Associative cropping, which consists of planting different crop species together, is increasingly promoted as a sustainable strategy to reduce pest pressure and enhance agroecosystem health and resilience. Planting oilseed rape (Brassica napus) alongside faba bean (Vicia faba) has proven to efficiently reduce oviposition punctures by the rape stem weevil (Ceutorhynchus napi), a major insect pest of oilseed rape. Using a combination of behavioural assays, volatile profiling and untargeted metabolomics, we investigated how cropping context influences plant-mediated interactions between host plants and ovipositing females. Results showed that previous oviposition by conspecifics induced contrasting behavioural responses depending on cropping system. While females preferentially oviposited on previously attacked plants grown in monoculture, oviposited plants grown in association with faba bean became less attractive than their non-attacked counterparts and no longer elicited oviposition preference. Volatile analyses revealed increased emissions in associated plants as compared to monocropped plants. In contrast, untargeted metabolomics identified oviposition as the primary driver of non-volatile metabolic variation, with comparatively limited effects of cropping context. Together, these results suggest that associative cropping modifies the chemical information available to host-seeking females. By potentially disrupting the positive feedback normally associated with conspecific oviposition, associative cropping may reduce aggregation behaviour and oviposition pressure. These findings provide new insights into the chemical ecology of diversified cropping systems and highlight how changes in plant diversity can alter chemical cues and reshape insect decision-making.

[1] Breitenmoser, S., Steinger, T., Baux, A., and Hiltpold, I. (2022). Intercropping winter oilseed rape (Brassica napus L.) has the potential to lessen the impact of the insect pest complex. Agronomy, 12, 723

[2] Magnin, L., Hiltpold, I., Jullien, A., and Baux, A. (2025). Intercropping mitigates incidence of the oilseed rape insect pest complex. Pest Management Science. Advance online publication.