Role of parasitoids and landscape structure in aphid population dynamics in winter canola

•Two parasitoids with broad host ranges, Diaeretiella rapae (M’Intosh) and Aphelinus nigritus (Howard), parasitized aphids in central Oklahoma canola fields.•Aphid parasitism by D. rapae was positively associated with characteristics of the landscape surrounding canola fields, particularly the amount of landcover by wetlands.•Parasitism by A. nigritus was positively but weakly associated with landcover of summer crops, but not by other measured landscape variables.•There were fewer aphids and greater parasitism of aphids in field cages that allowed access by parasitoids than in cages that excluded natural enemies.•Guidelines for habitat management to increase biological control efficacy, guidelines for assessing potential for biological control based on knowledge of landscape structure, or both are potential outcomes of the research.