"Developmental delays cannot be argued away"

Feeding studies: Developmental delays

Sciarid fly larvae were fed on pollen or plant parts from different maize varieties in laboratory trials. Two genetically modified Bt maize varieties, Mon810 Novelis and Bt176 Valmont, and their respectiveisogenic parent  varieties , Nobilis (with and without insecticide treatment) and Prelude, were involved in the study, alongside the conventional variety Eurostar.

A whole series of factors were examined: the mortality rate, period to pupation, pupation rate, period to hatching and hatching rate.

Wolfgang Büchs emphasises one of the results in particular: It appeared that sciarid fly larvae fed on straw from genetically modified Mon810 Bt maize took longer to pupate.

<>"The period to pupation is a very significant parameter", Wolfgang Büchs explains. "It can be assumed that a long period of time to pupation is an ecological disadvantage." Insects in their soft-bodied larval stage are more susceptible to fungal attack, predatory insects and parasitoids . The longer the larval stage lasts, the more disadvantageous for the population.

The period to pupation heads the list of parameters relating to the developmental cycle of insects. "If there is a serious disruption in this early stage, it doesn’t matter if the subsequent hatching rates are high. They can only counteract a negative effect, such as an extended period to pupation, to a limited extent."

In the second stage the researchers wanted to know whether such an effect would carry through in the food chain. They fed the sciarid fly larvae, which had been fed on Mon810, to two typical natural predators of the larvae: the ground beetle Poecilius cupreus and the rove beetle Atheta coriaria. As a comparison the beetle larvae were also fed on sciarid fly larvae, which had only been fed on isogenic maize straw. It emerged that the beetle larvae which had been fed on the Mon810 sciarid fly larvae also took longer to pupate.

"The chips effect"

Surprisingly, both the sciarid fly larvae and the beetle larvae consumed more of the Bt food on offer.

Wolfgang Büchs has termed this phenomenon of organisms eating more and yet still taking longer to pupate, for example, the ‘chips effect’. "They eat more food faster but don’t get any healthier or increase their fitness, there is obviously no physiological gain. In fact, their development is actually delayed."

Is Bt toxin the cause?

It was noticeable that no developmental delays in the sciarid fly larvae were found with the second Bt variety tested, Bt176 Valmont, despite the fact that this variety has higher levels of Bt toxin than Mon810. This indicates that there is no correlation between the observed effect and the absolute toxin content of different maize varieties.

"Mon810 appears to be of inferior nutritional quality. We don’t yet know what role the toxin plays in this", says Wolfgang Büchs. In his view, however, it is not critical whether the toxin or other factors cause the effects. He is interested in the plants as a whole in his evaluation of the effects. Even with pesticides, it is not just the impact of the active ingredients which is evaluated, but the impact of the product which is applied to the field, the ‘formulation’ of the product. He maintains that this should also apply to GMOs: In this case the ‘formulation’ is the plant as a whole and how it interacts with its environment. "Similar effects might also occur with conventional varieties", stresses Wolfgang Büchs. "We should be far more analytical in our dealings with the different varieties, especially in relation to their impact on the ecosystem".

<>He basically draws two conclusions from the findings:

• It is essential to study more than one Bt maize variety and its isogenic partner, to avoid prematurely attributing effects to the Bt toxin.

• Consideration should be given to the consistent inclusion of conventional maize in case-specific post-market monitoring . Conventional varieties are currently tested only in terms of growing and yield criteria, although they can have similar effects on the ecosystem to genetically modified varieties.

A trend reversal

In contrast to the feed trials conducted in the laboratory, only Mon 810 Bt maize and its isogenic partner (again with and without insecticide) were compared in the field.

A trend reversal was noticed for three of the parameters investigated during the course of the three-year study. In the first year the greatest species diversity, highest hatching rate and highest rate of decomposition was found in the Bt variant. However, this trend was reversed in subsequent years.

"The only tangible thing that is noticeable here is that the Mon810 Bt maize straw contained 2.5 times more toxin in the second year than in the first", Wolfgang Büchs observes. He adds: "This could be the start of the chips effect; the species abundance diminishes as the period of development increases."

But Wolfgang Büchs takes a cautious approach to interpreting these findings. Although a trend reversal was identified, the three-year duration of the project was far too short to be able to produce accurate scientific evidence for the effects observed in the field trials.

"All we can do is flag them up and highlight those trends and tendencies which require closer observation in post-market monitoring."