Low doses of pesticides found to harm wild bees

Researchers discover that bumblebees feed on less nutritious flowers after being exposed to small amounts of a neonicotinoid insecticide

Emily J. Gertz

TakePart

As bee colonies have continued to collapse around the world, wild bees have received less attention than their domesticated cousins.

But wild bees are important pollinators for both agricultural crops and wild plants, and a new study suggests they can be harmed by the same pesticides affecting honeybee colonies.

The study is the first to look at how small amounts of neonicotinoid pesticides affect bees as they feed on wildflowers, said Nigel Raine, an ecologist at the University of Guelph in Canada who focuses on pollinator conservation.

Bumblebees had a harder time foraging for nectar and pollen from wildflowers after being exposed to a sublethal 10 parts per billion concentration of a widely used neonicotinoid insecticide called thiamethoxam, according to the research, which was published Monday in the journal Functional Ecology.

The dosage was based on the pesticide levels bees would encounter on or near farms where neonics are used.

A recent study in Poland found that bees from collapsed colonies carried low-level residues of dozens of pesticides, including neonics.

Raine and ecologist Dara Stanley conducted the research while both were at the Royal Holloway University of London.

“The most significant thing we found was that the pesticide-treated bees chose different flowers among two species we know bumblebees really like and can usually handle,” said Raine.

Bees exposed to thiamethoxam foraged more often from bird’s foot trefoil than from white clover, a more sugar- and amino-acid-packed wildflower.

All things being equal, you would expect the bees to prefer the more nutritious flower,” said Raine.

The two groups of bees also showed different learning capacities. “The untreated bees took significantly fewer visits to learn how to handle the same wildflowers successfully compared to the pesticide-treated bees,” Raine said.

If exposure to neonics changes how bees forage from wildflowers, it could also change how they handle flowering food crops. “There are more and more studies suggesting that the diversity of visitors to crops is important, and that the visits by these wild pollinators are undervalued economically and practically,” Raine said.

He said the study’s findings were consistent with recent research showing that bees were less effective at pollinating apple trees after being exposed to low concentrations of pesticides.

Wild plant biodiversity is also at risk.

“Most people think of honeybees in a hive—it’s about honey production and commercial pollination,” Raine said. “We need to start looking at solitary bees, which make up the vast number of bees, and start looking at other pollinators.”

Emily J. Gertz is an associate editor for environment and wildlife at TakePart.