Nov 26, 2002

Research Projects

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Ecological impacts of insect-resistant Bt maize on various insects and the European corn borer

(1999 – 2002) RWTH Aachen University, Chair of Biology V, Aachen; Federal Biological Research Centre for Agriculture and Forestry (BBA)(since 2008 Julius Kühn Institute (JKI)), Institute for Biological Control, Darmstadt

Topic

Two problem areas are discussed in relation to Bt maize, which has a resistance to the European corn borer: the effect of the Bt toxin on other insects (non-target organisms) and a possible development of resistance among European corn borers. Both these issues were researched in this two-part project.

The project investigated the following individual questions:

• Does Bt maize pollen have a harmful effect on other caterpillars?
• Are there differences between genetically modified Bt maize and conventional maize with regard to the incidence of arthropods and aphids and their antagonists?
• Does the resistance to the European corn borer lead to a lower infestation with fungi (Fusaria), leading to less contamination of the maize plants with toxic metabolic products (mycotoxins) from the fungi?

The following questions were investigated concerning the effect of the Bt toxin on the targeted pest:

• Various transgenic maize lines have been developed with different variants of the Bt toxin. Are differences in sensitivity to the Bt maize lines to be observed in European corn borer populations?
• How abundant are European corn borers with resistance to the Bt toxin?
• Can resistance to Bt toxins be produced in European corn borers under laboratory conditions?

The part-projects represent preparatory work for the development of suitable monitoring concepts for environmental monitoring of Bt maize.

Summary

Impacts on non-target organisms. Pollen from a transgenic maize line had a negative effect on the caterpillars of the diamond-back moth and cabbage white butterfly. A species of surface caterpillar (caterpillars that pupate in the soil) was not noticeably affected.

The choice of maize type – Bt maize or a conventional isogenic reference variety – had no recognisable effect on the incidence of arthropods, aphids and their antagonists.

Fungal infestation. When infested with aphids, the level of one fungal toxin (mycotoxin) in Bt maize plants was about half the level of that found in conventional maize plants. However, the level of another type of mycotoxin in the kernels was not significantly reduced by the Bt maize.

Impact on European corn borers. The various populations do not differ in their sensitivity to the Bt toxin.

Developing resistance. None of the larvae collected in the Bt maize fields were resistant to the Bt toxin.

Experiment description

The project consisted of laboratory investigations and the assessment of field trials in different cultivation regions.

The field trials compared:

• transgenic Bt maize
• an isogenic maize line for comparison
• conventional maize treated with chemical insecticides.

Feeding experiments with Bt maize pollen

Biotests (feeding experiments) were used to test for toxicity. The Bt toxin for these experiments was genetically engineered in E.coli bacteria.

Incidence of non-target organisms on maize plants

In the laboratory, maize plants from the trial fields were examined for differences in numbers of spiders and insects. Comparisons were made between Bt maize and the isogenic reference line with and without the use of chemical insecticides.

Various species of aphid were counted every two weeks on Bt maize plants and isogenic reference lines (neither of them sprayed).

Fungal infestation and contamination of the maize ears with mycotoxins

A sample was taken from each of five maize locations during the harvest and tested for selected mycotoxins.

Background: the feeding tunnels created by the European corn borer make it easier for fungi to colonise the maize ears, including fungi that produce powerful toxins (mycotoxins). According to this theory, Bt maize, is less severely attacked by fungi. Bt maize ears should therefore display a reduced level of mycotoxin.

Sensitivity of the European corn borer to Bt toxin variants

European corn borer larvae were collected and raised in the laboratory. Tests were carried out to see whether they react differently to the different Bt variants. The tests included two EU-approved Bt maize lines (Bt176 and Mon 810) and a conventional Bt preparation.

Development of resistance among European corn borers

The larvae of the raised European corn borers were reared on Bt-treated food or on Bt plants in each generation.

Because of impurities in the seeds, Bt maize fields are likely to contain 2 % non-transgenic plants, in which European corn borers can develop. These were collected and examined for resistance development.

Results

Feeding experiments with Bt maize pollen

Pollen from the transgenic maize line Bt-176 increased mortality among diamond-back moth and cabbage white caterpillars and reduced feeding and growth.

A species of surface caterpillar (Agrotis segetum) was not noticeably affected.

Incidence of non-target organisms on maize plants

Arthropods showed no preference for any of the three maize variants. Neither were there any noticeable effects caused by the cultivation method (use of pesticides).

Minor differences in the incidence of the two most common species of cereal aphid (Metopolophium dirhodum and Rhopalosiphum padi) on the two maize variants could not be statistically confirmed.

No impacts on the species diversity of the antagonists were found.

The various maize lines had no effect on the incidence of springtails.

Fungal infestation and contamination of the maize ears with mycotoxins

When the plants were infested with the European corn borer, the level of one mycotoxin (Moniliformin) was twice as high in the isogenic and conventional variety as in the Bt maize.

In the case of a type of mycotoxin produced by other fungi (DON = Desoxynivalenol) no significant reduction in contamination was found in the Bt maize. Bt maize did not significantly reduce the DON content in the kernels compared with conventional maize because the relevant fungus species often colonise maize ears in Central Europe, even where there is no European corn borer infestation.

Sensitivity of the European corn borer to Bt toxin variants

So far, no indications have been found that European corn borers react differently to the different Bt variants.

Development of resistance among European corn borers

The corn borer breeding programme is in its fourth generation and is being continued. No resistant corn borers have been found so far.

None of the collected larvae proved resistant to Bt maize.