How Do Honey Bees Survive the Winter Without Fresh Pollen?
What Distinguishes a Winter Bee from a Regular Worker is the Presence of Enlarged Fat Bodies
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All during the foraging season, honey bees collect pollen and nectar. They use nectar for energy to keep going from day to day. Any extra nectar is turned into honey and stored in combs. The honey may be used shortly after it is stored, or it may remain in the hive for years. Due to various enzymes added by the bees, honey has an extremely long shelf life.
Pollen is a bee’s main source of lipids, proteins, vitamins, and minerals. Young nurse bees eat a lot of pollen which allows them to secrete royal jelly that they feed to developing larvae. Without a high-protein diet, the nurses cannot raise new bees.
Pollen Does Not Store Well
But unlike nectar, pollen does not store well. Even though the bees increase its shelf life by adding enzymes and nectar and turning it into bee bread, the shelf life is relatively short. Most pollen is eaten immediately after it is collected, and the rest is eaten within weeks. Bee bread stored longer dries out and loses much of its nutritional value. The bees often remove it from the hive, and you may see hard marbles of pollen on the bottom board.
In spite of this problem, honey bees survive the winter without fresh pollen. Although not much brood is raised in the dead of winter, as spring approaches, the winter bee cluster warms up and brood rearing resumes. With little or no stored pollen, how do the nurse bees raise brood?
Fat Bodies and Vitellogenin
The secret to winter survival is found in the bodies of winter bees. Winter bees are so different from regular workers that some entomologists believe that they are a separate caste. The thing that distinguishes a winter bee from a regular worker is the presence of enlarged fat bodies. The fat bodies are bathed in hemolymph (bee blood) and produce large amounts of vitellogenin. In times of shortage, vitellogenin can supplement or completely replace a winter pollen supply.
Just as a queen bee can be raised from any fertilized egg by providing a rich diet of royal jelly, a winter bee can be raised from any fertilized egg by feeding an especially lean diet. This occurs in the fall at the end of the foraging season. Depending on your local conditions, winter bees begin to appear by September or October in most of North America.
The other thing that vitellogenin does is increase the lifespan of the winter bees. Whereas a regular worker has a lifespan of four to six weeks, a winter bee may live six months or more. The winter bee with her storehouse of resources, needs to survive long enough to feed the spring larvae.
In essence, a winter colony stores protein not in the wax cells but in the bodies of bees. If you’ve ever wondered how your honey bees can survive the winter without fresh pollen, winter bees are the answer.
Honey Bees in Winter May Need a Supplement
But even a body full of protein reserves will eventually run dry. As the nurses feed more and more bees, their fat bodies become depleted. If the winter is particularly long, the colony may not have the resources to wait for spring pollen. Or, if the beehive location is shady and cool, the bees may decide to stay home instead of forage.
For this reason, beekeepers often feed pollen supplements to colonies in the early spring. Pollen supplements should be timed to coincide with the beginnings of brood rearing. If lots of pollen is given too soon, the colony may become too large for the remaining food supply, or the excess ash may cause honey bee dysentery. If it is given too late, the colony may perish from lack of nutrition.
A good rule of thumb in North America is to hold back on pollen supplements until after the winter solstice. However, if you have a healthy hive that is expanding as spring approaches, you may not need pollen supplements at all.
Varroa Mites and Winter Bees
In order for a colony to survive the winter, it needs a strong and healthy crop of winter bees. Since these bees will emerge in the fall, it is important that varroa mites be under control before the winter brood is capped. If the winter bees are born with viral diseases associated with varroa mites, those bees will most likely die before spring, and their protein reserves will be lost along with them.
The best practice is to sample your hives for varroa mites in mid-August. If you find your mite counts are at treatment levels, treat the colonies before the end of August. If you wait too long, a number of your winter bees will be infected before they emerge, and infected bees have short lifespans.
Resent research has shown that varroa mites don’t feed on hemolymph but actually feed on the fat bodies that are bathed in hemolymph. This is another reason that varroa-infected colonies have a hard time making it until spring. If the varroa take the proteins for themselves, there may not be enough left over for the bees, even if the winter bees happen to survive.
Timing is Important
A good beekeeper remembers that timing is everything with a bee colony. Even though you don’t have a lot to do in winter, you need to do things on time. Mark your calendar so you won’t forget.
Just for fun, when you find some dead bees, turn the bees on their backs and open the abdomens for a look inside. You can clearly see the difference between a winter bee and a regular worker. A winter bee is filled with cloudy white fat bodies all throughout her abdomen, while a regular worker is not.
Have you ever looked inside a winter bee? What did you find? Let us know.