The suitability of sown wildflower strips as hunting grounds for spider-hunting wasps of the genus Trypoxylon depends on landscape context

Abstract

Subsidized wildflower strips aim at counteracting insect species loss in agricultural landscapes. Little is known yet about their effects on insects that not only feed on pollen and nectar but also hunt for arthropod prey for larval nutrition. Here, we provide new evidence that wildflower strips may benefit the provisioning of larval prey for spider-hunting wasps. Woody semi-natural habitats in central Germany were selected as trap-nest locations along independent gradients in distance to wildflower strips and percentage of grassland in the surrounding landscape. From these nests, spider individuals hunted by wasps of the genus Trypoxylon (Crabronidae) were collected. In addition, spiders were collected in the associated wildflower strips and the similarity between spider communities in nests and in flowering strips was calculated. The similarity of spider communities decreased with the distance to the next wildflower strips, but the percentage of surrounding grasslands modulated this relationship. This concurred with an observed positive effect of grassland on spider species richness in trap nests, especially if wildflower strips were distant from the nests. In contrast, landscape context did not affect spider species richness in wildflower strips. In conclusion, our results suggest that wildflower strips are used by Trypoxylon wasps for hunting spiders as prey for larvae, yet only if strips are close to nesting habitats and well connected by high shares of grassland. Our results substantiate the importance of wildflower strips for species richness and trophic interactions in agroecosystems.