Bees brave British winters
10 March 2010, by Sara Coelho
Bumblebees can now be spotted all year around, especially in Southern England where winter-flowering, non-native plants found in urban gardens provide the food they need to survive the cold months of our British winter.
Tagged bumblebee workers in their nest - RFID tags (small gold rectangles) can be seen glued onto the backs of the bees.
Bumblebee colonies in Britain collapse at the end of the summer, when the old queen dies and its daughter queens go into hibernation before emerging to start their own nests in the following spring.
But since the 1990s, there is increasing evidence of a second generation of bees active during winter. This is likely due to several reasons. 'Warmer winters are an important factor,' says Dr Thomas Ings, an ecologist from Queen Mary, University of London. 'But the availability of food throughout the winter, in the form of exotic, winter-flowering plants in gardens, is crucial.'
To see if bumblebees are collecting enough nectar and pollen to sustain them during winter, Ings and his colleague Ralph Stelzer set up several colonies on the roof of their department at Queen Mary.
They used automatic radio-frequency identification (RFID) technology to tag individual bees and monitor their comings and goings around the colony. They also weighed each bee before and after foraging trips to see how much pollen and nectar they were collecting.
'We found that the bees were coming back with a good load of nectar in a short time,' says Ings.
During latter part of the winter of 2006/2007, 14 bees from one of the Queen Mary colonies were monitored over 261 foraging trips where they collected on average 100mg of nectar per flight, about half the weight of a bee. The foraging trips averaged only 20 minutes. This is enough to keep a healthy bumblebee colony going, so there is no shortage of food during winter.
Very few plants native to Britain flower during winter, so where are the bees getting their nectar and pollen from? To find out, Ings's colleague Marc Carlton paid weekly visits to Kew Gardens to monitor bee activity during winter.
Carlton spotted bumblebees feeding on imported evergreen shrubs such as the popular Mahonia and other winter-flowering plants like strawberry trees or honeysuckles.
Ings says: 'Winter active bumblebee colonies are widespread in Southern England, but activity is restricted to urban areas where there are plenty of exotic flowering plants in parks and our gardens."
Another possible explanation for surging bee activity during winters may be interbreeding between local bumblebees and other subspecies, imported from warmer climates to pollinate tomato and strawberry crops.
Some Mediterranean bumblebees are known to produce active colonies during the winter and they may be passing this ability on to their British cousins. Ings is currently investigating this, among other possibilities.
Ralph J. Stelzer, Lars Chittka, Marc Carlton, Thomas C. Ings. Winter Active Bumblebees (Bombus terrestris) Achieve High Foraging Rates in Urban Britain. PLoS One, published 05 Mar 2010 | doi:10.1371/journal.pone.0009559
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