What's the Buzz with ATTTA # 128

Thursday, 8 December 2022

Both practical beekeepers and academic researchers are focusing efforts on understanding the impact that climate change will have on honey bees.  Last week, we concentrated on one aspect of honey bee biology as it relates to overwintering success and climate change.  Additionally, concerns over antimicrobial resistance, incidences of brood disease, honey production and emergence of novel pathogens have all been mentioned in the same breath as climate change.  As weather patterns shift, some unforeseen problems, or perhaps even benefits, for honey bees may yet emerge!  One ongoing battle for beekeepers, and the greatest risk to honey bees, must be considered in the context of climate change.  That is the Varroa mite!  This week, we will examine, through the lens of our changing climate, this deadly pest.

Climate Change and Honey Bees: Pest and Disease Management!

Most of the pests and diseases which beekeepers must manage are variable across the season.  Chalkbrood is often thought of as a spring problem.  Vairimorpha disease (formerly Nosema) will fluctuate across the season with typically higher levels in the spring reducing to lowest levels in the autumn.  Strong honey flow and hive growth in the early summer may precede an EFB outbreak.  In consideration of what is understood of honey bee pests and diseases, the suggestion that changes in weather patterns impact overall honey bee health, is not inconceivable.

A small but growing body of research warns of an increased threat from the honey bee antagonist, Varroa destructor, due to climate change.  The caution expressed by these researchers is reenforced by beekeeper’s experience.  The observed trends in Atlantic Canada are for earlier springs and longer falls.  This extended season provides a lengthened period of brood production which could benefit the colony in terms of overall population size.  The concern is, due to the Varroa mite life cycle being linked to brood production, this provides an increased opportunity for this pest to grow in numbers during a longer beekeeping season.

Varroa destructor Antagonist of honey bees (Photo: ATTTA 2022®)

The reproductive phase of the Varroa mite takes place in the brood cells of honey bees. A foundress mite will enter the cell containing a worker, or preferentially a drone, pupa.  She will hide under the pupa to avoid inspecting nurse bees.  Now safely ensconced within the capped cell, the female Varroa mite will produce between 1 and five daughters depending on conditions and type of brood cell (drones cells allow higher production). 

A typical female Varroa mite will have, at a maximum, 7 reproductive cycles in her life.  The number of cycles is dependent on the length of time in the capped cell which will be 12 or 15 days for worker or drone cells respectively.  This, in part, demonstrates the reproductive potential of a single mite.  A high fecundity female producing 5 daughters per cycle, for a season containing seven reproductive periods, would equal near 80 000 daughters.  If a longer season means one more reproductive cycle this number would be an unimaginable 390 000 mites.  This example is theoretical only to make a point and luckily there are factors, including beekeeper management, which limit this type of unchecked growth. 

The behaviour of Varroa mites changes across the beekeeping season.  Sexually mature mites, mothers and daughters, will focus on reproduction and be found mainly in the brood during the early season as the colony is expanding.  As brood production slows, increasingly, mites will be found on the honey bees.  This increased concentration of mites on the honey bees will be reflected in beekeepers seeing more mites in washes.  Also, in part, why the economic threshold for treatment increases later in the season.

So it is known that warmer spring and fall temperatures increase the level of V. destructor infestation in the bee colonies[1].  Longer beekeeping seasons will require added vigilance in controlling Varroa mites.  Continual monitoring and perhaps looking at mid season treatment options are becoming more important.  These challenges are not a hypothetical, future problem but upon us now.  One proposed contributing factors to the high 2021/2022 overwintering losses is the preceding longer beekeeping season leading to increased Varroa mite populations. 

Awareness is the first step in addressing climate change!  Longer growing seasons, supportive of Varroa mite reproduction, needs additional management focus.  As discussed last week, the asynchrony between flower phenology and honey bee foraging behaviour extending further into autumn, also presents challenges.  Long term changes in weather patterns may have a greater effect on honey bees as their behaviours are strongly influence by temperature.  Research and information will be required to support the beekeeping industry through these new challenges!  

[1] Hillayová, M.K., Korený, Ľ. and Škvarenina, J., 2022. The local environmental factors impact the infestation of bee colonies by mite Varroa destructor. Ecological Indicators, 141, p.109104.

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What's the Buzz with ATTTA #127

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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