It is widely believed that population outbreaks of the southern pine beetle (Dendroctonus frontalisZimm.) are caused by vagaries of climate, such as periods of severe drought. According to this view,D. frontalispopulation dynamics are dominated by density-independent processes. We have statistically analyzed a 30-yr record ofD. frontalisactivity in east Texas and have assessed the relative roles of density-independent and density-dependent factors in beetle population fluctuations. Regressions of the rate of population change on three climatic variables were not significant. By contrast, both time-series and regression analyses provided strong and consistent evidence for delayed density regulation ofD. frontalispopulations. Thus, in contrast to previous analyses, we conclude thatD. frontalisoutbreaks are driven not by stochastic fluctuations of weather, but by some unknown population process acting in a delayed density-dependent manner. This result provides a starting point for a current study that will experimentally test various hypotheses concerning the role of natural enemies inD. frontaliscycles.