Landscape and habitat effects on pest control and seed predation by carabid beetles

In both natural and anthropogenic environments, predation by arthropods plays a crucial role in the control of weeds and pests. Carabid beetles (Coleoptera: Carabidae) are key generalist predators feeding on a wide range of prey. The composition and functionality of carabid communities are shaped by multiple factors, both at the local and landscape scale, but these effects can vary depending on the environmental context. Our aim was to explore the effects of landscape composition and local habitat type on carabid community diversity and on insect pest and weed seed predation. We sampled 96 sites belonging to three habitat types (crop field margin, semi-natural and urban green area) selected along a gradient in landscape composition across four regions in northern Italy. Carabid communities were sampled using pitfall traps, insect pest predation was assessed using dummy caterpillars and seed predation was measured using seed cards. Predation rates varied across habitat types, with both pest and seed predation rates decreasing in urban environments compared to crop field margins and semi-natural habitats. Increasing crop areas in the surrounding landscape increased carnivorous carabid diversity and abundance, which in turn increased insect pest predation, while these effects were not observed for seed predation. At the local scale, maintaining semi-natural patches and herbaceous crop field margins, especially in intensive landscapes, represents an effective measure to safeguard carabids and promote the ecosystem services provided by this key arthropod group. However, agricultural expansion at the landscape scale favored carabids and their predation activity indicating that many species are generalist, well-adapted to intensive agricultural landscapes.