Science Interviews


Sun, 6th Jun 2010

Ready, Steady, Stop!

James Nieh, University of California at San Diego.

Listen Now    Download as mp3 from the show Creatures in Colonies

Helen -   Bees communicate in a number of ways, including that wonderful famous waggle dance that they use to indicate where all the best bits of food are.  In February 2010, researchers discovered that honeybees also have a warning signal that they use to tell each other to avoid certain areas, and it shows us that their language is really much more complicated than we already thought.  Dr. James Nieh led the team from the University of California at San Diego that made that discovery and he joins us now.  Hello, James.  Thanks for joining us on the Naked Scientists.

James -   Hello.  Thank you.  It’s a pleasure.

honeybees on honecombHelen -   So, tell us more about this new "stop sign" that you've discovered in honeybees.

James -   We’ve known for a long time that honeybees face various perils at food sources.  For example, they're often attacked by ambush predators such as crab spiders, which you can sometimes see in your garden flowers.  They're cleverly camouflaged to look like the same colour of the flower.  We’ve known recently that this danger affects [the bees] ability to waggle dance so that they try to recruit fewer bees to food sources which they perceive to be dangerous.  But what we didn’t realise is that there’s another system at play that allows a bee that’s been attacked to warn other bees about her situation and we looked at this in two contexts.  One, in terms of competition from other bees for a natural food source - which happens, although it’s somewhat more rare, you can occasionally see bees from different colonies, fighting over a good food source.  Secondly, what happens when bees are exposed to signals of danger such as alarm pheromones or being physically attacked by a predator.

Helen -   So how did you go about looking at these ideas you had?  Were you looking at bees in the laboratory or were these wild bees flying around in the open air?

James -   We had a bee colony in the laboratory and we were able to see inside through the glass, what the bees were doing.  We had them trained to an artificial feeder so that we could control the situation more carefully.  Occasionally, we had feral bees that would come and would try to take over the feeder.  We had an assistant who was removing these feral bees.  All the bees that we had trained were marked and were identified so we can tell if they come back to the colony, that they are from our colony.  Now, what we would do sometimes is we would let the feral bees continue to feed at the feeder.  We would not remove them and then we would see these fights ensue.  Sometimes the feral bees would attack our bees and in that case, the bees actually came back and they produce this curious signal called the “stop signal” where they go around and they will target a bee that’s been visiting the same location.  We know that it’s based on the odour of the food source.  So she'll target that bee.  She will jam her head up against the bee that’s waggle dancing for that location and give this brief piping sound that causes the waggle dancer to momentarily freeze.  She will then reduce the number of waggle runs that she receives, depending in part upon the number of these stop signals that she gets.

Helen -   So essentially, these bees have found, they've detected a problem, something that they're scared off out in their foraging area, they come back and they essentially tell everyone else to stop.  They turn down almost the volume of those announcements that are going out, telling bees to go back to that site.  So it’s almost damping down that signal that goes out to say, “Go out and look at this particular flower” because actually, it’s going to be quite dangerous.

James -   Exactly and maybe some of your listeners are wondering, “Well why would she give up so easily?” and it’s interesting that she doesn’t.  Initially, our bees attack the feral bees and try to retain control of the feeder.  And when they do so, they actually don't produce stop signals.  In fact, it seems that they actually ramp up the recruitment of nest mates.  But when that tide of battle turns and as more and more bees are attacked, they come back and report this by producing stop signals, so that when eventually, it’s impossible for them to win the battle, and to keep the feeder, they stop recruiting for it.

Helen -   So we’ve got the waggle dance, we’ve got stop signals.  Do we have any feeling that there are other ways that the bees are communicating that we’re still going to discover?

Honeybee carrying pollenJames -   That’s an interesting point.  There are some interesting behaviours.  There’s something called the tremble dance which is highly correlated with the stop signal.  We’re not sure exactly what it means, but it does in some context re-allocate labour inside the colony.  So you have this super organism as your previous speaker talked about in which they have different tasks.  But there’s no single bee that controls all of this and is telling them what to do.  So there necessarily are these signals that help to reallocate labour for where it’s needed.  The tremble dance is one of those signals where we’re not really sure what’s going on.  There’s also another signal called the “shaking” signal which again seems to re-allocate labour, but again, we’re not exactly sure what it does.  So there are quite a few mysteries that remain.

Helen -   As you say, lots of mysteries remain, but we are learning a little bit more to understand that language of the bees.  But we also know that a lot of bees are facing quite a big problem at the moment, and we hear more and more about colony collapse disorder, and I believe that’s something that you're looking into as well.  Is language going to come in to our understanding of what’s going on and why bees are facing problems today?

James -   Well, we’ve been looking at the effect of this pesticide which is often sprayed on plants.  It’s sold in Europe and the United States as Gaucho but it’s known by its chemical name, imidacloprid.  It’s actually been banned in some EU countries now because it’s thought to be associated with bee death.  This is again one of the dangers that bees face when they forage.  They could come in contact with the pesticide and bring back small quantities.  Now, there is a lethal dose of any pesticide, and it’s thought that this was not so detrimental to bees, but we’ve been finding that extremely minute quantities of these pesticides when ingested by bees can actually affect their behaviour.  Other research has shown that it seems to affect their waggle dance behaviour.  They don't seem to waggle dance as much when coming back, after receiving this pesticide.  But we were interested in two things; we know that in colony collapse disorder, we have this strange situation of a colony that’s depleted.  It’s sort of like the Mary Celeste, you come aboard, everything is empty and where have the bees gone?  There are no dead bodies of bees around, as you would have in a normal disease.  So one of the things we wondered is whether or not there is a nutritional imbalance that’s occurring. 

What we found in our preliminary studies is that bees that receive very small quantities of this pesticide develop what we call a picky eater syndrome.  In humans, this is akin to someone not wanting to eat certain things, and actually, typically eating things that are unhealthy.  In terms of bees, what we find is that the bees who would now normally accept relatively low sugar concentrations, what you typically find in nectar are shifted.  They become extremely picky and they will only consume the sweetest nectars.  Now you might think this wouldn’t be bad but in the environment, you don't often have your pick of food, and if you're going to reject most of what’s available, that means that less sugar, fewer calories are entering the colony.  There is a second aspect as well which also relates to human picky eaters syndrome.  There’s a nutritional imbalance.  Bees need to collect pollen and nectar.  Pollen is providing them with their protein and interestingly enough, pollen foragers are ones that genetically are predisposed to not be picky about sugar.  In other words, they will feed at very low sugar concentrations, and of course, they’ll collect pollen.  We suspect that what will happen, and we’re doing these experiments right now, is that when pollen foragers are fed very minute quantities of this pesticide, they will actually shift away from collecting pollen because now, they will develop an appetite more similar to that of nectar foragers.  And if you have a colony where few bees are collecting pollen, you're going to have a nutritional problem, there won't be sufficient brood, and the colony will eventually decline.

Helen -   Well that’s all absolutely fascinating stuff.  Thanks very much, James.  That was James Nieh from University of California, San Diego, telling us about how bees communicate, how learning to really understand their language, and most importantly, how we’re really starting to unpick, that it isn’t just if things like pesticides can stray it out, kill insects like bees, but if it interrupts their ability to talk to each other and makes them picky eaters, that could also explain why so many colonies of bees are doing very badly at the moment.


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