Sunflower Power for Bees (Ep. 13)

There’s a lot of creative thinking that goes into scientific research and being able to think differently when the results aren’t going your way. Today we’re looking at a study that found sunflower pollen greatly reduces a gut pathogen in the common eastern bumblebee. Dr. Lynn Adler shares with us how they got to the answer, and what they learned along the way. 

We’re looking more closely at bombus impatiens, the bee and Crithidia bombi, the pathogen. We learn about nectar and pollen and the different benefits they bring to bees and the fascinating interplay between the floral and pollinator world. 

Dr. Lynn Adler has a PhD in Population Biology and is currently a professor in the Biology Department at the University of Massachusetts in the United States. Her work focuses on how plant traits mediate interactions with herbivores and pollinators and more recently, the role of floral traits in bee-pathogen interactions. You can learn more about her and her team’s work with pollinators here. 

To dig deeper into Lynn’s research into sunflowers, check out the main study we discussed in the episode. 

Did you know?

Helianthus is a genus comprising about 70 species of flowering plants known as sunflowers. That’s a lot of disease-fighting potential! Except for three South American species, sunflowers are only native to North and Central America.

Lynn’s work with sunflowers is still ongoing. She and her collaborators recently discovered the spines of the sunflowers are as effective as whole pollen in reducing infection. Learn more here.

Transcript

[00:00:00] Welcome to The Bee’s Knees. I’m your host, Jacy meyer. Pathogens and infections are a major driver in the decline in global bee populations. Today, we’re going to talk about a study that looked at one bee species, one disease, and one flower. Dr. Lynn Adler from the University of Massachusetts and her team have done some fascinating research looking at how sunflower pollen affected common eastern bumblebees infected with the general gut pathogen.

Lynn, thank you for being here. What led you to look at sunflower pollen as a possibility in reducing the occurrence of infections in bees? Back when I was in grad school, there are an awful lot of people who study interactions between insects and plants. They make up a huge amount of the biodiversity on this planet.[00:01:00]

And the world was kind of divided into the camps of people who study insects that eat plants and all the ways that plants defend themselves against getting eaten, all of the chemicals that plants make, as well as thorns and spines, because plants can’t run away. So plants are amazing chemists. They make all kinds of bioactive compounds.

And so people studied those interactions and how plant defenses affect how much plants get eaten and how insects that eat plants get around those defenses. And that was kind of a world. And then there’s the world of people who study plant pollinator interactions and all of the floral traits that plants make, the color and the scent and the nectar and the pollen, all the rewards that can affect whether pollinators visit plants and how effective they are and how, how those plant traits, floral traits might evolve in response to pollinators and how pollinators might make decisions based on floral traits.

And then there’s, there’s, you know, other areas too, but those are two big camps and those worlds didn’t necessarily speak to each other very much. I got excited about [00:02:00] how, say, defensive traits might affect pollinators, um, because it turns out that when people stop and look, a lot of the offensive chemistry that people had studied in leaves or roots or stems is also present in nectar and pollen.

And so it can affect pollinators as well, but that wasn’t something that people were really looking at very much. Uh, similarly, all of the attractive traits that plants make. Kind of attract a range of negative consequences too, um, insects that eat flowers, insects that lay their eggs on flowers, insects that rob, um, diseases that get transmitted to plants through pollinators visiting.

There’s all these negative consequences too. And so that floral evolution may be more of a compromise between trying to maximize your beneficial interactions and minimize your negative ones. And those kinds of interactions really interest me. At heart, I’m a little bit more of a plant person than an insect person, although I enjoy both sides.

And for a long time, I sort of asked questions from the plant point of view. I should also acknowledge that for a lot of this research, I have a longtime collaborator, Becky [00:03:00] Irwin, who’s at North Carolina State now. We’ve both moved several times, but she has been a major part of all of these stories as well.

And yeah, so we started looking at like, how weird is it that there might be defensive compounds in nectar and like, why would a plant do that? Why would you put yucky stuff in your nectar? And we started asking those questions first from the plant point of view, are there benefits to a plant of having defensive compounds in nectar?

Um, but then when people started getting more concerned about pollinator declines, there’s a range of stressors that pollinators are experiencing, but on the list is parasites and pathogens. And in the herbivore world, it’s been known for a long time that these defensive compounds can deter, you know, can deter animals that eat plants, herbivores.

But if, if those animals can get around those defenses somehow, it can also help protect them against their own diseases, their own parasites. I mean, people are great at this, right? Most of our medicines come from [00:04:00] plant defenses that we’ve figured out how to use in small doses therapeutically to treat a range of issues.

So people thought about this in the herbivore world a lot, but we started wondering like, okay, pollinators are being exposed to these chemicals through consuming nectar and pollen. I wonder if that could, what the impacts of that are for pollinators and whether it could help protect them against their own diseases.

What bees and what disease did you decide to investigate? We’ve been working with the common eastern bumblebee, um, bombus impatiens mostly. In part because it’s so common, in part because it’s commercially available, and so it’s, it’s logistically very easy to work with. And we’ve been working with, uh, mostly a gut pathogen called Crithidia bombi.

It doesn’t have a common name, we just call it Crithidia, but it’s, it’s not the baddest of the bad as the pathogens threatening pollinators go. It’s, it’s, it’s one on a list, but, um, I, I would, I can’t say that this is the one that’s been most [00:05:00] strongly implicated in pollinator declines. But it is by far the most common pathogen.

So in our area, especially we can find it in up to 80% of the bumblebees sometimes in some sites. Yeah. It’s sort of shocking and 50% is very common for us. It’s very easy to work with. It’s very common. It has a range of negative impacts and it’s in the gut. And so. If something’s going to be impacted by diet, that’s a pretty logical place to start.

So that has been the one that we’ve worked with mostly. How did this study work? So we scoured the literature for every compound we could find that had been documented in nectar where they actually gave a concentration so we’d know the ecologically realistic amount to use. And that was commercially available so we could obtain it.

We ended up with eight compounds. And we started working with bumblebees and we do a lot of experiments where we basically infect the bees with a known dose of Crithidia so that they’re all starting with the same exposure and then assign them to eat different diets, feed them those different diets for a [00:06:00] week and then look at the infection levels to see did some of those diets reduce infection relative to others.

We do a lot of experiments like that. And we started with these nectar chemicals. And we found that four of the eight chemicals that we tested had significant effects in reducing infections, some of them up to like 60 to 80% lower cell counts. So we’re really excited about this. We got an NSF grant, we got a USDA grant.

I went off on sabbatical, you know, sort of powered everything down in the lab. And then, yeah, we got these two grants, came back all like ready to go and start this new stuff up. And then spent a year doing experiments, the same kind of experiments we’ve done before, with the same kind of chemicals, and the Crithidia was like, we don’t care.

We don’t care. No effect, no effect, like the same things we’d been doing. And this Crithidia didn’t care. Eventually we figure out that Crithidia strains vary quite a bit in how sensitive they are to these chemicals. We got really lucky the first time around. Um, and when we started up again, we had Crithidia strains that didn’t [00:07:00] matter.

And so, you know, while you’re spending a year doing experiments that aren’t giving you the answers you’re expecting, I mean, there were still legitimate answers. It was good science, but we’ve gotten these grants to look at effects of nectar chemistry that were sort of predicated on the idea that there would be an effect and now we’re not seeing an effect.

And so you start thinking about what am I missing or what other avenues could there be? That maybe we’re overlooking and we started to say like, you know, maybe the, the concentrations of the defensive chemicals and nectar are quite, quite low on the order of sort of parts per million. And maybe we’re missing the boat by not looking at pollen. From a plant point of view.

You know, nectar is a sugar water reward that you make to entice pollinators, but pollen is your, your sperm. It’s your male gametes. It’s a much bigger investment. Protein and fats are expensive for plants to make. They’re usually the limiting resources for [00:08:00] insects too. So like. What, if you’re a plant, what you kind of want is like, come drink the nectar, take the pollen, deliver my pollen to the next plant,

don’t eat my pollen. And so pollen tends to be much more chemically defended than nectar is much higher levels, much more diversity of compounds. We thought maybe there’s something interesting going on with pollen that we’re missing because this nectar stuff’s not going anywhere. We picked a few that we thought either like we knew something about the defensive chemistry and the flowers and thought it might be interesting or some plants that we were interested in for other reasons.

And sunflower has a lot of, interesting defenses in the seeds and the flowers that are already known. So we’re like, Oh, we tried, we tried sunflower and buckwheat and rape, which is sort of closely related to canola. Seriously, that was picking three of a list of maybe six choices that were out there. So it was just luck.

And so we did one of these experiments. We infected the bees and instead of manipulating the nectar, [00:09:00] we gave them different kinds of pollen and this was an undergraduate honors thesis in my lab. Great undergrad. And when I checked in with him, I was like, Jonathan, how’s, how’s the project going? And he’s like, it’s really, really weird.

You know, when we feed the bees sunflower pollen, they’re just, they’re just not infected anymore. Like a week and the infection is just gone. And the data we’re just eye popping. Yeah, about two thirds of the bees had no detectable infection after a week, which is just so much more dramatic than anything we’d ever seen with nectar chemistry.

And, um, and that has turned out to be like ridiculously repeatable. It works with lots of different kinds of sunflower. It works with different strains of Crithidia, but in common eastern bumblebee, at least it’s, it’s incredibly consistent. Which is weird because like, in ecology, you know, you always kind of joke, like, if you get a really cool result, don’t repeat that experiment because you’re never going to get the same thing twice.

But like, this always works for the common eastern bumblebee. Um, it’s been, it’s been [00:10:00] remarkable, but yeah, it was. It, it came out of other things not working and a good element of, and you’re thinking a little bit differently and, and a bunch of luck. I think you mentioned, but I want to clarify, you found this excellent result across the sunflower family.

But we did end up testing 14, I think, different kinds of sunflowers, both different domesticated varieties and different wild accessions because sunflower is also a native perennial in North America. There’s like wild sunflower, not so much in the east, but out west there’s a lot of wild sunflowers. So we’ve got different populations of wild sunflowers.

We got two, um, sunflowers that were a different species, so like all the domesticated ones are Helianthus annuus. But we got, yeah, two different Helianthus species of different species of sunflower. And then we were even [00:11:00] lucky enough to put a honeybee hive out in a field that had a lot of goldenrod and get pretty pure goldenrod pollen as well of two species.

Um, and goldenrod is in the same family as sunflower, but it’s not that close of a relative within the sunflower family. So we tried all of these different kinds of sunflower and the goldenrod and they were all pretty effective. You know, there were some slight variations in each one as to how effective, but we compared them to in that first trial, buckwheat pollen would result in pretty high infection levels.

Um, so we often use that as a control if we want to compare it to just one other single species. And then we also compared to just a wildflower pollen mix, so something that’s a little more ecologically relevant, bumblebees are generalists, so they might be consuming different kinds of pollen. And, um, I think pretty much all those different kinds of sunflowers, substantially reduced infection compared to [00:12:00] buckwheat and most of them compared to wildflower too.

So it seems like it’s a pretty broad spectrum effect which is remarkable.

Now, from what I understand, sunflowers aren’t the most nutritious for bees. Is that correct? I’m really glad that you asked about that. Sunflowers are low in protein and missing a couple of amino acids that are necessary for honeybee development. So if you ask a beekeeper about sunflower pollen, they’d be like, that stuff’s garbage.

You know. And if you try to raise bumblebees too on a diet of pure sunflower pollen, they do very poorly. So the solution is not plant sunflowers everywhere. Um, I also want to say something about the specificity of bumblebee species this is affected by, but I want to answer your, this question right now first.

We, the other reason that we often use buckwheat as our control is that it is similarly low in protein. And so it’s nice that we’re [00:13:00] comparing two pollens that both have low protein, but have very different impacts on infection. So I don’t think protein differences are the cause of the effects that we see.

I do have a new, okay. So yeah, but we have found that if you mix sunflower pollen in about a 50 50 ratio with wildflower pollen, that seems to, the bees, the bumblebees seem to do okay on that relative to a pure wildflower pollen and you still retain the, um, the parasite reducing effects. So you can get this kind of

middle ground of a mixed diet where you seem to be able to get, at least in the lab, maybe the best of both worlds where you have enough wildflower pollen to have reasonable sort of colony growth and performance, but enough sunflower pollen to suppress the infection. But you still wanted to know more.

What did you do next? We purchased bumblebee [00:14:00] colonies, confirmed that they were starting out without Crithidia or other infections that we could detect visually, um, under the microscope, and then deployed bumblebee colonies out at 20 farms, 20 different farms that varied from having no sunflower to as much as we could possibly find.

And then we would assess, we would kind of go to each of these colonies and collect foragers that were coming back to the colony and assess them for pathogen infection. And then also track how the colonies did over the course of the season, because we really didn’t know like, okay, maybe having more sunflower might reduce infection, but maybe also the colonies will do poorly because sunflower’s not that nutritious and yeah, it’s no good

curing the common cold, if you’re going to starve in the process, and we want to know, like, what are the costs and benefits of sunflower for the colony, not just for individual bee infection levels. So yeah, so that [00:15:00] was a lot of work. We also quantified, every flowering resource on those farms that bees use.

So you know, maybe what matters is not how much sunflower you have, but the diversity of different things that are flowering at the farm or somebody, I thought mince had some interesting chemistry or maybe, maybe, you know, total floral abundance on the farm. Like we were able to look at other predictors too, and we looked at other

pathogens in the bees too, we had some of the bees we looked at with visual methods where we could look at three pathogens that you can see in the gut under the scope. But we also sent some of the bees to a molecular collaborator, Quinn McFredrick, who analyzed them, who could look at those pathogens, but also a bunch of viruses.

But the big story that came out was really sunflower sort of stood out as being the floral resource that mattered and its impacts on Crithidia. And we did find. It’s really gratifying when sort of something that you see in the lab [00:16:00] actually plays out and has an impact on sort of realistic scales too, and we found that the more sunflower in the, at the farm, the lower the probability that bees would have a detectable infection.

And if they did have an infection, the lower intensity that infection would be so like lower, less chances that you’d be infected at all in the ways that we could pick up and if you were, the infection was sort of lighter that the more sunflower at the farm, the more daughter queens, those colonies produced.

So sunflower having this dramatic effect, increasing the number of daughter queens that a colony is producing means that it actually seems to be improving the reproduction and sort of how well colonies are doing. Um, so if there is a nutritional cost, it seems to be being outweighed by the benefits of really knocking back infection in the fall when colonies are sort of [00:17:00] in that reproductive stage.

So, yeah, we got those results and I read it as like, oh, sunflower is reducing infection. That means bees are able to forage better. They don’t have to expend resources into fighting off infection. They can, they can reproduce more. Now, this, this focus study focused on one type of bumblebee. Do you believe this disease fighting effect from sunflower pollen may cross over into other bee species?

You’re asking all the right questions. I’m so glad. It’s like all, you’re hitting all the points I think it’s really important to me. That’s great. Thank you. You’re asking perfect questions from my point of view. So that was our next thing is like we’ve been doing all this research in common eastern bumblebee.

And does this impact other bees? The beekeepers want to know about honeybees, of course, but we’re also interested in other bumblebee species because common eastern bumblebee is actually not in decline. It’s doing quite well, whereas other bumblebee [00:18:00] species, many of them are disappearing and kind of common eastern bumblebees sort of filling those niches.

So, um, it’s harder to work with other bumblebee species because they’re not commercially available. And so to do other species, what we have to do is catch queens in the spring. So that was a few weeks ago. We were all out netting queens and then try to convince them in the lab to set up shop. And make a little nest and rear up their workers in the lab and, and wild queens are quite finicky and some species are easier to get to settle than others.

And they have certain temperature requirements, certain humidity, you need to put them in a dark room and not disturb them. Like, it’s, it’s definitely an art that some of my grad students are have cultivated that I don’t necessarily have, but, um, yeah, so it’s a lot more work, you’re going to have fewer bees to work with, but my former graduate student, Alison Fowler

um, was able to rear enough of three other bumblebees species to be able to test [00:19:00] sunflower pollen on them. The other trick is that like, what Crithidia are you going to use? So like we use, you know, for all of our experiments, we maintain Crithidia in bumblebees in the lab. But is Bombus impatiens Crithidia, the right Crithidia to use for a different bumblebee species or with, you know, I mean, they definitely, they share Crithidia back and forth, but I don’t know how much

sort of different Crithidia strains might be adapted to different bumblebee species. So we were trying to get the Crithidia from each species to work with, which means you have to hope that you catch some queens that are actually infected with that Crithidia to rear. So it’s just, it’s just logistically not straightforward.

I would call that a logistical nightmare actually. Yeah, yes. That’s, that’s fair. She was able to pull off three species, three other species that she tested, and two of those species if you kind of sort of squint and look at it right, sunflower [00:20:00] sort of kind of reduces infection a little bit. Oh, we also did wild common eastern bumblebee species because we’d always been working with commercial ones.

And, and sunflower did its sunflower thing in wild, wild common eastern bumblebee just as well as it did in commercial. So it’s not a commercial wild difference. It seems to be a species difference, but those other wild species, two of them. It sort of reduced infection a little bit, but not super dramatically the way it does in common eastern bumblebee.

, and then in, um, one of the other bumblebee species, it’s like no effect at all. We had really big sample sizes for that species, really clear and there’s like sunflower doesn’t do anything, um, which is fascinating for a variety reasons, but, but it also again suggests that like now, like if we’re going to make recommendations, we want them to be responsible ones like, um, so sunflower pollen, [00:21:00] I feel very confident benefits common Eastern bumblebee.

 . Um, so like if, if your goal is you’re a grower and you’re purchasing colonies from bubble bee colonies to benefit your crops or for whatever reason, I feel comfortable saying growing sunflowers is going to benefit those colonies. But if your goal is sort of bee promoting bee diversity in a broader context, is it going to help?

Like if we plant more sunflowers, that’s going to benefit a bumblebee species that’s doing well anyway. It has less benefits, as far as we can tell, on some of the other bumblebee species that are not as abundant. So are we just helping the competitive dominant bee even more competitively dominant? Is it going to, you know, crowd out these other species?

Or by knocking back pathogen in bee, by far the most abundant bumblebee species out [00:22:00] there are we sort of lowering the amount of disease in the whole community in a way that might sort of have knock on benefits for these others by just reducing how much Crithidia is out there? What do you believe is the biggest threat to native bees now and what can we do to help?

There are a lot of smart people studying this issue much smarter than I am, and I, if there were a simple answer, we would have figured it out already. But there’s so much in the way that we have changed our land use. I mean, if you look at sort of a map or a visual of what countries and their lands look like, and relative to a hundred years ago, the way that we’ve imposed so much monoculture, so much intensive, I mean, I think intensive agricultural practices, to be honest, but you know, converting [00:23:00] land to houses, converting land, land conversion, lack of habitat.

But intensive agriculture and all of the things that come along with that. And that’s a challenge and a struggle. We need to eat there’s a lot of people to support on this planet I’m definitely not vilifying farmers who work very, very hard to make a living that is not easy to make and have a lot of challenges and things to be supported.

But there is rampant use of pesticides in cases where context where it’s not always clear that there’s benefits. One of the challenges is, um, seed treating. So, um, a lot of, of companies have, have produced seed coatings. So a crop and it’s got a seed coating, a pesticide on it that then gets taken up by the plant.

And so that’s sold as some kind of, you know, it’s a lot of, it’s like it’s marketed as like an insurance policy. You know, this is a way you make sure that you don’t need to treat later, because you’ve sort of baked in the [00:24:00] pesticide to the plants from the start. But the challenge with that is that you then committed to using this pesticide, whether you need it or not.

Um, and, and many of these pesticides are ending up in the, are systemic, and they end up in the nectar and the pollen. Several of the neonicotinoid, uh, pesticides do that. And so there’s, there’s multiple issues with that you know, one, you’re putting a lot of pesticides into the environment. That don’t break down that easily and that aren’t necessarily needed.

There’s a lot of, Scott McCart has done a nice meta-analysis of sort of all the situations where people have used seed treated or not and whether it actually improved yield. And in many cases it doesn’t, sometimes it does, you know, sometimes these things make sense in certain crops, in certain places with certain pests, but by and large, an awful lot of the time it’s, it’s not helping.

It’s often hard to buy bulk seed that’s not seed [00:25:00] treated these days. Like if you actually don’t want to put pesticides on your crops, it can be hard to, to find that. And in many cases it’s not helping. So there’s sort of this, an indiscriminate use of pesticides in contexts where they’re not needed. You know, I’m sort of a fan of nuance and using things in the situations where it makes sense.

I rarely find the world is as black and white as people would like to make it seem. Pesticides can be valuable tools in an arsenal, but I would like to see them be more of a last resort and not a first choice. There’s a lot of integrative pest management methods out there where you work with the biology of your pest and you, you do regular sort of checking

and if you get above a certain threshold, then you treat, but it’s not the first thing that you do and you use other methods to try to keep your pests off of your crops as that’s, I mean, as far as what we can [00:26:00] do a regular sort of citizen who’s not a grower, certainly avoiding pesticide use in your own home growing, unless it’s really necessary, allowing mowing your lawn less frequently.

How good of a message is that? Like mow your lawn a little less often, you know, let the clovers and the dandelions and some of these other resources, flower and do their thing that it’s, it’s can support a surprising amount of, of diversity. Um, certainly if you have the opportunity to plant flower’s, great.

It’s great to focus on native perennials if you can. Mowing your lawn less frequently. Only using pesticides as a last resort. Lynn and her team discovered some fascinating insights. But like we discussed, there’s still so much more to learn. There’s a link in our show notes to Lynn’s lab at the University of Massachusetts so you can see the latest findings from her and her team into pollinators, pollen, and [00:27:00] more.

Thanks again to Dr. Lynn Adler for joining us today, and thank you for listening. It would mean a lot if you could leave a review, follow the show, and tell a friend. Keep buzzing.