This research will extend concepts and theory on three trophic level interactions. The central theme is that the dynamics of modular plant parts, the shoots, defines plant architecture, and in a predictable way, the dynamics of herbivores and their enemies in space and time. Plant architecture of the arroyo willow, Salix lasiolepis, defines resources for the herbivore, shoot-galling sawfly Euura lasiolepis, because the metamere, or internode, is the resource utilized, and those on the longest shoots have the highest probability of attack by sawflies. In turn, metamere quality defines gall characters that influence access to the herbivore by the third trophic level. Thus, studying the population dynamics of plant modules is basic to understanding the dynamics of this herbivore, and its interaction with enemies. This research addresses four major questions: 1. how willow clones grow and display resources through space and time; 2. how sawflies respond to these displays; 3. how sawflies influence displays of resources; and 4. How resources influence the herbivore-enemy interaction. These questions are approached by describing conditions in wild clones and using field experiments with potted clones to understand better the mechanistic dynamics of the system. Plant/animal interactions is a major area of ecological research which provides the information base for biological control strategies in agriculture.
