The intercropping of two or more crop species on the same piece of land at a given time has been hypothesized to enhance crop yield stability. To address this hypothesis, we assessed the grain yield stability of various barley-pea and wheat-faba bean mixtures grown in seven experimental field trials (locations) across Europe during two years with contrasting weather (2017 and 2018). Three different yield stability measures were used, all based on the expected yield variability of the mixture components grown as sole crops, and the corresponding observed yield variability of the same components grown in 50:50 mixtures in a replacement design. Stability indices were calculated as ratios between the expected and observed variabilities, with values > 1 indicating greater stability of the intercrops. Mean grain yields tended to be higher in intercrops than sole crops. However, in contrast to our hypothesis, the observed (intercrop) yield stability was similar or lower than the expected (sole crop) stability in most locations except one. Furthermore, yield stability significantly increased with increasing mean yields when assessed across differentially productive locations. The results are relevant for the designing of intercropping systems as a means to increase yield stability and the resilience of cropping systems.

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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.