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.
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| 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
Physiology, 136, p.104348.
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