Anke Dietzsch: Effects of Pesticides on Native Bees and Honey Bees (030)

Anke Dietzsch: Effects of Pesticides on Native Bees and Honey Bees (030)

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Opener: Welcome to 2 Million Blossoms - The Podcast with host Dr. Kirsten Traynor. 2 Million Blossoms is dedicated to protecting all pollinators, from the solitary bee to colorful butterflies, to feisty hummingbirds, and of course, the honey bee. We bring you informative guests to awaken your understanding of the vast diversity of pollinating insects and animals worldwide because the more we know about pollinators, the better we can provide their habitats and protect them from disappearing forever. Sit back and listen as Kirsten and her guest share in the passion they feel for all pollinators.

Dr. Kirsten Traynor: Today's guest is Dr. Anke Dietzsch, who works at the German National Institute of Bee Protection at the Julius Kühn-Institute, the Federal Research Center. She has worked with many different bee species over the years with a focus on toxicology. She has also approached the interaction between plants and pollinators from the plant perspective, looking at what happens when a plant species invades new terrain. Anke is also coordinating a joint initiative to establish a research cooperation with four African partner countries. I'm really looking forward to learning more about her different areas of expertise. Anke, so good to have you on the show.

Dr. Anke Dietzsch: It's super great that you have me. Thank you for inviting me.

Kirsten: It's always fun chatting with a bee scientist. You work at the Julius Kühn-Institut at the Institute for Bee Protection in Germany, which is involved in many different areas of bee research. What is your own specialization? Can you give us a little bit of background?

Anke: Yes. To be honest, the Julius Kühn-Institut, which is the Federal Research Centre for Cultivated Plants, it's actually mainly working on crops and crop plants basically, and plant protection as well. We are a tiny part of the Julius Kühn-Institut. We are from the Institute for Bee Protection within Julius Kühn-Institut. We're looking mainly at bees and effects of pesticides on bee health and bee populations, be it honey bees or also wild bees. That is mainly focused on bees in Germany or in Europe because we are working a lot with European partners as well.

There are quite a lot of different areas we try to cover. We do lab experiments, but we also have semi-field and field experiments. We try to replicate that within Germany. Although we are situated in the center of Germany, we try to cover the southern, the northern, the eastern, and the western parts as well. We often have collaborators like you who are working together with us on those pressing questions.

Kirsten: Your own area of focus within this?

Anke: My own area is more in the agroecology part of it. I do some work on pesticides as well and risk assessment of different pesticides for honey bees. Mainly I work on native wild bees. That can be also social bees like bumblebees, but it's in most cases solitary bees.

Kirsten: Are you going out into the field and monitoring different populations or are you establishing different-- I know you've been working on establishing a bunch of different bee species for testing of the impacts of plant protection products, but what is a typical research experiment you might-

Anke: A typical research experiment.

Kirsten: -get involved in?

Anke: Usually, it's actually a combination of different aspects. There are lab experiments that I'm involved at as well where we treat different bee species with different pesticides or with one specific pesticide and different concentrations and look at their survival and at their behavior, but I'm mainly doing semi-field and field experiments, so going out to the fields doing monitoring of different habitats, mainly agricultural sites. We also work in urban sites where we look at different measurements that can enhance bee populations or certain single bee species that are specialized on certain plant species.

It's mainly using different methods of monitoring to see how bee populations develop and how they look over time in different environments.

Kirsten: There are some arguments about what is the best method to use. There's talking about removing actual bees so you can identify them down to species. Then there are different trap methods with different colored bowls. Are you applying a whole range of different monitoring techniques? Do you have a favorite one that is easy to apply and still delivers good data?

Anke: That really depends what you actually want to look at and what's your monitoring goal. We use mainly pan trapping, using sets of three different colors of pan traps and set them up at different sites within one environment or different environment. The advantage of this method is that you can sample all those sites within more or less the same time range and have a comparable data set in the end.

If you look for a specialized bee species or rare bee species, that's not the optimal method to be used because then you are within quite a specialized environment. It's then much better that you do it with a netting, so you catch them with a net or you just do observations in front of their favorite flowering plant species to see their interactions with those plant species.

It really depends what's your goal of monitoring in that way. Plus, as you can imagine, if you do pan trapping, you catch quite a lot of different species and you also have a lot of bycatch. Depending on the site you're working at that might be not what you want to because you take specimens out of these sites. That might be, especially with rare species, not a very good method to be used.

Kirsten: Okay. That makes a lot of sense.

Anke: If you really want to look at Germany as a whole and want to see how bee populations develop over a longer time scale, pan trapping is a super good method to achieve this goal. If you use a net, obviously you also need people who use the nets, and that's very time and labor-intensive.

Kirsten: It gives you a very good broad overview, but of course, it's biasing towards the species that will be attracted to pan traps.

Anke: Yes. Exactly. Those are certain families that you might actually catch better with pan traps than with other methods. To be honest, that's also the case when you use a net because the very tiny species, you have to be a very experienced observer to actually catch the very small solitary bee species with a net. You might actually not really monitor certain groups with a net either.

One of my colleagues did a comparative study on different trapping or monitoring methods and he could show that depending on the method, you have a very unique species group you only can catch with this method, but not with the other methods. That's also actually true with pan traps. From his results, he could show that pan traps are a very good method to get a good overview of what's out there at your site when you use it as a method.

Kirsten: Of course, they have the benefit that they're cheap, you can put them out and then collect them. You don't need a whole lot of expertise, whereas with catching live bees, you need to be pretty fast, have good wrist movement, and know what you're doing.

Anke: Yes. Exactly. You need quite a lot of experience plus if you use different people for the netting, then yes, it's not necessarily comparable because they have all a different background-- The results from different individuals might look very different rather than being comparable. You might not actually get very good replicates in your [crosstalk]

Kirsten: Fair enough. You've also, in some of your work, focused on developing different bee species as a model system for understanding the impacts of plant protection products. Can you tell us a little bit about this work? Why is it so important that we test substances on multiple bee species, instead of just honey bees and bumblebees, which is the usual culprits for science because they're easy to get your hands on?

Anke: That's true. They're easy to get your hands on, and they're social species, so you actually have a lot of individuals you can use from bumblebee or honey bee hives, especially that is also the disadvantage. They interact within their colonies together, they have certain behaviors that make them quite unique, whereas the majority of bee species that we find outside in the environment are actually solitary bee species, where each female basically is responsible for their own offspring. Their behavioral patterns, and also how they approach flowers, what their preferences are, how they collect pollen and nectar, it can be quite different to what you see in bumblebees and honey bees.

For that reason, particularly because each individual female has her own offspring, for this reason, it's also very important to cover the risks for these bees. Sometimes their populations are quite small or they're very specialized on certain plant species and then there might be a different risk attached when they get in contact with for example pesticides, or if a certain habitat is decreasing in its size, or a certain flowering species is disappearing from a site, the risk for them to survive or have a healthy population might be a very different one than for bumblebees or honey bees.

Kirsten: You must run into quite a lot of trouble trying to get the numbers that you would need for a study. With honey bees, we can hang a frame of emerging brood in an incubator and then we have a few thousand for our studies. I would imagine with some of these solitary species it's not so easy to get at the offspring.

Anke: Yes. That is absolutely true. Nowadays, there are a few solitary bee species, particularly within the Osmia genus that can be bought. They're used for commercial pollination, especially in fruit production. Those you can get your hands on in quite good numbers. They're often used for experiments with pesticides as well. However, the problem with these are they are not nesting in-- they're not ground-nesting species, which the majority of solitary bee species are. That also brings some difficulties with it. You have not the whole range of characteristics you want to see in your model bee species there.

We used basically individuals for our experiments that we caught in the wild from populations that we knew about, of different species within the Andrena and Colletes group. However, you already said it, you can't get them commercially in huge numbers, so there's always the restriction of having enough replicates for your experiments in the lab.

Kirsten: Right. Then are you waiting for them to emerge with the new batch? Otherwise, how do you know age, what they've already been through, what their exposure has been?

Anke: Basically, you wait for the first ones to hatch. You have to time your experiments exactly for their hatching time, which is quite a challenge. You have to use also multiple populations to have not everything from one population. In terms of logistics, it's quite a challenge to get them and to tie the experiments around it.

Kirsten: In the US we have the expression it's like herding cats. I would imagine herding bees is even more complicated than herding cats.

Anke: You probably could say that. Obviously, even if you have caught them you also have to keep them alive in the lab. You always have a control group as well, where you can see if your treatment in the lab is working okay so that they are actually surviving in the way you are treating them, in the way you have them together in cages, for example. Since they're solitary bee species you can't have them in cages with a lot of individuals, for example, and then it becomes a challenge to measure how much they feed on, if they actually take the pollen you provide for them, if they feed on them.

Kirsten: If you have specialty species in there that only collect pollen from specific plants.

Anke: We haven't made that step yet I have to admit. This is a big challenge basically, to then provide the specific pollen. Some species only forage on bellflowers, for example. Then to get enough of that pollen is basically a challenge. Plus with the laboratory studies we've done so far, we have looked at adult bees, or only at adult bees, and looked at their survival after they were treated with pesticides. The next step would be to get them as a system established in the lab where they also breed. That comes with its own challenges basically, because you need to give them the right crowd to nest.

Kirsten: I was going to say you have to give them the right romantic conditions so that they decide to mate and rear offspring for you.

Anke: Yes. My colleagues actually managed to get one Colletes and one Andrena species nesting in flight cages in the lab. That was-

Kirsten: Oh, wow.

Anke: -a huge success. Everyone was applauding. However, it's also something that is super difficult to replicate, right?

Kirsten: Yes.

Anke: To have a standardization within those measures it will take us much, much longer to have that been established as a system that you can use for risk assessment in general, I think.

Kirsten: I think this is something we tend to overlook. People are always saying, "Oh, we need to broaden what species we're looking at. We need to understand the better behavior of the solitary species." What does that mean when you want to use them for a standardized type of protocol? It means you have to have enough individuals, you have to be able to rear them in the numbers you want. You have to be able to feed them and keep them alive. That's a lot more complex for some species, especially I would imagine for the ground-nesting species than for our bumblebees, honey bees, which are very user-friendly.

Anke: Yes. You're absolutely right. It's good to have the solitary commercial species. There have been huge successes in getting them established as study systems in a standardized way in lots of cases. However, even with them, although you have them in numbers that you can replicate an experiment well, there are always boundaries, how you can handle their larvae, how you actually access any effects that you see in the offspring as well, which obviously with a honey beehive, you can always say, "Okay, did they make it over the winter? Are they growing well in the next season?" Even with the bumblebees, you can look at the new bumblebee queens.

Kirsten: Yes. The number of reproductives is a good indicator.

Anke: Yes. Whereas with the solitary bee species, that is still quite a challenge to really assess the next generation and the health of the next generation in general. Still, a long way to go.

Kirsten: What is one thing from working with these different species that you've learned that maybe surprised you a little bit?

Anke: It surprised me a little bit. I often find it surprising that you always say solitary bee species and you often overlook that even with the so-called solitary bee species, there are a lot of social elements in there. It's not being social or being not social. There's a whole lot out there where sisters nest in the same pocket area and guard together their nest entrance. They still have their own offspring and reproduce as an individual, but there are a lot of elements of sociality in there as well. That is often something people forget about it. That's one thing that I'm fascinated by, the ecology you can look at.

Kirsten: A little bit like communal defenses and utilizing resources together so that when they're nesting together, they probably have more defense against predators or one's more likely to be there to make sure no parasites are invading the nest.

Anke: Yes. Exactly. Plus, there can be also different generations and differences in sizes of individuals, depending on which generation they're in, if they're the overwintering generation or the one that's actually going into summer. Even within a genus, you can have completely solitary species, but you can have very social species as well. Within the halictids, for example, you have so many different traits you can look at in terms of sociality. That, I find very fascinating.

Plus, I also find fascinating how well they are adapted sometimes also to small environmental changes. Actually, like open ground, for example, I leave this habitat as it is. I'm not touching anything, but in some cases, that might actually not be good for the bees because they need open ground. If you just go away and leave the habitat as it is, it might all overgrow and then there are no bees anymore, right? They need a certain type of disturbance to feel happy with the habitat they're in.

Kirsten: Okay. You might actually need herd animals coming through and browsing to tear up a little bit of the ground.

Anke: Yes. Exactly. Obviously, I'm not saying you have to dig the whole ground, but some disturbance is good to keep the habitat favorable for our ground-nesting bee species.

Kirsten: How fascinating.

Anke: Yes. Oh, actually, this also includes a third aspect that I find fascinating, which hasn't been really researched a lot, that although you might not think about it, but even in fields of the crops you see around here, you find bee species nesting. That's something that I wouldn't have thought that they actually maybe don't mind that much that you have mechanical disturbance of the upper soil for seeding or for weed removal. Depending which species you're looking at, they still are able to nest in the middle of a field and survive to the next generation.

Kirsten: That's pretty impressive when you consider the size of the equipment that runs over those fields.

Anke: Yes. Exactly. I think we don't know yet that much about that, which type of manual disturbance they can take, so how deep you might actually dig before a nest is really so much destroyed that there won't be any offspring anymore. That will be important question for the future as well, to have more insight into--

Kirsten: We're missing some of the fundamentals on their nesting biology to really understand how deep in the ground is the main heart of the nest for a lot of species.

Anke: Yes. For sure. Obviously, is already a lot been known about it, but for a lot of bee species, there isn't. Since we're dealing, in Germany, at least, with about 600 bee species, you imagine that there are these question marks.

Kirsten: There's a bit of work you have to do.

Anke: Yes. Exactly.

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Kirsten: Now, we're back with Anke. You've done quite a bit of work on the impact of alien plant species and how they are used by native pollinators. Do native bees adapt to these new introduced plants?

Anke: That really depends on the plant species, but it's often that the invasive species that become invasive or the alien species that become invasive are also the ones that can be visited and pollinated by native bee species. If they have flowers that are well accessible for native bee species, they are more likely to produce seeds, and then obviously, spread, have populations established at certain sites. In a lot of cases, alien invasive species do provide good food sources for native bees.

Kirsten: How can this impact the native plants? It's probably quite competitive then in soil resources.

Anke: It definitely is, or it can be. There has been quite a bit of research been done in this area. If you look at the outcomes, you can't really predict it beforehand if it is detrimental for native pollination. It's very much connected to the traits of the invasive species, if it is covering the soil in a good way, how fast it is spreading. The plant species that I've worked on in Ireland, Rhododendron ponticum, definitely has an aspect of taking over the native flora and covering huge areas in a monocultural type of way. That is definitely taking a toll on the native flora, so to say.

Kirsten: Is this because there's nothing browsing it away, or why is rhododendron able to thrive as well as it does in Ireland?

Anke: First of all, it's a perennial species that can grow for decades, so it can get bigger and bigger and bigger. Is shading out a lot of the native flora because it's not only a herb, but a proper shrub, you could say. It can become the size of small trees. It just takes up space and just shading out, but it also releases toxins into the ground that have an allelopathic property, which then is keeping other plant species from growing very well.

Kirsten: Okay. There are some trees that we have in the US that love to do that. They poison the ground for everybody else.

Anke: For Rhododendron ponticum, that's basically also the case. Since it does produce so many seeds per plant, up to, I think, estimated a million seeds per individual plant that are-

Kirsten: Oh, wow.

Anke: -then wind dispersed as well. It can basically reach any spot that is favorable for its growth. That makes it the perfect invasive species, so to say.

Kirsten: Yes. That's a crazy amount of offspring investment.

Anke: Yes. Definitely. It's a crazy amount of offspring. Obviously, because I wanted to work on plant communities, I didn't go to the sites where there was only Rhododendron ponticum, but I used sites where the invasion levels were not so high to compare what's happening there, not necessarily the early stages, but when rhododendron hadn't taken over completely. The density there was not always that high.

I could see in comparison that at this stage there wasn't a huge impact on visitation rates, for example, for most of the plant species. I also conducted one experiment where I used sites with different Rhododendron ponticum density. There it was clear that visitation rate and also deposition of native and alien invasive plant pollen really depended on the density of the alien invasive plant. You have this impact of density. The denser the rhododendron was growing, the less one of the native plants, in this case, I used foxglove, the less it was visited by pollinators and the more alien pollen was deposited on the foxglove flowers as well, which--

Kirsten: Okay. The floral fidelity we know so well from honey bees is of course not always the case.

Anke: Yes.

Kirsten: The bees are actually spreading the rhododendron pollen not just on the rhododendron, but also on your native species.

Anke: Yes. Exactly.

Kirsten: Does that block up the system? Does that then?

Anke: It was interesting because I didn't see any effects on fruit sets. It seems that this wasn't the case that it blocked up the system, but you could envision that at very, very high Rhododendron ponticum densities that might be the case. If a pollinator is mainly carrying Rhododendron ponticum pollen and not pollen from any of the native species, then obviously there is no reliable pollen transfer within those native species anymore. I didn't observe that in my system, but again, I didn't actually used super densely invaded sites.

Kirsten: Okay. You might have been on the easing and it might have been going in the other direction, wants the rhododendron.

Anke: Yes. Exactly.

Kirsten: Ireland has quite a lot of pollinator diversity. What is visiting the rhododendron then?

Anke: For that it is an island where it is actually raining a lot, [laughs] it actually does have quite a lot of pollinators. It has far less pollinators than we have in Germany. You have around 100 pollinator species. Nowadays, a few more because it's changing as well, some disappear, some are rediscovered or are making their way over the Channel and distributing in Ireland as well. The main pollinators I was looking at were bumblebees as well in this case. They were also very well adapted to the weather, so they would also fly in light rain. [laughs] They would get out and still collect pollen and nectar.

Those were the main pollinating species I observed in the systems I worked at. There were also solitary bee species that would visit.

Kirsten: Okay. I feel like Southern Germany has been resembling Ireland this summer. We've had so much rain that [laughter] it's been really, really hard to get research experiments off the ground because I think in the month of May, we had four days of sunshine.

Anke: Oh my gosh, and a lot of flooding.

Kirsten: Yes. Where we are, there hasn't been so much flooding, but it's just been constant rain that the water content in the honey is way too high. The bees are just not flying. We're just wrapping up our bee experimental research block. One of the groups was supposed to be looking at pollinators on potted plants, and there's so little flying at the moment because it's been so cold. Today the weather is warm, so this week it's supposed to be nice. It's the first real week of flying weather. I feel for you in Ireland in trying to document what pollinators are showing up.

Anke: [laughs] The good thing is that the pollinators in Ireland are adapted to those weather conditions, right? Whereas, usually, especially with you down in the south of Germany, you have such a huge diversity of bee species, even in comparison to where we are here in Braunschweig, we only have a subset of what you have, because usually you are in the sunny spot of Germany. Obviously, for bee populations down in the south, I think this summer has been devastating.

Kirsten: It's going to be really interesting to see what populations are there next year and how cyclical it is and if we have a really-- Yes, it'll be interesting.

Anke: Yes, I agree. That also shows how many-- That you actually have to measure quite a lot of different parameters if you want to predict bee populations and their development, right? Something like the weather shouldn't be underestimated because it makes a huge difference if it's very cold during the period when bee species that are only active for maybe two or three weeks, if it's cold or even freezing temperatures, they might not be able to come out and provide for their offspring.

Kirsten: We've been running some experiments over multiple years to try and understand pollinator preferences, year is just such a huge effect because the populations from year to year can be so different as to what's visiting.

Anke: I'm very glad that you're actually bringing up this point because that is often the problem with experiments as they're run these days. You have one, if you're lucky, maybe two years of field research being done. I think that is often far too little to really see effects that might be there because the variation between years can be immense. The effects that you're looking for might actually disappear or you think you have seen an effect, but in the end, it was just an effect between years and not the effect itself that you thought it would be.

Kirsten: I can fully get behind that statement. We do a lot of cooperation in Heidelberg with Institut für Gartenbau for plant cultivation. In '22, we had large amounts of bumblebees, and in '23, we had next to no bumblebees on the exact same plots. Then you're trying to understand trends over time, but it's very, very, very difficult to disentangle the impacts of year and weather and temperature. We of course measure all of those points so that we can try and understand it, but it is amazing what differences there are between years.

Anke: Yes. That way, it is actually good that there are those huge efforts now on a European level that we will have long-term monitoring established with standardized methods all over Europe, hopefully, that will show us those long-term trends as well because, in a lot of cases, we have no idea what they are. Obviously, there are some long-term data sets that can be used, but they're so patchy and they often are not necessarily set up to what we are interested in in our research questions as well. Being mostly in protected areas, but not in agricultural settings.

It is a challenge to get across long-term data that can be used. I'm really looking forward or I'm really glad that there are all these efforts now to establish monitoring with the thought, keeping in mind that this needs time and we need not only 2 years of data but 20, 30, 40 years of data.

Kirsten: It's hard to convince the funders that this is the type of data we need because it's not as sexy and exciting to monitor what's actually there over time.

Anke: Absolutely. I absolutely agree. I think we are at the point where people realize that this-

Kirsten: The value.

Anke: -is still very valuable and might actually get to the source of what can be also changed in the way we treat our ecosystems to make them good places for bee populations.

Kirsten: Yes. I think that's critical. We need to understand the baselines. We need to have systems in place to really understand what is there and how it's changing over time.

Anke: Yes. We are actually involved in one project that is testing methods for long-term monitoring, again-

Kirsten: Oh, exciting.

Anke: -using pan traps and looking at the feasibility of doing that at the same time in a whole region of Germany. Also combining it with other methods for identification, because obviously if you use pan trapping, A, you have a lot of individuals and usually the identification that comes after the catching is a huge challenge-

Kirsten: The time-consuming [crosstalk]

Anke: -and time-consuming. We are testing on how well metabarcoding is actually working for identification. If you can use it and if you get enough information out of your data set to say something about the communities really, or if this aspect that can't be really covered yet very well with metabarcoding, the abundance of species. If that is not something that is so valuable that one should actually identify the bee species the traditional way, I say.

Ultimately, hopefully, on a European level, we can come up with a set of methods to be used and also obviously not having so many sites that you can't work them anymore, but having just the minimal set of sites that can still give us a good data set on the long run.

Kirsten: That probably involves a lot of modeling and trying to understand how much variance there is across a landscape.

Anke: Yes. It gets better because also something like remote sensing data is better available on a European level, I'd say these days. You can combine different methods to have a better idea of what's out there, what do we expect in terms of our bee populations to look like, what do we find when we go there. Yes, I agree, a lot of modeling and combination of data sets, but it's really exciting.

Kirsten: It does sound exciting. I appreciate all the insight you've given us into the work you do. I ask all of my guests, and you don't get to escape the question either, if you had to choose a pollinator species or plant to represent you, what would you pick?

Anke: Ooh. Okay. Whoa. Pollinator species, I think I would like to be one of those really tiny, small bee species that like to only collect pollen from bellflowers. I love bellflowers. [laughs] It definitely has to be a bee. Although, I think butterflies and hoverflies are amazing as well, but I would say I'm definitely a bee person. [laughs]

Kirsten: Okay. A specific species or you're leaving it a little more open?

Anke: Not really, but I--

Kirsten: So long as you get to sniff bellflowers, you're happy.

Anke: Yes. Exactly. [laughs] Pick your favorite.

Kirsten: Too funny. Thank you so much for sharing your insight. It's been a pleasure having you on the show. I wish you much-continued success with your research.

Anke: Thank you so much. Thanks again for having me.

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