Queen bees hibernate in pesticide-contaminated soil, U of G study finds

Bumblebee health, survival and reproduction could be at risk.  

University of Guelph environmental sciences researchers Nigel Raine and Sabrina Rondeau have discovered that bumblebee queens are more likely to hibernate in soil contaminated with pesticides than in clean soil.

“Some bee behaviours are not well understood, and we wanted to see if these bumblebee queens exhibited avoidance behaviour that might reduce their risk of harm from pesticide exposure in the field,” Raine said in a recent university release. “But these results were alarming.”  

Field experiments included newly emerged queens of the common eastern bumblebee (Bombus impatiens) that were left to fly freely in outdoor enclosures, mate and then choose a site in which to hibernate for the winter.

The choice was between clean soil or soil contaminated with common pesticides, insecticides or fungicides, across different concentrations.

Researchers then carefully searched through the soils for hibernating bumblebee queens.

Results had shown that queens avoided the pesticide-free soil and were about twice as likely to be drawn to the soil that was pesticide-contaminated.

“This raises serious concerns for bumblebee health, especially as this group of important insect pollinators already face many challenges," Raine said.

Bumblebee queens typically hibernate underground during winter before emerging in spring to start new colonies. Researchers wanted to investigate how bees respond to contaminants at this key but vulnerable life stage.  

According to the release, previous studies showed pesticides on crops can either attract or repel bees, depending on the type, the environmental situation and the concentration used. Raine and Rondeau initially speculated that bumblebee queens would simply choose to avoid pesticide residues in soil.  

“We were not expecting this result,” Rondeau said. “It suggests that queens could actually prefer these contaminated soils, though we don’t yet fully understand why.”

One possible explanation is that pesticides altered the soil properties and made it more appealing to the queens.

Another possibility is that the queens could have developed an “acquired taste” for pesticides, according to researchers, due to prior exposure in their environment.

They might also be looking for something new, as novelty-seeking behaviour is common for bees and often leads the colony to discover new resources.

Researchers say exposure to pesticides can impair bees’ movements and their ability to collect and feed on nectar and pollen. These effects could have dire consequences for the global food system.

Further research is needed to determine if these findings apply to other bee species.  

“As we move forward, it’s crucial to investigate how agricultural practices, like the types of pesticides used, the methods of application and the management of vegetation impact the accumulation of pesticide residues in soils where queens are likely to hibernate,” Rondeau said. 

“By better understanding how pesticide residues accumulate in soils, and how they affect bees, we can find ways to protect these essential pollinators.”  

This work was supported by the Ontario Ministry of Environment and Climate Change (MOECC) Best in Science grant, Natural Sciences and Engineering Research Council (NSERC), and the Food from Thought: Agricultural Systems for a Healthy Planet Initiative, by the Canada First Research Excellence Fund.

Rondeau was supported by graduate scholarships from The Arrell Food Institute, the Fonds de recherche du Québec – Nature et technologies (FRQNT) and the Ontario Agricultural College (OAC). Raine is supported as the Rebanks Family Chair in Pollinator Conservation by the Weston Family Foundation.