Predation by American crows reduces overwintering European corn borer populations in southwestern Ontario

Abstract

American crows (Corvus brachyrhynchos) overwintering in Canada's largest known crow roost near Essex, in southwestern Ontario, often forage during the day in surrounding fields of corn, Zea mays, where they perforate cornstalks and eat overwintering larvae of the European corn borer, Ostrinia nubilalis. Survival of overwintering larvae was ca. 50% less in uncaged than in caged plants in a field 26 km from the roost. Although crows perforated stalks in all fields < 25 km from the rookery that were sampled, the number of perforations per cornstalk was negatively correlated with the distance from the roost to the cornfields. In Essex county migratory crows do not arrive until October when most corn has been harvested and they leave in March, before corn is planted. Thus overwintering crows usually do not damage standing corn, increasing their importance as biological control agents.