Podcast: Common parasite hampers bees' homing ability



28 October 2014 by Sue Nelson

This week in the Planet Earth podcast, Stephan Wolf of Queen Mary, University of London, and Jason Lim of Rothamsted Research explain why some honeybees may be struggling to make it back to the hive after foraging trips.

To assist those who find text-based content more accessible than audio, a transcript of this recording is available below.

Sue Nelson: Not all honeybees make it back to the hive and scientists have found one reason why. I'm Sue Nelson and this time in the Planet Earth podcast we're at Rothamsted Research Base at Harpenden in Hertfordshire, and I'm joined by Stephan Wolf from Queen Mary University of London who led a recent research project that found that a common parasite is bad news for bees. We're going to be joined by a radar engineer a little later on, but let's start with you, Stefan, you are actually based here at Rothamsted when you did this project and we're beside five rather familiar looking wooden structures.

Dr Stephan Wolf: What you can see here are five honeybee hives. They are all quite happily foraging around at the moment.

Sue Nelson: So how many bees are in these five beehives?

Dr Stephan Wolf: I haven't opened these hives but I guess something in the range between five and eight thousand bees should be in there by now because we are approaching winter and that should be the number of bees you have to have them survive the wintertime.

Sue Nelson: Now this project was part of the insect pollinator initiative, so how does a honeybee normally forage to and fro a hive like these ones here?

Dr Stephan Wolf: Well the honeybees... it is interesting because when they hatch from their pupation period they spend a lot of time in the hive first and only after a couple of weeks when they care for the brood and build the comb that we know they start to become foragers. They do an orientation flight in front of the hive, you can't see that, and only if they are familiarised to the landscape then they start to forage in the wider landscape and that can be up to four to five kilometres away depending on the resources are scattered in the landscape. That is when they really start going and then they know where the landscape resources are.

Sue Nelson: Well we're stood beneath a Canadian oak, we've got nettles and various wild flowers and weeds in front of us, so what sort of food close by will appeal to these honeybees?

Dr Stephan Wolf: Well this time of the year - it is autumn now - I think there is a second nectar flow in full swing and that is mostly ivy.

Sue Nelson: I would never think of ivy as providing nectar to bee.

Dr Stephan Wolf: It's very important for the bees to get this in because it is a very important crop late in the year.

Sue Nelson: So what did you do then in order to find out that a particular parasite was having an effect on the bees foraging?

Dr Stephan Wolf: As you can see the bees are flying in and out and it is very hard to tell one bee from another and it is also very hard to tell whether the bees infect it or not, so we had to approach the entire question very experimentally. What we did, we took a brood frame of a hive, which is very, very young bees, basically bees that haven't even hatched yet, put them in an incubator at exactly the same temperature at in the hive and then we waited for them to come out and these bees were marked with an individual number tag on the back their thorax and then these had been grouped and randomly in three different groups. The one group just became sucrose and was very happy with that, the second group became sucrose and got extract which did not contain any diseases and the third group got sucrose and also the disease itself had been extracted from other bees.

Sue Nelson: So what disease was this and why did you choose it?

Dr Stephan Wolf: The disease is called Nosema ceranae and is closely related to Nosema apis which is a common parasite in honeybees in Europe. Nosema ceranae, however, is an introduced disease and it originates from China from Eastern honeybees and since its arrival in Europe it has spread really, really quickly around entire Europe, especially in the warmer countries.

Sue Nelson: So how prevalent is it within the UK?

Dr Stephan Wolf: Very prevalent. Across the UK there might be a couple of aperies in, say, Scotland where you don't find it all but generally it is pretty much everywhere.

Sue Nelson: Wow! So it's that common then?

Dr Stephan Wolf: Yeah.

Sue Nelson: So you want to find out exactly whether this parasite has any sort of effect on the foraging behaviour of the bees or not?

Dr Stefan Nelson:Yes, indeed. There has obviously been some research conducted already showing certain effects of this disease but these are mostly restricted to the lab and we wanted to see whether these bees actually have a real impairment of their flight behaviour from this disease and at the same time it is really hard to tell how the flight behaviour changes if we can't see it, and having the radar equipment at our hands obviously that made complete sense to look into that and see whether there are any hidden effects there.

Sue Nelson: Well that's where Dr Jason Lim comes in, because he's a radar engineer from Rothamsted Research and he should be here with us any minute now with his radar equipment.

Dr Jason Lim: Hello, how are you? We are going to the hive view to observe the radar, so if you could join us then we will be able to show what we are doing down there.

Sue Nelson: Okay, right. Well we will walk along and join you.

Right, well I am at the field now where Dr Jason Lim has set up, almost like a base camp. You've got a radar dish on the back of a trailer here, you've got a generator by the barbed wire fence surrounding the field and in your hand you've got what look like almost, I would call them dressmaker pins, stuck into some polystyrene. What are they?

Dr Jason Lim: This is a transponder that we use to attach this on the back of the bee so that we could track it with the radar behind me here. As you can see there is a small semi-conductor device in the middle.

Sue Nelson: It's so small I think I need my reading glasses!

Dr Jason Lim: This device will help us to convert the signals from the fundamental frequency to a harmonic signal in which we will be able to detect it from a noisy environment from the radar [unintelligible] So if we use the radar as a normal device it will pick up signals from the trees, from the hedgerows, from the tractors and stuff so you wouldn't be able to distinguish whether it is a bee or a moving car, for example. So this transponder will allow us to do that.

Sue Nelson: That is incredible. Where do you actually see your display? How do you follow the motion then of your individual bee?

Dr Jason Lim: We have a computer at the back of the camper van here, so we will be able to see real-time where the bees are going to and all this data will be recorded and we will extract the information afterwards.

Sue Nelson: There are small computer screens in the back there.

Dr Jason Lim: I will turn on the computer for you. Okay, so we are just starting the computer now and then I will be able to show you how the radar screen looks like.

So, if I turn on the radar software you will be able to see a standard PVI screen where we [unintelligible] planned decisions indicator. It is just like you see in the movies where you have a bull's eye in the middle and it spins, so it will show up as a cloud of points and in this you will be able to identify as the bee or the response from the transponder.

Sue Nelson: And what was the furthest range that you could go with the bees from those hives - there goes a tractor behind us there.

Dr Jason Lim: Currently we are able to track individuals up to about six to seven hundred metres, so if you spin the antennae dish around then we will be able to double the distance, so that's about one to one point four kilometres.

Sue Nelson: Stefan, what did you actually find then?

Dr Stephan Wolf: We took a bee from the entrance of the hive and displaced it about one hundred and twenty metre in the landscape so the bee had no idea where she is, we released her once the transponder had been attached and we wanted to see how they could find their way back to the colony. And these incorporated two different aspects of the foraging itself, one being orientation in the landscape which is important to find the colony but also the flight itself and while we did that what we found is that about 30% of the infected bees did not make it home to hive, which is very, very surprising because that is a high percentage for one but also it is not a very long distance from the hive. One hundred and twenty metres is actually a very, very short flight distance for a bee.

Sue Nelson: So if one in three bees didn't make it home, what happened to these bees?

Dr Stephan Wolf: We don't know exactly what happened to the bees. We lost it from the radar screen, so these bees literally dropped out of the sky and we couldn't see them any more. Most likely these bees died in the middle of the field where they landed. Unfortunately we haven't seen any of these bees back.

Sue Nelson: Had this ever been discovered before?

Dr Stephan Wolf: Well there was a research project done before in a mix of Nosema ceranae and Nosema apis but a lot closer foraging distances or homing distances is about thirty metres and that showed very much the same effect in a way. What had been done there is just to count the bees returning once they have been released, so you would only get the result of the homing flight. What we have done now is obviously because we had the radar data, we could also look into how the result of the homing flight came about and we could actually look why did the bees not come home or why they took a lot longer to come home as had been shown with the previous study - is it because the bees sit in front of the hive or close to the hive for a long time or sit in the landscape because they are exhausted or do they fly around are disorientated and take a long time to redefine their bearings coming back to the hive, so we could actually see and look into that actual radar track data.

Sue Nelson: This is very important research in terms of giving us an idea of what's going on in honeybee colonies, particularly as they are now saying earlier this year it was said that European countries are facing a honeybee shortage, potentially. So are there any treatments for this parasite if it is so widespread?

Dr Stephan Wolf: Well there used to be a treatment which was fungicide because Nosema is taxonomically very close to a fungus but that had been banned about two years back in light of being a pesticide, so you would actually then apply your pesticide inside of the hives which is also not particularly nice. So at the moment there is a lot of research going on to find new cures for this disease but at the moment there is no actual remedy available on the market.

Sue Nelson: Dr Stephan Wolf and Dr Jason Lim - thank you both very much indeed and that's the Planet Earth podcast from the Natural Environment Research Council. You can follow us on Facebook and Twitter and we will post some pictures of today's recordings at the hives in Rothamsted Research. I'm Sue Nelson and thanks for listening.