Fears that mobile phone signals were responsible for a dramatic decline in bee numbers have proved wrong after new research identified the real culprit.

Researchers at Landau University in Koblenz published research in April suggesting that bees were being "confused" by mobile phone signals.

The scientists stated that this was driving the spread of Colony Collapse Disorder (CCD) and leading to the bee deaths.

CCD has caused the death of up to 90 per cent of commercially managed bees in the US, putting $8bn worth of crops at risk which rely on bees for pollination.

But researchers from US universities have identified a virus which they claim is causing the deaths. It is believed to have come from imported bees and royal jelly and has spread rapidly through apiaries.

"We used an unbiased metagenomic approach to survey microflora in CCD hives, normal hives and imported royal jelly," said the report published in the journal Science.

"Candidate pathogens were screened for significance of association with CCD by examination of samples collected from several sites over a period of three years.

"One organism, Israeli acute paralysis virus of bees, was strongly correlated with CCD."

The virus can spread quickly through an entire colony, at which point the infected bees become paralysed and die outside the hive.

The research team suggested that other factors, such as the practice of transporting bees around the country in closed trucks, may have put undue stress on the bees and made them vulnerable to the virus.