Skellam's model of random dispersal, fitted to the rate of spread of larch casebearer (Coleophora laricella) since its discovery in the Northern Rocky Mountains in 1957, suggests that the avg female casebearer oviposits its eggs 4.8 mi. (7700 m) from its point of emergence. Less than 4 of the female progeny survive to reproductive maturity.A discrete-time version of the Verhulst-Pearl-Reed Logistic equation, fitted to the observed growth of 10 casebearer populations in Montana, indicates an avg net reproductive rate of 4.6/year. The upper density asymptote, or carrying capacity, appears to be inversely related to stand tree density.A random-walk model, fitted to observed occurrence of the braconid parasite,Agathis pumila, along transects intersecting 2 parasite-release sites, suggests that the avgAgathisfemale produces about 12 reproductive female progeny. Eggs are laid at intervals of approximately 300 ft (90 m).A parasite-host model, developed for theAgathis-Coleophorainteraction and extended to include dispersal terms, predicts that these reproductive and dispersal rates would allow control ofColeophorabyAgathisover a 50-square mile (108square meters) area within 8 years.