As part of our on-going USDA NIFA (National Institute for Food and Agriculture) sponsored University of Illinois Extension IPM Program, our research team, led by Nick Tinsley (Postdoctoral Research Associate, Department of Crop Sciences), surveyed 28 counties between June 10 to 22 for first-generation European corn borer injury. The counties and six regions surveyed are listed below.
Regions and Counties Surveyed
Northwestern Illinois: Bureau, Knox, Mercer, Ogle and Whiteside
Northeastern Illinois: Kane, Kankakee, LaSalle, Livingston and McLean
West-central Illinois: Adams, Fulton, Logan, McDonough and Morgan
East-central Illinois: Christian, Clark, Effingham, Piatt and Vermilion
Southwestern Illinois: Bond, Jackson, Macoupin and St. Clair
Southeastern Illinois: Gallatin, Jefferson, Lawrence and Massac
Five cornfields were randomly selected in each county and within each field, 100 consecutive whorl-stage plants were sampled for any signs of whorl feeding or the presence of European corn borer larvae. An action site was sampled for European corn borer moths near each field by making 100 sweeps with a standard insect sweep net. We characterized action sites as dense stands of tall grasses in roadside ditches or nearby waterways. Within these action sites moths congregate and mating occurs.
Remarkably, no European corn borer moths were recovered at any of the 140 locations (28 counties X 5 fields) in spite of making a total of 14,000 sweeps! Of the 14,000 whorl-stage plants examined, only 68 had shot-holing (evidence of first-generation injury). The mean percentage of plants with first-generation whorl feeding by region was very low: East-Central – 0.28%, Northeast – 0.56%, Northwest – 0.64%, Southwest – 0.75%, Southeast – 0.25%, and West-Central – 0.44%.
The extensive use of highly-effective Bt hybrids and the areawide suppression brought about by these transgenic hybrids is the primary explanation for these very low densities of European corn borers. According to USDA ERS (Economic Research Service), the use of “stacked gene varieties” accounted for 88% of the corn grown in Illinois during the current growing season. The stormy weather pattern that enveloped much of Illinois during our sampling efforts also likely contributed to the poor establishment of the first-generation of borers.
During some of my summer meetings, a few producers mentioned they had discovered first-generation borers in their non-Bt cornfields. To some extent, this observation caught them by surprise. Although the overall European corn borer population is down across Illinois, this once prominent insect pest flourished for decades (prior to the widespread adoption of Bt hybrids) in many cornfields each season across the Corn Belt. Where non-Bt corn is grown, European corn borers have the potential to infest these fields and cause losses. Therefore, don’t neglect to scout those fields carefully and be prepared to apply a timely rescue treatment. To date, there is no evidence of field-level resistance development by European corn borers to Bt hybrids. This is a remarkable success story nearly 20 years after the commercial release (1996) of Bt hybrids aimed at this insect.
Mike Gray, Professor and Extension Entomologist