fed high-fructose corn syrup. For bees fed honey or sucrose, we also observed gene expression profiles consistent with a higher nutritional state, associated with physiologically younger individuals. That is, there was significantly higher expression of vitellogenin and insulin-like peptide 2 and lower expression of insulin-like peptide 1 and juvenile hormone acid methyltransferase in the brains of bees that consumed honey or sucrose syrup relative to those that consumed invert syrup or high-fructose corn syrup. These findings further our understanding of the physiological implications of carbohydrate nutrition in honey bees and have applied implications for colony management.

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.

Overwintering honey bees: biology and management.

In temperate climates, honey bees (Apis mellifera) survive the winter by entering a distinct physiological and behavioral state. In recent years, beekeepers are reporting unsustainably high colony losses during the winter, which have been linked to parasitization by Varroa mites, virus infections, geographic location, and variation across honey bee genotypes. Here, we review literature on environmental, physiological, and social factors regulating entrance, maintenance, and exit from the overwintering state in honey bees in temperate regions and develop a testable model to explain how multiple factors may be acting synergistically to regulate this complex transition. We also review existing knowledge of the factors affecting overwintering survival in honey bees and providing suggestions to beekeepers aiming to improve their colonies' overwintering success.