Illinois Natural History Survey - University of Illinois

European Corn Borer Management: Past and Present

 

 The European corn borer (ECB), Ostrinia nubilalis, is one of the most destructive insect pests of corn in the Midwest. ECB reduces corn yields by 5% annually (a loss of 540 million bushels) at an estimated farm value of $1.1 billion. Populations of ECB in recent years have increased because the trend for less tillage causes less disturbance of overwintering larvae, and early planting of long- season hybrids enhances both generations of ECB. Corn borers may attack any part of the plant above ground from the early whorl stage until corn is harvested. Borers injure plants by feeding on ears and tunneling in stalks and ear shanks. The holes and tunnels weaken the stalks and provide entry for pathogens that cause stalk rot, premature drying, broken plants, ear drop, and subsequent yield loss.

Growers have managed ECB with cultural practices like stalk destruction and fall plowing to reduce overwintering densities. During the growing season, they may apply chemical or microbial insecticides if scouting reveals that ECB densities have exceeded the economic threshold. Although applicators use microbial insecticides, like DiPel, that contain the delta endotoxin of the bacterium Bacillus thuringiensis (Bt) to control ECB in the Corn Belt, the effectiveness of these insecticides has been inconsistent. However, the use of Bt for control of ECB entered a new era in the spring of 1996 when Ciba Seeds and Mycogen Plant Sciences received approval from the Environmental Protection Agency to sell transgenic corn (Bt- corn) with "built- in" insect resistance.

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Adult Europena corn borere moth.

Bt is a bacterium that produces a crystalline protein (delta endotoxin) that is toxic to certain insects. When ingested by a susceptible insect, the protein breaks down in the insect's midgut, causing gut paralysis. The affected insect stops feeding and dies within a couple of days. Modern gene transfer techniques have been used to develop corn plants that contain the endotoxin- producing gene [Cry1A(b)] taken from Bt. The endotoxin is expressed at high concentrations in the leaves and other green tissues throughout most or all of the growing season.

For the past three years, scientists at the Illinois Natural History Survey have worked with extension entomologists at the University of Illinois to examine the efficacy of Bt- corn against ECB. Bt- corn greatly reduces the amount of leaf and stalk feeding by ECB larvae, resulting in more erect plants, fewer dropped ears and broken stalks, and higher yields. One of the benefits of controlling ECB with Bt- corn is reduced use of chemical insecticides. Bt- corn is not hazardous to the environment and is not toxic to humans and other mammals, birds, fish, and beneficial insects.

The effectiveness of Bt- corn varies among hybrids. Because the level of expression of the endotoxin declines in some hybrids after pollination, second- genera-tion borers may survive and tunnel in the stalks, shanks, and ears. Growers must be aware of these differences and adjust their expectations accordingly.

A major concern about the use of Bt- corn is the potential for ECB to develop resistance to the Bt endotoxin. Although field populations of ECB currently are not resistant to Bt, a laboratory colony exposed to selection pressure by Bt has developed resistance. Therefore, resistance management strategies for the deployment of Bt- corn are crucial.

Current studies at the Natural History Survey will help farmers make decisions about using Bt- corn. In the near future, transgenic technology likely will produce plants resistant to black cutworms and corn rootworms. These tools will be used in a completely integrated pest management program for long- term benefits to agriculture.

John Shaw and Kevin Steffey, Center for Economic Entomology



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