Low mortality of Dutch honeybee colonies this winter

Last winter saw the lowest winter mortality of bee colonies for many years. While the loss rate was still around 20% in 2011, it fell below 10% over the last two years and this year was just 6.5%. Winter mortality in the Netherlands is measured by a honeybee surveillance programme conducted by Naturalis and Wageningen UR in partnership with the Dutch Beekeepers Association (NBV).

Bees@wur (Wageningen UR) and NBV together conducted a telephone survey on winter mortality in cooperation with the honeybee surveillance programme commissioned by the Dutch Ministry of Economic Affairs. The study was funded by the government (51%) and the Dutch Crop Protection Association Nefyto (49%). The cooperation of all beekeepers in the sample and survey was essential for the success of the study and for determining winter mortality in bee populations, as well as the factors responsible for this.

Koos Biesmeijer of Naturalis explains that data from over 500 selected beekeepers was assembled in a randomised sample. "The sample was representative of mortality among Dutch beekeeper colonies," adds Sjef van der Steen from Bees@wur. The 534 beekeepers prepared 5919 colonies for winter, of which 5537 survived. This corresponds to a survival rate of around 93.5% and a winter mortality of 6.5%.

Jan Dommerholt, chairman of the Dutch Beekeepers Association, suggests that the 6.5% winter mortality is "natural", that is to say, a level which was normal before the Varroa mite arrived in the Netherlands. Koos Biesmeijer from Naturalis, who coordinates the honey bee surveillance programme, is pleased with the low winter mortality as it is good news for both beekeepers and the pollination by honeybees of fruits and vegetables which are vital to the economy.