[Bonus] Short - Dr. Dewey Caron: Fat Bees and Overwintering Success

[Bonus] Short - Dr. Dewey Caron: Fat Bees and Overwintering Success

[music]

Jeff Ott: Welcome to Beekeeping Today podcast shorts. Your quick dive into the latest buzz in beekeeping.

Becky Masterman: In 20 minutes or less, we'll bring you one important story, keeping you informed and up to date.

Jeff: No fluff, no fillers just the news you need.

Becky: Brought to you by Betterbee, your partners in better beekeeping.

Dr. Dewey Caron: Hi. I'm Dr. Dewey Caron. I come to you from Portland, Oregon, on the way to Northern California.

[music]

I present another audio postcard on communication, my continuing series of once-monthly Beekeeping Todayshort podcast. Topic this month, September is Fat Bees, where these audio postcards I have been discussing communication on three levels, be scientist to beekeeper, beekeeper to bee, and bee to bee. We start with bee scientists to beekeeper. I reference studies by Mehmet Ali Döke, a student from Turkey who received his PhD at Penn State. The thesis title was Electrophysiology of Overwintering in Honeybees.

He has published his research with a major professor, Christina Grozinger, and an overview of Overwintering of Honeybees with Maryann Frazier and Dr. Grozinger. References are in our notes. His work defines important factors that occur in colonies preparing for winter. What do we know? Honeybees survive the winter in a metabolically and physically active state using the food stored earlier in spring and summer to generate heat inside the thermal regulatory cluster.

The colonies produce winter bees in the fall, what we call fat fall bees, a term coined by Doug Somerville of Australia. Fat bees store reserves in their bodies, a process that involves the blood protein called vitellogenin. Another term sometimes used is diutinus, a Latin word for long-lasting. Diutinus bees are, therefore, long-lasting bees. Winter fat body, fat bees, or diutinus bees exhibit substantially increased longevity. Honeybees do not hibernate. They survive the winter in that metabolically and physically active state.

As winter approaches, the pollen supply, temperature, and photo period decrease, inducing a gradual decline in brood rearing. The queen usually stops egg laying when the outside temperature is too low, but she must restart when temperature and photo period rise again to prepare the colony for rapid growth in spring. Clustering occurs when the hive temperature begins to drop below 60 degrees F, and clusters generally are well-formed around 50 degrees Fahrenheit.

The cluster is unique. It helps the colony survive the winter. Clustering bees organize an insulating sphere with the queen at the center of the cluster. To produce heat, bees shiver their wing muscles. At colder temperatures, the cluster is well-defined, becomes more compact when the outside temperature is lower inside the hive. Depending upon whether there is brood or not, the core temperature is warmer, in fact, in the 90s Fahrenheit, when brood is being reared. The cluster moves to stay in contact with honey. Insulating bees of the shell move inward as their individual body temperatures fall.

They need to maintain a body temperature above the critical threshold of 50 degrees Fahrenheit, when bees would enter a state of chill coma. Winter bees can live 100 days on average, as compared to spring workers who live on average 30 to 40 days, and summer bees who live on average a significantly shorter 25 to 30 days. Within colony, all of these workers are female, and all our sisters, bred from the same queen, yet their different lifespans vary greatly. Drones will not be part of the cluster.

With little to no brood production during the winter, and in order for the hive to survive months of cold temperatures in northern climates, the development of healthy winter bees with their longer lifespan is critical for colony survival. The physiological differences between winter and spring or summer bees, in addition to their greater longevity, are, the level of juvenile hormone is lower in winter bees than in summer bees. A lower juvenile hormone level is generally associated with in-hive tasks.

Winter bees have enlarged fat bodies. Winter bees have enlarged hypopharyngeal glands, and winter bees have a higher level of protein in the form of vitellogenin in their hemolymph and fat body. The fat bodies in bees produce vitellogenin, which both enhances the immune system and increases the lifespan of bees. Vitellogenin is used at brood for production, in the production of royal jelly, as well as in the regulation of foraging behavior.

Both queens and newly emerged workers have high levels of vitellogenin at emergence, and while the level drops as worker bees age, it remains high in the queen, the longest-lived female. As the level of vitellogenin drops in worker bees, the level of juvenile hormone begins to rise, and the hive bees then switch tasks, leaving hive duties to become foragers. Unfortunately, beekeepers have little control over the timing and quantity of winter bees produced.

The gradual replacement of summer bees by winter bees has been shown to correlate less to environmental conditions, things such as temperature and day length, and more to conditions within the hive. Winter bees can develop while the hive is in a broodless state during the late summer and early fall months. Normally, however, their development begins while brood is still present, although declining as early as August and during September. Studies have experimentally manipulate colonies.

We can see winter-like bees develop with a removal of larvae, i.e., in a broodless state, plus when colonies are not queenright, and during dearth when queens stop egg laying. One can see the effect of the cycle of the seasons. When there's little pollen coming in, forging decreases, and it's related forage or pheromone increases. The forgers remain in a hive, not out forging. Brooding decreases as do its attendant pheromones, triggering production of winter bees with their higher level of vitellogenin.

In the spring, the reverse occurs. Brood development triggers a reduction in vitellogenin due to brood pheromone, which in turn increases the level of juvenile hormone, which then stimulates pollen forging. Long-lived winter bees enabling winter survival evolve through an increase in a worker bee's capacity for that accumulation of vitellogenin. One thought beekeepers have is bee stock may influence their overwintering success.

Döke and collaborators test four different US honeybee stocks, two bred in southern and two bred in northern regions under standard beekeeping practices, and three different Avery locations in central Pennsylvania. They found that stock or region of origin of the queen was not correlated with overwintering success. However, overwintering success was influenced by the weight and population size of the colonies reached prior to winter. Higher colony weight is a strong predictor of overwintering survival.

Weather conditions correlate to overwintering success. Seasonal weather conditions affect both forage availability and thermal regulatory success, and thereby both directly and indirectly influence honeybee health and survival. Growing degree days in a prior summer was the strongest predictor of overwintering survival. This agronomic index of heat accumulation probably relates to floral resource availability. In other words, flowering plants.

Both precipitation of the warmest quarter and the wettest quarter were important, which would again influence how well flowering plants do. Following completion of his degree, Mehmet took a postdoctoral position in Puerto Rico. One of his studies there examined whether the seasonality of honeybees in a tropical environment could produce workers similar to winter bees of temperate areas. Puerto Rico has strong seasonal differences of wet-dry seasons based on flower phenology that can create a similar stressor to temperate region bees, where forage resources are reduced or absent in winter.

The study experimentally manipulated the amount of bee larvae, resulting in a more pronounced increase in worker longevity. This suggested a mechanism for how expanding lifespan may occur. Fewer mouths to feed means longer lifespans, so subtropical bees possess the physiological capacity to adjust their lifespans seasonally in response to resource availability, flowers. Pollen unavailability seems to be the major clue. In subtropical wet seasons when bees have very limited forage opportunities, the winter bee characteristic, especially the enlarged hypopharyngeal glands, are present.

One other item to add. A study from Tucson Bee Lab with Washington State University collaborators used the Varroa population dynamics model developed by the USDA to model future climate projections for the Pacific Northwest. With climate change potentially expanding the geographic area with warmer autumns and winters, honeybee flight will extend later into the fall. The simulations of Varroa pop support the hypothesis that late season flight will, one, alter the overwintering colony age structure, two, skew the population towards older bees, and three, lead to greater risk of colony failure in the spring. The winter bees necessary to survive the colder months will not be as robust a population in colonies, according to the model. That certainly is not good news.

Let's go on to beekeeper-to-bee communication. How do we communicate to our bees to rear the bees that are going to overwinter, what we call those winter or those fat fall bees? A fat fall has a second connotation. Fat colonies need to be fat in food reserves to provide the overwintering reserves for when the weather turns colder. Good queen stock improves overwintering, but by September, it's too late to attempt to re-queen. Weaker units can be combined to form stronger ones to bolster the population going into the winter if no disease is present. Adding summer bees will not help, and sometimes the weak colonies have not yet begun winter preparations.

Colonies fat with a new queen, fat worker bees, and colonies fat with adult bees help ensure overwintering success. What do we want to communicate to our colonies? Elevated mite populations will negatively impact successful overwintering colonies. Mite numbers need to be below 2% adult infestation, counting mites removed by sampling when you use either alcohol or powdered sugar, and then dividing by the sample size. It's often too late to reduce mite numbers in September. Our mite control needs to be continuous, all season long, to have healthy colonies in the fall. We absolutely do not want colonies fat with mites in the fall.

In a previous Beekeeping Today short, I discussed mite control planning and how to reduce mites. Our major fall management is then feeding. Start with feeding the bees that will rear the fat fall bees. You would feed carbohydrate, in other words, sugar, so the colony becomes fat with sufficient high-quality honey stores. Think storage, not stimulation with fall feeding. We believe a more concentrated sugar solution, two parts sugar dissolved in one part water by volume or weight, is a good plan. Transferring honey-filled frames is an even better choice.

We might feed protein, that is, pollen patties, to help the bees conserve bee-bred stores for use next spring. Feeding helps fatten up, i.e., compact the brood area with honey stored to the sides and above the brood, the existing brood when you're feeding, so winter clusters can move upward, keeping in constant contact with honey. Sugar for fall feeding needs to be of high quality with few contaminants.

Some natural honeys are less useful compared to syrups made with cane or beet sugar because they may crystallize rapidly in a comb, canola and ivy are examples, or ferment, lavender may do this, or may have higher levels of acids, minerals, et cetera, such as goldenrod and knapweed, making them less desirable than sugar water honey for overwintering. Sugar water honey offers great overwintering qualities.

To communicate to your bees and ensure the bees take and store the sugar water you offer, place it right over the top box or in a division board feeder adjacent to the brood area. Entrance feeders or feedlot feeding are less desirable, as you might be increasing yellow jacket pressure. To encourage the bees to take more syrup, fatten the offer by adding a smell, a few drops of essential oil, or you will use one of the many food stimulants, supplements, such as Honey B Healthy, for example. Some beekeepers also fatten the syrup with microbiologicals, probiotics, or amino acid boosters, or an increasing variety of feed additives.

Independent data on plain benefits of most of these additives is lacking, but if you have success, and you feel your bees overwinter better with their use, then continue with them by all means. Lastly, bee-to-bee communication. The communication to fatten up for winter has been explained already. All bees get the message internally, and no means of communicating from bee to bee has not yet been demonstrated. One measure that may involve bee-to-bee communication is the kicking out of drones in the fall as temperatures cool and brood nests compact.

Timing varies between colonies and seasons. A few colonies, often those with excessive amounts of brood, those with a late-season queen event, or those that are queenless, may kick out only a portion of their drones. Drone expulsion by colonies in southern regions is often prolonged. Adult drone eviction may not always be obvious. Expulsions may include drone adults and brood. The expulsion of drones was dramatized by Nobel Prize-winning author Maurice Maeterlinck's essay, The Massacre of the Males, from his book, The Life of theBee.

I have a reproduction of his account on box 21, page 176 of my text, Honey Bee Biology and Beekeeping. He writes, and this is only one sentence, "One morning, the long-expected word of command goes through the hive, and the peaceful workers turn into judges and executioners." The "word of command," from his description, remains elusive. Google AI says worker bees recognize drone honey bees primarily by size and their larger eyes. This is highly unlikely. The recognition of the male is probably due to differences in the cuticle of drones having a different odor from that of the worker.

No buzz run, as in swarming, nor a special dance behavior such as the tremble dance, have been found a single, "Kick them out." It is unknown if the new winter bees do the expulsion. Likely, it is the last activity of foragers who will not continue to live long into the winter season based on the changes that they are internally experiencing. The three correlative factors we recognize are, one, changing temperatures and brood nest contraction. As the weather cools and the hive's brood nest shrinks in preparation for winter, the female worker bees begin to evict drones.

Two, reduce foraging and resource scarcity. With the end of the mating season and the onset of colder weather, nectar and pollen become less available. Drones, whose primary role, of course, is to mate with the queen, consume valuable hive resources without contributing to food collection or defense. Worker bees will prioritize conserving resources for the queen and the workers. Three, the queen's laying behavior. The queen's egg laying slows down considerably in the fall, eventually stopping altogether. This signals the end of the breeding season, rendering the drones present in the hive unnecessary.

Seeley and a student in a 2003 Insect Society article explored drone production and fall elimination as an investment policy whereby a colony allocates limited resources among the various physiological functions fostering colony growth, survival, and reproduction. When energy is a limited resource for a honeybee colony, the colony faces a strong trade-off between energy investment and current reproduction and future survival. Drones become an energy drain and unnecessary, as reproduction of queens is not a priority. Rearing of drones ceases much earlier in stronger fall colonies, and the empty drone cells and it actually can become honey storage cells over the winter.

Fat fall bees and fat colonies, the key to building toward a successful wintering. Next time, I'll discuss helping the bees in Langstroth colonies overwintering by fattening the insulation of the beehive. I have some homework for you. It's critically important to provide top insulation to all colonies. This is a topic for my next Beekeeping Today short podcast. The homework is to review a series of four videos on the website Sustainable Beekeepers Guild of Michigan on the topic of ventilating and condensing hives.

Also, look at a plus one publication by Ashley St. Clair, Nathaniel Beach, and Adam Drozal. They found in central Illinois, only one colony died with top insulation of 22 in the test, while 6 of 21 died without top insulation, and the colonies with the top insulation used 10% less of their food resources. These are both listed in the endnotes for this presentation. Beekeepers can reduce winter losses by understanding factors important to bee communication and communicate to our bees our expectations. Until next time, be well.

[music]

[00:19:57] [END OF AUDIO]