Experts are mystified by the way the bee plague is transmitted.

Deformed wing virus is suspected of causing abnormalities to honeybees including damaged appendages and stubby useless wings, which typically lead to them being expelled from hives and dead within 48 hours.

It had been assumed that deformed wing virus replicated inside the parisitic varroa mite but new research shows no evidence of the virus growing within the mite, suggesting it cannot be passing on the infection the conventional way when it feeds on bees.

Deformed wing virus has been linked to the collapse of honey bee colonies in the UK. The virus is found in colonies infested with varroa, which spreads a number of bee infections.

Earlier this month experts at the National Bee Unit, near York, blamed a combination of harsh weather, disease and parasitic predators for leaving Yorkshire's 900 beekeepers reeling with average recorded losses of 14 per cent in honeybee colonies so far this year.

Nationally annual colony losses have doubled in the past five years from just over five per cent in 2003 to nearly 12 per cent in 2007.

In the latest research study, scientists used an antibody technique to track the viral particles. They discovered that the virus was only found in the mite's gut, suggesting it was merely eaten. It did not appear to invade the mite's cells and reproduce within them.

Chief researcher Professor Teresa Santillan-Galicia, from Rothamsted Research Institute in Harpenden, Hertfordshire, said: "The presence of deformed wing virus in large amounts in mite faeces suggests it is picked up during feeding on an infected bee. However, one important question remains – how is the virus transmitted to bees?"

Varroa mites cannot regurgitate gut contents so would not be able to transmit the virus while feeding.

Prof Santillan-Galicia said further research was needed.