A simulation model of the population dynamics ofScirpophaga incertulas(Walker) was developed for ultimate use in pest management programs. The processes of development, mortality, migration, and oviposition are modeled. Information from literature and field data were used to set the model's parameters. The model satisfactorily simulated the timing of egg, larval, and pupal population density peaks in farmers' fields for both the 1987 wet and 1988 dry seasons in the Philippines. Most population peak numbers lie within ±2 SD of the field means. Sensitivity analyses indicated that the most important factors in the system were egg, larval, and pupal developmental rate; egg mortality rate due to predation and parasitism; larval mortality rate related to plant age; immigration rate; and oviposition rate. Effects of growing resistant varieties, releasing egg parasites, and applying insecticides on larval populations in the 1987 wet season were evaluated with the model and discussed in regard to their implications for pest management.