Common Pesticide Inhibits Bumblebees From Collecting Pollen

Bumblebees' ability to gather food is impaired by the pesticide imidacloprid, which is routinely used on crops despite an ongoing controversy surrounding its link to harming bees, UK researchers report. 

Even at very low levels of contamination, bumblebees that ingest imidacloprid show a 57 percent reduction in the amount of pollen they can carry, and that effect lasts for at least one month after exposure, according to researchers from the University of Sussex and the University of Stirling. Imidacloprid is part of a class of pesticides called neonicotinoids, which are the most widely used incecticides in the world. Such pesticides are effectively neurotoxins and their role in disabling bee colonies is well documented.

Imidacloprid is widely used on corn crops in the US, and because commercial bee keepers feed their bees high-fructose corn syrup (harvesting the bee's honey for sale) bees can be indirectly exposed to it. Direct exposure can also occur through pollen harvesting. 

Previous studies have implicated imidacloprid in colony collapse disorder, a phenomenon that causes bees to leave their hives, the effect of which is widespread and destroying bee colonies around the world.

This new research focuses on how the neurotoxin affects bee's pollen-gathering abilities.

"Pollen is the only source of protein that bees have, and it is vital for rearing their young," said Dave Goulson, senior author of the research. "Collecting it is fiddly, slow work for the bees and intoxicated bees become much worse at it. Without much pollen, nests will inevitably struggle."

Use of the pesticide imidacloprid is currently under a 2-year moratorium in the EU, but Goulson worries that ban will be lifted. He and his colleagues say their research is supporting evidence to institute an outright ban of imidacloprid use.

"It is unclear what will happen when the moratorium expires, as the agrochemical companies that produce them are in a legal dispute with the EU over their decision," he said. "Our new study adds to the weight of evidence for making the ban permanent."

To test the bees, the researchers fitted them with tiny electronic tracking tags and recorded their weight each time one entered and exited its nest. The researchers documented that many pesticide-treated bees failed to collect any pollen at all, and those that did tended to collect less than untreated bees.

University of Stirling's Hannah Feltham, who carried out the experiments, said: "This work adds another piece to the jigsaw. Even near-infinitesimal doses of these neurotoxins seem to be enough to mess up the ability of bees to gather food. Given the vital importance of bumblebees as pollinators, this is surely a cause for concern."

The research is published in the journal Ecotoxicology.