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Effects of Bt maize on butterflies and their antagonists

(2001 – 2004) Max Planck Institute (MPI) for Chemical Ecology, Department of Biochemistry, Jena

Topic

Maize possesses an indirect plant defence mechanism against butterflies. Following grazing damage by caterpillars, the maize plant produces volatile emissions (scents), which attract the antagonists (parasitoids) of the butterflies.

Interaction between maize plant, caterpillar and parasitoid

Drawing: T.G.Köllner

The aim of the project was to check whether the indirect defence mechanism is affected by the Bt toxin:

  • Are there differences in the emission of volatile matter between Bt maize and control plants?
  • Does infestation by caterpillars which are not supposed to be controlled by the toxin (non-target lepidopterans) affect the scent pattern of Bt maize?
  • Can the Bt toxin affect the indirect defence mechanism of the plant?

Summary

No qualitative differences in scent emissions were found between the pairs of maize varieties (transgenic and non-transgenic) either in the field or in the laboratory. However, significant differences in the emitted volume were found between Mon810 and its control variety. It was demonstrated that this difference is caused by a varietal effect, rather than by the introduced Bt gene.

The differences in composition and quantity of emitted scents between commonly cultivated varieties far exceed the differences found between Mon810 and its control strain.

Experiment description

Field apparatus for collecting emissions

Measuring scent emissions in the field

An apparatus was developed for measuring scents outdoors, and field measurements were carried out on two Bt maize varieties and their isogenic strains from 2001 to 2003. The scents formed by the plants were captured and analyzed for quantity and composition.

Scent measurements in the laboratory

Scent measurements on these strains and on a few commonly cultivated varieties were also carried out in the laboratory under controlled conditions.

Results

Scent emissions in the field

The field measurements revealed no qualitative difference between the maize varieties. These results were confirmed in laboratory experiments. However, significant differences in the emitted volume were found between Mon810 and its control variety, with the transgenic variety releasing more even when not infested. It was possible to demonstrate that this difference is caused by a varietal effect, rather than by the introduced Bt gene.

Scent measurements in the laboratory

In further experiments, the scent patterns of Bt maize and the control strains were compared with various commonly cultivated maize varieties. Here it was possible to demonstrate that each variety has a characteristic terpene mix, which can differ very significantly both in terms of absolute quantity and composition from other maize varieties. These differences far exceed the differences found between Mon810 and its control strain.