麻豆淫院

Dikes are indispensable for bees, especially if they are home to many different plant and flower species. A large census conducted on 157 dikes along rivers in the Netherlands revealed that more and rarer bee species live on dikes than previously thought. According to ecologist Constant Swinkels, many more dikes can be made bee-friendly. "Many food products depend on pollination by bees. We really need these little creatures."

Over a period of three years, Radboud researchers, together with colleagues from knowledge centers, collected extensive data on the presence of bees on 160 dikes in the Netherlands, mainly in the Rhine delta (including the Waal and IJssel rivers) and along the Meuse. They encountered a total of 154 different bee species. "That's almost half of all the species found in the Netherlands," says ecologist Swinkels, first author of the study in Proceedings of the Royal Society B: Biological Sciences.

Several times a year during the bee flight season, the researchers went out onto the dikes with a butterfly net, always at the same spot, to count the bees along a 150-meter route. "Sometimes we saw as many as 400 bees in 15 minutes, other times only three," says Swinkels. But overall, the biologist was pleasantly surprised by the number of bees they encountered.

More bees on dikes than in flower strips

"Flower-rich dikes attract many more bees than, for example, flower strips in agricultural areas," says the researcher. "And especially more endangered species. About 10% of the bees we found are on the red list, such as the Knautia bee, the red cuckoo bumblebee, the meadow bee and the variegated wasp bee. These species are rare and their populations are declining in the Netherlands."

Dikes seem attractive to bees because the slope warms up in the sun, making it an ideal place to build a nest, and because all kinds of different plants can grow there.

"Dikes are a kind of insect highway. Many bees enter the Netherlands via the dikes," says Swinkels. "There are sometimes beautiful landscapes around dikes, such as the Ooijpolder on the Waal near Nijmegen. These areas are interesting for bees because of the varied landscape where they can build their nests. Flower-rich dikes are a valuable addition to this, quickly attracting bees. This is more difficult in agricultural strips, where all kinds of crops are sown and the surrounding farmland is less suitable for bees."

Good for food supply

The researchers discovered that the number of bees on a dike increases rapidly when there are more different types of flowers, but that this effect stops fairly quickly: at eight flower types. Above that, bee populations do not grow as quickly. This could be due to a shortage of nesting sites.

"A bee needs two things," explains Swinkels: "Food, which they get from pollen and nectar from flowers, and a place to build a nest. If you have the flowers but nowhere to build a nest, that's the end of the line." Further research is needed to determine whether the number of bees will continue to increase if there are more nesting sites, or whether other factors are at play that prevent populations from growing further.

Nevertheless, having more different types of flowers on dikes is beneficial. The number of red-listed species is increasing, even above eight flower types. Many of these wild bees need specific types of flowers, so the more types of flowers there are, the more different bee species you attract.

Swinkels adds, "We have more than 17,000 kilometers of dikes in the Netherlands. Although there are some real flower-rich gems, the vast majority are still closely mowed and flower-poor, so there is still a huge area with great potential.

"If we allow more flower species to grow on all those dikes, this could result in many more bees. This is very important for biodiversity and for our food supply, because more than 75% of all plants in the Netherlands are pollinated by bees and are therefore dependent on these creatures. What's more, species-rich dikes are stronger than dikes with fewer species."