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

我的研究目的是通过更好地了解影响天敌调节森林取食昆虫的因素，提高我们管理森林昆虫的能力。具体而言，我探讨了与昆虫天敌种群死亡率和群落多样性相关的问题，重点是了解和操纵本地拟寄生虫和捕食者。最近引入加拿大的几种主要森林昆虫（翡翠灰螟，亚洲长角甲虫，Sirex木蜂）使我们能够比较本地和外来天敌的复合物，并探索这些群落影响寄主死亡率和害虫入侵的机制。我目前的工作是测试关于外来物种和群落如何取代本地物种的假设，以便更好地了解森林中的入侵过程。在这篇论文中，我测试了敌人释放假说（ERH），更具体地说，是非本地物种的敌人减少假说（ENRS）。我提出的问题是，ENRS是否解释了本土（Ips）和外来（Tomicus）树皮甲虫的敌人攻击模式和宿主生产力，或者是否有生物抗性（BR）的证据。东松雕刻甲虫（I. pini）原产于北美，而T. piniperda（另一种取食韧皮部的柱头虫）是20世纪90年代从欧洲引进的。后者已经确立；它们都是同域的，在安大略省南部的林分中以同样的本地松树（P. strobus， P. resinosa， P. banksiana）和外来松树（P. sylvestris）为食。使用这种外来/本地树皮甲虫系统，我将测试ERNS关于这两种甲虫的捕食水平、寄生水平以及敌人和同伴的群落多样性。我预测本地甲虫的敌人会比非本地的Tomicus更多样化，出现的密度也更大。生物地理和生物成因数据将通过甲虫密度的梯度来量化敌人存在的程度，并解释甲虫的死亡率和生产力。这些结果将增加我们目前对入侵动力学的理解，并在应用层面上有助于指导外来森林昆虫入侵的管理策略。

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.