Negative impacts caused by the accelerated spread of feeding insects.

Risk assessment must be carried out as part of the approval procedures for genetically engineered plants. This is to identify any risks to the environment arising from the cultivation of genetically engineered plants and to prevent possible damage.

In the meantime, there is ample evidence of effects on the environment from the widespread cultivation of transgenic plants that have not been taken into account in risk assessment. Complex interactions often play a decisive role in this context. Three examples:

(1) In China, moth larvae (Helicoverpa armigera) infected with certain viruses are increasingly spreading in Bt cotton fields. The reason: infected larvae develop resistance to the Bt insecticide more quickly and, therefore, have a selection advantage over their non-infected conspecifics in the transgenic fields. In conventional cotton fields, on the other hand, larvae infected with these viruses are hardly ever observed.

(2) The cultivation of transgenic soybeans in Brazil, which are glyphosate-resistant and produce insecticidal Bt toxins, has resulted in the increased spread of the scale insect, ‘whitefly’ (Bemisia tabaci). The scale insects that feed on these genetically engineered plants are more fertile and the number of their offspring is significantly increased. A possible cause of the spread could be the Bt toxins, as they are non-toxic to the whitefly and may have a stimulating effect on their reproductive capacity. A further factor being considered are unexpected interactions in the genome of the soybean plants resulting from the genetic modifications, which could have a positive effect on the reproduction of the scale insects. Similar effects were observed several years ago when a strong proliferation of moth larvae (Spodoptera eridania) was observed in glyphosate-resistant Bt soybean fields.

(3) Herbicide-resistant weeds, e. g. several species of amaranth, are spreading in fields where transgenic soybeans that are herbicide-resistant and produce Bt toxins are grown. Amongst others, these serve as a food source for certain moth larvae (Spodoptera cosmioides). If the larvae feed on both a species of these herbicide-resistant weeds (Amaranthus palmeri) and on insecticidal Bt soybean plants, they grow larger and have a higher overall fitness. These pests benefit from a combination of increased spread of herbicide-resistant weed species and unintended effects of Bt soybean plants.

With the large-scale and long-term cultivation of genetically engineered plants, the probability of more complex interactions within ecosystems and resulting damage is much higher than was originally thought on the basis of small field trials, as these are usually only carried out for one year. Complex interactions between different transgenic organisms have also not yet been taken into account in the context of the approval procedures. It is, therefore, important to take a systemic approach to the technology and risk assessment, ensuring that this goes deeper than just examining the safety of individual genetically engineered organisms.

Further information:
TA report
Environmental risks new genetic engineering

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