The relationship between agricultural intensification and biological control: experimental tests across Europe.

Agricultural intensification can affect biodiversity and related ecosystem services such as biological control, but large‐scale experimental evidence is missing. We examined aphid pest populations in cereal fields under experimentally reduced densities of (1) ground‐dwelling predators (−G), (2) vegetation‐dwelling predators and parasitoids (−V), (3) a combination of (1) and (2) (−G−V), compared with open‐fields (control), in contrasting landscapes with low vs. high levels of agricultural intensification (AI), and in five European regions. Aphid populations were 28%, 97%, and 199% higher in −G, −V, and −G−V treatments, respectively, compared to the open fields, indicating synergistic effects of both natural‐enemy groups. Enhanced parasitoid : host and predator : prey ratios were related to reduced aphid population density and population growth. The relative importance of parasitoids and vegetation‐dwelling predators greatly differed among European regions, and agricultural intensification affected biological control and aphid density only in some regions. This shows a changing role of species group identity in diverse enemy communities and a need to consider region‐specific landscape management.