Associating cultivars or species with complementary traits is key for enhancing aphid control through bottom-up effects

Organic farming promotes diversification strategies to enhance ecological functions. However, early field studies suggested that not all cereal polycultures confer benefits in terms of pest control. Our research involved a trait-based field study to evaluate the advantages of different wheat polycultures on aphid control and yield. We also explored the bottom-up and top-down effects underlying aphid control. We established 10 treatments replicated in five organic fields: three wheat monocultures (Florence-Aurora [FA], Montcada [MO], and Forment [FO]), a mixture with similar-traits cultivars (FAMO), and a mixture with different-traits cultivars (FAFO), each duplicated with and without a burclover undersowing. We analyzed aphid abundance, number of aphids per tiller, parasitism rate, predatory arthropods' abundance, and crop yield. FAFO and burclover undersowing significantly lowered aphid abundance and the number of aphids per tiller on FA. However, the treatments did not affect the abundance of predators or parasitism rates. Finally, wheat yield was similar across treatments, except in 2021 season when FA yielded significantly less. Our findings suggest that polycultures' benefits on aphid control are cultivar specific. Mixing wheat cultivars with complementary functional traits (height and odor profile) and the association of wheat monoculture with a burclover undersowing enhances aphid control by bottom-up effects without compromising crop yield. Nevertheless, stacking the cultivar mixtures with burclover undersowing did not outperform the results of a single diversity practices, probably because of functional redundancy of resistant cultivars and burclover cover.