Data from: Spatial scale, neighbouring plants and variation in plant volatiles interactively determine the strength of host-parasitoid relationships

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.