Insect biomass of protected habitats under the impact of arable farming in Germany

Five years after the well-known study on insect biomass decline in nature protected habitats in Germany over three decades, the project DINA (Diversity of Insects in Nature protected Areas) has investigated the status of insects in 21 selected nature reserves across Germany in the years 2020 and 2021. We used the same methods and protocols for trapping and measuring the biomass of flying insects as in the mentioned study. Across two seasons, we accumulated a comprehensive data set of 1621 data points of two-week emptying intervals. The measured overall insect biomass remained at low levels and corresponds to the published latest figures from the years 2007-2016. There were no significant regional differences, but biomass was negatively correlated with agricultural production area within 2 km of nature reserves. Differences between the two consecutive years were very likely due to well-known natural fluctuations of insect populations, changes in agricultural cultivation and local weather events. The results show that protected habitats are essential for insects, but not sufficient in their function, and that further steps need to be taken for a better protection and sustainment of insects, which fulfil key functions in many ecosystems.