integrated pest management


Fall Surveys for European Corn Borers in Illinois

The European corn borer, Ostrinia nubilalis (Hübner), was accidentally introduced into North America from Europe in the early 1900s, probably in shipments of broom corn from Hungary or Italy. The European corn borer was discovered first in North America near Boston, Massachusetts, in 1917. By 1952, the European corn borer had spread throughout most of the major corn-growing areas in the United States. It first appeared in Illinois in 1939. After it became established in North America, the European corn borer was recognized as one of the most economically important insect pests of corn throughout the Corn Belt. For information about the biology and management of European corn borers, refer to our fact sheet.

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Second-generation European corn borer larva
Second-generation
European corn borer
larva in corn stalk

History and Objectives of the Fall Surveys

Cornfield to be surveyed
Cornfield to be surveyed
for second-generation
European corn borers

As the European corn borer spread throughout North America, scientists became interested in monitoring its spread and estimating densities. Consequently, entomologists in many north-central States initiated formal and systematic surveys of second-generation European corn borers. Entomologists at the University of Illinois and Illinois Natural History Survey conducted the first survey of second-generation European corn borers in 36 counties in Illinois in 1941. Fall surveys have been conducted in essentially the same way every year since 1942. We have annual data from these fall surveys from 1943 through the present, except for 1997 and 1998, years during which the survey was not conducted.

The objective of our fall surveys is to obtain estimates of densities of second-generation European corn borer larvae in crop reporting districts (refer to the Illinois Agricultural Statistics Service) in Illinois. Not all counties are sampled every year. The number of counties surveyed in Illinois each year has varied over time; however, 35-50 counties usually are surveyed within a given year. Although some counties have been surveyed virtually every year since 1943, other counties have been sampled less frequently, and some counties have never been sampled. Results from nearby counties can be used as reasonable estimates of corn borer densities in counties that have never been surveyed.

The estimates of second-generation European corn borer densities can be used to estimate economic impact of corn borers during any given year. The economic impacts can be compared over time and among counties and districts in the state. In addition, population trends can be determined. Although densities of second-generation European corn borers in a given year suggest potential overwintering population densities, predictions of densities of corn borers for the following year are tenuous. Many factors (e.g., weather, natural enemies) regulate European corn borer populations, so predicting populations from one year to the next is not an exact science. A review of average densities of second-generation European corn borers in Illinois from 1983 through 2002 (20 years) reveals the unpredictability of populations from year to year.

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Thumbnail of European corn borer survey in Illinois
European corn borer survey
in Illinois, 1983-2002

Fall Survey Procedures

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Team of entomologists and educators
Team of entomologists
and educators surveying
for second-generation
European corn borers

The counties to be surveyed during a given year are determined in advance. University of Illinois Extension entomologists coordinate the survey effort, requesting assistance from other state entomologists and from Extension educators throughout the state. Each surveyor or pair of surveyors is provided with a list of counties to survey.

Within each county designated for surveying, the surveyor drives along highways and county roads, randomly selecting 10 fields that fairly represent the different areas of the county. The surveyor walks into the field at least 50 paces beyond the turn rows and counts off 25 consecutive plants for examination. The type of information recorded within each field is shown on the representation of the form used during the survey. However, not all of this information has been assembled into the database.

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Evidence of infestation
Evidence of infestation
by second-generation
European corn borers

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Splitting a corn stalk
Splitting a corn stalk
in search of second-
generation European
corn borers

All plants infested with European corn borer larvae are counted and recorded. The stalks, shanks, and cobs of two of the infested plants are split with a knife, and all borers are counted and recorded. The stage of development of each European corn borer found is recorded (instar [I, II, III, IV, and V on the form]; pupa [ P on the form]; and emerged, or empty pupal case [E on the form]).

The surveyor also notes the numbers of stalks broken above and below the ear and the number of ears dropped on the ground. The percentage of infestation and average number of borers per infested plant are determined for each field. After all 10 fields have been sampled, the percentage of infestation and average number of borers per plant are determined for the county. The county data are used to determine averages for crop reporting districts.

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Second-generation European corn borer
Second-generation
European corn borer
larva in corn shank