The cereal leaf beetle, Oulema melanopus (L.) (Coleoptera: Chrysomelidae), is a new invasive insect pest of oat, wheat, and barley in western Canada. Biological control with its principal larval parasitoid, Tetrastichus julis Walker (Hymenoptera: Eulophidae), is the primary management strategy. However, to implement control successfully, a thorough understanding of the spatio-temporal dynamics of the interactions between these two species is important. We examined the nature of spatial associations and distribution dynamics of O. melanopus and T. julis with reference to host plant nutrients and plant vigor traits using Spatial Analysis by Distance Indices. A grid design was used to understand spatial associations between O. melanopus and T. julis. Distributions of O. melanopus and T. julis indicated the presence of significant patches and gaps. Plant nutrient availability and plant vigor varied across the grid in all study years. On a spatial scale, O. melanopus and T. julis represented a tightly coupled system demonstrating the strong density-dependent nature of parasitoid dispersal. Among the factors examined, plant vigor traits significantly influenced field distributions of both O. melanopus and T. julis. Areas across grids with high plant density, greater plant height, and high availability of plant leaves indicated higher establishment of O. melanopus larvae, consequently exhibiting bottom-up effects on T. julis distributions. Maintenance of uniform plant vigor can be a critical aspect in mitigating yield losses from O. melanopus infestation.