Tougher controls on importing bumblebees are needed to protect native bees, scientists have urged after a study revealed widespread disease in colonies being brought into the UK.
Around 40,000 to 50,000 commercially reared bumblebee colonies are imported into the UK each year, to pollinate greenhouse crops such as tomatoes, to boost pollination of other plants such as strawberries and even for use in gardens.
But DNA testing of 48 colonies of buff-tailed bumblebees purchased from European producers found that more than three-quarters (77%) of the colonies were carrying parasites.
All but one of 25 samples of pollen supplied with the colonies as food for the bees were also infected with parasites, the study published in the Journal of Applied Ecology showed.
Further research by the team from the universities of Leeds, Stirling and Sussex found that the parasites carried by the commercially reared bumblebees were viable and could infect both bumblebees and honeybees.
The researchers warned that commercially imported bumblebees could interact with wild bees and honeybees, spreading disease by visiting the same flowers as the other species.
Non-native subspecies of buff-tailed bumblebees are imported for use in greenhouses, but as the buildings have windows and vents to control temperature, they can forage outside while wild bees or honeybees can get in to feed on the crops.
Native subspecies of the bumblebee are used in open polytunnels and are even being marketed for use in people’s gardens, both situations where they can potentially spread disease to wild species.
Disease is one of the major issues facing bees, which are important pollinators of crops and wild plants. Two of the UK’s 25 bumblebee species have gone extinct and a further eight have seen significant declines since 1940.
Research in North America, South America and Japan suggests that parasites introduced from commercial colonies can be a major cause of population declines in wild bumblebees, with one species in Argentina facing extinction in a decade.
The findings of the UK study suggest that the current rules on ensuring imported bees are disease-free were not strong enough, the scientists said.
They called for tighter regulations which would include checking bees on arrival in the UK, better screening by producers, and the development of disease-free pollen food.
Import licences are currently only required for non-native subspecies of bumblebee, which make up around 75% of imported colonies, and while the licences demand the bees are disease-free, they are not screened on arrival in the UK.
No license is required for the 25% of imported colonies that are native subspecies of the buff-tailed bumblebee.
Co-author of the study Professor William Hughes, from the University of Sussex, said: “If we don’t act, then the risk is that potentially tens of thousands of parasite-carrying bumblebee colonies may be imported into the UK each year, and hundreds of thousands worldwide.
“Many bee species are already showing significant population declines due to multiple factors. The introduction of more or new parasite infections will at a minimum exacerbate this, and could quite possibly drive declines.”
He also said: “We’ve got three categories of factors, nutritional stress and habitat loss, pesticide exposure and exposure to existing parasites or new emerging parasites.
“All three are important, and the relative importance depends on the particular bees and location. Very often it is the interaction between them that is likely to be significant.”
For example, exposure to sub-lethal doses of pesticides could make it harder for the bees to fight parasite infection.
All the parasites identified in the imported colonies were already found in the UK, but it is not known whether they were different strains which could vary dramatically from ones to which wild bees in a given area had already been exposed.
Even if they were the same strains that were already in an area, the arrival of infected bee colonies could increase the amount of parasites in the local bee population and raise the risk of infection by multiple parasites, the study said.
Friends of the Earth’s Paul de Zylva said: “Limp regulation has already let in ash die-back and doomed millions of British trees.
“To avoid the same fate for our wild bumblebees, ministers must ensure bee importers comply with stricter rules.
“If the Government’s promised Pollinator Strategy does restore our wild bee numbers, farmers might need fewer imported bees to grow our food.”
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