AbstractA sequential egg-band sampling system for predicting defoliation of aspen by the forest tent caterpillar (Malacosoma disstriaHbn.) is described and its accuracy assessed. A probability method of predicting defoliation from the stage of the outbreak in each local area is also established. A third method, which promises to be the most accurate and consistent, is proposed. In this last system, egg-mass density is established and related to defoliation levels which are adjusted depending upon age of outbreak.