Insect Herbivory Density and Variable Selection on Components of Plant Defense

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Plant defenses against herbivory can be divided into two types of traits. Some traits influence the likelihood that herbivores will settle on and consume the plant, and are called resistance. Other traits affect physiological adjustments to mitigate the adverse effects of damage, and are called tolerance. The effects of defense traits on plant fitness will not be static, but vary as herbivore population densities wax and wane. Theoretically, selection on plant defense can be analyzed as selection on reaction norms for the defensive components. To test this theory experiments to determine, (1) How the contributions of resistance and tolerance to plant fitness vary with herbivore density, and, (2) whether there are trade-offs between resistance and tolerance that vary with herbivore density are proposed. This investigation will use the native weed, goldenrod (Solidago altissima). Genotypic replicates will be planted in plots where herbivore population density or infestation levels are manipulated. The results will reveal the sensitivity of selection on defense components to herbivore population density. Insights gained in this study can help in designing biological control programs for weeds, and breeding programs for crop resistance to insects.