Bees get a memory buzz from caffeine
Many of us like a cup of coffee to help us wake up in the morning, but it turns out that we’re not the only ones who get a kick out of the caffeine it contains: a new study of bumblebees has shown that caffeine strengthens bumblebee memory formation, meaning it can be used to train bees to be better pollinators for farmers’ crops, as Eva Higginbotham has been hearing from Sarah Arnold…
Sarah - We got a selection of bumblebee colonies, and these are commercial colonies that are bought by growers of fruit crops. And these normally will be deployed within the crop. So a strawberry grower might buy these and let the bees fly out and pollinate their crops. We brought these same colonies into the lab and we allocated them to different treatment groups. So some of these bee colonies received just plain sugar solution. Some of them received sugar solution and also an odour that resembled the smell of strawberry flowers. And the third group of bees received the same sugar, the same odour, but also caffeine in that sugar solution. So as the bees were drinking the sugar solution and smelling that out, they were getting caffeine into their nervous system. And then we released them into a flight arena, which is essentially a wooden box that we can put artificial flowers inside. And in these flight arenas, there were robotic flowers. Half of the robotic flowers had that same artificial strawberry scent that some of the bees had received in the nest and the other half had a distractor odour, so a different smell. And we wanted to see whether the bees that had had the caffeine as well were more biased towards visiting the strawberry odour smelling flowers compared to the distractor flowers, and sure enough, that's what we found. So the caffeine group had a much stronger initial preference for those flowers that smelled like strawberry.
Eva - So how much stronger was the association for the bees with the strawberry flowers who've had the caffeine already priming them in comparison to the bees that didn't have caffeine?
Sarah - The bees that had received caffeine previously chose the target flowers with a strawberry flower odour about 70% of the time at the start compared to that the bees that had received the odour, but no caffeine only chose those flowers 60% of the time. And the bees that had received neither the odour nor the caffeine only chose those flowers, perhaps 44, 45% of the time. So it's quite a noticeable difference.
Eva - And how long did the effect last? Is it kind of like you imprint on the bees that they're always going to want to go for strawberry or does this wear off over time?
Sarah - It does wear off over time. In our experiment, you'd probably expect that because both the distractor flowers and the target flowers had the same sugar reward on them. So it did wear off over time, but the initial effect persisted for perhaps the first 20 bee visits and that's in a very simplified setup. How that would work out in a field situation where everything's a little bit harder, the distances involved are much longer. And for example, on a farm, you wouldn't get strawberry flowers that were mixed in with herbs and weeds and things. On a farm they'd be quite far separated. So it could be more noticeable if you deploy this in a real-life field situation.
Eva - And how might you imagine doing that?
Sarah - What we envisage in the future is that potentially this sort of technology could be incorporated into those boxes of bumblebees that the growers purchase. So the grower would buy a box of bees and already inside that the bees would be getting the odour of the crop flower, a bit of caffeine, and a bit of sugar. So as soon as the grower gets that box and opens the little door on the front so the bees can fly out, they're already targeted and primed ready to go and visit those crop flowers.
Eva - And would a bee normally come across caffeine in the wild, or are they getting this caffeine from people's cups of coffee left on the table?
Sarah - That's a good question. Some bees would probably never encounter caffeine, but caffeine is a naturally produced product. Various plant species do produce it as part of their metabolism. Citrus plants. So like orange trees produce it in their nectar, for example. And recently a wildflower that's present in the UK called Sainfoin has been found to have caffeine in its nectar. So some plants do have it and lots of different sorts of plants. So it's not just concentrated in a single small group of plants.
Eva - Could it be that there's a benefit then to the plants to make caffeine in order to try and trick bees to come to them more often?
Sarah - Absolutely. We think that might be one of the reasons why plants have evolved to have caffeine present in their nectar. If it creates a stronger memory in those bee and other pollinator visitors to keep coming back more and more often because they remember that as being a really great food source, they're really excited about it, and so the plant wins their loyalty.