[Pollinator] The Economist: Colony collapse disorder

[Jennifer Tsang]

http://www.economist.com/node/21543469


Colony collapse disorder


Bee off


A possible explanation of why beehives sometimes vanish


Jan 28th 2012 | from the print edition 

Looking for the cause 

HONEYBEES are sensitive creatures. From time to time a hive simply gives up
the ghost and vanishes. Colony collapse disorder, as this phenomenon is
known, has been getting worse since 2006. Some beekeepers worry that it may
make their trade impossible, and could even have an effect on
agriculture-since many crops rely on bees to pollinate them. Climate change,
habitat destruction, pesticides and disease have all been suggested as
possible causes. Nothing, though, has been proved. But the latest idea,
reported in Naturwissenschaften by Jeff Pettis of the Bee Research
Laboratory in Beltsville, Maryland, suggests that this may be because more
than one factor is involved.

Dr Pettis and his colleagues knew from previous reports that exposure to a
pesticide called imidacloprid has a bad effect on honeybees' ability to
learn things and wondered whether it might be causing other, less
noticeable, damage. Since one thing common to colonies that go on to
collapse seems to be a greater variety and higher load of parasites and
pathogens than other colonies, they wondered in particular whether it might
be weakening the insects' immune systems, and thus allowing infections to
spread through a hive.

To find out, they gave 20 hives protein food (a substitute for pollen, which
is fed to developing larvae) that had been spiked with imidacloprid. In ten
cases the dose was five parts per billion (ppb); in the other ten it was 20
ppb. Previous experiments have shown that neither dose perceptibly harms
bees. A further ten hives were given unspiked food as a control. Then, when
the young bees emerged a few weeks later, Dr Pettis collected them and fed
them with spores of a fungal parasite called Nosema. Twelve days later, he
killed them and estimated the extent of their infestation.

Both of the groups that had been exposed to imidacloprid harboured an
average of 700,000 parasite spores in each bee. Bees from the control
colonies, by contrast, harboured fewer than 200,000 spores in their bodies.
The insecticide, in other words, was exposing bees to infestation, and thus
to a much greater chance of dying prematurely.

Whether this is actually the reason for colonies collapsing remains to be
determined. But it is a plausible hypothesis, and is likely to get
beekeepers buzzing with interest.

from the print edition | Science and technology 

 

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