Next week, the United States Department of Agriculture (USDA) and the Bee Informed Partnership (BIP) are expected to issue their annual report on honey bee losses during the winter. Many experts, citing the severe winter weather across many parts of the country, are expecting significant losses. Honey bees are already under stress from a wide range of potential factors including disease, pests, pesticides and lack of forage. The tough winter certainly didn’t help. However, this remarkable insect that pollinates one-third of the food we eat is highly adaptable.

As long as their basic needs – food, shelter and safety – are met, honey bees can survive long, cold winters and extended periods when there is no natural forage. Unlike most insects, honey bees are able to withstand cold winter conditions by producing individuals in the late summer more suited to surviving long, cold-weather periods confined in their hives. They harness the collective warmth generated by individual bees who cluster tightly together around the queen to maintain a constant, core temperature.

Although bees are generally not active outside the hive in winter, they are very busy inside taking steps to ensure the colony’s survival. Bees continue to access stored food – honey and pollen – and generate heat within the cluster to protect the queen. If adequate provisions have not been made during the summer and fall, then a colony is likely to collapse by the following spring because of starvation – a common cause of colony loss over winter in North America.

A second, major factor affecting honey bees in the winter is mite infestation. The greatest threat is from the Varroa mite, an exotic parasite introduced to North America in the mid-1980s. This mite feeds by sucking the blood of honey bees and it reproduces on the developing bee brood. Serious bee diseases are also vectored by the mite, which makes Varroa and its associated pathogens a very lethal mix. 

Recent scientific research has shown that the winter survival of individual honey bees and honey bee colonies is dependent on the level of Varroa infestation. The number of mites on adult bees peaks rapidly in late summer to early fall as the amount of brood within a colony decreases. The bees emerging from infested brood cells in late summer are winter bees. Adult winter bees that were infested with Varroa as immature bees within the brood cells do not fully develop the physiological characteristics typical of a long-lived winter bee. This makes them less likely to withstand the grueling environmental stressors associated with winter conditions and survive until the spring.

Last season, the Bayer Bee Care team In North America, in cooperation with beekeepers, placed a series of “sentinel hives” in various locations in the U.S. and Canada to get a better understanding of how honey bees were faring in close proximity to agricultural production. Information from that study and reports from beekeepers provided indications that overwinter colony losses could be lower in the spring of 2014. Factors contributing to this initial potential possibility include:

·         Lower Varroa mite levels because of the timely use of a newly approved varroacide and high replacement of infested colonies after the high losses suffered from Varroa over the winter of 2012/2013;

·         Later spring and shorter season in 2013 reduced time for mite problems to develop; and

·         Greater awareness about factors affecting bee health and greater effort by beekeepers in making proper provisions for their bees.

However, this past winter has been extremely long and harsh. Therefore, it will not be surprising to hear reports of many late winter/early spring losses. The losses under such extreme conditions could include causes such as starvation, dysentery, high moisture in hives (inadequate ventilation), shortened adult bee longevity if mites and viruses present, dwindling as a result of imbalance in individual bee losses relative to replacements, and queen issues.

While we hope this year’s winter losses won’t be as severe as last season’s, there is no denying that there have been losses of 30 percent or higher in most recent years  – higher than the 5-15 percent losses that normally were experienced prior to the introduction of Varroa and tracheal mites in the mid 1980s. More work is needed to change this trend. The recent Varroa Mite Summit, sponsored by the USDA, which brought together scientists across the globe, is a good place to start. 

At Bayer, we have supported honey bee health for more than 25 years. Over the years, we have come to understand the complexities of this most fascinating insect as well as its frailties. We also have a deep respect for the beekeepers who work diligently to keep their hives healthy. We know it will take the collaboration of a wide range of stakeholders to find the solution to declining colony health. We recently opened our North American Bee Care Center in Research Triangle, Park, N.C., so that researchers and others can work together to help improve bee health. No matter what this year’s overwintering report concludes, we continue to believe that together we will find a way to keep our honey bee colonies thriving now and in the future.

By Dick Rogers, Apiologist and Research Manager, Bayer Bee Care Center In North America 


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