Biotic resistance to Sirex noctilio across multiple spatial scales

Non-native species can have tremendous economic and ecological impacts on naive environments, but not all invasions are equal. Variable environmental and biotic conditions can strongly affect an invader's performance, making them massively impactful in some regions and benign in others. Sirex noctilio (Hymenoptera: Siricidae), the European woodwasp, is one such example, as it is the most important insect of plantation pine in the Southern Hemisphere, but is a fairly innocuous insect in northeastern North America. Interactions with native biota in North America may provide a degree of biotic resistance to this insect's invasion. I investigated mechanisms of biotic resistance across multiple spatial scales: 1) adaptation by native parasitoids to S. noctilio across the invaded region, 2) Stand and tree-level patterns of association among S. noctilio and co-colonizing agents (native insects and root rot disease fungi), and 3) within-tree effects of host species and bluestain fungal infection on S. noctilio development. My research has three major contributions to our understanding of cross-scale mechanisms of biotic resistance affecting S. noctilio: 1) pine host plays a key role in S. noctilio colonization and operates across spatial scales, 2) negative associations with native insect and their bluestain fungi occur at the sub-tree and tree spatial scale, but dissipate at the stand level, 3) pattern associated with hymenopteran parasitism is weak across scale, but North American parasitoids appear able to attack S. noctilio early in the invasion process. These findings suggest native parasitoids, cocolonizing subcortical insects, root rot disease, and insect-vectored fungi may be providing a degree of biotic resistance to S. noctilio in northeastern North America. Individually, none of these components are clear impediments to this insect's success, but in totality their collective detractions create unfavorable conditions. Understanding how mechanisms of biotic resistance operate in endemic populations of the northeast will provide a critical conceptual bridge for how this insect could operate in at-risk regions of North America because of the similarity in parasitoid and insect assemblage.