Preventing winter bee losses

Beekeepers advised to begin their winter preparations now

Aug 04, 2016
Peter Trodtfeld is an experienced beekeeper and Bee Health Expert at the Bayer Bee Care Center in Monheim, Germany.

Peter Trodtfeld is an experienced beekeeper and Bee Health Expert at the Bayer Bee Care Center in Monheim, Germany.

We are hearing a lot about honey bee overwintering losses at the moment. The honeybee research network COLOSS just announced the preliminary results of their survey of colony losses over the winter 2015-16 in Europe. The overall loss rate is estimated as 11.9 %, down from 17.4% the winter before but not as low as the 9% seen two winters ago. We talked to Bee Health Expert and beekeeper Peter Trodtfeld to find out why overwintering losses are important and what it means for future honey bee colony health


The honey bee research network COLOSS has been monitoring colony losses for many years to study and better understand the risk factors. An internationally standardized data protocol allows comparison and joint analysis of the data collected at country level. The survey methodology is also included as a chapter in the COLOSS BEEBOOK.

Interview with Peter Trodtfeld on honey bee colony winter losses and how beekeepers can monitor and reduce the Varroa mite infestation levels in their hives.

The preliminary results on the overwintering losses of honey bee colonies over the 2015/16 period are now available. They show great variability between different regions in Europe, and vary compared to last year, but overall, the average loss rate is lower than in 2014/15. Can you explain these results?

I am very happy to see that there has been an overall improvement compared to the previous winter, as demonstrated in Belgium for instance, where there were heavy losses of some 36% last year and only 12% this year. Particularly low loss rates were recorded in the Czech Republic with 6.4% (compared to 16.9% in the previous year). Unfortunately, a few countries had relatively high losses this last winter, such as Ireland (29.5% compared to 12.4% last year), Spain (22.1%, though not all regions were included so far) and Finland (17%, up from 8.7% seen previously). Last year we generally saw that higher mortality and losses were found in Central Europe and countries to the east. This year, however, the highest losses tend to be in the west and northern countries. This shows that it is normal that mortality rates undergo some fluctuation, between countries and even across different regions of some countries. There are many factors that can impact honey bee health and often several of them have a combined effect, so the fluctuations we are seeing from year to year can result from many different causes.

So honey bee mortality is influenced by many factors. COLOSS mentioned that losses due to queen problems were unexpectedly high in some countries. What about the role of the Varroa destructor?

The Varroa destructor is a key threat to the health of the Western honey bee. The mite weakens the bees’ immune system and transmits damaging viruses such as the Deformed Wing Virus, which is highly established in Europe.

Indeed, poor queen quality and consequential higher queen mortality is also increasingly affecting colony survival over the winter. Queen problems can be caused by a lack of support from worker bees, for example when the bee colony is infected with the Varroa mite. Another cause can be that the queen is old and has not been replaced early enough, as recommended, every second year.

In addition to that, insufficient or poor quality supplementary food provided by a beekeeper during the winter period can impact his colonies survival. Weather conditions can also have an impact.

Do you think the COLOSS overwintering results are useful to know?

Well, they give us a good baseline from which to compare loss rates from one year to another and also to get a broad overview of how well honey bee colonies in different countries across Europe are doing. However, as long as we (beekeepers, authorities, scientists…) are not using the data to take some action to improve the situation on bee health, this only gives us the year-on-year average winter losses for honey bee colonies in Europe. What we do see is that there is no obvious correlation in results with any particular factor which may impact honey bee health and overwintering mortality results are very variable.

You are a beekeeper yourself. Is there anything beekeepers can do to ensure that their losses are as low as possible?

Yes. We as beekeepers can influence bee health in a positive way. Especially this year, beekeepers in Central Europe need to keep in mind that after the long rainy periods we had earlier this year, bees may suffer from a food shortage in which case they will need to begin feeding their bee colonies sooner or provide more food than normal to compensatefor the bees reduced honey stocks.

It is also essential to monitor Varroa mite infestation levels and treat colonies accordingly as early as possible. If synthetic compounds are used, it is important to monitor the resistance levels of the Varroa mite in order to avoid low efficacy of the planned treatment. When using organic compounds such as formic acid which is quite temperature-sensitive, it is crucial to find the right application window to ensure its efficacy. For example, at temperatures above 30 degrees, there is a risk of evaporation which can have negative side effects on the treated bee colonies. It is also important to monitor after treatment to check that it has worked well enough to reduce the Varroa infestation to a manageable level.


To learn more about Varroa destructor, a key threat to the health of the Western honey bee, check the following website:  The Varroa mite.

To learn more about Varroa destructor, a key threat to the
health of the Western honey bee, check the following website:
The Varroa mite.

When should beekeepers start thinking about prevention against winter bee losses? Or is it rather about pursuing an ongoing management approach?

Beekeepers are normally well trained to deal with different and changing weather conditions. But this year is special: We are faced with very specific challenges due to the warm winter in 2015 and many periods of heavy rain during spring/summer. As a result, we expect a very high and dynamic population of Varroa mites in beehives and we also clearly see a nutrition problem with many of our honey bee colonies in Germany. In such a situation it is even more important that beekeepers monitor their bees’ health and the conditions in the beehive as much as possible and pursue good beekeeping practices responding to the given circumstances. If not, I fear that winter losses may very well be up again for the 2016/2017 season. So it is really very important that beekeepers pay close attention and act now.

  Thank you very much for your time. Is there one personal tip that you would want to share with other beekeepers?

My first personal wish is that beekeepers communicate frequently with one another. Exchanging knowledge and experience on good beekeeping practices with other beekeepers during the season can help when dealing with specific situations. This can be particularly useful for beginners, who are not as experienced and professional in their beekeeping practices yet.

Secondly, we as beekeepers should also share, as much as possible, our information about our bees’ health situation and especially Varroa mite pressure with local bee experts or Bee Institutes. Communication should go both ways so that overwintering losses are reduced by working together.


About Peter Trodtfeld

Peter Trodtfeld is Bee Health Expert at the Bayer Bee Care Center in Monheim, Germany. He is responsible for a diverse number of Bayer’s collaboration projects related to pollinator health. He is also an experienced beekeeper and takes care of the beehives at the Bayer Bee Care Center, conducting tours for visiting groups to explain various aspects of honey and wild bee health.

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