University of Illinois

No. 10/May 29, 1998

European Corn Borer Moths Reported Statewide

European Corn Borer Moths Reported Statewide

Reports of European corn borer moths throughout the state have been confirmed. As indicated in last week's Bulletin, we can begin to expect the initial spring flight of moths to occur when 374 heat units (base 50 degrees F) have accumulated from January 1. Based upon this old system of tracking heat units from January 1 to predict European corn borer phenology, this first flush of moths should begin to peak when 631 heat units have accumulated. Heat units (base 50 degrees F) from January 1 through May 24 range from 850 in southern Illinois to 550 in northern counties (Figure 1).

Figure 1. Actual heat-unit accumulation (base 50 degrees F), January 1 to May 24, 1998.

Have we reached peak flight activity in the southern one-third of the state already? Probably not. To project future biological events such as egg laying, more accurate temperature-based models rely upon an accumulation of heat units beyond the initial capture of spring moths. For instance, peak egg hatch is likely to occur when 100 heat units (base 50 degrees F) have accumulated beyond the first significant moth flight.

What is a "significant" moth flight? This can probably be best defined as the point at which moths are regularly splattering your windshield for the first time during an evening drive this spring. If average daily temperatures of 70 degrees F occur for 5 consecutive days following a significant moth flight, 100 heat units will have accumulated and peak egg hatch will be underway. Bottom line--European corn borer larvae will soon begin their leaf-feeding activities.

What are the survival prospects for first-generation larvae? Late planting and replanting of corn in many areas of Illinois mean that first-generation larvae will not survive on many of the plants having an extended leaf height of less than 18 inches, due to high concentrations of DIMBOA, a plant aglucone (2-4 dihydroxy-7-methoxy-1, 4-benzoxazin-3-one). The concentrations of DIMBOA begin to decrease as corn plants mature. Survival of corn borer larvae is better on plants in the mid- to late-whorl stage of development (22 to 36 inches extended leaf height). Because of the late planting and replanting experienced by many producers in Illinois this season, the second generation of European corn borers may represent a much more significant threat to corn production than the first generation. We will provide some projected European corn borer phenological developments in future issues of the Bulletin.

Mike Gray (, Extension Entomologist, (217)333-6652