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Bumblebee orienteering

Bumblebees (also quaintly known as dumbledores, long before the wizard was a twinkle in JK Rowling’s eye) have an image problem. Their fat and furry bodies, their ridiculous name(s), our preoccupation with their theoretical inability to fly – it just isn’t very rock’n’roll. Indeed, it’s all a bit Rimsky-Korsakov.

The humble bumblebee (Tony Wills, Wikimedia Commons)

But a research article just published in PLOS Biology (also discussed in an accompanying Synopsis) highlights a very different side of this animal. In contrast to the apparently shambling figure that seems to tumble chaotically from flower to flower, the bumblebee emerges from this study as a shrewd navigator walking an energetic tightrope. Critically dependent on the balance between the energy that it expends on foraging and the energy that it can acquire from these ventures, the bumblebee must be ever-conscious of economising.

Although a fair bit was already known about bee navigation, in the latest paper Lars Chittka and his co-workers go one step closer to how the animal performs route-optimising calculations in the wild. Chittka works at Queen Mary, University of London, and uses a combination of field studies, experimentation and computer simulation to tease apart the mechanisms that underlie insect behaviour.

A bumblebee visits one of the artificial flowers used in this study; a webcam keeps watch from above (Lihoreau et al., PLOS Biology 2012).

He and his colleagues glued tiny radar transponders to the backs of seven bumblebees and released them into an open field in bleak mid-autumn when natural food sources are rare. Here they placed five artificial syrup-filled “flowers”, each monitored by a motion-sensitive webcam (as you can see from the picture, realism wasn’t top of the agenda; instead the bees were pre-trained to recognise them as food sources).  The flowers were placed far enough apart that the bees couldn’t see one from another, forcing the naïve insects to figure out where the flowers are and to optimise their route between them.

Using the combination of radar tracking and video footage the authors were able to monitor the bumblebees’ learning curve over many forays, allowing them to guess at the bees’ optimisation strategy. And just when the bees thought they knew how the land lay, the authors messed with their little brains by removing some flowers and adding new, more distant ones to see how the bees adjusted and re-optimised their route.

From their data, the authors are able to deduce that the bees use a simple trial-and-error strategy, calculating, memorising and comparing the lengths of routes attempted, and choosing the shorter of the two each time. The authors could model this process and its reiteration, finding a good fit with the real bees’ performance. Just how bees are able to calculate distances traveled, incidentally, is the subject of an earlier PLOS Biology paper (and an accompanying Primer by Lars Chittka).

The new study extends the authors’ previous findings from artificial enclosed environments to the more realistic open field, but the greater distances seem to sharpen the bees’ need to optimise. The authors note that the strategy taken by individual bees, which depends on local vectors rather than a map-like representation of the environment, is reminiscent of the collective navigation tactics of ants, and wonder whether other foraging animals such as hummingbirds, bats and primates might take a similar tack.












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