Effects of herbivory on plant and insect growth

The effects of herbivory on photosynthesis vary widely among different plant-insect systems. The first goal of this research was to examine potential mechanisms that control the photosynthetic response to damage, such as insect feeding behavior and tradeoffs between photosynthesis and defense. The second goal was to predict the effects of photosynthesis under global change on insect growth.;Insect feeding behavior had different effects on photosynthesis. First instar Trichoplusia ni larvae produce smaller holes and avoid veins more than fourth instars. First instar damage on Arabidopsis thaliana leaves caused a 4-8% reduction in the maximum quantum efficiency of photosystem II photochemistry (Fv/Fm), but fourth instar damage had no effect on Fv/Fm. First instar feeding may hydraulically isolate patches of tissue, potentially causing stomatal limitation of photosynthesis.;Induction of defense partly explains photosynthetic depression following herbivory. Spatial coordination between photosynthetic and defense responses following herbivory was examined. In areas where defense was induced, photosynthesis was depressed, indicating a possible tradeoff. However, photosynthetic damage propagated further than defense induction, suggesting that other mechanisms may be involved.;The leaf chemistry of starch-accumulating A. thaliana mutants may be similar to that of plants grown at elevated CO2, which often have high C:N ratios and greater starch content. Larvae growing on two of the starch-accumulating mutants demonstrated compensatory feeding, consuming more tissue, but demonstrating variable growth. While starch mutants may be a good model for plants grown under elevated CO2, effects on secondary metabolism, such as glucosinolate biosynthesis, need to be fully characterized.;Different types of feeding behavior have variable effects on photosynthesis, and water stress may be an important factor. Physiological tradeoffs may partly explain reductions in photosynthesis that follow herbivory. Finally, the carbohydrate content of high starch foliage was similar to that of elevated CO2 foliage and appears to stimulate compensatory feeding. Plant responses to herbivory are complex and spatially distinct. The relationship between plants and insects may be altered by global change.