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By Richard Black
Environment correspondent, BBC News website
The decline of honeybees seen in many countries may be caused by reduced plant
diversity, research suggests.
Bees fed pollen from a range of plants showed signs of having a healthier
immune system than those eating pollen from a single type, scientists found.
Writing in the journal Biology Letters, the French team says that bees need a
fully functional immune system in order to sterilise food for the colony.
Other research has shown that bees and wild flowers are declining in step.
Two years ago, scientists in the UK and The Netherlands reported that the
diversity of bees and other insects was falling alongside the diversity of
plants they fed on and pollinated.
Now, Cedric Alaux and colleagues from the French National Institute for
Agricultural Research (INRA) in Avignon have traced a possible link between the
diversity of bee diets and the strength of their immune systems.
"We found that bees fed with a mix of five different pollens had higher levels
of glucose oxidase compared to bees fed with pollen from one single type of
flower, even if that single flower had a higher protein content," he told BBC
News.
You've now got large areas of monoculture; and that's been a fairly major
change in what pollinating insects can forage for
David Aston British Beekeepers' Association
Bees make glucose oxidase (GOX) to preserve honey and food for larvae against
infestation by microbes - which protects the hive against disease.
"So that would mean they have better antiseptic protection compared to other
bees, and so would be more resistant to pathogen invasion," said Dr Alaux.
Bees fed the five-pollen diet also produced more fat than those eating only a
single variety - again possibly indicating a more robust immune system, as the
insects make anti-microbial chemicals in their fat bodies.
Other new research, from the University of Reading, suggests that bee numbers
are falling twice as fast in the UK as in the rest of Europe.
Forage fall
With the commercial value of bees' pollination estimated at 200m per year in
the UK and $14bn in the US, governments have recently started investing
resources in finding out what is behind the decline.
In various countries it has been blamed on diseases such as Israeli Acute
Paralysis Virus (IAPV), infestation with varroa mite, pesticide use, loss of
genetic diversity among commercial bee populations, and the changing climate.
The most spectacular losses have been seen in the US where entire colonies have
been wiped out, leading to the term colony collapse disorder.
However, the exact cause has remained elusive.
A possible conclusion of the new research is that the insects need to eat a
variety of proteins in order to synthesise their various chemical defences;
without their varied diet, they are more open to disease.
David Aston, who chairs the British Beekeepers' Association technical
committee, described the finding as "very interesting" - particularly as the
diversity of food available to UK bees has declined.
"If you think about the amount of habitat destruction, the loss of
biodiversity, that sort of thing, and the expansion of crops like oilseed rape,
you've now got large areas of monoculture; and that's been a fairly major
change in what pollinating insects can forage for."
As a consequence, he said, bees often do better in urban areas than in the
countryside, because city parks and gardens contain a higher diversity of plant
life.
Diverse message
While cautioning that laboratory research alone cannot prove the case, Dr Alaux
said the finding tied in well with what is happening in the US.
There, collapse has been seen in hives that are transported around the country
to pollinate commercially important crops.
"They move them for example to [a plantation of] almond trees, and there's just
one pollen," he said.
"So it might be possible that the immune system is weakened... compared to wild
bees that are much more diverse in what they eat."
In the US, the problem may have been compounded by loss of genetic diversity
among the bees themselves.
In the UK, where farmers are already rewarded financially for implementing
wildlife-friendly measures, Dr Aston thinks there is some scope for turning the
trend and giving some diversity back to the foraging bees.
"I'd like to see much greater awareness among land managers such as farmers
about managing hedgerows in a more sympathetic way - hedgerows are a resource
that's much neglected," he said.
"That makes landscapes much more attractive as well, so it's a win-win
situation."
The French government has just announced a project to sow nectar-bearing
flowers by roadsides in an attempt to stem honeybee decline.
Richard.Black-INTERNET@bbc.co.uk