Warning on climate threat to vital work of bees

Flowering times of mountain lilies in the US appear to be out of synch with their bumble bee pollinators, evidence suggests.

As a result, fewer of the plants are being pollinated and bearing fruit.

The findings point to a phenomenon that may only be local, or could be globally widespread.

Reports of declining populations of bees and other flower-visiting creatures have raised concerns about pollination levels.

There are major implications for farming and food supplies: a third of the world's fruits and vegetables would not exist without the help of bees and other pollinators.

The new research provides early evidence that climate change may be playing a role in driving down pollination.

"Bee numbers may have declined at our research site, but we suspect that a climate-driven mismatch between the times when flowers open and when bees emerge from hibernation is a more important factor," said biologist James Thomson, from the University of Toronto in Canada.

Professor Thomson conducted a 17-year pollination study of the glacier lily, Erythronium grandiflorum, in the Rocky Mountains of Colorado – one of the longest investigations of its kind ever conducted.

He found a progressive decline in pollination over the years which was most pronounced early in the flowering season.

Three times a year Prof Thomson compared the fruiting rate of flowers that were left to be pollinated naturally, or given extra doses of pollen by hand.

"Early in the year, when bumble bee queens are still hibernating, the fruiting rates are especially low," he said.

"This is sobering because it suggests that pollination is vulnerable even in a relatively pristine environment that is free of pesticides and human disturbance but still subject to climate change."

Prof Thomson began his research in the late 1980s after buying a remote plot of land and building a log cabin in a meadow full of glacier lilies.

His findings were published today in the journal Philosophical Transactions of the Royal Society B: Biological Sciences.

The glacier lily's blooming period lasts about four weeks, typically from May to June.

Surveys have shown no clear evidence of a decline in bumble bee numbers in the region.

Prof Thomson said the pollination deficits he had observed were probably due to a "growing phenological mismatch between the blooming of E. grandiflorum and the emergence of its best pollinators".

He added that the activity levels of queen bumble bees and the lifespan of flowers may be highly sensitive to air temperatures, sunshine, precipitation and wind.

"If these factors are changing, subtle dislocations of bees and flowers seem plausible," said Prof Thomson.

The decline of honey bees recorded in the UK and some other countries is a further cause for concern among researchers looking for a cause.

Some scientists believe that bees rely on pollen from a diverse range of plants to keep their immune systems functioning properly.

Where that diversity of plants is no longer available, bees become less robust and population numbers suffer as a result, it is believed.