A review of the current understanding of forest tent caterpillar (Malacosoma disstria Hbn.) population dynamics in Ontario suggests that two climatic factors, the temperature at the time of larval feeding and the minimum temperature through the winter, play important roles in determining outbreaks. Comparing the pattern of defoliation to similarly scaled temperature records over 41 years in Ontario shows no relationship between the year to year dynamics of outbreaks and either the temperature through the larval feeding period or the minimum overwintering temperature. A long-term analysis suggests that outbreaks are less severe in those regions with low overwintering temperatures and a patchy distribution of host. This latter finding, combined with an analysis of the synchrony and spread of defoliation, suggests that adult dispersal may play an important role in shaping the dynamics of outbreaks. / Science, Faculty of / Zoology, Department of / Graduate