Outbreaks and interacting factors: Insect population explosions synthesized and dissected

Insect outbreaks have attracted a great deal of attention from ecologists, but an understanding of outbreaks has been elusive. We argue that a major reason for this lack of understanding is that most ecologists focus on single factor explanations, while most outbreaks are probably determined by multiple factors. This focus on single factors is not just due to investigator bias, but seems to be inherent in the major approaches used to study outbreaking insects. Theoreticians have focused on fitting mathematical models to time series of densities; we show, however, that this method is not capable of distinguishing among mechanisms. Field biologists typically rely on experiments that test only one factor at a time, probably due to the difficulty of performing experiments on an appropriate scale. We suggest that a way out of this problem may be to closely integrate models and experiments so that moderately complex mathematical hypotheses may be tested in the field without too great expense.