Winter oilseed rape (WOR, Brassica napus) is an economically important crop which faces increasing threats from multiple herbivorous insects. The emergence of insecticide resistance coupled with neonicotinoid bans in certain regions of the world drives the need for efficient alternative control measures. Recent studies have highlighted the potential of multi-cropping practices on lowering pest pressure in WOR fields. However, underlying mechanisms shaping multi-trophic interactions in diversified WOR landscapes are largely unknown. Here we present how service planting with faba bean (Vicia faba) can impact glucosinolate production in oilseed rape, with associated plants displaying altered defense responses to herbivory by an important coleopteran pest, the cabbage stem flea beetle (CSFB). Behavioral assays with adult beetles revealed that such shifts in secondary metabolite production could further explain part of protective mechanisms service planting can offer. Moreover, olfactometer assays suggest that service cropping influences the emission of volatile organic compounds, which may affect pest behavior and movement at larger spatial scales. Results obtained from laboratory and field experiments help shed light on complex chemical and behavioral interactions driving pest dynamics in diversified agroecosystems.