Field Crops News

Transgenic Bt-Corn and Predators

Transgenic crops, plants that have had specific genes from other organisms placed into them, are the new wave of agricultural technology. Genes from Bacillus thuringiensis, or Bt, inserted into corn plants produce caterpillar-killing toxins in the plant. The effectiveness of these transgenic plants is known, but many questions remain. For example, how do these Bt-transgenic corn plants affect insect predators that feed on pest caterpillars or their eggs?

In the Midwest, two common predators of caterpillar pests of corn are the twelvespotted lady beetle and the minute pirate bug. These predators choose places to lay their eggs using various chemical cues in their environment, including the plant. Will predators detect a difference in the plants and avoid Bt-corn as a place to find prey and to lay eggs? Predators were counted in Bt-corn and normal corn at pollen shed, post pollen shed, and dough stage in a 1994 study in Iowa. There were no differences in the total number of all life stages of lady beetles, minute pirate bugs and lacewings collected from the two types of corn.

These predators also feed on corn pollen in addition to the caterpillars. Since transgenic corn produces pollen containing the Bt toxin, could it affect natural enemy development? Studies conducted in Iowa indicate that survival and developmental time for the twelvespotted lady beetle and the minute pirate bug are the same regardless of whether they are raised on transgenic pollen or normal pollen.

These studies indicate that the use of Bt corn for suppression of the European corn borer, corn earworm, and fall armyworm does not have direct negative effects on insect predators attacking these caterpillars.

-Clinton Pilcher, Iowa State University

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