Bee may be the buzzword as World Bee Day is celebrated around the globe at Slovenia's initiative on 20 May, but the day underlines the importance of all pollinators, including bumblebees, which researchers say are doing a tremendous job.

Bumblebees, solitary bees, hoverflies, butterflies and other wild pollinators are responsible for more than half of pollination in agriculture, and food security depends on pollinator diversity.

An apiary on the roof of the National Institute of Biology in Ljubljana serves as a research lab for the breeding and study of bumblebees and solitary bees to protect them and thus preserve biodiversity.

The apiary was put up at the initiative of Danilo Bevk, a pollinator researcher at the Department of Organisms and Ecosystems Research, who has been studying pollinators for more than 30 years.

"My fascination with bumblebees started when I was less than ten and my father showed me how children used to catch them, put them in a box and bring them home," Bevk says as he shows the way into the apiary.

Reached by steep stairs, the rather simple and small wooden structure is full of life. The bumblebees fly freely in and out to forage for their own food. There is plenty around as the institute is located in a meadow near Rožnik Hill, a large wooded area, with a line of Japanese cherry trees in front of it.

"They live a pretty normal bumblebee life. But because they nest in a laboratory, we can observe them with various sensors without disturbing them too much," Bevk says.

They observe them using red light. Unlike people, bumblebees do not see red light, so they behave more naturally, while researchers can inspect their behaviour closely.

The first bumblebees were introduced in the apiary in April and there are seven families at the moment, each nesting in their wooden nest box. It is not possible to see the nest because it is covered with moss, but it is possible to spot bumblebees as they walk on it.

Each nest box has a special tube or a "bridge", as Bevk calls it, that bumblebees can use to go outside and collect food. "If you look closely, you can see pollen on their hind legs or on their hairy bodies," he points out.

The bumblebees are bred from native populations. "It would be easier to buy imported ones, but they are a different subspecies. Cross-breeding and introducing new diseases could endanger the native populations, so we don't want them to get into the environment," Bevk explains.

Before they are introduced to the apiary, bumblebee families are raised in a separate laboratory. Captured queens are placed in breeding containers and put in a chamber with the right temperature and humidity.

"The queens eventually lay their eggs and thus produce families. Once each family has at least 15 workers, they are moved to the nesting boxes in the apiary," Bevk explains.

Bumblebee research is important because bumblebees are important pollinators. "Without them many plants would not be pollinated, especially in bad weather. They are active in rain, cold and wind," says Bevk.

In spring when fruit trees are in bloom such weather is common and without bumblebees there would be no fruit. Their ability to warm their bodies, their stocky bodies, covered in dense hair make them adapted to flying even at low temperatures.

They are also fast. "They pollinate two to four times more flowers than bees in the same time. Bumblebees also leave more pollen on the flowers because they are more furry and bigger," Bevk adds.

Another advantage is their ability to pollinate with shaking, which is how tomatoes and blueberries are pollinated and which honey bees cannot do effectively.

"When it was discovered in the early 1980s that bumblebees can pollinate in such a way, a mass lab breeding of bumblebees started. Today it is worth more than €50 million. Bumblebees pollinate much more than you would think based on their numbers," says Bevk.