Where have all the insects gone?

Where have all the insects gone? This question has moved the media at least since the publication of data by the Krefeld Entomological Association in 2017, which showed that the biomass of flying insects caught in Malaise traps has decreased by more than 75 % within the last 27 years.

The studies by the Krefeld entomologists were not designed to systematically and representatively observe long-term developments in insect biomass or insect communities. Rather, data from existing individual studies were evaluated. Nevertheless, a dispute has arisen – also due to the successful marketing of the results – as to whether these statements are tenable, whether they can be transferred to the whole of Germany and, above all, who or what caused the decline.

No matter how this dispute develops: What is important is that this work has opened a political window that was previously closed – despite the scientific evidence that has existed for decades on the alarming situation of biodiversity in agricultural landscapes. Now, both the federal government and the states are launching activities to use scientific methods to prove how the biomass, species numbers and abundance of insects and other important organism groups are developing and which drivers may be responsible for these trends.

The question of the causes for the decline of insects, which is now explicitly addressed in the political-social debate, poses challenges for biodiversity research: On the one hand, the existing evidence base (i.e. the knowledge based on empirical evidence) must be compiled and evaluated in a superordinate manner. On the other hand, systematic monitoring of biodiversity in agricultural landscapes must be designed and implemented, which not only records trends but also allows causal conclusions to be drawn. This is important not only to inform policy-makers about trends, but also to be able to advise them on which specific adjustments should be made in order to bring about change.

In view of the fundamental importance of the ecosystem services provided by insects, such as pollination, natural pest control or soil fertility, research, society and politics can no longer rely on windshield oracles ("There used to be a lot more dead insects stuck to our cars") when it comes to effective protection and, in particular, use of biodiversity in agricultural landscapes. The federal and state governments are called upon to set up a coordinated biodiversity monitoring system that transcends departmental and institutional boundaries. The aim must be to identify long-term trends and perspectives as well as to develop short-term options for the current orientation of agriculture by incorporating existing knowledge.

Together with the Julius Kühn Institute and the Federal Office for Agriculture and Food, the Thünen Institute has developed an implementation concept and indicators for biodiversity monitoring in open agricultural landscapes (MonVIA). At the Thünen Institute of Biodiversity, we are working with volunteers to develop and test methods for the long-term monitoring of wild bees in order to monitor insects in particular.