Jan 31, 2012

Research Projects

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Effects of Bt maize containing three Bt proteins on arthropods

(2008 – 2011) RWTH Aachen University, Institute of Biology III (Plant Physiology), Worringer Weg 1, 52074 Aachen

Topic

The aim of this project is to investigate the potential effects of the genetically modified Bt maize cultivar MON89034xMON88017 on herbivorous insects – mirids, cicadas and thrips – which come into contact with Bt proteins as a result of their diet.

Herbivorous insects are themselves a food source for predatory insects, which could in turn ingest Bt proteins through their prey. They could also be harmed indirectly due to reduced prey density and/or quality.

This project will investigate the following questions:

• Is the occurrence and density of mirids, cicadas, thrips and their predators in trial plots of genetically modified maize lower than in plots of conventional maize?
• Is there a difference between the conventional varieties in this respect and if so, how great is it?
• How much Bt protein is absorbed by herbivorous and predatory insects in fields of genetically modified maize?
• Once ingested, are the Bt proteins bioavailable and bioactive?

Experiment description

The genetically modified variety, its isogenic parent variety and two further conventional control varieties will be grown in a field trial. This method enables researchers to distinguish between potential Bt effects and varietal effects. In addition, the isogenic variety in one part of the plot will be treated with an insecticide so that the effect of conventional pest-control methods can also be included in the study.

Determining the density and diversity of herbivorous and predatory insects

Flying insects and insects living in the maize foliage in specific sections of the field were caught with nets on three occasions during each growing season. Sticky boards were set up over a period of six to eight weeks and left on the field for a week at a time. Thrips were collected by shaking the male inflorescences when the maize plants were in full bloom. All the insects caught were identified in the laboratory to species level where possible. Samples were collected over three successive growing seasons to take account of natural population fluctuations and medium-term effects

Determining the exposure of the insects to the Bt proteins

The ELISA detection method was used to measure the amount of Bt protein detectable in the captured insects. It was then possible to estimate the extent to which these organisms had been exposed to it. These measurements were conducted on those species which were present in high numbers on the release site. In addition, controlled greenhouse experiments were conducted on _Trigonotylus caelestialium _ to investigate the uptake, path and breakdown of the proteins in the arthropods.

Determining the toxicity and bioavailability of the Bt proteins

Extracts from insects in which Bt protein had been detected were added to a synthetic nutrient medium, which was then fed to European corn borer larvae. Visible impairment of caterpillar development provides an indication of the bioactivity and availability of the Bt proteins.

Results

Determining the density and diversity of herbivorous and predatory insects

The composition of the species community on the trial field was comparable with that on the release site of the previous project. However, the proportions of the various species in the total community differed.

The predominant species at the start of the growing season was Javesella pellucida. Over the course of the growing season, there was a shift towards Zyginidia scutellaris, which was the dominant species overall. Among the true bugs, the predominant species was the rice leaf bug T. caelestialium.

Statistical analyses were carried out for all three years to see how the numbers of individual species were distributed across the different maize varieties and whether there were any significant differences. Varietal differences were found, but there was no indication of any significant impact of the genetically modified maize on arthropods in the vegetation layer or their predators.

Determining the exposure of the insects to the Bt proteins

The intake of Bt proteins, the path they take and how they are broken down were investigated using the bug T.caelestialium as a model. This bug is suitable for use as a model organism because it is common and feeds directly on the plant, so it is exposed to the Bt protein.

A breeding programme for mirid bugs was set up in Aachen using insects from the trial field. Feeding experiments were conducted with bugs from the field and from the breeding programme. They covered the entire life cycle of the insects and were repeated for all the maize varieties. Various different parameters were documented, including the hatching rate, length of time to pupation and mortality. The full-life-cycle test found differences between the various maize varieties, but no clear effect caused by the Bt maize variety.

In another feeding experiment, the feeding behaviour of the bugs was investigated in relation to the maize variety. To do this, the area eaten by a bug each day was measured. No differences were found between the various maize variants.

In order to check whether Bt proteins accumulate in the bugs or are excreted again, the bugs were kept on Bt maize and then moved to conventional maize. After six hours it was no longer possible to detect the Bt proteins in the insects. There is evidently no accumulation in the bugs that could then have impacts for the food web.

Determining the toxicity and bioavailability of the Bt proteins

Extracts from mirid bugs that had eaten Bt proteins were fed to corn borer larvae. 17 per cent of the larvae did not survive the test, which indicates that the Bt proteins were still bioactive.