Landscape complexity is not a major trigger of species richness and food web structure of European cereal aphid parasitoids

In fragmented farmland landscapes structural complexity and low agricultural intensification should decrease the abundance of crop aphids due to increased abundances and species diversity of aphid enemies, including hymenopteran parasitoids. Here we study the effects of landscape structure and agricultural intensification on parasitism rates, abundances, and species richness of aphids and their parasitoids in five different regions in Europe. While total aphid numbers did not differ significantly among regions, we observed marked differences between Scandinavian and central European sites with respect to the species composition of aphids and their parasitoids and parasitism rates. In the cross country comparison landscape complexity and agricultural intensification did not significantly affect total aphid densities, although we observed species-specific reactions to land use. We also observed a tendency towards increased parasitoid species richness at low agricultural intensification but not at high landscape structure.