Biodiversity and biological control

Agricultural intensity on the local field or farm scale and on the regional landscape scale affects the organisms utilizing the arable landscape, and may affect ecosystem services and functions. This thesis examines how plants, birds, community composition of ground beetles, and biological control of cereal aphids are affected by local agricultural intensity, organic farming and the surrounding landscape in Sweden and across Europe. The contribution of naturally occurring predator groups to the control of cereal aphid populations in complex and simple arable landscapes is also examined. Overall, an increase in yield or pesticide use decreased species richness of all studied organisms, and reduced the biological control potential. Organic farming was beneficial to plants, whereas the effect on ground beetles and birds differed between studies. Organic farming enhanced biological control potential in heterogeneous landscapes only. On conventional farms the biological control was similarly high in all landscapes. Plants and birds were more abundant and species rich in heterogeneous landscapes, whereas ground beetles, especially omnivores, were more abundant in homogeneous landscapes. Ground-dwelling and flying predators reduced both the density and population growth rate of cereal aphids. This thesis will improve the understanding of effects of agricultural intensity on biodiversity and biological control of cereal aphids across Europe. Although results vary among taxa and trait groups, they show that a shift towards farming with minimal pesticide use over large areas would affect biodiversity positively. The thesis also shows that naturally occurring predators are able to suppress cereal aphids and thereby reduce the need for insecticide applications. Finally, local management and landscape complexity need to be considered when developing future agri-environment schemes