Studies strengthen insecticide link to bee population decline

Two new studies have added powerful scientific evidence to the view that agricultural pesticides are contributing to a decline in bee populations across Europe and North America.

One research team in Sweden found that neonicotinoid insecticides (neonics) reduced wild bee numbers. The other in the UK discovered that bees prefer nectar containing neonics to uncontaminated nectar. Both studies appear in Nature, a leading scientific journal.

Neonics have become a cause celebre for the environmental movement in its battle against the agrochemical industry. Their worldwide sales are around $2bn a year, with Bayer of Germany and Syngenta of Switzerland the largest producers.

The EU imposed a two-year moratorium in December 2013 on the treatment of flowering crops such as oilseed rape with neonics, which are systemic insecticides normally applied to seeds rather than sprayed on to growing crops. The US Environmental Protection Agency is under pressure from campaigners to introduce similar restrictions.

The UK government opposed the EU ban on the grounds that the scientific evidence was not strong enough to justify depriving farmers of important weapons against insect pests.

One argument used by defenders of neonics is that studies showing their harmful effects on bees are generally carried under laboratory conditions not representative of the real world.

The new Swedish study, carried out by Lund University, met that criticism by comparing insect life in 16 fields of oilseed rape; half were planted with untreated seeds and half with seeds treated with Bayer's Elado insecticide, which contains a neonic.

Wild bumblebees and solitary bees were much less plentiful in the treated fields, with bumblebee numbers cut by half, said Maj Rundlof, the study leader: "In my view they are quite dramatic declines." But honeybees were more resilient, showing little effect from the pesticide.

David Goulson, biology professor and bee expert at Sussex University, commented: "This is the first fully field-realistic, well replicated trial so far - an impressive piece of work . . . It is no longer credible to argue that agricultural use of neonicotinoids does not harm wild bees."

Julian Little of Bayer CropScience disagreed. "Overall the method descriptions and results do not substantiate the conclusions that oilseed rape seed treatment with neonicotinoid insecticides affects wild bees," he said.

The other new research, at Newcastle University, showed that honeybees and bumblebees could not taste the presence of neonics in nectar. Given a choice the bees preferred to consume sugar solutions containing low concentrations of neonics - apparently because these compounds, which are chemically related to nicotine, have a pharmacological effect on the bee brain's reward cells.

The bees quickly learned the location of the neonic solution which was giving them a "buzz", said Geraldine Wright, the project leader: "If foraging bees prefer to collect nectar containing neonicotinoids, this could have a knock-on negative impact on whole colonies and on bee populations."

Anecdotal evidence suggests that bee populations have fallen substantially in recent years across the industrialised world, though reliable statistics are elusive. Wild bees and domesticated honeybees are both essential for pollinating wildflowers and crops - a service whose value is estimated at more than $150bn a year worldwide. Many factors besides pesticides have been blamed for the decline including changing land use, loss of floral biodiversity and various bee diseases.

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