Insects and nature conservation
Which flowering plants are healthiest for bees
Good food for bees? A wild bee collects pollen on the flower of a chicory
© Thomas Banneyer / dpa
Not everything that blooms brightly is healthy for bees. A new study names top plants for gardens and meadows. However, some also have disadvantages
Lavender, cornflowers, poppies – or maybe sage? Many people want Bees and bumblebees set the table and plant colorful flowering herbs in their gardens or on the balcony. Flowering islands are sprouting everywhere in inner cities to attract insects. But is what the bumblebees are flying to healthy for them? What nutrients do bees and bumblebees need and can they find them in the colorful flowering areas?
It is known that nectar is the most important energy source for bees, for carbohydrates such as fructose or glucose, while pollen mainly provides protein and fat. Without vital omega-6 and omega-3 fatty acids, bees die early because their immune systems weaken. A poor fatty acid mix, in turn, dampens brain performance. Amino acids are important building blocks for proteins in the body. But too much of them makes bees susceptible to pathogens such as the Nosema fungus, which causes the bee diarrhea feared as “spring consumption”.
The best pollen for bees? Surprisingly little research
So it’s complicated. It’s not just entomologists who are asking themselves the question: which pollen is best for the bees’ diet? However, surprisingly little research has been done on this so far. A study from Canada has now provided new data: a team of researchers from York University in Toronto had pollen from 57 important bee plants in North America analyzed for nutrients – in particular for free fatty acids and vital “essential” amino acids. These included various plant species that are also native to Europe: dandelions, white clover, viburnum and raspberry bushes, for example.
Optimal nutrition is becoming increasingly important for insects, as it makes the little flyers more robust against a growing number of stress factors that have been decimating bumblebees, wild bees and honey bee colonies for years. Diseases and parasites such as the Varroa mite are affecting them, climate change is shifting vegetation zones and changing the nutrient content of plants, wild herb meadows are being mown too often, and pesticides such as the notorious neonicotinoids are killing bees. This is devastating, because the more than 20,000 species of bees worldwide not only pollinate wild herbs, but also countless crops, from apple trees to zucchini.
Honey bees like it low in fat, bumblebees are generalists
However, not every pollinator has the same needs: honey bees prefer low-fat food, mason bees prefer protein-rich food, and the dark earth bumblebee is a generalist and will feed on up to 400 different flowers – if it can find them. When the researchers from Toronto compared the insects’ requirements with their pollen analyses for their study, a kind of “best list” emerged.
The favorite of the healthy honey bee diet, for example, was a yellow meadow flower: the buttercup, which is also native to Germany and is often planted by gardeners and beekeepers as a bee pasture. This certainly helps insects, because the buttercup species is less popular in agriculture and is sometimes even combated: in large quantities, the buttercup is poisonous to cattle and other grazing animals. In the garden, you should wear gloves when handling it, because its sap can cause skin redness.
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Why bees can’t resist
But even more harmless plants proved to be nutritious for bees, such as white clover and yellow bird’s-foot trefoil, raspberries and wild roses, as well as the viburnum bush with its white flowers. Among the larger plant families, the Asteraceae, which include asters, cornflowers and the light blue-flowering chicory, stood out positively. They proved to be a rich source of essential amino acids.
Bees and bumblebees live from mixed calculation
The researchers’ most important finding, however, was that although there are many good pollen plants, none are perfect. Pollen is usually rich in either fatty acids or amino acids, but not both. Bees and bumblebees therefore always have to rely on a kind of mixed calculation when collecting pollen. There are indications that bees “benefit more from a varied flower diet than from a single pollen source,” explains Sandra Rehan from York University, the lead author of the Canadian study. No single plant is therefore optimal for wild bee health.
To get a balanced mix of fatty and amino acids, bees always have to visit many different plants. They need help for this. Their study shows the importance of diverse flowering landscapes for the nutritional needs of wild bees, write the authors. Despite all the well-intentioned planting and gardening, it is therefore immensely important to preserve these areas in particular through nature conservation.