A Conversation on Pesticides

Dan Schmehl, a pollinator ecotoxicologist and beekeeper, discusses pesticides and honey bees.

with Dan Schmehl – Pollinator Ecotoxicologist
By: James Masucci

One of the best things to come out of Bayer’s acquisition of Monsanto was that I became friends with Dan Schmehl. Dan’s a pollinator ecotoxicologist for Bayer, who has done some incredible work testing the effects of potential new agrochemicals on bees. We share a passion for honey bees and consider ourselves “bee buddies.” Like me, he is not only a bee researcher, but a beekeeper as well. He has three different apiaries and got 1,000 pounds of honey this year. In addition, he sells a few nucs and generates some lovely candles. His beekeeping and love of bees helps him be a better researcher. His goal is not only to provide appropriate tools for growers, but to ensure that he wouldn’t mind their use next to his own hives. Some of his bees are next to fields of corn and soy, so that scenario is a distinct possibility.

Dan considers himself a “child of CCD” (colony collapse disorder). At the time (2007) he was an entomology graduate student at Penn State University where his interests were plant/insect interactions. While there, a commercial beekeeper, Dave Hackenberg, came to the university saying that something different was happening to his hives. The era of CCD had begun, and Penn State started getting funding in 2007. Dan started studying the effects of pesticides and nutrition on honey bees. He fell in love and his career in bees was launched.

As a graduate student, Dan was very anti-Ag. Anything that would harm bees was bad. After getting his PhD, Dan did a post-doctoral fellowship in Jamie Ellis’ lab at the University of Florida studying honey bee husbandry – how to keep honey bees healthy. His research focused on pesticide effects in lab studies. It was as a post-doc that Dan began to realize the complex relationship between agriculture and honey bees. Agricultural lands are intensively managed, and growers require crop protection products. Growers also require honey bees to provide the pollination needed to obtain optimal crop yields. So, Dan’s focus changed to addressing the questions, “how can you have both crop protection and honey bee health?”

At the time, Dan was critical of the large agricultural companies for having honey bee initiatives without having the necessary honey bee experts. He came to realize that the way for him to have the most impact in this space was to have a hand in the development of new crop protection products. He could be the one driving the necessary initiatives to make agriculture safer for honey bees.

When he joined Bayer in 2015 as a pollinator ecotoxicologist he was concerned about whether the company would listen and act on his ideas, and whether his integrity would ever be put in question. Thus far, his concerns have been unfounded, and he feels confident in the safety profiles of the chemistries now entering the market.

In conversation, Dan always gives a balanced response to questions regarding pesticides and honey bees. So, I thought he could provide us all with some perspectives on the risks we face with pesticides and what we can do about it.

I first asked him to describe the present pesticide landscape. What is the pesticide risk now for honey bees?

“Compared to 30 years ago, acute bee kills (walking up to a yard of dead colonies), are less frequent and more sporadic. This is the result of safer chemistries and improvements in best management practices. For example, better planting equipment has resulted in less dust emission during corn planting, and many growers are spraying pesticides in the evening when bee foraging is reduced. It is likely that the number of bee kills is under reported and may be due to the dependence of beekeepers on the landowner (you don’t want to bite the hand that feeds you). This is a problem. The only way to solve pesticide/honey bee issues is to know about them and to investigate them. However, word of mouth seems to confirm the reduction in bee kills,” said Dan.

Does this mean that pesticides are no longer a concern to beekeepers?

“No,” says Dan. “Right now, there is a lot of research into sublethal effects on honey bee colonies.” And Dan admits that this is an area of uncertainty. There isn’t any clear answer. For a while, it seemed like every article written on honey bees was saying how pesticides impacted some aspect of the colony: the queen’s ability to lay, a bee’s ability to navigate, a bee’s ability to forage, etc. It is possible that some of these effects could be the cause of a poorly performing colony, even if the colony survives.

Pesticide kills like this one, caused by drifting insecticide from an aerial spray, still happen. Although the frequency of these catastrophic kills is declining, there is still the issue of sublethal effects of pesticides. How likely are we to experience such an event and how do we identify one if it happens? I asked Dan Schmehl, an ecotoxicologist, for his thoughts on the subject. Photo by Tony Jadczak.

But sublethal effects are difficult to study and even more difficult to determine relevancy. Methodology is critical. Dan gave me an example from his own research as a post-doc at the University of Florida to highlight some of the complexities of doing these studies. He studied the effects of seven pesticides on larval development. He used the maximum doses that were detected in the field from pollen and wax and measured “everything” – from gene expression to brain size. He saw effects. But are they meaningful? First, some of his doses were determined by the level of pesticide reported in the wax, but the larvae in his study were exposed to the pesticide in the diet so the exposure level may not be environmentally relevant. Second, sometimes the effect of the lower dose was more severe than the higher dose. That calls into question the validity of the test. Toxicology tests rely on a dose response. You start with a dose that has no effect and you have multiple doses until you get to the dose that has maximum effect. The more toxin that is present, the more severe the symptom, up to the maximum. If you don’t see the expected dose response, you cannot be confident in the result, or in the pesticide levels that may cause toxicity to bees. That’s not to say the chemical isn’t involved, but additional studies are needed to answer the question.

Take blueberry pollination as an example. It’s been known for decades that bees come out of blueberry pollination in poor health. EFB levels tend to be high and brood patterns are poor to non-existent. For just as many decades, fungicides have been blamed by many beekeepers for this effect, yet researchers aren’t showing convincing evidence that fungicides are the cause. In fact, as they point out, the modes of action of fungicides have changed over the decades but the effect hasn’t. Who do you believe? I asked Dan about this.

Blueberries provide zero nutrition for bees. Yet the growers require the beekeepers to stay in the blueberries for six weeks (two brood cycles). “This is insane,” Dan said. “It is stressing the crap out of the bees. Plus, the weather is horrible for the bees (cool and wet). So, the bees are incredibly stressed even without exposure to the pesticides. It’s possible that the weather and poor nutrition may increase the sensitivity of the bees to pesticides, and there are ongoing studies to investigate this possible interaction.” We both wondered if the same weather conditions and pesticide applications occurred in canola, a nutrient rich crop for bees, would we see the same effect?

What can be done?

Dan says good communication between growers, applicators and beekeepers is key. Knowing what is being applied and how helps the beekeeper respond. Plus, growers and applicators should be thoughtful of when the bees are needed in the crop. Don’t keep them longer than they are needed and time treatments around the presence of the bees. Apply a product in the evening when bees aren’t out foraging on the crop and drift effects would be minimal. Use chemistries that are less prone to interactions when spraying multiple chemistry and use chemicals with safer profiles.

But what about the average beekeeper?

“For most of us, the hobbyists and sideliners that don’t do crop pollinations, the risk is relatively small. Personally, I have hives next to soybeans, corn and pastureland and haven’t had an issue,” said Dan. In fact, Dan coauthored a pesticide survey and risk assessment for hobbyist beekeepers when he was at the University of Florida (Demares, 2022). Dan thinks the biggest risk for the hobbyist beekeeper is probably from mosquito sprays. Most of the backyard bee kills reported in the news over the years were a result of mosquito sprays. If they are spraying in your area, find out what they are spraying and try to get them to spray at night. You can cover your hive (i.e., with a sheet) temporarily while the spray is happening to avoid drift but be careful not to leave the cover on too long or the hive will overheat.

How do I know if I have a pesticide event?

“If you walk into your yard and there are piles of dead bees in front of all the colonies, that is a good indication of a pesticide kill (see picture below). If this happens, you should take pictures and call your state regulatory agency. Hopefully, they will come and investigate, find the cause, and everyone will learn from it,” Dan said.

But how do you detect a sublethal pesticide event?

“Sublethal effects look a lot like everything else that impacts your hive. Spotty brood… Is that a pesticide? Is it a failing queen? Is it Nosema? Varroa? Knowing that something looks different is the first step. But linking a colony’s decline/death directly to a sublethal effect of a pesticide is near impossible. The good news, if you suspect a sublethal pesticide effect, it is likely something else. What you need is a longer duration of study. First, do all/most of the colonies in the yard show the same symptoms? It is likely that they are foraging on the same stuff, so most of the colonies should be affected in the same way. Is the symptom specific to a specific yard? Again, the pesticide exposure is probably a local exposure. If you’re seeing the same symptom in many locations, it is probably something else. Is this a long-term trend? Does this happen every year in the same location? If so, there is something specific to that location and pesticide exposure would be a suspect,” said Dan.

If you suspect pesticide issues, you should report them. Dan said that they need to know about the issues. Even if most of the issues reported cannot be traced back to a pesticide, the magnitude of the reporting may be meaningful.

I ended the conversation with a simple question, that I knew didn’t have a simple answer. If you had a pie chart of the different stressors that were impacting the bees, how big of a slice would it take to represent pesticides?

Bottom line, he didn’t know. For most beekeepers, it would be small. For those involved in pollinations and have their bees on intensely managed land, it would likely be larger. Overall, the risk is small, and, unless there is a catastrophic pesticide event, pesticides are one of multiple stressors in the hive that may interact to exacerbate colony health concerns. So, if your bees are in an area where pesticides are normally applied, find out what is used, how much risk that poses to your bees and see if they will apply the pesticide when your bees are less active. The best defense is to keep your bees as healthy as possible, allowing the colony to cope with low-level pesticide exposures that might occur.

Démares, F. J., et al. (2022). Honey Bee (Apis mellifera) Exposure to Pesticide Residues in Nectar and Pollen in Urban and Suburban Environments from Four Regions of the United States. Environmental Toxicology and Chemistry, 41(4), 991-1003.