Biodiversity in Baden-Württemberg: nature reserves are important for wild bees

• What is the flying insect monitoring project?
• The Krefeld study proved insect decline for the first time
• Insect monitoring in nature reserves and unprotected areas
• Initial results of long-term monitoring of flying insects in Baden-Württemberg
• Protected areas are important for wild bees
• Biomass comparable, species number decisive
• What we don't know yet ...
• How do the results help to better protect insects?
• What is the next step in monitoring flying insects?

What is the flying insect monitoring project?

In Baden-Württemberg, insects are caught and counted to find out how many and which species still exist. For example, flying insects are recorded on a random basis. This kind of systematic recording is called monitoring. The flying insect monitoring project of Baden-Württemberg focuses on wild bees, wasps and flies, among others. It is part of the collection of basic data on insect populations in Baden-Württemberg, which has been carried out since 2018 as part of the "Special Programme to Strengthen Biological Diversity".

Other parts of the monitoring project include butterfly monitoring, grasshopper monitoring and ground beetle monitoring.

The Krefeld study proved insect decline for the first time

In 2017, the Entomological Society Krefeld published a highly acclaimed study on insect decline. For the first time, a scientific long-term survey of the biomass of flying insects in Germany was evaluated, with results from almost 30 years. The findings of the study were alarming and highlighted the urgency of insect protection.

The flying insect monitoring programme in Baden-Württemberg is one of several continuations of this survey and is also planned as a long-term project. This will enable us to compare the data collected with that from the past and derive trends.

Insect monitoring in nature reserves and unprotected areas

Our tasks include setting up and maintaining so-called Malaise traps, which are used to take a random sample from the insect communities every two weeks. As the focus is primarily on insects in open cultural landscapes, all sampled areas are located on meadows; insects in forests, for example, are not recorded.

Another special feature is that half of the areas are located in nature reserves and the other half outside them. This allows for assessment and comparison of the insect communities in nature reserves and in unprotected areas.

Since most insects are not active in winter, the surveys take place from spring to autumn. Every year, ten stations are set up, which look like small tents. The insects are caught in a bottle that can be easily unscrewed for sampling. But the most important part comes afterwards: archiving the samples. To preserve the insects for a very long time, they are preserved in containers with ethanol and stored in freezers. The aim is to be able to identify the species accurately at a later date. Since the same areas are surveyed every four years, it will be possible in future to document the development of insect populations at these locations. This will provide answers to important questions: Do the same species occur over a longer period of time or do some disappear? Are new species spreading? And how big is the problem of insect decline in Baden-Württemberg?

The biomass of flying insects can be recorded particularly quickly. The samples are usually weighed immediately after collection. The biomass can be used to estimate the approximate number of insects in the area, as more weight usually means more insects.

Initial results of long-term monitoring of flying insects in Baden-Württemberg

Unlike weighing biomass, accurately identifying species is much more time-consuming. So far, our team has managed to identify the wild bee species from three years of monitoring (2019-2021). By 2022, a total of 14,199 bees had been sorted individually and examined in detail under a stereo microscope, and a total of 239 species had been identified. In addition to the complex identification process, time is also required for preparation, labelling and archiving in the collection. It took five years after the start of the project before the evaluation and description of the results could begin. By way of comparison, the biomass data has already been evaluated for the entire period from 2018 to 2024.

Bees are the first insect group that we have been able to evaluate on a larger scale. As there is not yet sufficient long-term data available, for example over 8 or 12 years, reliable statements can currently only be made about the conservation status of the areas studied. How the populations of individual species are developing can therefore only be analysed in the future.

Fun fact: In Germany, there are approximately 580 (wild) bee species in total, 460 of which occur in Baden-Württemberg.

Protected areas are important for wild bees

At the end of last year, we published our initial findings on the bee species we identified and the total insect biomass in a scientific journal (Frenzel et al., 2024). Our findings show that there are more bee species in protected areas than in unprotected areas. We also took other factors into account in our evaluation, such as the plant species found in the areas and the composition of the surrounding landscape. The nitrogen content of the soil and the number of insect-pollinated plant species also played a role, but had less influence than the protection status: on average, 14 additional bee species can be attributed solely to the protection status of the nature reserves. Although we already expected to find more bee species in nature reserves, it was important to prove this correlation. On the other hand, the nitrogen content of the soil in unprotected areas is significantly higher, as estimated from the respective plant communities on the sites. It is likely that nutrient input into non-protected areas is higher due to more intensive cultivation of the surrounding landscape.

Biomass comparable, species number decisive

Another finding is that the biomass of flying insects is the same in protected and non-protected areas. We did not expect this at first, but it is not unusual, as comparisons with similar studies show. We conclude that it is all the more important to look closely at species, as biodiversity and insect biomass do not necessarily follow the same patterns. Even if this is very time-consuming in the case of insects. The evaluation of Red List species also shows that it is necessary to take a closer look. This is because there were not only more bee species in nature reserves overall, but also more endangered species from the Red Lists of Germany and Baden-Württemberg.

What we don't know yet ...

So far, we can only look at the first few years of a long-term project. At this stage, it is therefore not yet possible to make any statements about long-term trends. To do this, monitoring must be carried out for longer and the samples already collected must be further processed. For example, we cannot yet say whether the number of bee species in the protected areas is stable. Evaluations of other long-term studies have shown that although the number of butterfly, bee, beetle and spider species is generally higher in nature reserves, the species are disappearing from the landscape at the same rate as in non-nature reserves (Cooke et al. 2023; Rada et al. 2018). The causes are not yet fully understood. Climate change, habitat loss, pesticides, light pollution and other harmful influences certainly play a role, but much more research is needed to understand the exact relationships between the many factors.

How do the results help to better protect insects?

The results will help us in the future to find strategies to better protect our native insects. If, for example, it turns out that the number of bee species in Baden-Württemberg's nature reserves is indeed declining, we could recommend establishing buffer zones around the protected areas where no insecticides should be used.

What is the next step in monitoring flying insects?

As methods for identifying insect species will continue to evolve in the future, the samples can be further examined at any time. On the one hand, it is conceivable that automated image recognition will enable accurate identification of insect species in a few years or decades, which would be significantly faster than manual identification under a microscope. On the other hand, molecular identification methods could be developed that enable reliable identification by detecting insects solely on the basis of DNA residues in the environment. In the meantime, however, research data will continue to be collected and published, and the insects will be added to the entomological collection and archived for the long term. Flying insect monitoring is thus an interface between current research and traditional museum work.

The following people are or have been involved in the flying insect monitoring project: Sonia Bigalk, Dr. Tobias Frenzel, Raffaele Gamba, Dr. Sebastian Görn, Dr. Michael Haas, Dr. Maura Haas-Renninger, Andreas Haselböck, Thomas Hörren, Prof. Dr. Lars Krogmann, Dr. Martin Sorg, Hubert Sumser, Florian Theves, Dr. Mike Thiv, Ingo Wendt.