06/29/2018

Hive Mind: Inside The Complicated World of Bee Colonies

20:31 minutes

a dozen bees crowded around each other in a hive
A colony of Bombus terrestris bumblebees, with workers attending to the brood. They are filling wax pots with nectar and pollen. Credit: Ash Samuelson

Bumblebees and honeybees are two species of bees that form colonies. The colonies of bumblebees are smaller compared to their honeybee cousins, who’s hives can house tens of thousands of individuals. But both of these colonies have complicated compositions and structures that help them thrive.

For bumblebees, recent studies showed that colonies located in urban areas may actually be more successful than nests located in agricultural areas. Reporting in the journal Proceedings of the Royal Society B, scientists found that city bumblebee colonies produced more individuals compared to their country counterparts. Biologist Ash Samuelson, who is an author on that study, talks about why urban environments might be a haven for bumblebees.  

[You might think this slick dark-furred creature frightening, but one neuroscientist says it’s as adorable as Star Trek’s Tribbles.]

Then, entomologist Ramesh Sagili chats about his study published in the journal Scientific Reports. He examined what happens when the queen of a honeybee hive dies and how the surviving bees choose the next queen.

a large clear plastic box with a smaller cardboard box inside sits uncovered in tall grass
Inside the field nest box, bee colonies were housed in wooden nest boxes. Credit: Ash Samuelson

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Segment Guests

Ash Samuelson

Ash Samuelson is a PhD student in the School of Biological Sciences at Royal Holloway, University of London, in Egham, England.

Ramesh Sagili

Ramesh Sagili is an associate professor in Apiculture at Oregon State University in Corvallis, Oregon.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow. This hour, we’re going to talk about the bees– bumblebees and honey bees in particular. They’re two species of bees that live in communities. And like any group of animals living together, it can get complicated.

First, the bumblebee. When you think about bees, what picture pops into your head? A bee buzzing around a flower in a picturesque field of glowing color. Well, I’m betting you don’t picture a bee in an urban city environment, unless you’re trying to swat one away as it interferes with your morning latte.

Scientists have been interested in how these two different environments affect bumblebees where they live– their nests. Is there a difference in the reproductive success of city versus country living bumblebees? And the results are going to surprise you.

The study was published this week in the journal Proceedings of the Royal Society B. And my next guest is an author on that study. And she’s here to fill us in on the details. Ash Samuelson is a PhD student in biology at Royal Holloway. That’s University of London in Egham, England. And she joins us by Skype. Welcome to Science Friday.

ASH SAMUELSON: Hi there. Thanks for having me on.

IRA FLATOW: And just in passing, how are the bumblebees doing in the UK and Europe? Are they healthy?

ASH SAMUELSON: Yes. Well, there’s a big range of effects of various environmental stresses on bumblebees in Europe and the UK in the same way that there is in the US. But some species are doing well, but other species are really at risk here in the UK.

IRA FLATOW: Now, we talk about bumblebees as living in nests and honey bees living in hives, correct?

ASH SAMUELSON: That’s correct.

IRA FLATOW: Can you tell us what is unique about bumblebee nests, how it’s different from the honey bee hives?

ASH SAMUELSON: So you can kind of think of bumblebee nests as a kind of primitive version of honey bee hives. And so honey bee colonies are huge colonies from 20,000 to 60,000 bees. Whereas in bumble bee colonies, we have about 200 bees at any one time.

So they’re a lot smaller. They’re a lot more simple. So if we think of that really distinctive hexagonal honeycomb structure that you see in honeybees, you don’t see that in bumblebees. So they have this kind of primitive wax pot system that they use to store their honey or their nectar and pollen.

IRA FLATOW: Let’s talk about the study of the living conditions and the success rates of reproduction between the city bee and the country bee. What was the question you were trying to answer and what was the result? So what we were looking at was whether bee colonies– so bumblebee colonies– have higher reproductive success in urban areas compared to agricultural areas.

And we’re interested in this because previous research has suggested that, actually, we’re seeing higher densities of bumblebees and other bees in the city than in the countryside. And we were thinking, why is this? Is it that they’re moving from other areas? They’re just migrating in? Or is it that they’re actually more successful in these areas?

So what we did was, we placed colonies of bumblebees out in the field across a gradient of urbanization. And then we measured various things about their colony’s success. But the key thing that we measured was how many new reproductive offspring they produced. So how many new bumblebee queens and males were produced out of these colonies?

And what we found was that colonies in the urban landscapes produced more reproductive offspring than those in the countryside, which basically means that they’re more fit. So it’s kind of the key in biology. You want to be able to pass your genes on to the next generation. And that’s what’s happening here. Those populations are going to be stronger.

IRA FLATOW: You know, that’s so counter-intuitive to what we would think.

ASH SAMUELSON: Right.

IRA FLATOW: Why are they more successful in the city than they might be in the country?

ASH SAMUELSON: Well, yeah. So it sounds counter-intuitive initially, because we think of cities as really unnatural environments and the countryside as completely natural. But actually, that’s not the situation at all.

So the kind of countryside that we have in England and a lot of the world now is this very intensive agriculture. And this is very different to the environment that the bees evolved in. And so what I think it more showed, rather than urban areas are particularly ideal for bees, is, it really shows agricultural areas are not that good. And this is probably because of a combination of things.

And I’d say the main two candidates for that are pesticide use– so exposure to agricultural pesticides in the agricultural areas. This has been shown to negatively affect colony success in bumblebees– but also forage availability.

So we know that cities and towns have huge amounts of floral resources in gardens and parks, whereas, in the countryside, actually, there’s really not that much, in terms of wildflowers, when you’ve got huge areas of monocultures and not that much for bees to feed on.

IRA FLATOW: So there is enough, then, in the cities and urban environments. There’s enough food and resources for the bumblebees to survive and seem to do very well.

ASH SAMUELSON: Yeah, absolutely. Yeah, so we can’t say for certain that it is because of the food. Because our study doesn’t show the mechanisms behind the increased colony success in the urban areas. But we do find indicators.

So one of the results that we had was that bees in the city were more likely to contain food reserves, which suggests they have plentiful food coming in. So they have a surplus, so they’re able to store it. So there are definitely suggestions that there is lots of food available in the city.

IRA FLATOW: You know, we talk about bees a lot on Science Friday, and we know that they have natural enemies. They have parasites, things like that. Do the city bees have the same kinds, or less?

ASH SAMUELSON: Yeah. So we looked at two types of parasites in this study. We looked at internal parasites– so what we think of as diseases. And we found, actually, that there was no difference in the amount of parasites that were in the bees in the urban and the rural environments.

But we also looked at a different type of parasite, and that’s a brood parasite. So these are called cuckoo bees. And so they are very, very similar to the cuckoo bird.

What they do is– it’s a type of bumblebee. So it’s a different species of bumblebee. And what they do is, they come in and they steal the nest of a buff-tailed bumblebee, which is the species that we did our experiment on.

So they come in when the nest is already established. They’ve got lots of worker bees ready to go. They’ve got lots of food stores.

The cuckoo bee comes in, kills the queen, and then takes over the workers for herself. And she doesn’t have to produce any workers. She gets all that work done for her.

So we also counted the number of invasions by cuckoo bees in the urban environment and in the rural environment. And we actually found that there were fewer invasions in the city than in the countryside. And in fact, in a very central city, we found no invasions by cuckoo bees at all.

So there’s a number of reasons that this could be. But one of them could be that the smell of the nest, which is how cuckoo bees locate them, could be masked by pollution from cars and such.

IRA FLATOW: So there’s a silver lining to all the pollution and noise and whatever in the city.

ASH SAMUELSON: (LAUGHING) Yes, exactly. Yes. I’m not necessarily advocating for more pollution to save the bees, but–

IRA FLATOW: [LAUGHS] I know you’re not. Is there anything we city-dwellers here in New York can do to help the bumblebees survive better? Anything we can help them with?

ASH SAMUELSON: Yeah. So I think what our study is showing is that cities can provide a refuge for bees in the fact that they do provide so many floral resources. But not all flowers are good for bees.

And a lot of particularly the very highly bred horticultural varieties of flowers can actually provide no nectar at all, or they’re so showy that they’re actually inaccessible by bees. So it’s really important, when people are planting their gardens and trying to attract bees, to really look up– and there’s lots of information available online about which plants are particularly attractive to bees.

And once we completely fill our cities with flowers, then they do provide a really good resource. But I think we also need to be doing that in the countryside. I think what this is highlighting is how much more we need to be focusing on increasing floral resources in the countryside than in the city.

IRA FLATOW: So planting diverse kinds of very simple flowers– showy, simple flowers.

ASH SAMUELSON: Yes, so more simple flowers is generally the case. It’s not a hard and fast rule. And there’s research out there to say which flowers are better and worse. But generally, the really highly bred varieties are inaccessible to bees.

IRA FLATOW: Yeah. I see them all over the clover and things like that, just simple stuff. So what else would you like to know? Where is your research taking you, in what direction?

ASH SAMUELSON: So the way we’re heading now is to really delve deeper into that foraging question. So what are bees foraging on in the city, and is it easier for them to find food?

So actually, we’re switching over to the other type of bee that you mentioned in your intro, the honey bee, for this experiment. So what we’ve been doing is, we’ve been using the honey bee waggle dance, which is a unique form of communication that honey bees have. And bumblebees don’t have this, which is why we switch over to the honey bees.

But what it is is, the honey bees perform a dance to tell their nestmates where they’ve been forging– so where a really profitable patch of food is. And so we can decode this dance and track where the bees have been going. So we’ve done that across urban areas and rural areas with hives that we’ve set up in those areas. And then we’re plotting out where they’re foraging. And we’re saying, are they having to travel further to find food in the countryside than in the city?

IRA FLATOW: So you’re involved in that study right now?

ASH SAMUELSON: Yes. Yep. That’s in the works.

IRA FLATOW: How many hives do you have to put out to study them? What does it take? Is it 10, 20, 100?

ASH SAMUELSON: So with the study that we’re talking about now, the bumblebee study, we put out 38 hives. So generally, because the colony itself is kind of the unit that you’re measuring, you end up having to work with any kind of social bee or ending up having to work with a lot of bees in total. But you’re working on that colony as the individual unit.

IRA FLATOW: Wow, it’s fascinating. I wish you great luck.

ASH SAMUELSON: Thanks very much.

IRA FLATOW: And good luck in your PhD work.

ASH SAMUELSON: Thank you.

IRA FLATOW: Ash Samuelson is a PhD student in biology at Royal Holloway University of London in Egham, and she joins us by Skype. Have a good weekend. We’re going to take a break, and when we come back, we’re going to talk about the queen bee. We’re going to switch to honey bees, talk about the queen bee.

What does the hive decide to do when they lose the queen? We’ll talk about it– it’s fascinating– after the break. Stay with us.

This is Science Friday. I’m Ira Flatow. Last month, the royal wedding of Prince Harry and Meghan Markle was a big event. But for the British royal family, everyone already knows who’s next in line for the throne after Queen Elizabeth. Sorry, Harry.

But for another type of monarchy, that line of succession is less clear. And I’m talking about honey bees. If a honey bee queen suddenly dies, it’s up to the rest of the hive– her kids– to pick who takes over. But how do they make that decision?

Researchers wanted to know how the hive comes to this decision and their results were published in the journal Science Reports. Ramesh Sagili is author of that study. And he’s also an associate professor in apiculture at Oregon State. Welcome to Science Friday.

RAMESH SAGILI: Hi, Ira. Thank you.

IRA FLATOW: That’s the study of bees, right– apiculture?

RAMESH SAGILI: Yeah, study of bees, or keeping bees as well, yeah.

IRA FLATOW: Keeping bees. Tell us a bit how the structure of a honey bee hive works. How many queens would the average honey bee hive go through?

RAMESH SAGILI: Yeah, so in general, when we talk about a functional hive, there is only one queen. And in rare instances, you will see multiple queens. But usually, it’s not. So I would say 99% of the time, there is only one queen in a hive. And thereabout, it depends on the time of the year. There could be anywhere between 25,000 to 50,000 bees.

These are female workers. They are sterile. That means they don’t lay eggs as long as the queen is in the hive.

And then there are drones, which are the males. And their only function is to mate with virgin queens that are produced during the swarming season or even later. So basically, that’s the structure.

They have very well-defined caste system with a queen who is the egg-laying machine. She keeps laying eggs throughout her life. It could be two years to five years. And then they produce drones seasonally. Maybe they are about 5% of the colony’s whole strength.

So when a queen bee suddenly dies, the hive has to find an emergency queen, right? Why would a queen die suddenly?

RAMESH SAGILI: Yeah, that’s an emergency situation. That’s way this term has been used for a while– emergency. Because queens are made at different times of the year as well based on their need, like swarming. When you see all these huge swarms coming in May or June, when the colonies get to a certain strength, they have to divide. So it’s a colony [INAUDIBLE]. So they have to divide the colony reproduction.

So at that time, queens are produced. That’s more natural. But then, emergency arises when a queen accidentally dies. It could be because the queen was infected with a disease or she had some parasite load. Or it could be a beekeeper as well. As beekeepers, we try to manipulate hives. And accidentally, she might be smushed between the frames or the tool that you’re using. So there could be multiple reasons why a queen can die.

IRA FLATOW: Huh. So how does the hive know the queen’s died? I mean, there’s not an emergency alert system. Maybe there is.

RAMESH SAGILI: Yeah. So it’s a very fascinating social insect. As far as you know, honey bees are the most advanced social insects that I can think of. So they have this fascinating mechanism as soon as the queen dies. So the queen is emitting a pheromone.

It smells to them. But you can’t smell that pheromone. But pheromone communication is a huge thing in these colonies. So as soon as the queen is dead, within hours, the bees will know, because they are not getting any pheromone from the queen. And that’s when they know that they have to make a new queen that can be functional and help the reproduction of the colony.

IRA FLATOW: Yeah, that’s right. And what’s really interesting is that your study looked at how the hive chooses to make a new queen. And you found that they chose the chubby larva in the rear and turn that one into a queen. Take us through what you did in the study and how you found that out.

RAMESH SAGILI: Yeah. So no, honey bees have evolved for millions of years. And then, still, there is not a very clear understanding, especially in the emergency situation, how do these worker bees make a decision to choose which larva? And no, colony fitness is huge. Because honey bee queen is such a vital entity for the hive, because everything is dependent on her queen egg-laying rate.

So that’s a reason why it’s such an important task to pick a larva that should be fit. So there was not much understanding before our study. There was speculation that there could be even kin selection. That means that the larva could be based on some nepotism. Because all the individuals that you see– those 30,000 or 50,000 worker bees– they’re not always closely related. Some are only related to 25% extend, and then to 75% as well. It depends on how many drones the queen was mated with.

If the queen has mated in the sky with 15 drones, so there are 15 patrilines. That means each bee may have– not each bee– maybe a subset of bees. Maybe 1,000 bees may have one father, and the mother is the same for all.

So there was, in the past, in the ’80s and ’90s, there was this notion that maybe kin selection or kin discrimination is also involved, and they can really choose who is closely related to them to choose a larva which can become a queen in the hive. So here, what we did is– it is a well-defined caste system, as I said earlier. So the female caste, especially the workers the queen, they are decided based on the nutrition. So we thought maybe nutrition should be tested.

So what we did is we deprived a certain age of larva– it was one-day-old larva. So we were depriving them of their brood food. That means we were depriving them for nutrition for about four hours.

And then we gave them back to those colonies after they were queenless, and then we allowed them to pick a larva which could become a queen. And then we always saw that they were preferentially picking the larva which were not starved. That means they were not deprived of brood food for that four hours.

So your analogy of chubbiness– I know they may not look chubby because it’s an age group where four hours doesn’t make them look very different. But we think that the larva were emitting pheromones conveying the nutritional stress so that the bees could pick them based on that nutritional status to become a queen.

IRA FLATOW: And so when they pick their larva, how do they turn it into a queen?

RAMESH SAGILI: So yeah, it’s a very complex series of. It’s a cascade of events that happens when they do this. So usually, a queen is fed a different diet when compared to a worker. So as soon as a queen lays an egg, it’s basically a female. So you can make a queen or a worker out of that egg that has been laid. It’s a diet. As I said earlier, nutrition decides whether you become a queen or a worker.

So they’re feeding a different food, which is– we’ll loosely use this language of royal jelly. So when you are fed royal jelly, which is a little different in the food composition when compared to what you are feeding a worker, you can get a queen out of that.

IRA FLATOW: Wow. How does the jelly kick off the DNA or whatever is going on in there to choose it, make it into a queen? It’s just fascinating.

RAMESH SAGILI: Yeah it’s pretty fascinating. So what we think is– so the bees, actually, are feeding more quantity of food as well. So most of this protein food that I’m talking about is rich in sugars. And so the queen larva that they have decided to make a queen out of it, they are fed a huge amount of this food, which is high in sugar content.

And so the queen’s guts– the larval gut– has stretch receptors. And as soon as you feed them a lot of this food, the stretch receptors are expanding. So that sends a signal to the brain and so all these hormonal changes and all this cascade of events happen, and that’s how you get a queen.

IRA FLATOW: Fascinating. Never heard the word “stretch receptors” use about a bee before. That’s great. It’s great to know. That’s why we talk to you. Because we like to learn these things.

Thank you. Thank you very much–

RAMESH SAGILI: Yeah, no, absolutely.

IRA FLATOW: –Dr. Sagili. It’s been fascinating. Ramesh Sagili, he’s author of a study that’s in Scientific Reports, plus associate professor of apiculture at Oregon State. Thanks for taking time to be with us today.

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