Pesticides impair bumblebees' ability to forage

Long-term exposure to pesticides harms bees' ability to forage for pollen and may be changing their choices of which flowers to visit, a new study has found.
Scientists used Radio Frequency Identification (RFID) tags, which are similar to those used by courier firms to track parcels, to monitor the day-to-day behaviour of bumblebees.
They found that prolonged pesticide exposure significantly impaired the bees' foraging activity.
"Bees pollinate many of our crops including most of our fruits, vegetables, nuts and coffee. In fact, one in every three mouthfuls of food we eat depends on bee pollination, so it is particularly worrying to see such a chronic impairment of their foraging behaviour," lead researcher Dr Richard Gill from Imperial College London, said.

"Bees have to learn many things about their environment, including how to collect pollen. Exposure to this neonicotinoid pesticide may be preventing bees from being able to learn essential skills," co-lead researcher Professor Nigel Raine from the University of Guelph, said.
The scientists, who carried out the research whilst at the Royal Holloway University of London, monitored 259 bumblebees from 40 colonies over a four-week period and measured the impact of two pesticides, neonicotinoid (imidacloprid) and pyrethroid (lambda cyhalothrin).

Bumblebee colonies that had been exposed to the neonicotinoid pesticide brought back significantly reduced amounts of pollen in comparison to untreated colonies, suggesting that persistent exposure weakens the foraging performance of bumblebees.

To compensate for the lack of pollen being brought back by each individual bee, the scientists suggest that neonicotinoid-treated colonies also sent out more foragers.
When scientists looked at the colour of collected pollen they also found evidence to suggest that exposed foragers preferred different flowers to forage on.
Results also revealed that pesticides are preventing bees from improving their pollen foraging ability as they age. Foragers in untreated colonies carried larger pollen loads as they got older and more experienced.
The scientists are urging for environmental policy-makers to consider reforms of the risk assessment guidelines for pesticide use.
"Pesticide risk assessments should consider how prolonged exposure to low levels of pesticide might affect foraging performance. Our data suggest that these tests should be conducted for extended periods to detect the effects of chronic exposure," said Gill.

The study suggests that pesticide use could have serious knock-on consequences for the growth and survival of colonies.
The research was published in the journal Functional Ecology.