The bumblebee will become increasingly crucial for the pollination of crops such as fruit and beans as the population of its honey bee cousin goes into serious decline, the researchers say.
Managed colonies of honey bees - which had taken over the role of natural pollinators such as the bumblebee - have declined by one-third in the past 30 years. Beekeepers expect a further decline following migration from the Continent of the Varroa honey bee parasite, detected for the first time in England last March.
Juliet Osborne and Naomi Saville, postgraduate students at Cambridge's department of zoology, have just completed a three-year study of the role played by bees in farm production and the habitats necessary for bumblebees to thrive.
Bumblebees - which have a 'jersey' of yellow and black stripes - have also been in rapid decline over the past 50 years due largely, scientists believe, to changing agricultural practices that have destroyed their habitats.
Crop spraying, destruction of hedgerows and annual ploughing that disturbs perennial wild flowers have all contributed to a drop in the number of bumblebee species commonly seen in Britain from 19 to about 6, the researchers say.
Colonies of honey bees, kept by hobbyists and commercial beekeepers, have offset the effects on crops of the decline in natural pollinators such as the bumblebee, Ms Osborne said. Only one-third of a crop of beans, for instance, will set seed without bees, and cross-pollination by bees of oilseed rape produces a much better quality crop, she said.
If the effects of the Varroa parasite - a spider-like mite that infects hives - follow those seen in the rest of Europe, the added strain on the honey bee population could send it into terminal decline within the next few years, Ms Osborne added.
Ms Saville said that the Varroa parasite could be a blessing in disguise for the bumblebee. 'If Varroa has the same effect here as it has on the Continent we're not going to have much choice between bumblebees and honey bees.'
Bumblebees live in colonies of up to 300 individuals, compared with honey bee colonies of 30,000 or more, and are unaffected by the Varroa mite. Some species have longer tongues than honey bees and this makes them better pollinators as they are less likely to 'rob' a flower of its nectar by biting it at the base, which means the perpetrators avoid brushing against a flower's sex organs to cause pollination.
The researchers found that bumblebees need to feed on perennial flowers, which are rich in nectar, between March and September and require undisturbed, sunlit land for building nests.
'They nest in old mouse holes, under grass tussocks or in trees, so the soil must not be ploughed up each year. The queens hibernate by digging into the soil and so must also be undisturbed in winter,' Ms Saville said.
Farmers will need to consider leaving strips of unploughed and unsprayed land in sunny parts of the farm to build up the bumblebee population. 'Management to establish undisturbed sward and provide sunlit and sheltered areas will enhance farmland and farm woodland habitats for bumblebees,' the researchers say.
The bumblebee research was jointly financed by the Natural Environment Research Council, the Forestry Commission and the Department of the Environment.
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