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

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Globalization ensures that invasive species will continue to arrive, establish, and cause significant disruption in our ecosystems, leading to major global change. My research aims to increase our ability to manage such species through improved understanding of community interactions that affect the natural enemies regulating their populations. NSERC-DG funding will enable my research team to conduct the primary ecological studies proposed here, work that will elucidate key mechanisms driving these changes, as well as potential avenues for their mitigation in forests. Species interactions underpin the theories of enemy release and biotic resistance, and are a major thrust of my research. There is a great need to understand such processes in invaded forests, and my research program represents one of the few academic groups in Canada actively working in this area of invasive species and biological control.Recent introductions into Canada of several major forest insects (emerald ash borer (EAB), Asian long-horned beetle (ALHB), Sirex woodwasps) allow us to compare native and exotic natural enemy complexes, and to explore mechanisms by which these communities affect host mortality and pest invasion. I am best known for my contributions augmenting native natural enemies for biological control in forested systems, widely cited work still definitive in the field, however, my current research explores hypotheses around displacement of native species in order to better understand the invasion process. My specific interests are in community patterns of natural enemies following the introduction of exotics or through forest manipulation. Here, I investigate the enemy release and biotic resistance hypotheses as possible explanations for the community patterns observed as a new species establishes in the forest. I ask the question, which hypothesis better explains enemy attack and host productivity in two closely-related beetle systems; one indigenous (eastern pine engraver beetle, Ips pini), and one recently introduced from Europe (Tomicus piniperda). Both bark beetles are sympatric phloem-feeders attacking native and exotic pines across eastern Canada.Using this exotic-indigenous model system, I will test these two hypotheses with respect to levels of predation, parasitism, specialization, and community diversity of enemies and associates. I predict that in contrast to Europe, natural enemies of the indigenous North American beetle (Ips) will be both more diverse and specialized, and occur at greater densities than those on the nonindigenous beetle (Tomicus), and that this will lend support for the enemy release hypothesis. Biogeographic and ontongenic data will be derived across a gradient of beetle densities to quantify the degree to which enemies are present, and can account for beetle mortality and productivity. By comparing communities (natural enemies, mutualists, and competitors) and patterns associated with these beetles under manipulated densities and controlled biotic interactions, I will be able to establish the best explanatory mechanism. Results from this primary research will add to our understanding of invasion dynamics in our forests, and at the applied level, help to direct management strategies for alien insect species. They will be of interest to scientists, bio-control researchers, as well as policy-makers who regulate invasive species and the public and forest industry concerned with the ecological and economic effects of such species. My proposal requests funding to fuel not only basic knowledge underpinning processes of ecosystem resilience, but also to achieve unique and complementary HQP capacity in invasion biology for Canada’s most significant renewable resource, our forests.