Experimental Testing and Modeling Analysis of Regulation in a Host-Parasitoid System

9629316 Murdoch用寄生蜂Aphytis防治柑桔害虫加州红蚧是生物防治最成功的例子之一。规模保持在非常低的密度，和人口是显着恒定的丰度和动态稳定。该项目的目标是解释严重的害虫抑制和动态稳定性的共同发生，这与基于此类系统的简单标准数学模型的预期相反。先前的研究已经将潜在的解释缩小到只有几个，使用现场和实验室的观察和实验相结合来研究机制，并开发包含这些机制的详细数学模型。其余的机制包括：（1）不同的行为反应的规模和规模密度的个人属性，（2）密度依赖性增加的速度，其中阿菲蒂斯杀死先前奠定的寄生卵和（3）小规模的空间异质性的脆弱性规模的攻击阿菲蒂斯。检验这些假设的主要方法是进行大规模的实地实验。葡萄柚树将被单独关在笼子里，树上的鳞片密度在一组树中增加10倍，在第二组中增加50倍，在第三组中保持环境密度。预计随着时间的推移，高密度树木的尺度密度将收敛到环境密度树木的尺度密度。当这种“密度收敛”发生时，将通过监测各种系统响应来检验这一假设。在笼子里同时进行的小规模实验将集中在Aphytis的攻击反应。还将通过比较包括或省略各种机制的系统的详细数学模型的不同版本的结果来测试假设。这项研究对生态理论有着广泛的影响。它还将有助于了解生物防治，并有助于更广泛和有效地利用生物防治。

9629316 Murdoch Control of California red scale, a pest of citrus, by the parasitoid wasp, Aphytis, is one of the most spectacularly successful examples of biological control. Scale are kept at very low densities, and populations are remarkably constant in abundance and dynamically stable. The goal of this project is to explain the co-occurrence of severe pest suppression and dynamic stability, which is contrary to expectations based on simple standard mathematical models of such systems. Prior research has narrowed the potential explanations to only a few, using a combination of observations and experiments in the field and laboratory to investigate mechanisms, and the development of detailed mathematical models that incorporate these mechanisms. The remaining mechanisms include (1) various behavioral responses of Aphytis to individual properties of scale and scale density, (2) a density-dependent increase in the rate at which Aphytis kill previously-laid parasitoid eggs and (3) small-scale spatial heterogeneity in the vulnerability of scale to attack by Aphytis. The primary approach to testing these hypotheses involves a large field experiment. Grapefruit trees will be individually caged and the density of scale on the trees increased 10-fold in one set of trees, 50-fold in a second set and left at ambient density in a third set. It is expected that, through time, the scale densities on higher-density trees will converge to those on ambient-density trees. The hypothesis will be tested by monitoring various system responses as this "density convergence" occurs. Small-scale experiments carried out concurrently inside cages will focus on attack responses of Aphytis. The hypotheses will also be tested by comparing the results of different versions of a detailed mathematical model of the system that include or omit the various mechanisms. This research has wide-ranging implications for ecological theory. It will also contribute to understanding of biological control and to the ability to use it more broadly and effectively.