Tage der Biodiversität 2027

Agricultural intensification is a major driver of biodiversity loss in agro-ecosystems, affecting both insect communities and the plant resources they depend on. Diversified cropping systems, such as strip cropping, are increasingly implemented to support biodiversity and ecosystem functioning. However, evaluating their effectiveness and ecological value remains challenging because insect communities are highly mobile and change throughout the growing season, vegetation surveys reveal which plants are present, but not necessarily which resources insects potentially use.

In this study, we used DNA metabarcoding to analyze insects and their associated plant communities, assessing the effects of strip cropping while accounting for neighboring flowering plants. Sampling was carried out in experimental strip cropping systems with spring wheat, coriander, and caraway. Insects were sampled by sweep netting along transects, with sampling repeated across three crop phenological stages to capture temporal variation in insect communities and associated plant-traces.

Across the growing season, insect species richness increased, but functional community composition shifted. Pest taxa dominated early and late in the season, whereas pollinators peaked during coriander flowering. Coriander and caraway were associated with distinct pollinator assemblages, suggesting complementary rather than interchangeable floral resources. The later flowering of caraway in August may contribute to extending floral resource availability towards the end of the sampling period. However, flowering of coriander and caraway did not address the June resource gap for pollinators. This highlights that suitable floral resources in cropping systems alone are not sufficient to safeguard biodiversity, but supporting measures need to provide the right resources at the right time. Plant-trace DNA further indicated seasonal shifts in plant resource signals, with Asteraceae repeatedly detected across all sampling periods, suggesting the importance of co-flowering vegetation as a persistent resource for insects in agro-ecosystems.

Overall, our results show that biodiversity benefits in strip cropping systems depend not only on increased plant diversity, but also on resource timing and seasonal continuity. We demonstrate that DNA metabarcoding can link insect community composition with plant-trace signals throughout the growing season, thereby substantially expanding biodiversity monitoring in agro-ecosystems