Bumblebees in danger
When hearing or reading about declining bee populations, most people think of our honeybees. But here in Europe, honeybees are not actually wild bees; they live largely under the care of beekeepers – and, in most countries, their populations are actually not in decline.
This is very different for our wild bees. There are over 560 species of wild bees in Germany alone. Most wild bees live (and die!) in obscurity – they often occur during a few weeks only, most species live a solitarily life, i.e. they stay alone, and many species are very small, even for insects – some are only a few millimeters in size.
Wild bees play a crucial role in our ecosystems and in agriculture, pollinating a vast array of plants and crops. In Germany all wild bees are under protection. Many bee species are in decline or even severely threatened – they need our attention!
Off all wild bee species, bumblebees are probably the best known. More than half of the 36 bumblebee species found in Germany are considered endangered and 16 are on the ‘red list’ of threatened species.
The ‘Krefeld study’
These sobering numbers may not seem too startling at first glance – the ‘red lists’ of endangered species are getting longer and we have become accustomed to the idea that many animal species are becoming increasingly rare. Nevertheless, a study published in 2017 raised worldwide attention to the plight of insects:
the Entomological Society of Krefeld, in cooperation with several universities, published the results of a long-term study of data collected in over 60 different areas in Germany.
The data clearly showed that the number of flying insects in Germany has declined by an average of sixty-seven percent over the past thirty years. The New York Times titled ‘The Insect Apocalypse is here’ and insect decline had fully entered the public discussion. Numerous other studies have since confirmed the trend found in the ‘Krefeld study’, and very similar trends have been documented for birds, for example. There is no question that we are experiencing a dramatic and widespread decline in biodiversity.
What do we know about the causes?
- The list of anthropogenic changes during the past decades is long. But experts agree that changes in our agricultural landscapes are the most important factor in the widespread insect – and thus bumblebee - decline. Where there was once an abundance of flowering plants, pollinators are now faced with increasing habitat loss. Like all pollinators, bumblebees are closely linked to flowers - without flowers, there are no bumblebees, and without bumblebees and other wild pollinators, there will be no colorful flowering meadows.
- In Germany, about fifty percent of the land area is used for agriculture. And there have been dramatic changes in agriculture in recent decades. Ever larger machines are used on ever larger fields, structures such as field margins and hedgerows have largely disappeared. In these 'tidy' landscapes, bumblebees no longer find food or places to build their nests. Due to heavy use of fertilizers and very frequent mowing, grasslands have become green deserts for insects. Our bumblebees cannot follow flowering resources! As they build nests in which they collectively raise their brood, they depend on a continuous, near-by food supply.
- The heavy use of 'pesticides' also threatens bumblebees: Almost all crops are treated several times a year with a variety of herbicides, fungicides and pesticides, 'weeds' no longer stand a chance. As a result, not only does the bumblebee's food supply disappear - bumblebees are also directly exposed to these various agrochemicals. Even though agrochemicals are often marketed as 'bee-friendly', an increasing number of studies provides evidence of sub-lethal damage (i.e., changes in the organism that are not directly lethal, but nevertheless harmful). How regularly pollinators are exposed to agrochemicals and at which concentration is often unclear and under debate.
The Bees & Trees Foundation is therefore currently funding a scientific study that fills this gap and provides insights into the pesticide exposure of our bumblebees.
In addition to agriculture, which no longer provides a habitat for wild bees, light pollution and climate change with increasingly extreme weather also contribute to the disappearance of bumblebees.
Measuring the invisible threat – bumblebees as ‘pesticide scouts.'
About half of the area of Germany is currently used for agricultural purposes. Here (and unfortunately also elsewhere, for example in private gardens or along railroad tracks) increasing amounts of chemicals such as insecticides, fungicides and herbicides are used.
Bumblebees, like all other wild bees, encounter these pesticides in a variety of ways: for example, by flying through chemical spraying during flower visits, or by ingesting pesticide residues found in nectar, pollen, or surface water. Bumblebees store nectar and pollen in their nests. Chemical exposures can accumulate in the nests, and the entire brood of a nest can be exposed.
An increasing number of laboratory studies is showing negative effects of individual agrochemical substances on our wild bees. However, the ‘field-realistic’ concentrations of the agents are often disputed; and there is a serious lack of data on the actual chemical exposure of our wild bees. Which chemicals do bumblebees come into contact with, in which concentrations and combinations, how much do they accumulate in their nests, and how does this exposure change for adults, as well as for the brood, over the course of a bumblebee season?
The Bees & Trees Foundation is currently funding a scientific study at the University of Konstanz to fill this gap. Forty bumblebee colonies were deployed at various field locations in 2021 and regularly sampled for nectar and pollen. The samples are currently being analyzed for over 200 common pesticides. The methodology developed in this study will provide useful information on how to use bumblebees as ‘pesticide scouts’ in the future; and the results of this study will provide important information for scientists, environmental activists and politicians.
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