LJUBLJANA (Reuters) - When you visit the main congress center in Slovenia’s capital you may get more that the usual conference: how about a jar of honey?

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Since 2011, the center -- Cankarjev Dom -- has been hosting bees on its roof, producing about 120 kg (265 lb) of honey per year which are used for gifts to business partners.

It started at the Apimondia world congress of beekeepers in 2003, held at Cankarjev Dom.

“There was a beehive set in the nearby park and ... a memory of my teenage years came back when I helped my uncle who had bees,” said Franc Petrovcic, head of maintenance of mechanical equipment at the center.

Petrovcic, who last week won an international agriculture fair award for the quality of his honey, started a movement that is spreading fast.

It is estimated that bees are now to be found at about 150 locations in 300,000-population Ljubljana, mostly in gardens, on roofs and terraces.

Gorazd Trusnovec keeps bees on 15 locations in the capital, among them the roof of the building of the state radio channel, Radio Slovenia, where there is a wonderful view on the Ljubljana castle on one side and the Alps on the other.

“Ljubljana has a huge potential (for beekeeping) because it is very green and located in the middle of forests,” Trusnovec said.

Petrovcic, meanwhile, says recent tests showed that urban honey is very healthy. For one thing, it has no traces of pesticides since there are no large fields in the vicinity.

Bee populations across European Union have been in decline for years mostly due to an extensive use of pesticides in agriculture.

Slovenia, an Alpine state of 2 million people, has about 10,000 beekeepers and thus a higher concentration of them than in any other European Union country, according to the national statistics office.

The country has proposed to the United Nations that it declare May 20 as World Bee Day to commemorate the birth date of the one of the Europe’s first beekeepers, a Slovene Anton Jansa, born in 1734. The initiative gained support of the Food and Agriculture Organisation (FAO) last month.

Beekeeper Trusnovec hopes the declaration will raise global awareness that there is no life without bees because they are needed for pollination.

He said roofs are excellent for beekeeping because “bees are wild animals with defense mechanisms so they need to be kept at some distance from people”.