Host-plant Age, Phenology, and Vigor as Determinants of Herbivore Performance

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Plant-feeding insects are generally not uniformly distributed among host plants or within individual hosts. Instead, certain hosts, and sites within hosts, are preferentially attacked by insects. The timing of feeding within a growing season is also frequently circumscribed. Determining the extent to which theses feeding preferences are correlated with insect survival and fecundity is crucial to understanding what factors trigger and terminate periodic outbreaks of insects. The proposed research will examine interactions between a leaf-mining moth and its quaking aspen host trees in northern Minnesota, where the moth frequently reaches outbreak densities. Experiments will test whether miners preferentially feed at particular sites within leaves, or on leaves on particularly large and/or rapidly growing shoots and branches, as some current theory suggests; if the distribution of feeding over the growing season is correlated with herbivore performance; and whether aspen trees develop resistance to herbivory as they mature. %%% Outbreaks of herbivorous insects occur both in natural & human dominated ecological systems.This research addresses pivotal questions concerning how natural temporal and spatial variation in foliage quality influences herbivore performance & potential for population outbreaks. It details the extent to which high herbivore density results in the use of inferior resources, an important component of the population dynamics of plant-feeding insects. In addition, the results will have important implications for management of stands of quaking aspen, a commercially valuable tree species.