OCTOBER 18, 2024
Bumblebee queens choose to hibernate in pesticide-contaminated soil, scientists discover
by University of Guelph"Some bee behaviors are not well understood, and we wanted to see if these bumblebee queens exhibited avoidance behavior that might reduce their risk of harm from pesticide exposure in the field," Raine says.
The choice was between clean soil or soil contaminated with one of five common pesticides, including insecticides and fungicides, across different concentrations.
The School of Environmental Sciences researchers then carefully searched through the soils for hibernating bumblebee queens.
"This raises serious concerns for bumblebee health," says Raine, "especially as this group of important insect pollinators already face many challenges."
Previous studies showed that 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 says. "It suggests that queens could actually prefer these contaminated soils, though we don't yet fully understand why."
Pesticides make soil more appealing, but more research needed
For example, the fungicides used in the study could have killed soil fungi and nematodes, and queens might avoid soils with fungi because they can be harmful during hibernation.
Another possibility is that the queens could have developed an "acquired taste" for pesticides, as researchers put it, due to prior exposure in their environment.
They might also be looking for something new, as novelty-seeking behavior is common for bees and often leads the colony to discover new resources.
More research is needed to fully understand the mechanisms behind this unexpected queen behavior. But the findings suggest the need to reconsider how pesticides are used and managed in agricultural settings.
Environmental risk must account for pesticides in soil
In addition to sometimes being fatal, 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 our global food system.
Questions remain about whether bumblebee queens would be attracted to contaminated soil in wider spaces than those used in the experiments, where real-world scents and field characteristics might mask the presence of pesticides. Further research is also needed to determine if these findings apply to other bee species.
Current pesticide risk assessments do not take into account soil as a key route of exposure for bees. The study calls for improvement to such assessments so that they consider this newly discovered behavior.
"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 says.
"By better understanding how pesticide residues accumulate in soils and how they affect bees, we can find ways to protect these essential pollinators."
More information: Sabrina Rondeau et al, Bumblebee (Bombus impatiens) queens prefer pesticide-contaminated soils when selecting underground hibernation sites, Science of The Total Environment (2024). DOI: 10.1016/j.scitotenv.2024.176534
Journal information: Science of the Total Environment
Provided by University of Guelph
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