Prey‐dependent benefits of sown wildflower strips on solitary wasps in agroecosystems

Sown wildflower strips can support insects that collect pollen for their larvae. How these strips affect flower visitors with carnivorous larvae, however, is almost unknown. We studied the impact of wildflower strips and their surroundings on two common solitary wasps: the caterpillar‐hunting Ancistrocerus nigricornis Curtis and the spider‐hunting Trypoxylon figulus Linnaeus. Trap‐nest locations at 22 semi‐natural habitats in central Germany formed independent gradients in landscape complexity and distance to either one or several wildflower strips in their surroundings. For each brood cell, we recorded the number of prey items, total caterpillar weight and spider species richness. Ancistrocerus nigricornis built more cells in proximity to wildflower strips and with increasing amount of surrounding grassland. Fewer prey items provided in landscapes with large shares of semi‐natural habitats suggest that in these landscapes high‐quality prey is available. In contrast, T. figulus built more cells with increasing distance of nests to wildflower strips. If there were few strips, T. figulus built more cells in grassland‐rich landscapes, whereas low shares of grassland were compensated when several wildflower strips were present. Benefits of flowering strips for T. figulus seem related to flower resources for adults, rather than through prey provisioning. In conclusion, wildflower strips promote prey‐hunting wasps through species‐specific effects on adult and larval food provisioning. Considering the differential effects of wasps on crop pests (caterpillars) and natural enemies (spiders), the functional role of wildflower strips in agroecosystems may be much greater than assumed when solely focusing on pollination.