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Effects of Bt maize containing three Bt proteins on ground beetles and spiders

(2008 – 2011) Bavarian State Research Center for Agriculture, Institute for Plant Protection (IPS 2d), Lange Point 10, 85354 Freising

Topic

The aim of this project was to investigate the potential effects of the genetically modified Bt maize cultivar MON89034xMON88017 on ground beetles and spiders found in maize fields. This maize produces three Bt proteins, making it resistant to both the European corn borer and the Western corn rootworm.

Ground beetles and spiders are key organisms in the maize field ecosystem. They are exposed to Bt proteins both directly through ingesting maize litter and maize pollen, and indirectly through eating prey which feeds on the maize plants (e.g. the European corn borer).

This project examined the following questions:

  • Does the cultivation of MON89034xMON88017 maize cause significant changes in the incidence and density of ground beetles and spiders?
  • Is it possible to determine statistically a typical species pattern for ground beetles and spiders in the maize field, which will then serve as the basis of assessment for the long-term monitoring of genetically modified maize varieties?
  • Are Bt proteins transported to other locations, and therefore to other food chains outside the field?
  • To what extent do Bt proteins remain biologically active and potentially toxic in the insects’ gastro-intestinal tract?

Zusammenfassung

Field: The community of ground beetles and spiders was recorded over the three years of the project. Over 70,000 predatory arthropods were captured and identified. The analyses do not provide any indication that Bt maize has an effect on the abundance or species diversity of ground beetles and spiders. However, an effect caused by the soil insecticide was found on some sampling dates.

Laboratory: Bt proteins were identified in ground beetles from the trial field. In feeding experiments with Poecilus cupreus, Bt proteins were not found to have any negative impact on the pupation rate, hatching rate, development, weight at emergence or fertility of the beetles.

Experiment description

Field and laboratory experiments were used to investigate the questions listed above. Not only did the study compare the genetically modified variety with its isogenic parent variety, it also included two further conventional maize varieties so that a distinction could be made between maize varietal effects and Bt effects. Some plants of the isogenic variety were also treated with a soil insecticide.

Pit trap

Soil trap

Field investigations

Soil traps: Two soil traps were set up in each plot on the trial field to record the species pattern and the density of individual species. They were emptied weekly from June to September. The captured insects were identified to species level.

Laboratory investigations

ELISA analyses: The contents of the digestive tract of different ground beetle species were examined in the laboratory at various periods during the growing season. Marked antibodies were used to measure the quantity of Bt proteins in the beetles.

Feeding trials with Bt proteins: To investigate whether ground beetles are harmed by ingesting Bt proteins, ground beetle larvae were given Bt proteins and examined to assess impacts on the pupation rate, hatching rate, development, weight at emergence and fertility.

Results

Field investigations

Emptying a pit trap

Beetles caught in a pit trap

Ground beetle density in the different maize variants 2008, 2009 and 2010
MON = Bt maize
DKC 5143 = isogenic variety
Tefluthrin = isogenic variety with insecticide treatment
Benicia and DKC 4250 = two other conventional varieties

Soil traps: More than 70,000 predatory arthropods were counted and assessed over the three-year investigation period. The density of ground beetles and spiders did not differ significantly between the Bt maize plots and the conventional maize plots. By contrast, on a few sampling dates there were clear differences between the Bt maize variant and the plots with soil insecticide.

The composition of the ground beetle community varied over the course of the three years, but no differences were found between the different plots.

Laboratory investigations

ELISA-analyses: Bt protein Cry3Bb1 was found in around 45 per cent of the beetles collected in the Bt maize plots before the maize flowered, and in around 17 per cent of the beetles from the conventional maize plots. The beetles from the Bt maize plots were found to contain about twice as much Bt protein as the beetles from the conventional maize fields.

A considerably higher proportion of the ground beetles collected after the maize had started flowering were found to contain Bt protein Cry3Bb1, but the protein quantity was no higher than before the flowering season.

Further tests with the Bt proteins Cry1A.105 and Cry2Ab2 are not yet complete/have not yet been conducted.

Feeding trials along the food chain maize > European corn borer > ground beetle have been carried out and are currently being evaluated.

Feeding trials with Bt proteins: Feeding trials with Bt proteins: A breeding programme for ground beetles was set up successfully using Poecilus cupreus. Over 600 beetle larvae were tested and fed on beetle-specific Cry3Bb1 and on a protein mix containing all three Bt proteins. The concentrations of the Bt proteins were based on the maximum Bt protein level in the Bt maize plants. An analysis of the results showed no negative impacts on the pupation rate, hatching rate, development, weight at emergence or fertility of the beetles.