Massive New Study Concludes Neonicotinoid Pesticides Harm Bees

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A massive new study on the “real world” effects of neonicotinoid pesticides has concluded they are harmful to both wild bees and honeybees.

Neonicotinoids are a group of synthetic insecticides that are chemically related to nicotine and used by farmers to stamp out pests. They have come under a lot of heat in recent decades over their effects on the surrounding environment, namely on honeybees but also birds, aquatic invertebrates, and other wildlife. The European Union is quickly moving towards banning them, yet some have argued this is based on weak evidence as many of the studies have artificially fed neonicotinoids to bees.

This new research by the Centre for Ecology and Hydrology (CEH) hoped to settle this debate with the most extensive look at neonicotinoid pesticides and free-living bee populations to date. The study, published in the journal Science, involved scientists documenting wild populations of three bee species across 33 large rapeseed farmland sites in the UK, Germany, and Hungary.

They found that exposure to crops treated with neonicotinoids – clothianidin or thiamethoxam – reduced the overwintering survival rate of honeybee colonies in two out of the three countries. Populations dropped by 24 percent in Hungary by the following spring and the UK also saw a significant decline in numbers. However, the study found no negative effects on the honeybee population after being exposed to the insecticides in Germany.

"The neonicotinoids investigated caused a reduced capacity for all three bee species to establish new populations in the following year, at least in the UK and Hungary," Dr Ben Woodcock of CEH said in a statement.

Bayer, a chemical group who manufacture neonicotinoid pesticides, have a different interpretation of the results. They argue that the variation seen in the result from Germany shows there’s “no consistent results on the impact of neonicotinoid seed treatments.”

"We do not share the CEH’s interpretation that adverse effects of the seed treatments can be concluded from this study, and remain confident that neonicotinoids are safe when used and applied responsibly,” said Dr Richard Schmuck, director of environmental science at Bayer’s Crop Science division.

So, what can we take away from these rather fiddly findings?

“It’s not like a lab of a chemistry experiment, where you always get the same results every time," Professor Dave Goulson, a bumblebee ecologist at the University of Sussex, told IFLScience. "It is messy and complicated in the real world.

“In Germany, the bees didn’t much feed on the crops. There were presumably other tasty flowers somewhere else, so not surprisingly they weren’t as affected. Industry keep pointing towards the Germany part of the study and saying: ‘It’s all fine!’ when everything else suggests otherwise… There have now been hundreds of studies of this subject and the large majority have found adverse effects.

“It's reached a point where it's getting silly to deny that there is a link between these pesticides and harm to bees. There’s so much evidence now.”

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