Link between weakened honeybee hives and neonicotinoid established

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Honeybee, Pollinator, Pollination

A new study has established a link between weakened honeybee hives and a key pesticide neonicotinoid thereby almost putting to rest the decade old debate on whether honey bees are at danger from commonly used pesticide.

Centre for Ecology & Hydrology (CEH) researchers have published results of a pan-European field-realistic study that assessed impact of neonicotinoid on honeybees and wild bees in the peer-review journal Science. Scientists undertook the experiment in UK, Germany and Hungary wherein they exposed three bee species to winter oilseed rape crops treated with seed coatings containing neonicotinoid clothianidin, from Bayer CropScience, or Syngenta’s thiamethoxam.

Neonicotinoid seed coatings are designed to kill pests such as the cabbage stem flea beetle, but were effectively banned in the EU in 2013 due to concerns regarding their impact on bee health. According to researchers exposure to treated crops reduced overwintering success of honeybee colonies in two of the three countries. In Hungary, colony number fell by 24 percent in the following spring. In the UK, honeybee colony survival was generally very low, but lowest where bees fed on clothianidin treated oilseed rape in the previous year. No harmful effects on overwintering honeybees were found in Germany.

Researcher say that lower reproductive success was linked with increasing levels of neonicotinoid residues in the nests of wild bee species buff-tailed bumblebee (Bombus terrestris) and the Red Mason Bee (Osmia bicornis) across all three countries.

The study spanning 2,000 hectares, equivalent to 3,000 full scale football pitches, took account of bee disease and surrounding landscape quality in addition to colony growth rate, worker mortality and overwinter survival.

Co-author Professor Richard Pywell, Science Area Lead, Sustainable Land Management at the Centre of Ecology & Hydrology, said, “Neonicotinoids remain a highly contentious issue with previous research on both honeybees and wild bees inconclusive.

“This latest field study was designed, as far as possible, to reflect the real world due to its size and scope. We therefore believe it goes a considerable way to explaining the inconsistencies in the results of past research, as we were better able to account for natural variation in factors like exposure to the pesticide, bee food resources and bee health for different bee species.”

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