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Page last updated at 03:37 GMT, Monday, 17 May 2010 04:37 UK
Our bees are buzzing off. But why?

By Matt Walker
Editor, Earth News

From the UK to Japan, bees are disappearing

In many places, the country air has become just that little bit quieter. The reason: our bees have stopped buzzing.

Over the past few years, honeybees have suddenly and inexplicably disappeared from colonies that once thrived across the northern parts of the American and European continents.

A mysterious malaise has struck down the fittest and most able bees, laying waste to billions and leaving empty hives starved of once industrious workers.

But we are no nearer understanding the exact cause of this carnage.

According to a recently published scientific review, there may be multiple causes, each interacting and creating a more complex problem than previously thought.

Mass die-off?

The initial assumptions that bees were dying out all around the world are not correct, as Prof Elke Genersch of the Institute for Bee Research in Hohen Neuendorf, Germany explains in a review published in the journal Applied Microbiology and Biotechnology.

Over the past five decades, the global number of man-managed honeybee colonies has increased by 45%.

In more recent years, southern European countries such as Greece, Italy, Portugal and Spain have reported a considerable increase in honeybee numbers.

Yet at the same time, honeybees have quickly declined within other parts of Europe, including the UK, Germany, Austria, Sweden and Switzerland, as well as across swathes of North America and Japan.

So in some parts of the world, something odd is happening to honeybees.

But it may not be the same thing.

Honeybee on purple flower

To understand why, it is worth taking a look at two things that we know do much harm to honeybees: honeybee pests and honeybee pathogens.

Prof Genersh details in the article, Honeybee pathology: current threats to honeybees and beekeeping, how honeybees are now known to be severely afflicted by one parasitic mite, three viruses, two bacterial species and one group of fungi.

The pest, a type of mite called Varroa destructor, is a natural parasite of the Eastern honeybee (Apis cerana).

However, early in the 20th Century it twice jumped across to infect commercial honeybees (Apis mellifera), and today it is almost impossible to find a honeybee colony free from the mite.

V. destructor can directly impact honeybees, reducing the development of pupae and potentially lowering the immunity of adult bees.

Paralysing viruses

Other causes of the disappearing bees may be three viral pathogens.

One, deformed wing virus (DWV) does what its name suggests, deforming or atrophying bee's wings.

The others, acute bee paralysis virus (ABPV) and Israeli acute paralysis virus (IAPV), are also aptly named, paralysing and killing bees.

Such viruses are spreading, with scientists reporting that they have spread to beehives in Argentina for the first time, for example.

Varroa mite
Varroa mites now infect almost all honeybee colonies

The problem though, in terms of solving the mystery, is that none of the above seem able to cause such quick, widespread declines in honeybee numbers.

Honeybees have a long association with their parasitic mite, suggesting that it is not the sole cause of the recent population crashes.

Also, none of the aforementioned viruses tend to be harmful when passed naturally between bees.

They only kill when they are ingested by the mite, and injected back into a bee.

So the mite appears to be dramatically boosting the virulence of the viruses.

Foulbroods and fungi

Honeybees also suffer from two known bacterial pathogens, both of which only harm bee larvae, not adults.

However, the bacteria cause diseases known as foulbroods, and infected larvae die from starvation. This leads to huge losses for beekeepers.

For years across Europe, many colonies appeared to spontaneously recover from foulbrood infection.

A British beekeeper tells the BBC he welcomes new funding into bee research

But in some countries, such as the UK and Switzerland, European foulbrood has become a major problem for apiculture, with the disease almost spreading out of control in Switzerland.

And if that picture isn't complicated enough, Prof Genersch details one other natural enemy of honeybees: a fungus known as Nosema, which comes in a variety of related species.

All infect the guts of honeybees, often killing them.

But to what extent remains unclear, and it is possible that the fungus only kills bees in hot climates.


That means that the fungus might be causing honeybee declines on a regional, not global level.

"These examples show that, even in Europe, diverse pathogens are involved in the presumed 'inexplicable' colony losses," writes Prof Genersch.

"Although the decline in managed honeybees equally seems to be a problem in the US, Europe and Japan, the factors responsible differ from continent to continent and region to region."

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