June 27, 2008

Amid Flower Shortage, Bumblebees Turn To Plant Lice For Sugar

The Bumblebee Conservation Trust (BCT) reports that insufficient numbers of suitable flowers may be driving bumblebees to feed on the sugary secretions of aphids instead.

Although these secretions provide a substitute for nectar, they do not contain sufficient amounts of protein to keep the bees healthy.

Bees are critical pollinators of crops and flowers.  

BBC Scotland recently displayed images on its web site that show the bees visiting tree leaves covered with aphids in a garden in Nairn. There are warnings that bumblebee and wild bee populations in Britain are undergoing "catastrophic declines", and this phenomenon could be a further sign of the problems facing the insects.

BCT director Dr Ben Darvill cited several reports of the behavior, although the reason for it remained unclear.

"It's hard to say for sure, but it does seem as if this behavior is becoming more common," Dr Darvill, a research ecologist based at the University of Stirling, told BBC News.

"Bumblebees are known to feed from aphid secretions, and from extra-floral nectaries on unlikely plants like bracken - but it's more usual to see it in upland areas where there are few other flowers around."

"The fact that it is now frequently observed elsewhere may suggest that there are fewer of the right sorts of flowers around in people's gardens and in the wider countryside," he said.

The bumblebees' ability to smell the sugar was among one of the more fascinating aspects of the behavior.

They normally choose flowers according to color, he said, but are known to have "smelly feet" allowing them to sense if a flower has already had its pollen obtained by another bee.

However, Dr Darvill's fascination is mixed with concern for the bumblebees.

"Bumblebees have struggled in recent decades from habitat loss - three species are extinct in the UK and many more are threatened - so perhaps bumblebees are having to find innovative ways of finding food," he said.

"Although the aphid secretions provide them with a sugary solution, a substitute for nectar, they provide no protein," added Dr Darvill.

"Bumblebees can only get their protein from pollen, which they feed to their growing young, so it is essential for a healthy population."

Research conducted at the University of Stirling has found that certain pollens are particularly rich in protein, according to Dr Darvill.

To assist declining bumblebees, gardeners, farmers and land managers must ensure a constant supply of plants from March through September, he said.

Flowers from the mint and pea families appear to be especially beneficial.

Craig Macadam, a Scottish officer with the conservation organization Buglife, told BBC News that aphids were typically considered a garden pest, although he would not want to see them eliminated.

"Ants often protect the aphids from other predators such as ladybirds and in return they take the honey dew secreted by the aphids."

"There is a fine balance to be struck in the garden - the answer is to put plants in the garden that are of benefit to bees," he said.


On the Net:

Bumblebee Conservation Trust

University of Stirling