The black cutworm moth is an occasional pest of corn that is particularly attracted to no-till fields. The larvae cause 5 to 80% losses of plant stands in infested fields. The black cutworm recolonizes areas in North America above 38 30'N annually and is unable to overwinter north of this latitude. Determining when adult moth arrive in Ontario as well as the larval population structure in relation to corn seedling development was the objective of this investigation. Adult moth appear in Ontario in early to late April, with males and females often arriving simultaneously. This is in contrast to what was found by investigators in Iowa and Illinois, where males were often captured by pheromone lures before females entered blacklight traps. The results in Ontario may be a reflection of a more mature source population, as first captures were also later in the season. Females are generally already mated when they arrive. Cutting of seedlings by larvae can be expected within 135 centigrade degree-days of initial trapping of an adult moth of either sex. The maturity of the larval population present in the field, as determined by head capsule measurements, was significantly greater with increasing corn leaf stage. Damage to corn is caused by larvae already present in the field at planting time and very little new recruitment takes place subsequently.