How Pesticides Endanger Wild Bees (Ep. 72)

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Imagine raising your family in a home surrounded by a toxic chemical cocktail. It sounds extreme, but for many ground‑nesting bees, especially those living in agricultural landscapes, this is every day reality.

In this episode, Dr. Sabrina Rondeau reveals how current pesticide regulations, which often focus narrowly on honey bees, overlook a critical pathway of exposure: the soil. Her research uncovers alarming evidence, including bumblebee queens overwintering in pesticide‑laden soils and the dangerous interactions between fungicides and insecticides that can amplify toxicity. These findings challenge long‑held assumptions about what makes chemicals “safe” for pollinators.

Sabrina calls for a more comprehensive regulatory framework—one that accounts for chronic and sublethal effects of pesticides and reflects the complex, real‑world conditions bees encounter.

Photo by Matheus Bertelli

A postdoctoral fellow at the University of Ottawa in Canada, Dr. Sabrina Rondeau specializes in ground‑nesting bees in agricultural areas and studies how climate change and pesticides together impact hibernating bumblebee queens. You can read the research we discussed here and check out more of Sabrina’s work here. 

This conversation builds on a growing body of research exposing the threats pesticides pose to native bees. Previous episodes have featured:

Good to know

Sabrina’s study looked at two bee species: bumble bees and the hoary squash bee. Bumble bees are social insects that live in colonies, but their queens spend six to nine months overwintering underground. The squash bee is solitary—each female digs her own nest directly in crop fields. That nesting behavior places both the mother and her offspring in constant, close contact with pesticide residues in the soil.

Transcript

Jacy: [00:00:00] Welcome to the Bees Knees a podcast wild about native bees. Wild and native bees are under threat worldwide. In each episode, we look at actionable things we can do to support these adorable little guys whose pollination work is crucial for maintaining biodiversity. I’m Jacy Meyer, and I thank you for being here.

The ground beneath us isn’t just dirt. It’s home for most wild bees. It’s where they nest, where Bumblebee, queens hibernate, and where the next generation begins. But that soil is often laced with pesticides. And new research shows those chemicals may be quietly putting pollinators and our food systems at risk.

Ground nesting bees spend much of their lives in direct contact with the earth, which means what’s in the soil matters more than we’ve realized. Today I am joined by Dr. Sabrina Rondeau through a mix of field work and lab [00:01:00] studies. She’s uncovered how pesticide residues in farm soils are reshaping the survival and success of two wild bee species.

Together we’ll dig into whether current pesticide regulations are really protecting pollinators. And what needs to change to secure the future of pollination? So the majority of wild bees nest underground, unlike honeybees. How does this difference change the way they’re exposed to pesticides? And why do you think it’s been overlooked in risk assessments that are done?

Sabrina: Yeah, so it surprises a lot of people, but roughly 80% of all bee species nest underground. These are mostly solitary bees. So species where instead of living in a hive with thousands of workers like honeybees do, a single female does all the work. She digs her own nest in the soil and provisions little chambers with.

Pollen for developing offspring and because of this lifestyle, while soil is their home, right, the haded females are constantly in [00:02:00] contact with soil while building their nest and their eggs, larvae and pupae developed entirely underground, and they are also surrounded by soil for months at a time. Then there are also other species that don’t dig a nest underground per se, but still spend part of their lifecycle under the ground, like Bumblebee Queens, for instance.

So in Bumblebee Queens, after mating in the fall, the queens borough into the soil to over winter, they can spend seven or even eight months down there before emerging in spring to start a new colony. So now in agricultural landscapes, we know soil can contain residues of many pesticides on top of the more familiar pesticide exposure route, which is consumption of contaminated pollen and nectar, while ground nesting bees and bumblebee queens are also exposed through direct contact with contaminated soil.

But despite its importance. The soil route has been almost entirely overlooked from current pesticide risk assessments, and this is [00:03:00] because our regulations reliably on this one single species that you mentioned, the honeybee, Apis mellifera, and honeybees live above ground, which means they have almost no contact with soil.

And this explains why this type of exposure was and still is overlooked.

Jacy: So you discovered that Bumblebee queens, while over wintering sometimes prefer the pesticide contaminated soils. Do you have thoughts on why this might be and what are the consequences?

Sabrina: Yes. So we found something quite interesting in our experiment, Bumble, bumblebee queens that were offered a choice between different types of soil to overwinter in, didn’t avoid pesticide contaminated soil, and in some cases they actually chose it more often than clean soil.

Now, whether. That’s a true preference or more of an indifference is still unclear, but here’s what we think might be going on. So bumblebees, including queens, don’t seem able to detect [00:04:00] pesticide very well either in food or in soil. Their mouth parts don’t recognize many of these compounds, so they may simply not know they are there instead of recognizing pesticides, another.

Possibility is that pesticide could be indirectly changing the soil community, so the organisms living in the soil, sometimes in ways that queens might find beneficial. So insecticides might, for instance, reduce harmful soil, parasites, and nematodes or fungicides might reduce soil fungi and can lower over wintering survival.

So in other words, queens may be responding not to the pesticide itself, but to the resulting soil conditions. So that’s one possible explanation, but to be honest, we still don’t really know, and that’s what makes it so interesting. Scientifically. What we do know is that queens are not avoiding these residues, which has real consequences.

And if there really is a preference and contaminated sites become wintering [00:05:00] hotspots, then the queens could be exposed for months at a time during a very sensitive period in their lifecycle.

Jacy: So. You’ve also found that pesticide mixtures in orchard soils contain up to 29 different chemicals, which was just unbelievably shocking to me.

What does this tell us about the real world challenges bees face compared to the simplified tests that these chemical regulators rely on?

Sabrina: Yeah, well, the short answer is that, well, real life is messy. Uhhuh and bees are dealing with that complexity. So finding up to 29 different chemicals in a single soil sample shows that bees aren’t exposed to one active ingredient at a time.

The way we test them in the lab, instead, they’re exposed to mixtures in soil as in pollen and nectar and mixtures can interact. So sometimes one chemical makes another one more toxic. For example, a fungicide might. Suppress these detoxification enzymes, making an insecticide that is [00:06:00] normally mildly toxic, suddenly much more harmful.

But current pesticide assessments, largely test chemicals one by one. In isolations, we’re missing how these combinations behave in the real world, and this means that if we want regulations to reflect reality, then we need to incorporate at least the most common, most likely mixtures into risk assessments.

So another

Jacy: bee that you studied was the squash bee, and you found that fungicides, which are often thought as being bee safe, can actually reduce the pollen collection and the offspring in these squash bees. How does this change the way we think about which chemicals are risky?

Sabrina: Mm-hmm. It really challenges the way we define safe.

So risk is usually described as toxicity times exposure. And toxicity here usually means laterality. So in other words, how much of a chemical it takes to kill a bee. And by that [00:07:00] measure fungicides, uh, often look pretty safe. You usually need a very high dose to kill a bee outright, so they’re considered low toxicity and therefore low risk.

But that’s only one piece of the story. Bees don’t just die or survive. They have behaviors and biological processes that are essential for reproduction and for keeping populations healthy. In our squash bees study, the fungicides didn’t kill the bees, but they reduced how much pollen females collected, and things got much more complicated when the fungicide we tested combined with an insecticide that has also been assessed.

As having low toxicity. So on their own, the fungicides didn’t kill the bees. But when bees were exposed to both the fungicide and the insecticide, then they produce fewer offspring. So for a solitary bee species where each female produces a relatively small number of offspring per season, that reduction can have big population level consequences.

So this tells [00:08:00] us that little toxicity isn’t the whole story. Sublethal effects, like changes in behavior, health, or reproduction can have population level consequences, and that’s why evaluating both lethal and sublethal effects is essential if we want to understand which chemicals truly pose risk. So

Jacy: what would you like to see changed when it comes to pesticide regulation?

Sabrina: I’d love to see the risk assessment process become more representative of real bees in real landscapes, right? So for me that means three things. First, the need to include relevant exposure, routes like soil, uh, exposure for ground nesting bees, not just nectar and pollen for honey bees. Second to evaluate chronic and sublethal effects, and not just whether a bee dies after 24 or 48 hours as it’s currently done.

And third, to consider realistic mixtures or at least the combinations that bees encountered most frequently. I would also [00:09:00] like to see more regular assessment of pesticides once they’re on the market. So landscape, you know, uh, application patterns and scientific knowledge, all change over time and regulations need to keep up.

Jacy: So in all your time working with bees, what’s one discovery that made you feel like a bee hero? Like you are really making a difference?

Sabrina: That’s a good question, and I wish I could feel like a bee hero more often, and I think many bee researchers would say the same. But what I can say is that one moment that stands out was when our research on soil exposure started gaining traction.

So realizing that we were helping reveal an entire overlooked route of pesticide exposure, one that likely affects the majority of bee species felt. Meaningful, it made me feel and continues to make me feel like we are genuinely pushing the conversation towards better protection for wild bees, and that motivates me to keep going.

Jacy: What we’ve heard today shines [00:10:00] a light on a big gap in how we look at pesticide safety. By focusing almost entirely on the honeybee, regulators miss the very real risks facing most wild bees, especially those that nest underground. These bees come into contact with pesticides in different ways and often deal with complicated mixes of chemicals in the soil.

As Sabrina’s work shows, if we want to protect pollinators, we need to rethink how risk assessments are done. Taking into account long-term impacts, sub lethal effects, and the reality of multiple exposures, that’s the only way we’ll be able to protect biodiversity and the food systems we all rely on. A huge thank you to Sabrina for sharing her work and to you, my listener, for joining us in this conversation.

Buzz over to the Bees Knees website where I’ve linked to some past episodes talking about pesticides. Until next time, keep [00:11:00] digging.