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uni'wissen 01-2016_ENG

The passion flower offers its nectar to a wasp species that is perfectly suited to this flower. Photo: Catalina Gutiérrez Chacón “Not every plant with a pretty flower is useful for the insects.” disorder. This phenomenon was first observed in the USA, says Klein, and has become more frequent in the past ten years. It involves honey- bees leaving their hive, never to return, for reasons as yet unknown. Tested insects have been found to be infested with Varroa mites, but scientists do not believe that these parasites alone are responsible for the loss of entire colo- nies. “The question is what causes these mites to spread,” says the ecologist. It probably involves an interplay between many factors. Possible candidates include combinations of bacteria and viruses, pesticides like neonicotinoids, malnutri- tion, or climate change. Bees are known to change their behavior when they come into con- tact with pesticides. These substances bring about a change in the sex ratio of bumblebee colonies, and they cause some species of wild bees to stop reproducing. Besides honeybees, says Klein, wild bees have also experienced a severe population decline in Germany. The reasons include intensive agricul- ture, an increase in monocultures, and a resulting loss of biodiversity. “Wild bees and bumblebees can’t find enough food, nesting sites, or material to build their nests in the extensive cultures.” In addition, several wild bee species and bumble- bees have special needs with regard to foraging resources, as the ecologist points out: “The pollinators need the right kind of flower.” Long- tongued bumblebees, for instance, are ideal pollinators for red clover, whose nectar is buried deep in its long floral tubes. The morphology or external structure of the pollinator determines how it can achieve optimal access to nectar and pollen, says Klein. Hardly anyone wants to imagine a world in which there are no bees to pollinate crops. We therefore need to study bees’ needs with regard to food and habitat and factors that could prevent them from meet- ing these needs. Besides various honeybee species, however, the community of pollinators also includes many other winged insects, such as wild bees, bumblebees, flies, beetles, and butterflies. That is the finding of a large-scale study co-authored by Alexandra-Maria Klein. The University of Freiburg professor of nature conservation and landscape ecology studies the entire process of pollination and all actors involved in it. “We should not ignore the role of pollinators that do not belong to the typical bee species, as has often been done in the past,” demands the ecologist. These insects have a much larger part in the pollination process than previously assumed, even though the effect of an individual fly on a flower is a lot smaller than that of a single bee. The European honeybee is only one of more than 570 bee species in Germany and 20,000 worldwide. Since they live in sheltered colonies with up to 70,000 workers, they are at an advan- tage even just in terms of numbers. Plants can also be pollinated by wind or water, but most crop plants profit when insects visit their flowers, particularly when they are bees. A worker from a hive of honeybees, for instance, makes contact with the male organ of a flower, the stamen, when foraging for food. It collects pollen in its bright yellow “pollen basket” on its hind legs. Then it flies to the next flower. If it has brought the right kind of pollen, it lays the foundations for the development of fruit in the gynoecium, the female part of the flower. Bees have received increased public attention in recent years due to so-called colony collapse 21