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Insect death in Germany is progressing. Even designated nature reserves do not offer sufficient security for the animals, at least when they border on arable land, as researchers have now found out. Man-made hazards such as pesticides also endanger insects in the surrounding areas. According to the authors of the study, the solution to the problem depends to a large extent on cooperation with local farmers.
Since the 1990s, insect biomass in Germany has declined by three quarters, even in nature reserves, as a long-term study revealed in 2017. Due to declining populations, more and more insect species are being put on the Red List. Around 87 percent of water beetles are endangered or even extinct. The same applies to every third species of grasshopper and every fifth species of butterfly. The insect die-off has devastating effects on ecosystems. Without insects, plants lack pollinators and birds lack food. One of the main drivers of the insect decline is the intensive management of arable land, which involves spraying toxic pesticides.
Data from 21 German nature reserves
A research team led by Sebastian Köthe from the German Nature Conservation Union (Nabu) has now investigated how insect diversity in nature reserves is related to agricultural activity in adjacent fields. To do this, the scientists collected samples in 21 different nature reserves across Germany that are in the immediate vicinity of arable land. Among other things, they set up so-called malaise traps, i.e. tents in which flying insects get lost and finally end up in a container with ethanol. The high-proof alcohol kills and preserves them. The scientists not only used the malaise traps to determine insect diversity, but also analyzed plant traces and pesticide residues that the insects carried into the ethanol.
With the help of DNA analyses, the scientists found out which insect species got lost in the traps and which plants or pesticides they brought with them. This enabled them to extrapolate how diverse the insect and plant world was in the corresponding nature reserves and how this diversity was related to the pesticide exposure. In addition to the samples from the malaise traps, Köthe and his team also included climate and landscape data in their analyses.
Pesticides from arable land endanger insects
The result: arable land leads to a clear decline in insect diversity in the adjacent protected areas. "We have seen that there is a correlation between a high proportion of arable land and low insect diversity with regard to the wider environment of the protected areas," reports Köthe. This has to do with the fact that pesticides sprayed on arable land can be deadly for insects and, for example, are blown into nature reserves with the wind. Accordingly, the more pesticides the scientists found in the Malaise traps, the lower the insect diversity in that area. The size of the protection zones was also irrelevant: "Even large nature conservation areas in the vicinity of an observation site cannot compensate for the negative influences of agricultural areas," explains Köthe.
How could this problem be solved? To find out, the research team also held a series of dialogues with farmers and conservationists. The different perspectives on the topic were recorded in questionnaires, among other things. Köthe and his colleagues got the impression "that the protection of insects is generally supported." However, implementation often fails due to legal hurdles and insufficient funding. In addition, there is often little local data available that would allow tailor-made measures for individual arable land. According to Köthe's team, more location-based data on insect diversity is therefore needed in order to counteract the insect die-off in a targeted manner. In order for the measures based on this to really be successful, they would also have to be worked out directly with the farmers.
Source: ISOE - Institute for Social-Ecological Research, Article: Biodiversity and Conservation, doi: 10.1007/s10531-022-02519-1