Direct and indirect effects of agricultural intensification on a host-parasitoid system on the ribwort plantain (Plantago lanceolata L.) in a landscape context

Context Intensification of land use is known as a major driver of worldwide decline in biodiversity. Trophic interactions might be especially affected by a changing landscape structure due to agricultural intensification. Objective In this study we investigated the effects of increasing land use intensity on a tritrophic system at different spatial scales in a landscape context. Methods We examined two weevil species, Mecinus labilis Herbst and M. pascuorum Gyllenhal, as well as their common parasitoid, Mesopolobus incultus Walker, living on a common native herb, the ribwort plantain (Plantago lanceolata L.), at 76 sites in three geographic regions in Germany. The effect of land use intensity on species abundances was analysed across a range of spatial scales (100–2000 m) around the study sites. Results In all three regions and across most spatial scales, an increasing proportion of intensively managed grasslands in the surrounding landscape directly negatively influenced herbivore abundance. An increasing proportion of semi-natural habitats had a direct positive influence on herbivore abundance. The abundance of M. labilis was best explained at radii of r = 1500–2000 m, that of M. pascuorum at r = 100–500 m. The parasitoid, M. incultus, was indirectly influenced by land use intensity via the density of its two hosts. Conclusion Agricultural intensification of grasslands can profoundly affect the abundance of their herbivorous and entomophagous fauna at landscape scale. This may have important implications for landscape management and the conservation of higher trophic level organisms in agricultural landscapes. Keywords Grassland Landscape composition Land use intensity Host-parasitoid interaction Ribwort plantain Spatial scale Tritrophic system Trophic interaction