Enhancing rape pollen beetle parasitism within sown flower fields along a landscape complexity gradient
Abstract:• Sown flower habitats not only are employed in agri-environment schemes in the European Union to enhance pollinators and birds, such as partridges, but also are hypothesized to contribute to the biological control of pests such as the rape pollen beetle Meligethes aeneus Fabr. by improving habitat and resource availability for its specialized parasitoids.
• In the present study, we selected 20 sown flower fields that included one of the pollen beetles' host plants Sinapis alba L., each centred in a landscape of varying complexity, to test the influence of the surrounding landscape structure on parasitism rate and herbivory by M. aeneus. Additionally, plant cover of S. alba plants within the sown flower fields and numbers of S. alba flowers were also included in the analyses.
• Landscapes with high proportions of semi-natural habitats supported higher parasitism rates, and sown flower fields with dense S. alba plant cover hosted more parasitoids and suffered from less herbivory.
• We conclude that sown flower fields are not only important for pollinators and birds, but also are long-term undisturbed, unploughed, insecticide-free habitats with rich food (nectar/pollen) and host resources for parasitoids, contributing to the build-up and maintenance of large parasitoid populations, which are important biocontrol agents of rape pollen beetles.