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An artificial flower is being visited by a bumblebee worker. The bee obtains a small sugar solution reward when it visits the flower. The flower can be refilled by remote control so the behavior of bees was not disturbed during the experiment. (Mathieu Lihoreau)
Bumblebees, Bombus terrestris, decide on their route between flowers based on the biggest rewards and the shortest distances, according to a new study published in the British Ecological Society’s journal Functional Ecology.
Mathieu Lihoreau and colleagues at Queen Mary University of London observed bumblebees tagged with numbers moving between and collecting nectar from five artificial flowers with varying rewards in a pentagon arrangement.
"Animals which forage on resources that are fixed in space and replenish over time, such as flowers which refill with nectar, often visit these resources in repeatable sequences called trap-lines," said Lihoreau in a press release, referring to a feeding strategy whereby they visit a circuit of resources just like trappers check their lines of traps.
"While trap-lining is a common foraging strategy found in bees, birds and primates, we still know very little about how animals attempt to optimize the routes they travel."
The team looked at how the bees optimize routes based on distance and reward size, similar to a mathematical problem called the Traveling Salesman.
"The Traveling Salesman must find the shortest route that allows him to visit all locations on his route," said co-author Nigel Raine in the release.
"Computers solve it by comparing the length of all possible routes and choosing the shortest. However, bees solve simple versions of it without computer assistance using a brain the size of grass seed."
The bees decided to visit high-reward flowers first if the increase in travel distance was small.
"When the flowers all contain the same amount of nectar bees learned to fly the shortest route to visit them all," Lihoreau said. "However, by making one flower much more rewarding than the rest we forced the bees to decide between following the shortest route or visiting the most rewarding flower first."
There is thus a trade-off between distance and reward with bees optimizing both variables based on a trap-line feeding strategy whereby they visit a circuit of specific flowers.
"We have demonstrated that bumblebees make a clear trade-off between minimizing travel distance and prioritizing high rewards when considering routes with multiple locations," said co-author Lars Chittka in the release."These results provide the first evidence that animals use a combined memory of both the location and profitability of locations when making complex routing decisions, giving us a new insight into the spatial strategies of trap-lining animals."
