DEVELOPMENT OF ECONOMIC INJURY LEVELS FOR EUROPEAN CORN-BORER (LEPIDOPTERA, PYRALIDAE) ON CORN GROWN FOR SEED

Experiments were conducted to quantify the relationship between the percentage of plants infested with European corn borer, Ostrinia nubilalis (Hubner), larvae and yield to establish economic injury levels (EILs) for com (Zea mays L.) grown for seed. In 1988 and 1989, three inbred genotypes were infested manually with neonates at the mid-whorl or flowering stages of com development to simulate natural infestations by first- or second-generation 0. nubilalis, respectively. Infestation levels ranged from 0 to 84% of plants with larvae. Susceptibilities of the inbreds to infestations of European com borer ranged from relatively susceptible to moderately tolerant, based on visual injury scores. Yields of salable seed decreased as the percentage of plants infested increased, with infestations at either stage of crop development. Observed yield losses were converted to potentially preventable monetary losses based on variable field production costs of$10 and $20 per 80,000-kernel unit of salable seed. EILs were calculated using current insecticide and application costs and levels of control that might be expected with timely insecticide application(s). The EIL for whorl-stage infestation of European com borer would be exceeded when >2-3% of the plants have larvae present in the whorl, and the EIL for flowering-stage infestation would be exceeded when >10-17% of the plants have larvae in leaf axils.