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75 percent decline in insects in parts of Germany

A recent study on the disappearance of insects is making headlines: it found that the insect biomass has declined by more than 75% in certain areas in Germany that were monitored by the study over a period of 27 years. The authors believe that the dramatic decline in insect biomass is down to industrial agriculture, which is therefore in conflict with certain bioeconomic principles: the sustainable cultivation of biomass and the safeguarding of food supply.

BIOPRO spoke with Alexandra-Maria Klein, Professor of Nature Conservation and Landscape Ecology at the University of Freiburg, about the possible consequences for nature and humans of insect die-off, and the changes that need to be made in agricultural practices. Amongst other things, Klein examines how the biodiversity of plants and animals influences ecosystem functions and what effects the loss of biodiversity has on humans.

Insect die-off is omnipresent in the media – is this scaremongering or reality?

Alexandra-Maria Klein, Professor of Nature Conservation and Landscape Ecology © Felix Fornoff

Media interest in this subject has been aroused by a particular study carried out by the Krefeld Entomological Association (1). For 27 years, the members of this association have been catching and weighing flying insects at more than 60 nature protection areas in the German states of North Rhine-Westphalia, Rhineland-Palatinate and Brandenburg. The analysis reveals that the annual insect biomass has declined by more than 75 percent.

The study has several peculiarities: the field work was not carried out by scientists, but by hobby entomologists whose initial goal was certainly not to document the disappearance of insects, but to look for rare species. Although the study has some methodological deficiencies - some traps were not sampled at the same place each year - renowned researchers were involved in the analysis of the data to statistically balance these problems. The amount of data and the duration of the study are impressive and the results alarming.

The decline in insect biomass is therefore a reality, especially since the results of other studies also point to a considerable decline in insect biomass and we can all see that things are very different from how they were years ago: car windscreens stay almost clean in the summer.

Why have insect numbers declined?

The Krefeld study shows that some protected areas are surrounded by arable land. Think of them as small islands in a sea of cereal fields. The authors show that the increase in arable land in the immediate vicinity and the presence of nitrogen, in other words, intensive land use, is associated with the disappearance of the insects. We also know from our own studies that in intensively used and cleared agricultural landscapes far fewer insects as well as other types of insects can be found than in agricultural landscapes with a lot of wooded areas and flowering plants.

What about insecticide use?

The Krefeld study does not provide any information about this. Several studies have been carried out on insecticides, especially neonicotinoids. The picture is inconsistent. Insecticides seem to have different effects that cannot always be explained in biological terms. We also do not know how a mixture of pesticides affects insects. Further research under real field conditions is therefore urgently needed.

Does climate change play a role in this development?

The authors could not find any connection.

What effect does the vanishing of insects have?

Insects are at the base of an ecosystem: they are food for other animals, such as fish, frogs and birds. In the absence of insects, the number of vertebrates that feed on them declines as well. A decline in the number of birds has already been documented. Indirectly, insects also secure our food supply. They play an important role in biological pest control, because beneficial insects regulate pests. In conventional agriculture, however, the balance has long since shifted, i.e. nowadays there are more pests which in turn have to be fought off with insecticides. However, these insecticides also kill beneficial insects. And insects naturally pollinate a variety of our crops such as strawberries, apple and cherry trees, sunflowers, carrots and many rape seed varieties.

Dark bumblebee on an Echinacea flower. This bumblebee species is also used in greenhouse cultivation for pollinating tomatoes.
Dark bumblebee on an Echinacea flower. This bumblebee species is also used in greenhouse cultivation for pollinating tomatoes. © Juliette Irmer
Brimstone butterflies and other butterfly species pollinate flowers too.
Brimstone butterflies and other butterfly species pollinate flowers too. © Alexandra-Maria Klein

What happens if nothing happens?

Our ecosystems will become impoverished. This means that the biodiversity of animals and plants will continue to decrease. Colourful summer meadows with flowers in full bloom will eventually cease to exist and be replaced by green grass meadows, because most flowering plants rely on pollination by insects.

Fruit and vegetable production would also decline. But humans are inventive. Maybe we will manage to grow apple trees that no longer have to be pollinated by insects or build mini-drones that will take over pollination. However, this will take time and money.

A honey bee colony consists of about 40,000 bees in the spring. They are all hungry and pollinate our fruit and vegetable crops as they feed. Wild insects such as bumblebees, flies and butterflies do the same. This is the most natural and sustainable form of pollination and it has been done like this for thousands of years.

The economic value that insects generate by way of pollination has been quantified in several studies. Why has this been done?

The economic value of pollinating insects was estimated at around 153 billion euros per year for global agriculture and 1.6 billion euros for Germany (2). Pollination is one of the so-called ecosystems services – services provided by nature, in this case insects, from which humans benefit. The calculation of the corresponding monetary value illustrates the economic importance of these ecosystem services, and people tend to understand numbers. Ecosystem services are generally difficult to quantify - pollination is based on worst-case scenarios - but estimates are important because they serve as guidelines. Ultimately, it is not about taking ecosystem services for granted any more, but about taking them into account to ensure the sustainable use of nature. However, many nature lovers rightly believe that plant and animal species should be protected for their own sake - not just when they bring benefits to us humans.

How can the decline of insects be halted?

Hedges along apple orchards at Lake Constance © Vivien von Königslöw

Insects find neither food nor protection on intensively managed arable land. There are no weeds, the edges of fields are narrow and there are hardly any hedges. We cannot turn the clock back 100 years, but we can reduce monocultures and nitrogen input, grow hedges and generally promote smaller-scale farming with so-called polycultures and, for example, agroforestry systems. This involves combining agricultural production with the cultivation of trees and shrubs on the same area. For example, walnut or fruit trees are grown on wheat fields or pastureland. Small-scale agriculture in Baden-Württemberg is in a very good state of health. At the moment, for example, we are working on the land of a farmer who plants hedges around his apple trees and prunes his hedges or trees every year. Several families use the woodchips to heat their homes in winter.

Shouldn’t we also use fewer insecticides?

Of course, it would be better if pesticides were only used in a very targeted, rather than preventive, fashion. But we should not name and shame farmers. Large monocultures make it rather difficult to refrain from using pesticides. Moreover, a farmer cannot always risk losing a harvest just because he has decided not to spray fungicides when rain was forecast. Some substances are even allowed in organic farming. We cannot just ban the use of insecticides without offering alternatives.

How can your suggestions be implemented relatively quickly?

Agricultural policy must react directly and support farmers in the implementation of insect-friendly measures such as hedge planting. Currently, many of the regulations tend to be black and white: either you are a conventional farmer or an organic farmer. I would rather see something in between. This is what integrated farming is all about. We should not wait for the results of further research, although it is undoubtedly necessary. But by then it might be too late for some insects. Also, as consumers, we have to contribute: we have to demand food that has been produced in an insect-friendly way. Then governments will be forced to react.

At the moment, agriculture is yield-oriented. Are your solutions really realistic in the light of climate change and global population growth?

We can see things in whatever light we choose: if we continue as we have done so far, there will be negative consequences. We cannot exclude nature, but must realize that protecting nature is also good for us.


1. Hallmann CA, Sorg M, Jongejans E, Siepel H, Hofland N, Schwan H, et al. (2017) More than 75 percent decline over 27 years in total flying insect biomass in protected areas. PLoS ONE 12(10): e0185809. https://doi.org/10.1371/journal.pone.0185809
2. Gallai N, et al., 2009. Economic valuation of the vulnerability of world agriculture confronted with pollinator decline. Ecological Economics Volume 68, Issue 3, 15 January 2009, Pages 810-821. https://doi.org/10.1016/j.ecolecon.2008.06.014

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