Natural enemies emerging in cereal fields in spring may contribute to biological control

Biological pest control is known to depend on landscape heterogeneity. However, such relationship shows irregular pattern and seems influenced by local farming practices and natural enemies that overwinter within crop fields. The objective of this study was to assess the contribution of emerging natural enemies in spring to biological control, and their response to the interaction between landscape heterogeneity and farming intensity. We monitored the overwintering insect community using emergence traps and measured the local potential pest predation using prey cards in 30 cereal fields, in spring in France. Study fields were selected along a landscape heterogeneity gradient and farming practices were recorded. None of the ten emerging taxa influenced predation of lepidopteran eggs or weed seeds. On the ground, aphid predation was positively correlated with emerging carabid beetles. In foliage, aphid predation was negatively correlated with emerging parasitoids. Overall, the community of natural enemies that overwinter within crop fields seemed to benefit from lower crop diversity and higher edge density in combination with higher farming intensities. This suggest that they represent a subset of species adapted to. This study highlights a large broad taxonomic panel of emerging natural enemies and their potential local pest predation.