Landscape diversity increases aphid predation but not predator abundance in wheat fields

Developing sustainable agricultural systems requires understanding how landscape composition and agri-environmental measures (AEM) influence natural pest control. Flower fields, implemented as AEMs, can support predatory arthropods, but their landscape-scale effects and how the landscape diversity modulates their effectiveness remain poorly understood. Here we studied interactive effects of landscape diversity and flower field area on predatory arthropods, pests, and pest predation. Using pitfall traps, visual surveys, and aphid cards, we recorded ground- and vegetation-dwelling aphid predators, aphids, and aphid predation. Sampling was carried out across 27 study landscapes in central Germany in 2022 and 2023, before and after establishing 160 ha of flower fields. The landscapes spanned two independent gradients: landscape diversity and landscape-level area of flower fields. Flower field area and landscape diversity interactively affected spider activity, with flower fields being more beneficial in diverse landscapes. Carabid activity was negatively correlated with flower field area, while vegetation-dwelling predators showed no response to landscape diversity or flower field area. Aphid abundance was negatively correlated with carabid activity density. Aphid predation at the vegetation level increased with landscape diversity, whereas ground-level predation was unaffected. Flower fields and predator abundance did not affect aphid predation. Our results indicate that newly established flower fields provide limited support to natural pest control, whereas landscape diversity can provide positive but inconsistent effects. Enhancing natural pest control may require considering landscape composition and successional stage of AEMs rather than establishment of large areas of non-targeted agri-environmental schemes.