9318073 Schultz It has been established that oaks, like other tree species, experience altered leaf quality as a consequence of being attacked by gypsy moth (GM) caterpillars. These changes have at least two important effects on the GM: they reduce fecundity and decrease mortality due to disease. Either effect could influence population dynamics of GM (and other insects), but because their influences appear to be opposite, it is difficult to determine what the net effect of tree responses might be. No study of defoliation-induced changes in leaf quality has ever extended beyond 2 or 3 years. Since GM outbreaks recur every 9 or 10 years, these short-term studies can tell us little about the importance of tree responses to the overall pattern of population fluctuation. It is critical to establish the period over which leaf quality is altered, and how long changes last after defoliation has declined if we are to understand the role of the tree. This cannot be done with short-term studies. GM outbreaks must also alter the quality and quantity of leaves available to other herbivores in the same forest. Documented changes in leaf chemistry and the dramatic reduction in leaf standing crop during an outbreak must produce interactions - probably negative, or competitive - between the GM and other species. For the past 20 years, the ecological literature has been dominated by the view that such food-mediated interactions among herbivorous insects were unlikely. More recently, researchers have begun to appreciate the subtle, but significant, impact one herbivore may have another by altering host plant quality. It i s obvious that outbreaks provide an opportunity to quantify the impact of one herbivore (e.g., the GM) on other, yet this has not been done; there has never been a "before, during, and after" study of this type. This project addresses the first 5 years of a long-term (10-20 years) research program aimed at addressing these two major ecological problems. In a series of specific studies of defoliation-induced changes in oak leaf chemistry at a typical gypsy moth-impacted site in central Pennsylvania, three years of post-outbreak data on gypsy moth-impacted site in central Pennsylvania, three years of post-outbreak data on gypsy moth populations and oak leaf traits. have been accumulated. The traits of greatest importance are phenolics, especially hydrolyzable tannins, and oxidative capacity (e.g., phenoloxidase and peroxidase enzyme activity). These vary dramatically among trees, influence the gypsy moth and its diseases, and at least the phenolic constituents are altered by defoliation. Critical leaf traits of a large sample of 3 oak species will be monitored through two GM outbreaks, establishing the pattern of tree response in relation to measured insect population densities and defoliation levels. The relationship between leaf traits and virus prevalence in GM populations will be assessed by tracking infection levels in relation to insect density, defoliation, and tree leaf traits. At the same time, the possible impact of GM populations on other herbivorous insect will be investigated, by censuring those coexisting on the focal oaks and one non-host, red maple. Densities of non-GM herbivores will be related statistically to GM density, defoliation levels, and tree leaf traits. Although a long-term monitoring effort is the core of this program, the data-gathering is designed to test specific hypotheses right from the start and throughout the study. BY undertaking this long term program, for the first time it will be determined whether induced plant responses can be ecologically mea ningful, and whether negative interactions among herbivorous insects occur or are common in forested systems. K M K M F M M ? Dutch (scalable) R Symbol " Swiss (scalable) 1 Courier " h _ _ H ; Elizabeth M. Behrens Elizabeth M. Behrens
