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.
Environmental damage due to the uncontrolled spread of genetically engineered plants
It was originally assumed that genetically engineered plants would only very rarely spread in the environment, and persistence was improbable. According to the theory, the introduction of additional genes is effectively a disadvantage for the plants, as it will result in them being rapidly displaced in competition with other plants. Any spread of genetically engineered plants into respective centres of biodiversity is considered unlikely as long as there is no cultivation of genetically engineered crops in these regions.
Genetically engineered cotton has been spreading uncontrollably for several years in wild cotton populations in Mexico. Transgenes from herbicide-resistant and insecticidal cotton were evidently transferred into natural cotton populations (Gossypium hirsutum), even though these genetically engineered crops were not officially cultivated in this region at all.
Cotton plants produce a type of nectar whose production is increased by the infestation of pest insects feeding on the plants. This attracts predatory ant species, which then eat the insects feeding on the plants, and thus protect the plant in return. It has been observed that the production of plant nectar, as well as the number and composition of the associated ant populations, can differ in the offspring of transgenic cotton plants compared to the wild cotton plants.
Ants are not only important in controlling pests, but also in the dispersal of the cotton seeds. Therefore, any disturbance in the interactions between the transgenic plants and their environment can have significant long-term consequences. Higher nectar production, which attracts more ants, could result in the offspring of genetically engineered cotton acquiring invasive properties.
In fact, transgenic cotton plants are now spreading faster in wild populations than was originally expected. This may in part be due to the genetically engineered traits (insect toxicity and herbicide resistance), or a combination of these traits and associated side effects. New combinations of transgenes never tested in the laboratory have also been observed in the actively spreading plant populations.
Successive (hybrid) generations may have very different characteristics to the plants originally authorised for cultivation, e. g. greater invasiveness, which may enable them to spread even faster. Hence, there is a risk that natural cotton populations will be displaced by the spread of transgenic plants.
The above case study illustrates how unintended genetic and metabolic interactions caused by genetic modification can promote the spread of transgenic plants. In this case, the damage is considerable as it poses a threat to one of the centres of biodiversity for wild cotton.
Against this backdrop, there is an obvious need to introduce criteria for the discontinuation of approval processes if uncontrolled spread in the environment cannot be definitively ruled out. There should, in addition, be an international consensus prohibiting the release of genetically engineered organisms if their spread in the environment cannot be controlled.