Prolonged Exposure to Neonicotinoid Pesticide Disrupts Bee's Foraging Activity

A collaborative study reveals that prolonged exposure to neonicotinoid pesticide hampers a bumblebee's ability to forage for pollen.

For the last 20 years, neonicotinoids have been used widely to control a variety of pests, especially the sap-feeding insects and they make up to 30 percent of the global pesticide market. These relatively new class of insecticides are known to affect the central nervous system of the insects. But, these insecticides were linked to a dramatic fall in the number of bees and other pollinating insects. The bee colonies began disappearing, due to which the European Commission had banned three neonicotinoid insecticides.

A new study by a team of researchers from the University of Guelph highlights the downside of using neonicotinoid. They fitted tiny radio frequency tags on the bumblebees and they noticed that the long term exposure to the pesticide hampered the bees' ability to forage for pollen.

Led by Nigel Raine, a professor in Guelph's School of Environmental Sciences, and Richard Gill of Imperial College London, this study shows how prolonged exposure to neonicotinoid affects the bees' day-to-day behavior including the collection of pollen from flowers and which all flowers worker bees chose to visit.

"Bees have to learn many things about their environment, including how to collect pollen from flowers," said Raine, who holds the Rebanks Family Chair in Pollinator Conservation, a Canadian first. "Exposure to this neonicotinoid pesticide seems to prevent bees from being able to learn these essential skills."

With the help of radio frequency tags, the researchers tracked when each bee left and returned to the colony and the amount of pollen they collected and from which flower. They noticed that the bees from the untreated colonies were better at collecting pollen as they learned how to forage. But, those bees exposed to neonicotinoid insecticides were less successful in collecting pollen. Colonies treated with neonicotinoid, sent out more foragers in order to compensate for lack of pollen from individual bees. 

Apart from collecting less pollen, the neonicotinoid-exposed bees preferred different flowers as compared to those foraging bees from the untreated colonies.

Researchers evaluated the effects of two pesticides i.e. imidacloprid and pyrethroid, when used alone or together on the behavior of individual bumblebees from 40 colonies over four weeks.

"Although pesticide exposure has been implicated as a possible cause for bee decline, until now we had limited understanding of the risk these chemicals pose, especially how it affects natural foraging behaviour," Raine said. "If pesticides are affecting the normal behavior of individual bees, this could have serious knock-on consequences for the growth and survival of colonies."

The study researchers suggest reform pesticide regulations including adding bumblebee and solitary bees to risk assessments that currently cover only honeybees. Bumblebees are more sensitive to pesticide impact because their colonies comprise of only a few hundred workers.

The study was documented in Functional Ecology.