Prof. Lars Chittka and Dr. Mathieu Lihoreau from Queen Mary's School of Biological and Chemical Sciences and colleagues set up five artificial flowers in a 1 km diameter field. Each flower was fitted with motion-triggered webcams and had landing platforms with drops of sucrose in the middle. To keep the bees' focus on the artificial flowers, the experiments were done in October, when natural sources of nectar and pollen were scarce. To make the bees want to find all five flowers, each sucrose drop was only enough to fill one fifth of a bumblebee's crop. And to keep the bees from finding one foraging site from another visually, the flowers were arranged in a pentagon that was 50 metres on each side, which is more than three times as far as bumblebees can see.
"Using mathematical models, we dissected bees' learning process and identified how they may decipher this optimal solution without a map. Initially, their routes were long and complex, revisiting empty flowers several times," Lihoreau explained. "But, as they gained experienced, the bees gradually refined their routes through trial and error. Each time a bee tried a new route it increased its probability of re-using the new route if it was shorter than the shortest route it had tried before. Otherwise the new route was abandoned and another was tested.
"After an average of 26 times each bee went foraging, which meant they tried about 20 of the 120 possible routes, they were able to select the most efficient path to visit the flowers, without computing all the possibilities."
Chittka and colleagues had previously shown that bees were able to learn the shortest route possible to navigate between flowers in the lab but this is the first time they have been able to observe this behavior in natural conditions and to describe how bees may optimize their routes.
"The speed at which they learn through trial and error is quite extraordinary for bumblebees as this complex behaviour was thought to be one which only larger-brained animals were capable of," Chittka said. "Interestingly, we also found that if we removed a flower, bees continued looking at that location – even if it was empty for an extended period of time. It seems bees don't easily forget a fruitful flower."
The motion-triggered web cams and tiny bumblebee-mounted radar transponders tracked the bumblebees. The recordings on the flowers showed that bees exhibited considerable individuality; each one had a favored arrival and departure direction, different from the other bees. Head of Computational and Systems Biology at Rothamsted Research, Professor Chris Rawlings, added: "This is an exciting result because it shows that seemingly complex behaviours can be described by relatively simple rules which can be described mathematically. This means we can now use mathematics to inform us when bee behaviour might be affected by their environment and to assess, for example, the impact of changes in the landscape."
Citation: Mathieu Lihoreau, Nigel E. Raine, Andrew M. Reynolds, Ralph J. Stelzer, Ka S. Lim, Alan D. Smith, Juliet L. Osborne, Lars Chittka, 'Radar Tracking and Motion-Sensitive Cameras on Flowers Reveal the Development of Pollinator Multi-Destination Routes over Large Spatial Scales', PLoS Biol 10(9): e1001392. doi:10.1371/journal.pbio.1001392