No. 10 Article 3/May 28, 2004

Will European Corn Borer Reemerge as a Prominent Insect Pest in 2004?

European corn borer infestations across Illinois over the last five seasons have been anemic. Both the statewide average number of European corn borer larvae per plant and percentage of plants infested verify this observation (Table 2).

Because corn planting was early and proceeded so briskly this spring, considerable speculation
remains regarding whether the first generation of European corn borer will establish in healthy numbers. The percentage of plants infested in 2003 was very low (32.5%), and the overwintering population was just slightly above 1/2 borer per plant. Factor in other mortality- related issues, such as mechanical death due to harvest and diseases such as Nosema pyrausta and Beauveria bassiana, and it is reasonable to assume the first flight of moths this spring should be a "yawner."

However, during the first few weeks of June, if evenings are relatively mild and mostly storm-free, female moths may find great success in laying eggs on susceptible (non-Bt) corn plants. The biotic potential of European corn borers is impressive. Females can lay an average of two egg masses each evening over roughly 10 days. Each egg mass on average contains 20 to 25 eggs. Some quick math reveals that is 400 to 500 offspring. Even if the survival rate is only 10%, the potential for damage should not be taken lightly. Producers are strongly encouraged to scout their fields for European corn borer first-generation injury this spring. For detailed scouting procedures for this insect pest, click here.

Scouting for first-generation European Corn Borer injury.

First-generation European Corn Borer injury (shotholing).

Checking for European Corn Borer larvae in whorl leaves.

Many questions remain unanswered regarding the broader ecological effects of Bt hybrids on regional and statewide densities of European corn borer. It seems reasonable to suggest that in areas where the use of Bt hybrids is highly concentrated, densities of European corn borer may be pushed to very low sub-economic levels across the landscape. And even those producers who don't plant Bt hybrids will very likely benefit in varying degrees depending on their proximity to Bt fields.

How much credit should the use of Bt hybrids be given for the statewide shortage of European corn borers in recent memory? Some entomologists, including me, are beginning to believe that the population suppressive benefits of Bt hybrids across the landscape may have been underestimated initially. However, a review of fall survey data for European corn borer (in several states) reveals that this insect has gone through periods of very low densities well before the introduction of Bt hybrids. The interaction of environmental factors (biotic and abiotic) with the several life stages of the European corn borer is complex, and we still have much to learn.--Mike Gray

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