2023-05-31 20:00:00
The fears of beekeeper Sonne Copijn turn out to be correct: 2023 is off to a bad start for the Dutch honey bees. More than a quarter (25.6 percent) of the bee colonies did not survive the winter. Not that many bees have died in winter since 2010; then the percentage was 29.1.
Copijn discovered in March that there was no life left in eleven of her thirteen bee colonies. Some colonies were still active in January, but died after that. A survey that the director of the Bee Foundation conducted among dozens of beekeepers showed that many others were also struggling with sudden bee deaths. The winter mortality monitoring of Wageningen University and Research (WUR) confirms what Copijn already saw in March.
The Netherlands has more than 11,000 active beekeepers, mainly hobbyists such as Copijn. Of these, 2779 participated in WUR’s winter mortality study. 1075 of them did not lose any colonies and 280 beekeepers lost all colonies during the past winter. In the province of Utrecht – where Copijn also has her hives – bee mortality is the highest at 41.6 percent, and the lowest in Limburg at 16.6 percent.
Big swings
Winter mortality can vary greatly from year to year. In 2016, it was limited to 6.5 percent, in peak years such as 2010 and 2023 it was above 25 percent. “Still, there are patterns,” says WUR researcher Harmen Hendriksma. “In 2010, a Belgian feed supplier was found to have supplied contaminated sugar water. That explained 6 percent of the increase.”
Whether there is also such a demonstrable large factor remains to be seen. High bee mortality is often the sum of factors, Hendriksma emphasises. Weather influences are of great importance. The presence of the bee parasite varroa mite can also lead to a lot of mortality.
“Sometimes precisely when many people don’t expect it,” emphasizes Hendriksma. “Two years ago, half of Canada’s bee colonies died. There had been a beautiful spring and a long summer. Then bees develop well and beekeepers often think that the colony is healthy. But it is precisely then that bee parasites such as the varroa mite have also been able to develop properly.”
Pesticides and varroa mite
In Flanders, the mortality rate is about the same as in the Netherlands. In Germany it is considerably lower. “It is only possible to say more about the causes after further research. What we do know by now is that pesticides are not a major cause of bee deaths: those that caused the most damage have now been banned.”
What also applies: the better the varroa mite is combated, the more favorable that is for the survival of the colony. “This winter I myself conducted research at a hundred beekeepers into the crumpled wing virus, a bee disease that occurs in the presence of the varroa mite. If the virus is not or hardly present, there is also little mortality.” At the same time, the varroa mite certainly does not explain everything, says Hendriksma. “The high mortality in Utrecht and South Holland, for example, seems to be more at play.”
The COLOSS survey (COlony LOSSes) is conducted in more than forty countries each year. This year more beekeepers participated in the Netherlands than ever before. The research only concerns kept (honey) bees. It is not known whether wild bees also suffer from higher winter mortality than in other years.
Read also:
Honey bees died in droves this winter. ‘Every beekeeper’s fear is that you have done something wrong’
Beekeepers are very concerned as they open their hives. Many colonies of honey bees did not survive the winter. The cause of the bee death is still unknown.
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