Bee lifespan shortened by exposure to neonicotinoids, study says

Bees exposed to real-world levels of a group of pesticides known as neonicotinoids die sooner than those that are not exposed, researchers from Toronto's York University have found.

'It's no surprise at all,' says Ontario beekeeper

A new study has found that a common pesticide used on corn and soy has severe consequences for bee hives. (Jack Guez/AFP/Getty Images)

Bees exposed to real-world levels of a group of pesticides known as neonicotinoids die sooner than those that are not exposed, researchers from Toronto's York University have found. 

In a study published today in the journal Science, the researchers found that bees exposed to levels typically found in corn fields had their lives shorted by almost 25 per cent.

"We found higher worker mortality, deficits in learning and memory, differences in queen and reproductive biology," co-author Amro Zayed told CBC News. "All of these have been found in other experiments by other researchers. So we're validating all of these findings."

The findings in the latest study came as "absolutely zero surprise at all" to Tibor Szabo, a beekeeper in southwestern Ontario.

Szabo, a third-generation beekeeper, has lost so many bees over the past few years that he's cut his hive numbers in half since 2011. In 2014, he lost 1,165 hives, each containing about 1,000 bees. And the declines just keep on coming. He blames neonics.

"I keep a lot less bees because of the poisoning," he told CBC News. "I don't have bees in many of my yards that were good for decades."

To determine the levels of neonics taken in by the bees, the researchers from York studied 55 hives from 11 apiaries after they placed them in sites across Ontario and Quebec. Five apiaries were near fields planted with corn that was treated with neonics and six away from known treated corn.

They tested pollen collected by the bees for more than 200 agricultural chemicals, known as agrochemicals, and found 26 throughout all the hives.

Widespread use

Over the past decade, beekeepers have noticed declining populations in their colonies. While a common pest known as the varroa mite, along with other factors such as harsh winters, were considered to be contributing to their rapidly declining rates, many apiarists in Ontario, Quebec and parts of Europe noticed another similarity: their bees were living near corn or canola fields. 

While worldwide the number of bee hives have been on the rise, that's not the case in Canada and parts of Europe, according to the Food and Agriculture Organization of the United Nations. (Jonathan Pinto/CBC)

Today, most corn seed is treated with neonics in order to defend it from pests in the field. But many beekeepers say that it doesn't have to be applied as a preventative measure; it should be used on an only-as-needed basis.

Some of the arguments around the lethality to bees have also centred around the belief that neonicotinoid dust was spreading during spring corn seed planting. But this study covered the entire growing season, from early May to September. 

"We found that bees were exposed to neonicotinoids for most of the season, anywhere between three to four months on average. That was consistent across all of our study sites," said Zayed. "The level of pesticides, neonicotinoids, was fairly low, sub-lethal. It's not enough to kill a colony, but it's very persistent."

And the pollen that was collected by the researchers didn't come from corn: it came from nearby plants, plants that weren't even present at the start of the growing season. This suggests that the neonics are present in the soil near cornfields, the researchers said.

Effects on bees

In order to better understand what the long-term effects might be on bees, back at York University's research apiary, the researchers dosed some of their bees with the equivalent amount of neonics found in the field over 12 weeks.

While the neonics were present in sub-lethal levels, they had noticeable, adverse effects on the colonies, the researchers reported. For one, the worker bees lived five days fewer than those that hadn't been exposed. While that may not sound like a significant loss of life, since they only live in the summer about four weeks, it represents a 23 per cent reduction in their lifespan.

A honeybee worker has an radio-frequency identification (RFID) chip attached to its back that allows York University researchers to monitor when it leaves and returns to the colony, as well as when it is no longer active and presumed dead. (Amro Zayed/York University)

The researchers also found that the bees were out flying much longer — sometimes as much as 40 minutes longer — than bees with no exposure to neonics. This suggests that there may be some metabolic deficits or they're having a hard time foraging and returning to the hive, something previous research has suggested.

Bees also have hygenic behaviour, or the ability to detect diseased and dying brood and removing it from the hive before anything spreads. But the researchers found that bees exposed to neonics were unable to do that. They were also unable to take care of their queen adequately and unable to replace her if she died. 

Important pollinators

Bees are vital in both plant and crop pollination. A 2016 assessment by the Food and Agricultural Organization of the United Nations found that between $235 billion US and $577 billion US worth of annual global food production relies on pollinators. And while bees are not the sole pollinators, they are the most abundant, with more than 20,000 species around the globe, 700 of which are found in Canada.

As the use of neonics became tied to decreasing bee populations, some countries that were particularly vulnerable, such as those in Europe as well as Canada and the United States, began to take measures to protect the invaluable pollinator. 

In 2013, Europe put a two-year moratorium on neonicotinoids. Since then, the European Commission is calling for a complete ban

Research into the effects of neonics in Europe also published on Thursday in Science by the Centre for Ecology and Hydrology found that in a field study, winter oilseed rape crops treated with neonics resulted in lower reproductive success in honeybee colonies. In Hungary, for example, reproduction fell by 24 per cent.

Honey bees are important pollinators of blueberry flowers. (Hannah Burrack/NCSU Small Fruit IPM)

In 2015, Ontario became the first province to restrict the use of neonics, limiting their use to crops that only need them, rather than being used as a preventative measure. As well, Health Canada is considering a ban on two particular neonics, imidacloprid and clothianidin, which is the most widely used, with a final decision expected in 2018.

"It's clear that this concept application of neonicotinoids are having a negative effect on honeybee health," Zayed said.

It's certainly clear to Szabo, who believes his livelihood has been directly impacted by the widespread use of neonics.

"They just need to get rid of the stuff," he said. "I'd say there's not too many beekeepers in southern Ontario who haven't had a huge impact on their livelihood because of this stuff."

Chris Davison, head of corporate affairs for Syngenta, one of the makers of neonicotinoids, had not yet seen the embargoed study and said in an email: "We cannot properly review or comment on this study at this time as relevant information (i.e. methods, additional data) is not available."


Nicole Mortillaro

Senior reporter, science

Based in Toronto, Nicole covers all things science for CBC News. As an amateur astronomer, Nicole can be found looking up at the night sky appreciating the marvels of our universe. She is the editor of the Journal of the Royal Astronomical Society of Canada and the author of several books. In 2021, she won the Kavli Science Journalism Award from the American Association for the Advancement of Science for a Quirks and Quarks audio special on the history and future of Black people in science. You can send her story ideas at