Enemy release, biotic resistance and the success of invasive forest insects

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My research aims to increase our ability to manage forest insects through improved understanding of factors that affect natural enemies regulating forest-feeding insects. Specifically, I explore questions related to population mortality and community diversity of insect natural enemies, with focus on understanding and manipulating native parasitoids and predators. Recent introductions into Canada of several major forest insects (emerald ash borer, Asian long-horned beetle, Sirex woodwasps) enables us to compare the complexes of native and exotic natural enemies, and to explore mechanisms by which these communities affect host mortality and pest invasion. My current work tests hypotheses about how exotic species and communities displace native ones in order to better understand invasion processes in the forest. In this proposal, I test the enemy release hypothesis (ERH), more specifically, the enemy reduction in nonindigenous species hypothesis (ENRS). I ask the questions, does ENRS explain patterns of enemy attack and host productivity on indigenous (Ips) and exotic (Tomicus) bark beetles, or is there evidence for biotic resistance (BR). The eastern pine engraver beetle (I. pini) is native to NA, while T. piniperda (another phloem-feeding scolytid) was introduced from Europe during the 1990's. The latter has become established; both are sympatric and feed on the same native (P. strobus, P. resinosa, P. banksiana) and exotic (P. sylvestris) pines in stands across southern Ontario. Using this exotic/indigenous bark beetle system, I will test ERNS with respect to levels of predation, parasitism, and community diversity of enemies and associates on these two beetles. I predict that enemies of the indigenous beetle will be more diverse and occur at greater densities than those of the nonindigenous Tomicus. Biogeographic and ontongenic data will be derived across a gradient of beetle densities to quantify the degree to which enemies are present, and account for beetle mortality and productivity. These results will add to our current understanding of invasion dynamics, and at the applied level, help to direct management strategies for invasive alien forest insect species.