Introduction - Are population cycles and spatial synchrony a universal characteristic of forest insect populations?

Foliage-feeding forest insects have served as model systems in the study of animal populations for more than 50 years. Early studies emphasized identi fication of "key" mortality agents or density-dependent sources of mortalit y. However, these efforts became burdened by rhetorical ambiguity, and popu lation ecologists are increasingly focusing on characterizing population be havior and identifying the processes that generate that behavior. Two types of behavior seem to be common in forest insect populations: periodic oscil lations ("population cycles") and spatial synchrony (synchronous fluctuatio ns over large geographic areas). Several population processes (e.g.. host-p athogen interactions) have been demonstrated to be capable of producing per iodic oscillations, but the precise identity of these processes remains unc ertain for most forest insects and presents a challenge to future research. As part of these efforts, a greater emphasis is needed on the use of stati stical methods for detecting periodic behavior and for identifying other ty pes of population behavior (e.g., equilibrium dynamics, limit cycles, trans ient dynamics). Spatial synchrony appears to be even more ubiquitous in for est insect populations. Dispersal and regional stochasticity ("Moran effect ") have been shown to be capable of producing synchrony, but again more res earch is needed to determine the relative contribution of these processes t o synchrony observed in natural populations. In addition, there is a need t o search for other types of time-space patterns (e.g., traveling waves, spi ral waves) in forest insect populations and to determine their causes.