Climate Change and Honey Bees: Fall to Winter Transition

Thursday 1 December 2022

Beekeepers must be in-tune with weather and seasonal changes to properly manage our bees.  Historically, we have counted on seasonal milestones to support management decisions.  Climate change is causing a shift in these milestones.  Pollination of wild blueberries is weeks earlier than a generation ago.  Fall feeding extends well beyond the previously normal period, as we are experiencing double digit temperatures into the month of November.  We are adjusting as best we can with the recognition that climate is changing.  What this means for the bees is hard to determine but additional insight into their physiology may be helpful to understand potential impacts.

Climate Change and Honey Bees: Fall to Winter Transition

It is well known that in response to seasonal changes, honey bees can develop into “winter” or “summer” bees.  As the seasons shift from summer, through fall and into winter, there are specific triggers which determine which category of bees will develop in the hive.  All newly emerged honey bees have the potential to either remain winter bees or transition into summer bees.  Automnal decreases in resources combined with temperature changes prevents young bees developing into summer bees.  Summer bees will survive for 3 – 4 weeks of intense activity.  With the high fecundity of the queen, the mortality rate is exceeded, and the colony will grow in numbers despite the short life span of its workforce.  In colder climates, with temperatures and resources not being conducive to brood production, the bees have an increase in longevity as a strategy to survive through the winter months.  These winter, or diutinus, bees live on average about 100 days and have been reported to live over 300 days [1].

There are physiological differences between summer bees and winter bees.  There are endocrine variations, specifically the production of Juvenile Hormone (JH).  The production of JH is linked to foraging behavior[2].  This hormone is part of the mechanism which determines the worker bees progression through job roles in the hive.  This process, called age polyethism, will see worker bees progress from nurse bees to foragers, and all jobs in between, during the beekeeping season.

Foraging Summer Honey bees collecting pollen!

Winter bees will also have hypertrophied hypopharyngeal glands.  This gland enlargement is indicative of increased vitellogenin production and typical of nurse bees[3]. The hypopharyngeal gland produces the nutritional jelly which nurse bees will use to support brood production.  Changes, specifically a reduction, in the production of vitellogenin is a strong factor in the transition of hive bees to forager bees[4].

Winter bees will have higher fat body protein stores than will foragers.  It is thought that depletions of these fat stores are another trigger altering worker bees into foragers.  The complex endocrine pathway leading to this change is, in part, caused by vitellogenin reductions.  Vitellogenin suppresses JH slowing the changes which will transition the hive bees to foraging behavior.

Once bees begin to forage their longevity is reduced [5].  There are several intricate mechanisms involved in these behavioral changes and the exact triggers are unknown.  Changes in brood production, hive nutritive status, and ambient temperature are believed to be involved.  Interestingly, photoperiod does not affect honey bee behaviors in this respect.  So, the changes in day length are not a seasonal signal for colony transitions into winter torpor. 

This past autumn, provided two of the three signals for honey bees to increase foraging behavior: higher than usual temperatures and nutritive status within the hive.  It is also possible that weather conditions could have caused an increase in brood production.  This resulted in a theoretical and observed effect of an increase in honey bees foraging past the normal seasonal period.  Any physiological transitioning of hive bees to forager bees would result in a decrease in fat stores.  This is a reversible transition early on but the resulting prolonged reduction in vitellogenin and increased JH will, after a brief period, create permanent, short lived summer bee populations.  Also, honey is an energy source used for foraging activity.  In Atlantic Canada, there is relatively little pollen or nectar available in October and November and the energy used in late season foraging creates a net deficit of honey.  This leaves fewer winter stores for the colony.

Some researchers have suggested that milder winters will favor honey bees [5] but this is yet to be determined.  As outlined above there are complexities to honey bee behavior which may be challenging as weather patterns shift.  With anticipated global warming, beekeepers will have to take advantage where we can, perhaps with feeding further into the fall, and carefully observe for negative impacts on honey bee health.  A possible additional, negative impact of climate change may be related to pest and disease management.  We will look at this more closely next week.


[1] Southwick, E.E., 1991. Overwintering in honey bees: implications for apiculture. In: Insects at Low Temperatures (E.E. Lee and D.L. Denlinger, Eds.), Chapman and Hall, New York. pp. 446–460.

[2] Behrends, A. and Scheiner, R., 2010. Learning at old age: a study on winter bees. Frontiers in Behavioral Neuroscience, p.15.

[3] Münch, D. and Amdam, G.V., 2010. The curious case of aging plasticity in honey bees. FEBS letters, 584(12), pp.2496-2503.

[4] Guidugli, K.R., Nascimento, A.M., Amdam, G.V., Barchuk, A.R., Omholt, S., Simões, Z.L. and Hartfelder, K., 2005. Vitellogenin regulates hormonal dynamics in the worker caste of a eusocial insect. FEBS letters, 579(22), pp.4961-4965.

[5] Prado, A., Brunet, J.L., Peruzzi, M., Bonnet, M., Bordier, C., Crauser, D., Le Conte, Y. and Alaux, C., 2022. Warmer winters are associated with lower levels of the cryoprotectant glycerol, a slower decrease in vitellogenin expression and reduced virus infections in winter honeybees. Journal of Insect Physiology136, p.104348.

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