Species-specific responses to the environment can moderate the strength of interactions between plants, herbivores and parasitoids. However, the ways in which characteristics of plants, such as genotypic variation in herbivore induced volatiles (HIPVs) that attract parasitoids, affect trophic interactions in different contexts of plant patch size and plant neighbourhood is not well understood. We conducted a factorial field experiment with white cabbage (Brassica oleracea) accessions that differ in the attractiveness of their HIPVs for parasitoids, in the context of different patch sizes and presence or absence of surrounding Brassica nigra plants. Parasitism rates of experimentally introduced Pieris brassicae caterpillars and the presence of naturally occurring Pieris spp. caterpillars in the plots were assessed throughout the growing season. The abundance of Pieris caterpillars was neither affected by cabbage accession nor plot size. Later in the season, when B. nigra plants had senesced, fewer caterpillars were found on cabbage plants in plots with a B. nigra border. Parasitism rates fluctuated over the season, and were not affected by plot size. However, the B. nigra border negatively affected parasitism rates on the accession that is less attractive to the parasitoid Cotesia glomerata, but not on the more attractive accession. Our results show that plant variation in HIPVs can differentially influence herbivores and parasitoids depending on characteristics of the surrounding vegetation context. These findings underscore the importance of considering the interaction between focal plant traits and neighbourhood context to reliably predict trophic cascades.

Herbivore abundance

Data belonging to the monitoring of naturally occuring Pieris rapae caterpillars. Count data of Pieris rapae caterpillars in different field cabbage plots during mid-season and late-season. See read me file for explanation of the columns.

AartsmaHerbivoreAbundanceOikos.csv

Parasitism rates

Data belonging to the parasitism monitoring experiment, in which parasitism of experimentally introduced Pieris brassicae caterpillars by naturally occuring parasitoids was assessed. See read me file for explanation of the columns.

AartsmaParasitismAnalysisOikos.csv

Superparasitism rates

Separate file in which egg counts of parasitized recollected P. brassicae caterpillars from the parasitism experiment are specified per individual caterpillar. See read me file for explanation of the columns.

AartsmaSuperparasitismAnalysisOikos.csv