The frequency and severity of outbreaks of the southern pine beetle,Dendroctonus frontalisZimmerman, appear to be controlled by climatic variations. Monthly tabulations of southern pine beetle activity in eastern Texas were correlated with various climatic variables derived from the Thornthwaite water balance to determine climate-beetle relationships and to develop a predictive technique capable of evaluating future insect activity based upon past climatic conditions.The magnitude of potential evapotranspiration 3 mo prior to the evaluated insect activity represented the most important climatic component within the regression model. In general, the intensity of insect activity was directly related to moisture surplus and deficit, and inversely related to summer potential evapotranspiration. The regression model was tested against the most recent southern pine beetle outbreak data to determine its predictive capabilities. The model predicted the severe outbreak which occurred July 1973, and isolated the climatic trigger mechanisms responsible for the outbreak.