The Role of Cultivar Mixtures and Intercropping on Cereal Aphid Populations and Crop Yield in Mediterranean Organic Winter Wheat

Abstract Crop diversification has been proposed as a sustainable strategy for pest control in organic cereal fields. In this study aims at improving our understanding of the ecological processes related to aphid control in real farming conditions to enhance functional agrobiodiversity. We assessed the effect of genotypic (cultivar mixture) and interspecific (burclover undersowing) diversity and its stacking on cereal aphid populations, beneficial arthropods and yield. We analyzed several variables related to aphid population, parasitism rate and abundance of predators. We established 10 treatments differing in crop diversity: three single-cultivar wheat crops (Florence-Aurora (FA), Montcada (MO) and Forment (FO)) and two cultivar mixtures (FAMO and FAFO) duplicated with a burclover undersowing in five organic fields. Polycultures had a positive effect on yield. Wheat cultivars differed in aphid abundance, with FA being the most infested. The influence of genotypic diversity on aphid control was cultivar specific. FAFO significantly lowered aphid abundance and aphid density on Florence-Aurora tillers, whereas FAMO did not provide pest control. Further, a higher burclover ground cover was negatively associated with aphid abundance, particularly in the FA treatment. Therefore, the stacking of the two diversity treatments did not out-perform the implementation of a single diversity treatment. Planned diversity did not affect the abundance or richness of predators nor parasitism. Thus, our results suggest that aphid control in polycultures was related to bottom-up effects. To conclude, our study shows the potential of field research as a promising tool for designing functional multiple crop systems in real farming scenarios.