Density-Dependent Host Acceptance Behavior as a Possible Contributing Factor to the Population Dynamics of Insect Herbivores

9629776寄主植物对昆虫种群动态影响较大。爆发物种经历数量级变化，表现出不同的质量阶段，并影响可持续资源管理。本项目将调查昆虫种群密度和宿主接受行为之间的相互作用，作为昆虫爆发的一个促进因素。具体来说，人口密度和行为可能会产生相互的正反馈。这一假设将用树皮甲虫进行验证，树皮甲虫是针叶树的主要致死因子。当地种群通常局限于有压力的树木，但在某些条件下，它们可以杀死几乎所有的寄主树木，而不管先前的活力如何。树皮甲虫从地方性密度转变为爆发密度的潜在机制尚不清楚。它们与植物关系的几个方面表明，密度介导的寄主选择行为与数量变化之间存在联系：1)甲虫利用化学和其他线索定位受胁迫的树木；2)一旦进入，它们成功的可能性受到宿主抗性和对信息素作出反应的甲虫数量的影响：快速集中可以共同耗尽宿主的防御；3)野外观测表明，在流行期和爆发期可能会选择不同种类的树木。为了测试宿主选择行为的变化是否影响种群动态，首先必须了解个体行为是否随密度而变化。该项目将检验三个非排他性假设：1)随着年龄的增长或精力的消耗，个体的辨别力会减弱；2)其他甲虫的作用，如信息素，提高驱避阈值；3)选择压力随种群密度的变化而变化。这些问题将分别用一种爆发和一种非爆发的物种，云杉甲虫和松树雕刻来解决。一种常见的实验室分析将评估年龄、反复排斥、逃跑和脂质消耗、合成信息素和其他甲虫的存在以及种群阶段和对选择的反应的影响。树皮甲虫对各种针叶树物种造成了严重的经济损失。了解树皮甲虫寄主接受行为的变异来源将提高可持续森林生态系统管理的能力。

9629776 Raffa Host plants can strongly affect insect population dynamics. Eruptive species undergo order-of-magnitude changes, exhibit qualitatively different phases, and impact sustainable resource management. This project will investigate interactions between population density and host acceptance behavior as a contributing factor to insect outbreaks. Specifically, population density and behavior may exert mutually positive feedback. This hypothesis will be tested using bark beetles, which are major mortality agents to conifers. Local populations are usually limited to stressed trees, but under some conditions, they can kill almost all host trees regardless of prior vigor. Underlying mechanisms by which bark beetles convert from endemic to outbreak densities are not well understood. Several aspects of their plant relations suggest a link between density-mediated host selection behavior and numerical change: 1) Beetles locate stressed trees using chemical and other cues; 2) Once entered, their likelihood of success is affected by both host resistance and the number of beetles responding to pheromones: Rapid concentration can collectively deplete host defense; 3) Field observations suggest different categories of trees may be selected during endemic and eruptive phases. To test whether changes in host selection behavior influence population dynamics, one must first understand whether individual behavior changes with density. This project will test three nonexclusive hypotheses: 1) Individuals become less discriminating as they age or deplete energy; 2) Actions of other beetles, e.g. pheromones, raise repellent thresholds; 3) Selective pressures vary with population density. These questions will be addressed using one eruptive and one non-eruptive species, the spruce beetle and pine engraver, respectively. A common laboratory assay will evaluate the effects of age, repeated rejection, flight and lipid depletion, synthetic pheromones and the presence of other beetles, and popu lation phase and response to selection. Bark beetles are responsible for severe economic damage to various conifer species. Understanding sources of variability in bark beetle host acceptance behavior will improve the ability to manage sustainable forest ecosystems.