Jörg Romeis

Impact of Insect-resistant Transgenic Crops on Above-ground Non-target Arthropods

Genetically modified (GM) maize and cotton varieties that express insecticidal proteins derived from Bacillus thuringiensis (Bt) have become an important component in integrated pest management programmes worldwide. A number of other crops producing Bt toxins, or more broad-spectrum insecticidal proteins, are likely to enter commercial production in the near future. Because insecticidal GM crops target insect pests, an important part of the environmental risk assessment is their potential impact on nontarget arthropods. Those include protected species and organisms providing important ecological services such as biological control of herbivores. Non-target arthropods can be exposed to the plant-produced insecticidal proteins through various routes, but mainly by feeding on GM plant material or herbivores that have consumed GM plant material. The Bt proteins produced in todays GM plants appear to have no direct effects on natural enemies due to their narrow spectrum of activity. Furthermore, it has become clear that in crop systems where the deployment of Bt varieties has led to a decline in insecticide use, biological control organisms have benefited significantly. Future GM plants that produce broader-spectrum insecticidal proteins will need to be assessed for their potential non-target effects case by case and compared to the impact of the conventional pest control methods that they replace.

Insect-Resistant Transgenic Crops and Biological Control

Natural enemies such as predators and parasitoids fulfil an important ecological and economic function by helping to keep herbivore populations below the economic injury level. Thus, they contribute to sustainable integrated pest management (IPM) systems. It is well established that plant resistance factors that affect herbivores also interact with natural enemies and consequently with the biological control function they provide. Similarly, host plant resistance derived from genetic engineering will have an impact on biological control. There is evidence today that the currently available transgenic crops that express Cry proteins derived from Bacillus thuringiensis (Bt) have no direct effects on natural enemies due to their narrow spectrum of activity. However, the fact that the target pests are efficiently controlled by the deployed Bt crops has inevitable consequences for natural enemies that specialize on these species as hosts or prey. On the other hand, it has become clear that in crop systems where the deployment of Bt varieties has lead to a decline in insecticide use, biological control organisms have benefited significantly. Consequently, this technology can contribute to natural enemy conservation and thus be a useful tool in IPM.

Stacked Bt maize and arthropod predators: exposure to insecticidal Cry proteins and potential hazards

Genetically engineered (GE) crops with stacked insecticidal traits expose arthropods to multiple Cry proteins from Bacillus thuringiensis (Bt). One concern is that the different Cry proteins may interact and lead to unexpected adverse effects on non-target species. Bi- and tri-trophic experiments with SmartStax maize, herbivorous spider mites (Tetranychus urticae), aphids (Rhopalosiphum padi), predatory spiders (Phylloneta impressa), ladybeetles (Harmonia axyridis) and lacewings (Chrysoperla carnea) were conducted. Cry1A.105, Cry1F, Cry3Bb1 and Cry34Ab1 moved in a similar pattern through the arthropod food chain. By contrast, Cry2Ab2 had highest concentrations in maize leaves, but lowest in pollen, and lowest acquisition rates by herbivores and predators. While spider mites contained Cry protein concentrations exceeding the values in leaves (except Cry2Ab2), aphids contained only traces of some Cry protein. Predators contained lower concentrations than their food. Among the different predators, ladybeetle larvae showed higher concentrations than lacewing larvae and juvenile spiders. Acute effects of SmartStax maize on predator survival, development and weight were not observed. The study thus provides evidence that the different Cry proteins do not interact in a way that poses a risk to the investigated non-target species under controlled laboratory conditions.

The Role of Genetically Modified Plants in Sustainable Crop Protection

Potential yield loss (i.e. production without crop protection) of major crops is estimated at 50% to 80% worldwide, whereas actual yield loss (i.e. loss despite crop protection) ranges from 25% to 40% on average of crops. These figures show that crop protection plays a crucial role in safeguarding crop productivity against competition from pests (weeds, animals, pathogens and viruses) and in preventing pre- and post-harvest loss of food, feed and fibres. Sustainable crop protection should utilise all suitable techniques and methods which are compatible with economic, ecological and social requirements. Integrated Pest Management (IPM) is considered to fulfil the conditions of sustainability, and IPM is thus a strategy that can contribute most efficiently to food security. IPM is one of the most effective strategies to contribute to crop productivity per harvested area which reflects in sustainable production systems the desire to increase land use efficiency and income by minimising adverse environmental and social impacts.