Scientific name: Ostrinia nubilalis
Order: Lepidoptera
Family: Noctuidae

Info

Biological Description

• Moths: Straw-colored to light brown. Males are darker than females and slightly smaller. Forewings have a pale wedge containing a dark spot near leading edge, and a dark wavy line two-thirds of the way toward outer wing edge. Wingspan is about 1 inch.
• Larvae: Gray to cream-colored with numerous dark spots covering the body. Larvae have a black head. Full grown larvae are ¾ to 1 inch long.
• Pupae: Brown, cigar-shaped, ¾ inch long, with segmentation evident on one half of the body.
• Eggs: White at first turning a cream color as eggs develop. Just before hatch, black heads of developing larvae can be seen through egg surface.

Economic Importance

• The economic importance of the European corn borer varies from year to year. Annual scouting is recommended.
• Susceptible crops:
  • Corn borers can cause serious damage to field and sweet corn, peppers, potatoes, and snap beans.

Life Cycle

• The European corn borer overwinters as a mature 5th instar larva in corn stalks and stems of weedy hosts.
• Spring development begins when temperatures exceed 50°F. Pupation begins in May.
• The first adult moths emerge after 375 Fahrenheit degree days (FDD, base 50) have accumulated (in early June in south-central Wisconsin). Peak emergence occurs in mid-June at 600 FDD.
• Adults lay eggs in fields with the tallest corn. Eggs are deposited in masses on corn leaves. Masses of 30-40 eggs can be found on the lower leaf surface of corn leaves and near the mid-vein. Eggs hatch in 3-7 days depending on air temperatures. The first eggs of the season can be found at 450 FDD.
• Young larvae feed on leaves for 5-7 days (125 FDD, base 50) before boring into stalks. Boring usually begins when larvae are third instars. Larval and pupal development occurs within the corn stems. Larvae are present between 800-1000 FDD.
• For early maturing larvae, pupation lasts about 12 days, after which adult moths emerge from the corn stems. Alternately, if larvae mature late in the season they go into diapause and overwinter. Second generation adults fly between 1550-2100 FDD, with a peak at 1700 FDD (mid-August).
• Newly hatched second generation larvae tend to migrate to leaf sheaths and beneath ear husks. Larvae enter the silk channel at the tip of the ear, tunnel up the shank and into the ear, or bore directly through the husks and into the ear.
• All pupae from the second generation go into diapause for the winter.
• Generations:
  • There are two generations per season in Wisconsin.
  • The first generation has a peak adult flight at 600 FDD (mid-June)
  • The second generation has a peak flight at 1700 FDD (mid-August)

Damage/Symptoms

• Damage is a result of larval feeding on leaves and tunneling into stalks, ears, and ear shanks. This impairs plant growth and reduces yield.
• Early leaf feeding appears as pinholes as leaves emerge from whorls.
• Severe stalk boring from late-stage larvae will result in broken stalks and tassels, poor ear development, and dropped ears in dent corn.

Scouting Procedure and Economic Threshold

• Use blacklight traps to monitor adult corn borer flights. From the trap catch you can determine the timing and severity of potential infestations.
• Field scouting
• First generation scouting: Once corn reaches 18 inches extended leaf height, examine 10 consecutive plants in 10 areas of the field for leaf feeding. Pull the whorl leaves from two infested plants in each area and unroll the leaves to look for borers. Calculate the percentage of plants with recent leaf feeding and average the number of European corn borer larval per infested plant and consult the management worksheet for first generation corn borer below to see if treatment will be economical.
  
• Second generation scouting: Second generation European corn borer egg laying occurs over a long period of time and infestations can go unnoticed until damage is evident in the fall. Due to the extended egg-laying period, fields need to be scouted weekly for eggs. Egg masses will be on the undersides of leaves near the mid-rib, primarily on leaves near the ear or above. (In tasseling corn, approximately 90% of the eggs are laid on the two nodes directly above and the two nodes directly below the ear.) Use the management worksheet below to determine if treatment will be worthwhile.
  

Integrated Control

• Natural control: Weather conditions greatly influence European corn borer survival. Cool or dry weather may delay spring insect development. Very hot and dry weather can cause larvae to die from lack of moisture. Additionally heavy rainfall can drown newly-hatched larvae in whorls and leaf axils, or even wash them from the plant. Climatic variables will kill 22-68% of eggs and young larvae.
• Cultural control: By corn varieties are an economically viable way to control corn borer larvae when a field is under heavy infestation. Plowing under crop stubble and shredding stalks on a large scale will help to destroy overwintering populations, however soil erosion concerns in addition to the wide variety of plant hosts for European corn borer can limit the value of this technique.
• Biological Control: European corn borers are susceptible to a variety of predators, parasites, and diseases.
• Chemical Control: For current Wisconsin recommendations, consult University of Wisconsin-Extension Bulletin #A3646, Pest Management in Wisconsin Field Crops.

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Site Links

Insect Images

• Corn pest images

Extension Publications

• The European Corn Borer. University of Wisconsin-Extension, Publication A1220. 2005. Cullen, E.M. and Wedberg, J.L.
• Moth Identification Guide for Blacklight Trap Catch in Wisconsin. University of Wisconsin-Extension, Publication A3855. 2008. Schramm, S. and Cullen, E.

Web pages

• Research
• Insect Pest Management in Organic Agriculture: Organic crop plant nutrition and insect response

Wisconsin Crop Manager Articles

• First generation European corn borer in field corn. Wisconsin Crop Manager, Vol.14 No.15: June 15, 2007. Cullen, E.
• European Corn Borer Moth Flights Approaching Peak First Generation Field Scouting Resources. Wisconsin Crop Manager Newsletter, Vol.1 No.15, June 15, 2006. Cullen, E.
• European corn borer summer moth flights have peaked, prepare for 2nd generation. Wisconsin Crop Manager, Vol.12 No.22: 179-180. August 4, 2005. Cullen, E.

PowerPoint Presentations

• 2007 Pest Management Updates. (Slide 35). 2007. Cullen, E.
• Vegetable Crop Insect Issues: Managing the Expanding Corn Ear Pest Complex. Cullen, E.

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