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by Ric Bessin, Extension Entomologist

University of Kentucky College of Agriculture

European corn borer larva
USDA Insect and Plant Disease Slide Set
The European corn borer is a serious pest of corn and peppers in Kentucky. Corn borers overwinter as full-grown larvae in corn stubble. With the return of warm weather in the spring,development is resumed and the larvae pupate. Temperature plays a major role in determining the rate of corn borer development. The European corn borer has a 50 to 85F temperature range at which it is most comfortable. Below 50F it will not develop, and above 85F development will slow dramatically.

The rate of development of European corn borer can be predicted using this relationship. Dr. Grayson Brown at the University of Kentucky developed a degree day model which accurately predicts the occurrence of the different corn borer life stages. It is recommended that these predictions be used in combination with field scouting or pheromone trapping in order to make management decisions. These predictions will alert you to when it is necessary to monitor pheromone traps closely and scout fields for corn borers.

European corn borer

A degree day for European corn borer is one of degrees above 50F over a 24-hour period. For example, if the average temperature for a 24-hour period was 70F, then 20 degree days would have accumulated (70 - 50 = 20) on that day. These accumulations can be used to predict when corn borers will pupate, emerge as adults, lay eggs, and hatch as larvae. With European corn borer, begin accumulating degree days January 1 of each year. Accumulated degree day totals can be compared with the values in the tables below that correspond to various corn borer life history stages. Tables are available for the first and second generation, in some years a third generation may also occur. Values for the third generation are not available. Values corresponding to initiation indicate when the earliest individuals of that stage may appear.

For example, a degree day value of 750 would indicate that nearly 100% of adults have emerged from pupae, of which slightly more than 50% have flown, egg laying has begun, but is less than 25% complete, and that the earliest first instar larvae may be present. This example illustrates the need to compare the accumulated degree day total with values in several columns of the table. During the growing season there is usually a mixture of different stages in a field. Because corn borers emerge at different times, not all corn borers will be in the same stage at any particular time.

Current degree day accumulations are available for European corn borer as well as other insects for many locations in the state through the Agricultural Weather Center maintained by the University of Kentucky Department of Biosystems and Agricultural Engineering. Up-to-date European corn borer estimates are available through the World Wide Web using the following address "" Click on the Ag/Wx Calculators' to access the insect models.

European Corn Borer Life History Stages

First Generation
PercentagePupaAdultFlightEggLarval Stages
1st2nd 3rd4th 5th
Initiation250 420 550 610 750 970 1140 1290 1420
25% 340 540 690 790 920 1070 1220 1360 1490
50% 390 600 740 850 960 1110 1250 1390 1520
75% 450 650 790 900 1000 1140 1280 1420 1550
Peak 560 760 900 990 1090 1210 1350 1490 1620

Second Generation
PercentagePupaAdultFlightEgg Larval Stages
1st 2nd 3rd 4th 5th
Initiation 1440 1620 1660 1740 1860 1970 2140 2250 2370
25% 1580 1730 1880 2020 2160 2280 2420 2540 2800
50% 1620 1780 1950 2110 2250 2370 2500 2630 2930
75% 1660 1830 2030 2190 23302440 2580 27003060
Peak 1730 1940 2190 2360 2490 2590 2720 2840 3500

Issued: 4/93
Revised: 1/04

CAUTION! Pesticide recommendations in this publication are registered for use in Kentucky, USA ONLY! The use of some products may not be legal in your state or country. Please check with your local county agent or regulatory official before using any pesticide mentioned in this publication.


This page is maintained by Pat Dillon, Department of Entomology, University of Kentucky. Please send questions or suggestions to: