Climate change may alter the outbreak dynamics of forest-defoliating insects, with potential consequences for both the economy and the environment. Although numerous studies predict that climate change will increase the frequency and severity of outbreaks, few studies have examined whether recent climate trends have impacted outbreak dynamics. Furthermore, the results of those few studies have not been consistent. Outbreak histories of 10 forest-defoliating insect species and long-term climate datasets will be examined to determine whether the regularity, frequency, and magnitude of outbreaks have shifted over time relative to long-term norms, and to evaluate whether shifts in dynamics may be influenced by climate changes. Potential causes of shifts in outbreak dynamics will be investigated by fitting quantitative population growth models to historical outbreak data, and then integrating the results from the models with existing knowledge of biological interactions (e.g., disease, parasitism) that influence the population sizes of each defoliator species. Finally, the impacts of climate change on the outbreak dynamics of forest-defoliating insects as a whole will be assessed by synthesizing the findings for individual species.
This project will contribute to a better understanding of whether changes in climate have led to shifts in the population behavior of forest-defoliating insect species. The project will also shed light on the effects of changes in climate on the biological interactions ultimately responsible for population cycles. Broader impacts of this project include potential recommendations for pest control programs. For example, control plans could be modified by selecting biological control agents (e.g., diseases) that are likely to become more effective in the future due to climatic trends. In addition, research techniques and findings will be disseminated to science-curriculum supervisors for preK-12 schools.
This project increased understanding of the effects of climate change on economically and ecologically damaging outbreaks of forest insect pests. The studies focused on a class of pests known as forest defoliators, which exhibit periodic outbreaks in which large numbers of leaf-feeding insects defoliate large areas of forest. Such outbreaks can lead to increased tree mortality and have adverse effects on nutrient cycling and wildlife. Prior to this project, limited amounts of research revealed few general patterns about effects of climate change on the severity or frequency of defoliator outbreaks. In this project, analyses of historical records of defoliator outbreaks showed that the frequency, severity or regularity of outbreaks of individual species have shifted several times and in a variety of ways over past decades and centuries. One fairly common pattern observed among defoliator species studied here and elsewhere, however, is a recent decline in the tendency of outbreaks to occur at regular time intervals. Different species appeared to be respond in different ways to changes in temperature through time; while the occurrence of outbreaks in one species appeared to increase following increases in temperature, others exhibited lower outbreak activity following periods of high temperature. Effects of changes in amounts of precipitation on outbreaks appeared less common; however outbreaks of one species tended to follow periods of drought, which are expected to become more frequent or severe in some regions. In addition to highlighting correlations between climate changes and patterns of outbreaks, this project shed light on how climate patterns can influence the severity of outbreaks. Findings for the gypsy moth in North America, indicated that climatic conditions causing multi-annual periods in which weather conditions fluctuated relatively synchronously across large regions, as opposed to fluctuating out of sync, can promote increasingly widespread outbreaks of defoliating insects. The research techniques and findings of this project were integrated into workshops that trained science curriculum specialists and supervisors for K-12th grad schools in Virginia. Two climate science symposiums were held during meetings of the Virginia Science Education Leaders Association. Project personnel provided training to 143 curriculum supervisors and specialists, each with the potential to provide training to teachers in their respective school districts. Meeting attendees received training in fundamental principles of climate systems and ecological implications of climate change, and received information on suggested web-based resources such as online data bases. Follow-up training sessions addressed topics including graphical data analysis and the carbon sequestration ecosystem service provided by trees.
