Landscape composition affects parasitoid spillover

The intensification of agriculture has led to a severe simplification of agricultural landscapes, resulting in a marked reduction in the diversity of insect natural enemies. However, how this simplification shapes the movement of insect parasitoids between crop and non-crop habitats (i.e., spillover) is still unclear. We examined the potential spillover of tachinid parasitoids from semi-natural habitats into apple orchards across different landscapes. We sampled commercial apple orchards localized in three landscape types (forest-, grassland- or apple-dominated landscapes) to first evaluate if landscape composition affects the local species richness in apple orchards. Second, we tested whether the contribution of forest and grassland habitats to the local tachinid community composition of apple orchards changes according to landscape composition. We found that landscape composition did not affect local tachinid species richness in apple orchards, while it affected the species spillover. Independently of the landscape, we found highly nested communities of tachinids between apple orchards and forest habitats suggesting a strong spillover of tachinids between these habitats. In contrast, tachinids in apple orchards were nested with grassland habitats only in landscapes dominated by apple orchards. Our results have important implications for the conservation of insect parasitoids in agricultural landscapes, as the spillover of species in the crop can be affected by the type and the area of semi-natural habitats in the surrounding landscape.