New study links common pesticide to bee deaths
Two of the most extensive field studies conducted to date in Europe and Canada have confirmed the hypothesis that neonicotinoid insecticides are harmful to bees and other pollinating species.
The results, published Thursday in the US journal Science, also reveal that local environments can mitigate the impact of the pesticide, which is widely used in farming despite being dubbed a "bee killer."
The chemical -- which acts on the nervous system of insects -- had a "largely negative" effect on the pollinating insects that are essential to many crops. It reduced their reproductive success and boosted mortality rates, according to the research that was part funded by the German chemicals company Bayer and Switzerland's Syngenta.
"In the light of this new study, continuing to claim that use of neonicotinoids in farming does not harm bees is no longer a tenable position," said David Goulson, a biology professor at Britain's University of Sussex who did not participate in the study.
The first experiment, conducted over a total of 2,000 hectares (5000 acres) in Great Britain, Germany and Hungary exposed three bee species to winter oilseed rape crops with seeds coatings containing either clothianidin from Bayer CropScience or Syngenta's thiamethoxam.
The coatings were temporarily banned by the European Union in 2013 due to concerns regarding their impact on bee health, though there are now plans to ban them completely in fields but not in greenhouses.
The researchers found exposure to the pesticide reduced winter survival rates in Hungary, where the colony population fell by 24 percent and in Britain where survival rates were "very low."
Germany did not see a dramatic decline, which lead author Ben Woodcock put down to the availability of alternative flowering resources.
All three countries saw a decline in reproduction rates, linked to residual neonicotinoid in nests.
The second study conducted in Canada showed that worker bees and queens exposed to the insecticide died earlier, while the overall health of colonies was also weakened.
Worker bees exposed to the treated pollen during their first nine days had their lifespans cut short by 23 percent, were unable to maintain a healthy laying queen and had poor hygiene.
The researchers were surprised to learn the contaminated pollen the honeybees collected did not belong to corn or soybean plants originally treated by the insecticides.
"This indicates that neonicotinoids, which are water soluble, spill over from agricultural fields into the surrounding environment, where they are taken up by other plants that are very attractive to bees," said researcher Nadia Tsvetkov.
© 2017 AFP