Low winter mortality of bee colonies over last winter

Gepubliceerd op
15 april 2014

Last winter, beekeepers generally lost fewer bee colonies than in the years before. The national mortality percentage has been established at 9.2%. This is the outcome of a telephone survey among beekeepers carried out by the Dutch Beekeepers Association (NBV) and Wageningen University & Research centre (UR) on Tuesday 8 April.

Winter mortality of bee colonies has been alarmingly high for years. In some winters one in four colonies did not survive. The survey after the winter of 2012-2013 showed that mortality had decreased to about 13%. “These results are encouraging but it is too early to consider this as a trend”, says Bram Cornelissen of Wageningen UR.

Survey amongst beekeepers

The survey was held among members of the NBV, with over 6000 members the largest beekeepers association in the Netherlands. Members of the General Dutch Beekeepers Association (ANI) were involved in this survey as well. Together these two associations represent about 90% of the beekeepers.

Winter mortality percentage


To establish the winter mortality percentage the telephone panel asked beekeepers how they - in autumn – had prepared the colonies for winter and how many of these colonies were still alive at the start of spring. A total of 210 randomly selected beekeepers from the membership files were asked for the mortality of the bee populations over the last winter, from which a winter mortality of 9.2% (confidence interval 95%: 7.2% – 11.7%) was calculated; 69% of the respondents indicated to have had no colony mortality.

Lower winter mortality caused by mild winter?

At this moment it is still unknown why winter mortality over the last two years was lower than in the years before. Although the mild winter is suggested as possible explanation, this is not plausible because the severe winter of 2012-2013 also showed a relatively low mortality rate. 

Beekeepers play a major part

This year’s low winter mortality does not mean that the end of the mortality problems of bees is near. Bee mortality received a lot of attention over recent years. The beekeepers themselves are playing a major part in a good preparation of bee colonies for winter. This may now be bearing fruit. Favourable environmental conditions, however, are equally important for a healthy bee population.