86 Dr. Priyadarshini Chakrabarti – The Secret Life of Bee Nutrition (in English)

Speaker 1: From the Oregon State University Extension Service, this is Pollination, a podcast that tells the stories of researchers, land managers, and concerned citizens making bold strides to improve the health of pollinators. I'm your host, Dr. Adoni Melopoulos, assistant professor in pollinator health in the Department of Horticulture. What makes a bee a bee? In past episodes of Pollination, we've talked about some of the broad nutrients that bees get from flowers, namely the protein from the pollen and the carbohydrates from the nectar. But in this episode, we're going to uncover the secret world of the micronutrients that are in that pollen and nectar. And to help us do that, I've invited Dr. Priya Chakrabarti to the show.

Now Priya is a postdoc here at Oregon State University working in Dr. Ramesh Sagheeli's lab, and you'll remember Dr. Sagheeli from previous episodes. In this episode, Dr. Chakrabarti is going to be focusing on the micronutrients of pollen, primarily looking at honeybees. But as she'll mention later in the episode, a lot of this probably applies to many of our native bees, although should we have an interesting discussion about how it may and may not apply? Anyways, this is a nutrition-filled episode of Pollination. I hope you enjoy it. Welcome to Pollination, Dr. Chakrabarti.

Speaker 2: Thank you, Antoni. It's very exciting to be here.

Speaker 1: Which is just down the hallway from your office?

Speaker 2: Yes, and I'm glad it's inside because of the really wet, gloomy weather today here.

Speaker 1: It is not a nice day out there today. And I guess it's not a day that bees are out forging for sure here in Oregon. But when they do, and we've seen our very first pollen blooms here, everybody knows from this show, I'm sure by now, that bees are looking for nectar and pollen. And they know that the nectar is the carbohydrate source and the pollen is the protein source. But clearly, when we think about ourselves, we can't just live on carbohydrates and proteins alone. There are all sorts of other nutrients. Can you walk us through what are some of the key nutrients that are required to make a bee?

Speaker 2: So when we talk about bee nutrition, we mostly tend to focus on macronutrients, which are proteins and carbohydrates. But micronutrients, are equally important, even though they're required in smaller quantities. For bees, as you mentioned, proteins, and carbohydrates, are the micronutrients that pollen and nectar provide. But pollen also provides vitamins, and minerals, for example, salts, as well as sterols, which are like a group of lipids. But pollen is basically the only source of these critically required micronutrients for bees.

Speaker 1: Okay. So the nectar is really just providing the carbohydrates, but everything else is in the pollen. The pollen is really important.

Speaker 2: Nectar does tend to provide a tiny bit of the other nutrients, but it's like a major chunk is carbohydrates. So pollen is their only source.

Speaker 1: You know what I think about? Natural source. We think about some of the other pollinators, like hummingbirds will eat some insects and butterflies are going to eat some plant material.

This is a very, they've got a very specialized diet eating this pollen. Yes. Okay. One thing you mentioned there, and I know it's a key area of your research is sterols. Correct. What is a sterol and how does it function in bee development?

Speaker 2: So when we think about sterol, for example, in the animal system, we think of cholesterol. Similarly, the plant-based sterols are phytosterols. And this is what we are trying to look at for improving bee health. So these sterols, are a form of lipids. But what I have to mention is that there is a term called sterol oxotrophy, which essentially means the inability to produce sterols. All insects, including honey bees, in fact, all bees are oxotrophic for sterols. They cannot synthesize their own sterols and they have to sort of obtain these sterols through their diets. Gotcha.

So now we might wonder why the importance of sterols. Just to give you a brief background, we know that for an insect, the life cycle basically comprises egg, larva, pupa, and adult. In between this larval and the pupal stage, there are actually various, you know, like sub-stages, so as to say, like different insters, different stages of larval moltings that happen. So for a larva to molt into its successive stages, it needs molting hormones, like 20 hydroxydeicin, juvenile hormone, and it's usually a combination of the various titers.

Speaker 1: Okay. So these are hormones that the bee is making itself. Yes.

Speaker 2: And they're regulating. Within its physiology. Okay. So these sterols, are the precursors for these insect-molting hormones.

Speaker 1: Without these sterols, you would not have the successive generations forming. Okay. So the bees have to eat the pollen. The pollen has to get into the bee and then it gets turned into these molting hormones and that's what allows the bee to go from an egg to a larva to a pupa to an adult.

Speaker 2: And just like, as we all know, nurse bees, the young adults, they are the ones who basically consume these pollen and they are the ones who feed the colony. So bees inherently have endogenous sterols. So these are the sterols that they acquire from their diets. They store it in their bodies and they continuously supply these sterols to the growing brood through brood food.

Speaker 1: Just to take one step back because we've had a lot of people on the episode who've talked about solitary bees. And so the idea of nursing is a little weird. So in honey bees, it's unlike the solitary bees in that that young bee is going to eat the pollen and then they're going to metabolize it, I guess. Yes.

Speaker 2: It is a little different for honey bees because the diet that comes to the developing brood is through brood food, which has already been like semi-processed by the nurses. And on that interesting note, there are some studies. Not much is known about the sterol requirements in all bees. As I mentioned, mostly because they are important precursors for molting hormones, they are also building blocks of cellular membranes. So that is why we are trying to focus on them because, without these sterols, you would basically have a dead bee.

Oh, I can see that. OK. In honey bees, there is this one particular phytosterol, 24 methylene cholesterol, which is very important. There are some studies that have shown that bumblebees prefer pollens which have higher beta cytosterol and a little of 24 methylene cholesterol. So we are just trying to slowly understand, you know, as to what are the different sterol requirements across the different bee species, be it managed or solitary. OK.

Speaker 1: So we don't know a lot and it could be different sterols are important for different bees. Right. But the key thing is that in honey bees, the bees have these glands in their heads right to eat the pollen and then their body metabolizes it. And they turn it into this food that they're going to feed to the young. Correct. And that's how the young are going to get these sterols. Right. That allows them to do the next stage of development.

Speaker 2: To go to the next stage as well as they store the sterols in their body.

Speaker 1: Oh, wait, you mentioned that. The endogenous sterols. So when they grow up as an adult, they still have some sterols in their body.

Speaker 2: Stuck in their body. OK. All right. OK. That's very complicated but very fascinating.

Speaker 2: It is. And bee nutrition is actually we say that nutrition is probably a honeybee colony's first line of defense because a healthy bee, a well-nourished bee, can fend off pests, and parasites, as well as, you know, counteract pesticide stress better.

Uh-huh. And not much is known about the requirements of sterols and honeybees. There were some studies that were done in the late 1970s, and early 1980s. But then there has been this massive gap in knowledge for the last couple of decades.

Speaker 1: A scientist was working on it and they tragically died at some point. Elton Herbert. OK. So you're picking up that legacy. It's sort of like we are trying to.

Speaker 2: So as I'll talk to you later about it, like we did base some of our experiments starting, you know, from where he left off.

Speaker 1: Uh-huh. OK. All right. So we've got, but I also, imagine sterols are just one part. And you talked a little bit there. He said, well, you know, a big overarching goal is if we understand bee nutrition, then maybe it has these broader implications. Before we take a break, can you talk a little bit more about sort of why knowing these micronutrients and working this out is so important? Maybe just restate it. You mentioned it a little bit.

Speaker 2: Basically, the thing is that as I said before, micronutrients are also important even though they're required in smaller quantities. But holistically, looking at nutrition, it's just not one factor. It's a combination of all the nutrients that will eventually lead to optimal nutrition for a bee. So what we are trying to eventually look at is how to improve bee health.

And of course, we are now looking at sterols specifically trying to understand what is the optimal concentration of sterols, how much of it is required, how it may affect a bee and eventually trying to tie the story together as to how a well-nourished healthy bee can counteract pesticide stress, diseases, parasites, pathogens. Great.

Speaker 1: Well, let's take a break. I want to hear more about I know you've got a lot of research going on. It's almost dizzying how much work you're doing. So maybe we could work through how you're trying to address this problem in your current research. Absolutely. All right. Okay.

We're back. And so I want to know tackling this question, this, you know, legacy of neglected research on sterols. How have you started to go about asking questions about the role of steroids? How much sterols? Tell us how you started asking these questions.

Speaker 2: So when I joined the OSU Honey Bee Lab, Ramesh Sagi Lee, my PI, had already conducted some previous research where he was trying to look at colonies with some artificial supplements, as well as looking at colonies that were fed with natural multi-fluoro pollen. What he found was that after a point of time, colonies that were fed with pollen definitely survived and had brood. But the colonies which exclusively survived on these commercial diets, did not have any brood after a few weeks. So I guess the question that we started to have at that point in time was that is there no brood formation or if there is brood, it's not surviving. And if there is a dead brood, are the bees cannibalizing their larvae?

So having tried to look at that. So we sort of started addressing the question on sterols. Like if sterols are important, how much of it is required? And what would we call an optimal concentration? Okay.

Speaker 1: So let me just get this straight. So what Dr. Sighili did is he fed this artificial diet, which is made of.

Speaker 2: It's like a commercially available supplement and there are actually.

Speaker 1: It's not pollen. It's some kind of artificial.

Speaker 2: I honestly don't know what it's comprised of. I mean, the package detail would probably say.

Speaker 1: So there's some kind of thing that's not pollen. And when he fed that exclusively, he'd find that the process that you described in the first part of the interviews was interrupted. They didn't, and in some cases, they didn't seem to grow.

Speaker 2: Yes. After a number of weeks. But if you had full pollen in them, they would. Yes. And so you were wondering if the sterol might be what's missing? We were wondering if it's sterol that's missing. Okay.

There were also other recently published papers in the last two, or three years where this group showed that bees surviving exclusively on artificial supplements did not perform as well as bees, which had access to multifloral pollen. Okay. So it's not just us. There are groups who are kind of like discovering it. So what we thought was that if it is sterols, which is critically missing, then how much of it is required and what can we call an optimal concentration? So Elton Herbert, the scientist that I mentioned, had a seminal paper where he treated his bees with an artificial diet. We sort of built our artificial diet on that. So what he did was he added 0.1% dry diet weight of sterols to his artificial diet. Okay. But we had this question because it was not well, I would say, substantially explained in the paper as to why he chose that concentration. And we are, we also wondered that naturally.

plants sterile can range anywhere between 0.1% to maybe even 8 to 10%. Oh really? Yes.

Oh okay. So we were wondering what can we call an optimal concentration because we know it's a micronutrient. So we will not require a ton of it, but bees will require a critical amount.

Okay. So we built our artificial supplement on Herbert's work and we had equal quantities of proteins, carbohydrates, vitamins, and salts to these diets. We tweaked the concentration of 24 methylene cholesterol in these diets and then we checked for their survival. We checked their physiological responses. We checked their lipid contents, and their head protein contents and we were trying to see at which concentration these bees sort of performed better.

Speaker 1: Okay. I mean because the only thing that differed in these diets was the amount of sterile. Yes. Correct. Okay. So then you can figure out the effect of a sterile.

Speaker 2: Yes. That's it. And our main focus was on 24 methylene cholesterol because as I mentioned before it is the key phytosterol for honey bees. Gotcha. Okay. So we had it synthetically made and that was a little trouble because we also tweaked our molecule and we ran a lot of experiments with it trying to also see the translocation of this particular sterile across the bee tissues. And that was one baseline study that we did, an extensive study in 2017 summer. And based on that, this was done in the lab. We kind of concluded that perhaps 0.5% seems to be an ideal concentration.

Speaker 1: The 0.5% of dry diet weight of 24 methylene cholesterol.

Speaker 1: So this is higher, this is like five times higher than that paper that you read.

Speaker 2: Okay. Gotcha. Yep. So what we then decided to do was last summer we conducted this extensive flight cage study. It's like a semi-field study. Yeah. We had many nucleus hives set out in each of these flight cages and we treated each of these colonies with the same artificial diet formulation but with 0.5% sterile. Okay.

Speaker 1: So the previous experiment was like bees in a cage or something. In the lab. Okay. So this is an actual, so now you're looking, you look at the colony performance.

Speaker 2: All right. So we want to see how the colony performs. We had different versions of the diets, negative controls, and positive controls. So we had different ways we tweak the diet.

Okay. But one of those treatment groups definitely had 0.5% of the sterile. We are looking at the colony performance, brood production, and brood development. We are trying to see the physiology and the overall health of the colony and the individual honeybees.

Speaker 1: Why did you put the bees in a cage?

Speaker 2: We put the bees in a cage. This is because I mean, we do not want the bees to feed on natural pollen.

Speaker 1: All right. You just want them to eat the diet you gave them.

Speaker 2: Gotcha. All right. Even though we put them, some people might ask us like, why didn't you just trap on a pollen trap, you know, and then have the bees? But then there are so many, you know, nooks and crevices and there are so many ways a beak and just like sneak something in. So we wanted it to be an absolutely tightly controlled experiment.

Speaker 1: Okay. So these bees are the only thing they were eating and how long does it run for?

Speaker 2: We ran it for almost 10 to 12 weeks.

Speaker 1: So these bees were in this cage eating nothing, but this diet, which may or may not. Oh, okay. So can you tell us a little bit of what you saw?

Speaker 2: It's still a little preliminary because we've got over 12,000 images

Speaker 1: data points and we need to analyze it. So it's taking us a while. But of course, the pollen, the bees, which were fed with a multi floral pollen, they, of course, fed way better than any other group. But what we at least found was that the ones treated with this 0.5 percent sterol diet, were not so bad. Yeah. Okay. So the ones who were treated

Speaker 2: With the 24 methylene cholesterol, the synthetic version of the sterol in the diet, they fed pretty well compared to bees, which had no sterol whatsoever.

Speaker 1: What about the ones that didn't have either the pollen or the sterol? What did those colonies look like?

Speaker 2: They were almost crashing. I think we started with the very, I mean, so we equalized all the hives and we had like equal strength colonies going in sister queen. So we had like a very, you know, tight experimental control when we put them all in. But towards the end of the experiment, I mean, I'm still giving you like very preliminary what we saw, the control groups, which had no sterol whatsoever, or any pollen going into their diets, I think they were only left with like half a frame of bees at the end.

Speaker 1: So then we know the sterol. So your, you're, your thought worked is actually this concentration of sterol added to the diet is mitigating. It was starting to mimic.

Speaker 2: We are seeing some hopeful, you know, we are seeing some positive results. But as I mentioned before, it's just not one nutrient. It's like a combination of various factors. So we are focusing on phytosterols, specifically 24 methylene cholesterol for now. We are hoping to sort of also look at the other various factors that go into it.

Speaker 1: Now, I know we've talked about this before. This stuff is not cheap. It's not very expensive. So how will this be relevant for beekeepers? They obviously can't, you know, it's a great question.

Speaker 2: I'm glad you asked me that because this is also something that often people ask me. The reason why we used a very expensive synthetic version is because we want to know how much of it we are adding to the diet.

Speaker 1: That makes sense. Otherwise, you wouldn't know if it was this or something else.

Speaker 2: Exactly. We wouldn't know. I mean, there could be so many other forms of lipids that can go into the diet, which may have sterols in some version or the other. So we wanted to have this exact idea of how much of this particular sterol we are adding. But if you look at a beekeeper's perspective, if you look at like, you know, a very feasible, practical way of cheaply resourcing it, what we are now into is like a phase two of our experiment. So we have developed protocols in our lab with the help of the mass spec center here at OSU. We've got this fantastic gentleman, Jeff Murray.

He's like always excited to work with bees. So what we've done is we've established these protocols for quantifying in PPM. And let me focus on that. This is because a lot of papers that you'll see, they'll give you the relative percentage of phytosterols in pollen.

Okay. Or in other samples. But we have what we have done is it took us months to do that.

But now we have this expertise in our own lab where we can exactly quantify about 10 to 12 different phytosterols from not only pollen samples but also vegetable oils, commercial diets, and any other source that you may think bee colonies are given as their diets. Okay.

Speaker 1: So you've checked a whole bunch of different things that are way cheaper. Then the actual ingredient. Yes. That may actually have this compound in it. So you could use that instead of the. So were you able to find anything?

Speaker 2: We were. Actually, we find that the pollens. So on this, I have to say we only were able to test about eight different pollen types. I mean, we are going to continue the study we collect as many samples as we can. So we tested eight different pollens and three different vegetable oils. We tested one very commonly used commercial diet.

24 methylene cholesterol was definitely abundantly present in the almond pollens. Oh, and we did not find it much. Actually, it was like barely there. True. Very trace amounts in the commercial diet.

Speaker 1: That explains why people have been observing. They don't do so well just on that alone.

Speaker 2: Yes. All right. We also found a varying concentration, not so high as the pollen samples, but somewhere out there in the middle for the three different vegetable oil samples that we tested.

Speaker 1: Oh, so you might be able to in the future, as research progresses, Beekeeper may be able to take one of those commercial diets and add some of the oil and be able to. Well, isn't that a great finding? Absolutely.

Speaker 2: You know, just take some of the naturally available pollen or, you know, just add it to your commercial diet or add it to the patty that you formulate or add vegetable oil. Or even if your bees are just sitting out there, you know, in your holding yard or your backyard, just plant maybe these different native plants, you know, their pollens will have this.

So we are trying to build on that repertoire of knowledge. Along with phytosterols, we're also looking at the vast abundance of metabolites that are present because pollens also have phytochemicals, which are important for bees. Phytochemicals, for example, phenolics, and flavonoids. A lot of people are studying P-coumaric acid and quercetin.

Even campyphyrols. So there are these other compounds that are present in pollen that are important for bees. So we are also trying to look at the vast majority of metabolites, the amino acid composition, and the sugars. So we are trying to look at it and we are trying to see, like, not only just the phytosterols but holistically also, what is the nutritional composition of this particular crop pollen?

Speaker 1: Do we have any sense of what some of these flavonoids might do?

Speaker 2: Or is it as well worked out? Based on some of the studies, what we've seen is that they definitely improve bee survival. Some of them have reported that these flavonoids, improve bee immunity. So it's like, as I was mentioning before, it's just not like one miracle compound, which will be the solution, but it's like bringing together the holistic approach of looking at it. But we definitely are focusing on phytosterols to begin with, because this was neglected for years. Wow.

Speaker 1: Sounds like you've got your work cut out for you.

Speaker 2: Yes, yes a little. As I mentioned before, like personally, like I've worked with pesticides for over six years before I started working on bee nutrition. So for me, it is always interesting to see how these multiple stress factors can be negated or offset with, you know, improved bee nutrition.

Speaker 1: It's a great promise. I know there are bees in Oregon, they have to go through a lot of managed landscapes over the next few months, and being able to have something to help them mitigate some of those negative effects will be great.

Speaker 2: And the results we find, hopefully, I mean, it will definitely be an additional boost for beekeepers and the, you know, managed honeybee colonies. But I guess the information can also be translated for native bees because if you know what is present in pollen and you know what bee needs, you can actually have this fast knowledge database right in front of you. Fantastic.

Speaker 1: Well, let's take a quick break. We have a couple more questions to ask you. Ask all my guests these questions. Okay, after some negotiation, I think we got your three things down. The first thing is, I don't know, is what your favorite book you want to recommend to the listeners is.

Speaker 2: I really enjoyed reading this book. I have to say this book I read only after I moved to the United States. Tom Seely's Honey Bee Democracy. Oh, yeah. I really enjoyed that book. Obviously, I mean, it's a beautifully written book. It's got its simplicity for general people to understand who are not bee biologists. But it also has these little excerpts, scientific notes diagrams graphs, and studies, which kind of also very beautifully neatly ties the story together.

Speaker 1: He's such a great communicator.

Speaker 2: Yes, he's a master and that's his masterpiece.

Speaker 1: What a great recommendation. So the other question we have for you is, do you have a go-to tool for the kind of work that you do?

Speaker 2: I do and I'm kind of a little embarrassed to say this, but it's a bee vac. Oh, yeah. A bee vacuum. I mean, it is an amazing tool. Anything that goes wrong in the lab, anything that goes wrong in the field, you have your bee vac to suck bees in and dump them where you need to be.

Speaker 1: Well, I remember when I was a graduate student way back in the 90s, you couldn't get a bee vac that really worked. You do need a fair amount of suction. A bee does not just go and just just so people understand. It's not like you're they're going you take the bees and you vacuum it and they're actually fine. They can walk.

They are fine. They just walk away. They're going to like it's like some strong wind just suck them into this little vial and then you just take them and you release them somewhere.

Speaker 2: So what we do is we've kind of modified a vacuum cleaner with other tubes and accessories and fittings. And that is like now our bee vac.

Speaker 1: The Segeely Lab.

Speaker 2: Yes, the Segeely Lab bee vac.

Speaker 1: It's only available on special requests.

Speaker 2: Special requests. You have to ask for loans.

Speaker 1: But so what we do is I mean, it's got a pretty neat transparent cylinder. It's a plastic cylinder. So it's not very hard. And as we know bees tend to, you know, just bang their heads if they're confined in a small space.

Yes. So it's got a very neat, soft material, plastic cylinder, which is right in the middle. So when you like vacuum those bees, they sort of aggregate in that little pocket in between and they're perfectly fine. So all you have to do is just open the lid and release them. Wow.

Speaker 2: And this comes especially handy because we share our lab space like it's a massive hall, but half of it is us, the bee lab. The rest half is the Drosophila and the insect pest group. And they don't like the bees flying over there. I'm sure they wouldn't even if they don't say anything.

Speaker 1: I'm sure something that stings and flies around is not a happy sight. Would you be able to share a picture for the show notes?

Speaker 2: Oh, yes. Okay, everybody. I can definitely take a picture of the bee vac. Okay.

Speaker 1: Check the show notes for the bee vac. And the last question is, do you have a favorite pollinator species? Is it honeybees?

Speaker 2: It is honeybees. And I would be a little bit.

Speaker 1: The question would be why?

Speaker 2: Probably because I mean, so I've worked on three different honeybee species. I've worked on apis dorsada, apis sarana, apis milifera. I've also worked on bumblebees in England for a while. And I have to say my pick would be apis dorsada because they are incredibly difficult to work with. And I think the harder they are, you know, to get the more intrigued I am by them. I've spent six years trying to tame them, trying to work on them.

Speaker 1: Sometimes it helps a little bit about apis dorsada. So it's a Southeast Asian bee.

Speaker 2: Yes, it is native to the Indian subcontinent. And unlike sarana or milifera, they prefer open spaces, a lot of air and wind. And that's why you would see these massive hives, you know, these pictures hanging from it one.

Speaker 1: It's just one comb, right? It's one comb. One big, huge comb. Big, huge comb. It's just one frame, so to speak. And are they all, they're usually high up? They're not easy to get at, right?

Speaker 2: Usually, usually. Their combs are massive and they are like way high up in the tree branches or just, you know, hanging from a building ledge. Places you would not expect to see them.

Speaker 1: I remember seeing Dr. Bridgette had a slide of some tree with multiple nests on it. Yes. Which is just like, wow, that looks amazing.

Speaker 2: It is. And, incredibly, he can go to Thailand, you know, try to say your work on these incredible species.

Speaker 1: You and I are stuck here in the rain somewhere in beautiful Thailand. Mike is out there having a good time with all these. He has a great research program over there working with all these.

Speaker 2: That's true. That's that's incredible.

Speaker 1: Well, we are here and I'm glad you're here and you're doing amazing work with the nutrition. Thank you so much. Have you on in the future to learn more about what our bees need to eat? Absolutely.

Speaker 2: Thank you so much. And it's wonderful to be here.

Speaker 1: Thanks so much for listening. Show notes with information discussed in each episode can be found at pollinationpodcast.oregonstate.edu. We'd also love to hear from you and there are several ways to connect. For one, you can visit our website to post an episode-specific comment, suggest a future guest or topic, or ask a question that could be featured in a future episode. You can also email us at [email protected]. Finally, you can tweet questions or comments or join our Facebook or Instagram communities. Just look us up at OSU Pollinator Health. If you like the show, consider letting iTunes know by leaving us a review or rating.

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