Bees prefer nectar they can vomit up faster

The speed at which bees vomit is not a subject that’s been much discussed in scientific literature. But a new study from the University of Cambridge suggests that it affects the kind of nectar bees prefer - and therefore the kinds of plants farmers should be breeding. Hamish Symington explained to Chris Smith and Phil Sansom what they've done...

Hamish - I am a plant scientist at the University of Cambridge and we're looking at what it is that bees like about flowers, trying to make flowers more efficient at being pollinated. And if we're doing that, we need to know what the rewards are like, the nectar and pollen, when they actually get to the flower. And we don't want them to spend too long on the flower because then they won't get round enough quickly enough. But we don't want them to spend too short a time on the flower, then they don't get that energetic reward that they need.

Chris - So how did you do these studies?

Hamish - So we have a flight arena within our bumblebee lab, which is a box, about 1 metre by about 30 centimetres high. We have a little colony of bumblebees which we bought. They arrive in a small buzzing box in the post and scare the receptionist. We let one bee out at a time, we have a look at how much she drinks and then we can have a look inside the bumblebee colony. We've fitted it with a perspex lid and we can watch the bumblebee as she goes back into the nest. Now when she's taken this nectar into the nest, she will vomit it back up for her nest mates to drink, because not all of the bees in the nest will go out and forage.

Chris - So obviously the easier it is for a bee to find a flower, find a drink, draw up the drink, get back to the nest and then deposit that nectar reward, that's going to make that bee favour those flowers. And those bees are going to do better.

Hamish - Yeah, it's the trade off between it being really easy, which if it's water, that would be the easiest of them all, but they're not going to get any energy back to the nest there because they're not bringing home any sugar. They need to balance how easy it is to drink, how far they need to fly and how easy it is to spit it back up again when they get back to the nest and it's that last thing which nobody had ever looked at before.

Chris - The stronger the solution, the thicker it is, isn't it? You just have to compare golden syrup with say some water that you put a spoonful of sugar in and one's very watery, one's very, very sugary but it's really, really sticky and hard to draw up.

Hamish - Exactly. And it's not a linear relationship. It's actually exponential. There's very little difference between water which has 35% sugar and water that has 50% sugar in it, but when you get up to about 65 it starts getting treacly. That's about maple syrup territory there.

Chris - I'm intrigued because are those honey jars in front of you? How appropriate!

Hamish - I brought some fake nectar along which I made in my kitchen at home earlier today. I believe Phil has volunteered to be the Guinea bee.

Phil - Tell me what I'm doing because you're handing me these two jars which have identical looking what could be water, but it's obviously a lot thicker than water.

Hamish - So I've made two concentrations of fake nectar here. One has 35% sugar in and one has 65% sugar in and the 35% one looks quite watery and the 65% one is quite thick. So what I'm going to do, drinking for a bumblebee takes a couple of minutes. I'm not going to get you to lap it up. That would look rather weird and would not make good radio.

Phil - I appreciate that.

Hamish - So if you just take a mouthful of it, then when the bees are sick, they have to spit it back up through their oesophagus. I'm not going to make you do that as well because again, being sick on air would not be good, but I want you to spit it out through the straw into a cup which I've got here.

Phil - Okay. I do have a sweet tooth, but let's see if this pushes it to the limit. I'll do it now.

Hamish - Okay, so he's taking a drink and then he's going to spit it out through the straw and that went quite quickly.

Chris - So you emptied the whole mouth full in a second or so. It was very quick.

Hamish - So here we now have the 65% solution. This is more like maple syrup territory. So it's going to be quite a lot sweeter. And then I want you to try and spit that out again.

Phil - And by the way, the straw that you've given me is not a normal drinking straw. It's one of the extra thin ones you get in very nice cocktails.

Hamish - I stole it from my daughter's drink.

Phil - Very nice. Okay, here we go. I'll now drink a sip of a thicker one and spit this one out too.

Chris - Oh my goodness.

Hamish - He's got one drop out so far.

Chris - You're turning very red Phil, it's proving difficult.

Chris - Is it fair to say that was very hard to spit?

Phil - I couldn't even do it!

Hamish - Yeah, there we go. So bumblebees have to do that as well. So there is this trade off, this optimising of how they can get it.

Chris - Now, why are you doing these experiments? Why does this matter?

Hamish - There is going to be a large number more people on the earth in the coming decades, and insects around the world are generally in decline. We're going to need to make more food, but lots of our food relies on pollination. So if we can make plants more efficient at being pollinated, and better rewarding for the insects which visit them, then we'll be able to use those insects better to help produce food.

Chris - You're talking about actually tweaking nature so that plants make an ideal concentration of nectar to make this process more efficient?

Hamish - It's tweaking plant breeding and crops, not tweaking wild plants, but it's trying to inform our plant breeding and make us breed plants which are not only nutritious and good for us, but also beneficial for the insects.