‘Bee Safe’ pesticides not so safe for wild bees, U of G study reveals

GUELPH – Pesticides marketed as “safe for honeybees” can still cause harm to wild ground-nesting bees, according to new research from the University of Guelph.

The study is one of the first examining impacts of insecticides and fungicides on wild solitary bees and ground-nesting species. It’s also the first to assess the effects of pesticide exposure through soil – a route typically neglected in pesticide risk assessments, said a U of G news release.

“Current risk assessments primarily focus on honeybees but not the distinct behaviours of wild bee species, like when they make contact with the soil where they nest,” said Sabrina Rondeau, who completed the study as part of her PhD, in the release. “Unlike honeybees, many wild bee species spend a significant part of their lives underground.”

Rondeau, now a postdoctoral fellow at the University of Ottawa, and fellow researcher Nigel Raine, in U of G’s School of Environmental Sciences, are calling for the “bee-safe” designation to be re-evaluated and new pesticide regulations.

Insecticides marketed as “bee-safe” have emerged in recent years responding to concerns about neonicotinoids, a widely used class of insecticides known for neurotoxic effects on bees.

In findings published in Proceedings of the Royal Society B: Biological Sciences, the research team found wild squash bees exposed to the studied pesticides experienced reduced pollen collection, hyperactivity or changes in reproduction.

Those effects, though more subtle than those observed with highly toxic neonicotinoids, still pose significant risks.

One of the pesticides studied, flupyradifurone, an insecticide often sold under the name Sivanto Prime, has been deemed “practically non-toxic” to adult honeybees by the US Environmental Protection Agency. 

However, the designation may overlook risks posed to ground-nesting bees (more than 70 per cent of all bee species nest underground) which have different exposure routes, researchers said.

The study also highlights risks of pesticides when they’re combined.

 “While some pesticides, like fungicides, may individually pose lower risks to bees, combined exposure with insecticides can result in synergistic effects, amplifying their overall impact,” Raine said in the release.

The study examined effects of chronic exposure to the insecticide flupyradifurone, and a fungicide, a combination of azoxystrobin and difenoconazole sold under the name Quadris Top, on hoary squash bees. Those solitary bees are exposed to pesticide residues in soil due to their underground nesting habits.

Flupyradifurone persists in soil, posing a particular risk to ground-nesting bees, researchers said. The fungicide studied, commonly used on crops such as squash and pumpkin, exacerbates the risk as its systemic nature also leads to pollen, nectar and soil contamination.

“Label guidelines don’t allow us to apply tank mixtures of these pesticides to flowering crops,” said Rondeau. “But they can still each be used on the same crops during the same growing season, increasing the likelihood of co-exposure for bees.”

Raine emphasized the importance of comprehensive pesticide risk assessments considering acute and sublethal effects on ground-nesting bees, and other wild bee species. 

“With the phase-out of neonicotinoid insecticides, there is a pressing need to fully evaluate the potential risks posed for all beneficial insects, including pollinators, by alternative pesticides that are replacing them,” he said.