[Pollinator] Bad beehaviour - The strange case of the bandit bumblebees

[Sunny Boyd]

http://www.economist.com/news/science-and-technology/21576627-strange-case-b
andit-bumblebees-bad-beehaviour 


 


Entomology


Bad beehaviour


The strange case of the bandit bumblebees


Apr 27th 2013 |From <http://www.economist.com/printedition/2013-04-27>  the
print edition 



TO MOST people, bumblebees are charming, slightly absurd creatures that
blunder through garden and meadow with neither the steely determination of
the honeybee nor the malevolent intention of the wasp. If you are a plant,
though, things look rather different-for from the point of view of some
flowering plants many bumblebees are nothing more than thieves. They rob
them of their nectar and give nothing in return.

Nectar robbery, in which a bumblebee carves a hole in the side of a flower
as a bank robber might cut his way into a vault, was discovered by Charles
Darwin. This technique lets bees get at the nectar of flowers whose shapes
have evolved to encourage their pollination by insects with long tongues,
which can reach down narrow tubes.

Some bumblebees do have such tongues. But some do not. Short-tongued bees
are, however, unwilling to deny themselves the bounty of nectar inside these
flowers. Hence the hole-cutting. By breaking in in this way, though, a
bumblebee nullifies the 100m-year-old pact between flowering plants and
insects: that the plant feeds the insect in exchange for the insect
pollinating the plant.

The question about nectar robbery that has intrigued biologists from Darwin
onwards is whether the behaviour is innate or learnt. Darwin, though he
originated the idea that many behaviour patterns are products of evolution
by natural selection, suspected that it is learnt. Insects, in other words,
can copy what other insects get up to. Only now, though, has somebody proved
that this is true.

The observations were made by David Goulson (then at the University of
Stirling, now at the University of Sussex), and his colleagues. To test his
ideas he had to go from Britain to Switzerland, for only there could he find
a flower of the correct shape to conduct the study.

His crucial observation was that when the flowers of an alpine plant called
the yellow rattle are robbed, the entry holes-because of the structure of
the flower-tend to be unambiguously on either the right-hand side or the
left-hand side. Moreover, preliminary observation suggested that the holes
in flowers in a single meadow are often all made on the same side. This led
him to speculate that bumblebees in a particular area do indeed learn the
art of nectar robbery from one another, and then copy the technique with
such fidelity that they always attack a flower from the same side.

Crime and nourishment

His team monitored 13 alpine meadows during the summers of 2009 and 2011.
They painstakingly recorded the sites of robbery holes in yellow-rattle
flowers, and studied the behaviour of 168 bumblebees. They tried to follow
each bee until it had visited 20 flowers, though they lost sight of some
insects before they had reached this score. If they could, they then
captured the insect so as not to follow it again on another occasion.

Dr Goulson found, as he reports in Behavioral Ecology and Sociobiology, that
two short-tongued bumblebee species which live in the area, Bombus lucorum
and Bombus wurflenii, demonstrated handedness when they robbed flowers.
Moreover, if one species was behaving in (say) a left-handed manner in a
particular meadow, the other was likely to do the same. This suggests that
one species can learn from another-a trick previously thought to be confined
to vertebrates.

Handedness in any given meadow, Dr Goulson found, increased as the season
progressed. But each summer appeared to start as a blank slate. The
handedness that developed in a meadow in 2009 did not predict its handedness
in 2011.

The most reasonable explanation, Dr Goulson argues, is that each year a few
bumblebees which have learnt the trick of nectar robbery in the previous
season come out of hibernation and start robbing flowers again. By chance,
they make more holes on one side of the flowers than the other, and as the
habit is picked up by other, newly hatched bees, a preference for left or
right spreads by a process of positive feedback. The bees have, in other
words, created a simple culture. It is a criminal culture, admittedly. But
no one ever said that nature was pretty.

 

 

Sunny Boyd

Communications Manager and Webmaster

Pollinator Partnership

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San Francisco, CA  94111

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E.  sun at pollinator.org

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