A controversial pesticide is dramatically weakening already vulnerable honeybee hives, a large-scale field study in Europe found.
For more than ten years now, honeybee populations and other pollinators have been dwindling, and researchers have been looking into the decline. The common factors they have examined include parasites, disease, poor nutrition and pesticides, San Francisco Gate reports.
Studies and lab experiments have pointed to pesticides called neonicotinoids as one of the major reasons behind falling honeybee numbers. But this new research in Germany, Hungary and the United Kingdom is the biggest field study yet.
Researchers planted 7.7 square miles of fields with rapeseed, which is turned into canola cooking oil. Some of the fields were planted with seeds that had been treated with the insecticide in question, while others were planted with untreated seeds. Then the team tracked bees from the spring of 2015 when the seeds began flowering, to the next spring when new bees were born.
The hives in the fields in Hungary and Britain that has pesticide-treated seeds did not fare well through the following winter, the researchers discovered. In Hungary, the honeybees near the treated fields had 24% fewer worker bees the next spring, compared to the colonies near the untreated plants.
In Germany, however, the bees didn’t seem to be harmed. Hives in those fields were generally healthier and upon examining the pollen, the scientists found that the German bees had a broader diet, relying less on the pesticide-treated plants. Only 10% of the German bees ate the treated plants, compared to 50% in England and Hungary, according to Richard Pywell, study director.
When honeybee hives are already susceptible due to disease or parasites, then the neonicotinoids “pushes them over the edge,”
said Pywell. Many of the British bees died, both in treated and untreated fields, that scientists could not accurately calculate the effects of the pesticide.
Europe banned the use of neonicotinoids in 2013, so the researchers needed special permission. A similar study in Canada found the same problems with the pesticide. But the issue remains complex and other factors are contributing to the overall honeybee problem, other scientists say.
The study was published in the journal Science.