Predators, plants, and empires: the logistics of insect invasions
University of New Brunswick
Non-native insects have established throughout the world, facilitated by human activity. Due to their potential to cause ecological and economic damage, a variety of biosecurity and pest management measures are used to prevent new introductions and manage existing populations. These efforts rely on an understanding of the biological invasion process and the risks posed by specific species to specific regions. To better understand some of these processes and risks, I aimed to (1) test hypotheses relating to the relative overabundance of European non-native insects established in North America and Australasia, and (2) predict host suitability and biotic resistance in North America and Europe for the European spruce bark beetle (Ips typographus L.) and the North American spruce beetle (Dendroctonus rufipennis Kirby), respectively. Regarding my first research goal, I identified that the introduction of European plants, much of which occurred under colonialism, is the most likely explanation for the asymmetrical exchange of insects between Europe, North America, and Australasia. These plant introductions likely facilitated accidental introductions of associated insects and provided suitable hosts for later insect arrivals. Regarding my second research goal, I determined that Ips typographus would likely find abundant and suitable hosts in North America, but its pheromone blend would attract generalist bark beetle predators. Consequently, low-density founding populations of Ips typographus in North America may experience high mortality from predation. I determined that D. rufipennis may find Norway spruce (the dominant spruce species in Europe) to be a suboptimal host, possibly experiencing reduced reproductive success. On the other hand, it is likely to avoid some predation and competition by producing a pheromone blend that is inconspicuous to European predators or other bark beetles. My results help resolve the mystery of why Europe has been such a dominant ‘exporter’ of non-native insects, while providing new evidence of the large-scale facilitation of insect invasions through introductions of exotic plants. My results also provide new information on the potential suitability of the biotic environments of North America and Europe to non-native spruce bark beetles, which should aid the improvement of invasive species risk assessments.