Benefits of increased cover crop diversity for predators and biological pest control depend on the landscape context.
1. Increasing plant diversity in agricultural systems is a promising way to balance food production and biodiversity conservation. Biological pest control, a crucial ecosystem service delivered by natural enemies, could particularly benefit from increased plant diversity at the local scale. Such positive effects however often depend on the landscape context that shapes the pool of natural enemy species available and their ability to colonize newly created habitats. However, how the landscape context modulates the local effect of plant diversity on natural enemies and pest control services remains unclear. 2. Here, we manipulated the diversity of cover crops (2 versus 20 plant species) in nine pairs of vineyards located along a landscape gradient ranging from 20 to 60% of semi-natural habitats. We sampled natural enemy communities in the soil and foliage and measured the predation rate of an important moth pest in European vineyards (Lobesia botrana). 3. Diverse cover crops enhanced the abundance of natural enemies by 140% across the experiment, but without changing their taxonomic richness and composition. We further found a distance-decay effect of cover crops on natural enemy abundance across cover crop types. 4. The landscape context remarkably modulated the effects of local plant diversity on natural enemy abundance and predation rates. While predation rates were on average similar in the low and high cover crop diversity treatments across the experiment, diverse cover crops had higher positive effects on predation and natural enemies in simple (<50% semi-natural habitats) than complex landscapes. Predation rates increased from 11 to 42% in the high compared with low cover crop diversity treatments in simple landscapes. 5. Synthesis and applications: Our study demonstrates the benefits of increasing plant diversity at the local scale to enhance the abundance of natural enemies as well as the level of biological pest control services in vineyard agroecosystems. Diverse cover crops mostly benefit natural enemies and biological pest control in simplified landscapes, highlighting that the success of local agroecological practices in improving biodiversity and ecosystem services depends on the landscape context. Thus, we suggest that a strategic spatial arrangement of agricultural practices increasing local plant diversity is necessary to maximize beneficial effects on biodiversity and ecosystem services.