The dramatic and ongoing loss of biodiversity in our agricultural landscapes is largely caused by the intensification of agriculture (Seibold et al. 2019; Wagner 2020; Grass et al. 2021). In addition to the loss of habitats and the structural impoverishment of the landscape, chemical synthetic plant protection products (csPPP) and in particular chemical synthetic insecticides are considered to be the main cause of the general decline in biodiversity (Sánchez-Bayo and Wyckhuys 2019; Wagner 2020). A reduction in csPPP use is associated with the hope of halting or even reversing the decline in plant and animal biodiversity and associated ecosystem services in our agricultural landscapes (Zimmermann et al. 2021). However, our understanding of the effects of csPPP on biodiversity and ecosystem services is still inadequate. Previous studies on the effects of csPPP on biodiversity have mainly focused on small-scale areas such as individual arable fields or farms, although pesticide exposure of non-target species extends far beyond these areas (Brühl et al. 2021). Comprehensive csPPP reduction, as also envisaged by the European Commission until recently, will entail profound changes from the agricultural landscape as a whole to the regional level. There is therefore an urgent need for research into the effects of a landscape-wide csPPP reduction.

The aim of the research project is to investigate the landscape-scale effects of csPPP reduction on biodiversity. The studies carried out for this purpose are closely integrated and complementary to the other ecological studies in the project network. The data collected aims at a comprehensive understanding of the effects of csPPP on biodiversity and important ecosystem services of flying insects, birds and bats at the landscape scale.

The following hypotheses will be analyzed:

• Agricultural landscapes with a high proportion of conventional intensive agriculture are more polluted with csPPP than comparable landscapes with a high proportion of organic agriculture
• With increasing csPPP pollution at the landscape level, the species diversity, biomass and functional diversity of flying insects, birds and bats decrease; this is also associated with a decline in ecosystem services
• A spatially optimized and site-adapted csPPP reduction enables a partial restoration of biodiversity in agricultural landscapes

The investigations are carried out in close coordination and cooperation with the other ecological joint projects in a joint study design of the Biodiversity Cluster in 20 study landscapes of 1 km × 1 km each with different pesticide exposure. The VP9 records the species diversity, biomass and functional diversity of a broad taxonomic spectrum of flying insects (e.g. wild bees, wasps, flies, etc.), as well as birds and bats. To record insect diversity and biomass, Malaise traps are set up adjacent to four arable fields in each study landscape. The traps are emptied every 14 days to record phenological changes in the insect communities. The insects caught are identified using DNA metabarcoding and the insect biomass is weighed. The bird and bat communities are automatically recorded in each study landscape using four sound recording devices. Species identification is based on the recorded songs and calls of the animals using established software routines with artificial intelligence. In addition to species diversity, the functional diversity of the insects, birds and bats recorded is determined on the basis of specialist literature and databases, which enables the estimation of important ecosystem services.

The biodiversity and ecosystem service data obtained will be linked with data on csPPP pollution, landscape composition (e.g. proportion of arable land, grassland, management, etc.) and configuration (e.g. field size), and correlations between landscape structure, management, csPPP pollution and biodiversity will be derived. In addition, the collaboration of the joint projects (VP8,10,11) will enable a holistic view of the effects of csPPP on biodiversity. Furthermore, the intersection of ecological and economic data (VP16) will enable spatial trade-off analyses in which ecological and economic goals and consequences of pesticide reduction are weighed against each other.