Exhaust fumes from diesel could be changing the scent of flowers and making it harder for honeybees to collect pollen and nectar, according to a new study.

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© Tracey Newman, Guy Poppy and Robbie GirlingA bee lands on a oilseed rape flower
Pollutants found in diesel exhaust alter levels of chemicals released by flowers which honeybees use to locate and identify varieties with the largest amounts of pollen and nectar, researchers found.

Tests in a laboratory designed to mimic the effect of exhaust fumes on the smell of oilseed rape showed that the bees' ability to recognise the odour was reduced by about two thirds.

Although exhaust fumes are unlikely to be the main cause of the sharp decline in Britain's bee populations, they could be exacerbating the problem, researchers said.

Fumes which prevent honeybees recognising the smell of flowers could "have serious detrimental effects on the number of honeybee colonies" as well as reducing the pollination of vital crops and lowering honey yields, they claimed.

Bees play a crucial role in food production around the world by pollinating crops, and are thought to be worth about £430 million a year to Britain alone.

The government this summer launched an "urgent and comprehensive" review into the reduction in bee populations, with a third of colonies thought to have been lost the previous year.

Scientists from the University of Southampton carried out two experiments to examine whether the foraging behaviour of honeybees was being affected by exhaust fumes.

In the first, they blended eight chemicals which are released by oilseed rape flowers and exposed them to air containing levels of diesel exhaust similar to those recorded at busy roadsides.

They found that six of the chemicals reduced in volume and two vanished completely within a minute of exposure to the fumes, meaning their chemical signature, as interpreted by a bee, would appear completely different.

Further tests showed it was NOx gases (nitric oxide and nitrogen dioxide, both found in diesel exhaust, which appeared to be causing the change in odour.

A group of honeybees had been trained to pick up the scent of oilseed rape, but when the two chemicals worst affected by NOx gases were removed, the proportion able to recognise the odour dropped from almost 100 per cent to about one third.

Because NOx gases are found in greater quantities in petrol fumes, it is likely that these could have a similar effect, researchers added.

Dr Tracey Newman, who led the study, which was published in the Scientific reports journal, said: "Diesel alters floral odours and it is a significant enough change in the chemistry to impact on honeybees' ability to recognise that odour.

"It is not just about a bee getting confused because there's a new smell around, it is that the odour itself is being chemically altered."

This could force bees to spend longer foraging or having to make more foraging trips to help sustain the hive, she suggested, which would likely result in a drop in honey yields and "serious detrimental effects" on pollination activity.

Her colleague Prof Guy Poppy said air pollution could be one factor, along with other "stresses" like viral or mite infections, which are causing the decline in bee populations.

"Bees live in a relatively stressful environment and we think that the combinations of stresses is one thing that potentially might explain some of the dramatic losses in colonies," he said.

Paul de Zylva of Friends of the Earth said: "Bees are highly sophisticated creatures facing many threats including air pollution - this research is yet more evidence that they are under attack from all sides.

"The Government must draft a Bee Action Plan that combats the many threats that bees face."