Corn hybrids genetically transformed to incorporate a gene from the soil bacterium Bacillus thuringiensis Kurstaki, (Bt) exhibit tolerance to feeding by certain pests, especially those from the genus Lepidoptera. The Bt endotoxin is not harmful to humans, other mammals, birds, fish, or beneficial insects. The bacteria gene produces an insoluble crystal protein, that when eaten by a susceptible caterpillar, binds to and ruptures the pest’s gut lining resulting in death. There are a number of different protein products with efficacy in controlling different insect pests. These products are also introduced into the plant genome with different promoter regions and in slightly different places resulting in greater or lesser protein expression in different plant parts. Currently there are several different Bt events marketed in the US. The event name, protein, and pests controlled are shown in the table below. There is a number of “stacked” corn hybrids that contain two or more of the Bt events inserted into the same germplasm, often along with herbicide tolerance genes. These are sold under a variety of commercial names.

Some pests currently controlled by the Bt toxin may have the potential to develop resistance. Resistance typically occurs when pesticides are used repeatedly and at high concentrations. Companies that market this technology and farmers that use this technology are working together to minimize the likelihood of resistance development. Currently, resistance management is based on the principles of high dose and refuge. Bt corn produces very high levels of Bt Cry proteins with the goal of killing all susceptible European corn borer larvae. Refuge areas provide a home for pests where they are not exposed to Bt corn or Bt insecticides. These refuge areas provide Bt susceptible mates for potential resistant pests emerging from nearby Bt corn. Since the development of resistant populations on non-Bt corn is highly unlikely, the system is designed to produce an overwhelming number of susceptible pests for every resistant pest.

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Foliar pesticide is not needed to control the target insect. Less risk of potential off-target insect damage. Late plantings in Kentucky warrant Bt corn hybrids based on improved yields over conventional hybrids.

For more information on this or other topics related to corn production, contact your state extension corn specialist or your local extension educator/agent.

The following is the link to the corn extension specialists: state extension corn specialist