A honey bee visits a flower at the Mughal Gardens at the Presidential Palace in New Delhi, India, Friday, Feb. 12, 2010. (AP Photo/Gurinder Osan)

Vienna - Felix Munk gets stung up to 20 times a day but that doesn't stop him from regularly clambering up to the roof of the Vienna Opera and other city landmarks to check on the bees living above the heads of unsuspecting music lovers and government ministers.

Munk is a member of Vienna's Stadtimker, one of a growing number of urban beekeepers' associations who are trying to encourage bees to make their homes in cities, as pesticides and crop monocultures make the countryside increasingly hostile.

Bee populations are in sharp decline around the world, under attack from a poorly understood phenomonenon known as colony collapse disorder, whose main causes are believed to include a virus spread by mites that feed on haemolymph - bees' “blood”.

As well as making honey, bees are important pollinators of flowering plants, including many fruits and vegetables. A 2011 United Nations report estimated that the work of bees and other pollinators was worth 153 billion euros a year.

“Bees do very well in cities,” says Stephen Martin of the University of Sheffield, an expert on the deadly Varroa mite that has wrought destruction on honey bee colonies around the world since being exported from its native Asia in the 1960s.

“There are lots of plants and flowers in cities for bees to live on. Keeping them on rooftops is a great idea because it keeps them out of the way of people.”

“I think these initiatives are really good, as long as they maintain them properly,” he said. “Once the mite gets into a colony, which it will do, in a period of two to four years the colony will be killed.”

London, Paris and Melbourne are among the cities trying the same approach.

The Vienna Stadtimker get no central help from government but have persuaded officials at many of the city's landmark buildings to let them build “bee hotels” on the rooftops that overlook Vienna's parks and boulevard ring road.

Speaking to Reuters while swapping out honeycombs on the roof of the 18th century Chancellery where the government holds its weekly cabinet meetings, Munk said the honey harvest would go to the building's officials as gifts.

“It was surprisingly easy to persuade them to allow us to do this,” he said. “Many of them are really concerned about the environment and wanted to do something.”

Munk, 39, works part-time at his software programming job to devote as much time as he can to bees. He learned his craft from his aunt and uncle at the age of seven, but is a rarity in Austria, where most beekeepers are 55 or older.

“It's an old man's hobby,” said Robert Brodschneider, a researcher at the Zoology Institute at the University of Graz and Austria's foremost expert on bees. “There's a shortage not only of colonies but also of beekeepers.”

Brodschneider, who has been collecting data on bee populations in the region for five years, said he had seen a sharp rise in the percentage of bee colonies dying out in the past winter, according to early results of his latest survey.

In Austria alone, where bees have until now fared relatively well, one in four colonies died last winter, compared with a previous range of nine to 16 percent, said Brodschneider.

“I think it's going to be the highest year for losses all over central Europe,” he told Reuters, adding that it was not yet clear whether it was a blip or a sign of an acceleration in bee colony deaths. “We don't know what is going on.”

Munk is realistic about how fast his work can make a difference. “I'd say in under a generation we can't achieve much,” he said. “But everything in life takes time.” - Reuters