Study: Pesticide puts bees ‘over the edge’

WASHINGTON — A common and much-criticized pesticide dramatically weakens already vulnerable honeybee hives, according to a new field study in three European countries.

For more than a decade, the populations of honeybees and other key pollinators have been on the decline, and scientists have been trying to figure out what’s behind the drop, mostly looking at a combination of factors that include disease, parasites, poor diet and pesticides. Otherstudies, mostly labexperiments, have pointed to problems with the insecticides called neonicotinoids, but the new research done in Britain, Hungary and Germany is the largest field study yet.

Researchers planted about 7.7 square miles of fields of rapeseed. Some of the fieldswere planted with seeds treated with the insecticide, others with untreated seeds. Theresearchers followed bees from the spring of 2015 when the seeds flowered to the following spring when new beeswere born.

The bee hives in the Hungarian and British fields that used pesticidetreated seeds didworse sur- viving through the next winter, the researchers found. In Hungary, the honeybee colonies near treated fields had 24 percent fewer worker bees the next springwhencompared to those near untreated crops, according to a study published Thursday in the journal Science.

But in Germany, the bees didn’t seem harmed. Hives there were generally healthier to start and when scientists analyzed the pollen brought back to the hives, they determined that the German bees ate a far broader diet with much less of their nutrition coming from the pesticide-treated rapeseed plants, said study director Richard Pywell. Only about10 percent of the German bee diet was from neonicotinoid-treated plants, compared to more than 50 percent inHungary and England, he said.

When hives are weakened by disease, parasites or bad diet— asmany hives are worldwide — then the neonicotinoids “pushes them over the edge,” said Pywell, a scientist at the Center for Ecology andHydrology in England. So many of the British hives died, in both treatedanduntreated fields, that scientists couldn’t calculate the specific effect of the insecticide, he said.