Indirect side-effects of the cultivation of GM plants
Comment from DGS: There have been a lot of examples buried in the literature of unintended effects from genetic engineering. Some are primarily on the phenotypic level due to environmental influences, as in this case. Others occur at the genome level, due to interactions between transgenes/gene products and the genome. Most of the emphasis about the latter effects has been on possible impacts on human health. But I have long thought that there is a much higher probability of disrupting the complex balance that facilitates highly productive agriculture. The problem is that pleiotropic effects are largely unpredictable and often emerge only after commercial use of the crop, and only if monitored. Most will go undetected during field trials that are required before commercialization, in part because they often take several years to develop, or can be sporadic (e.g. only occur during drought, or if a particular pathogen or insect is present).
Indirect side-effects of the cultivation of genetically modified plants
13 March 2013 Schweizerischer Nationalfonds zur Foerderung der wissenschaftlichen Forschung
Press Notice
Winners and losers in the cotton field Genetically modified Bt cotton plants contain a poison that protects them from their most significant enemies. As a result, these plants rely less on their own defence system. This benefits other pests, such as aphids. These insights stem from a study supported by the Swiss National Science Foundation (SNSF). Only ten years ago, genetically modified cotton grew on 12% of all fields – today it is cultivated on over 80% of all cotton fields around the world. Bt cotton contains a gene of Bacillus thuringiensis, a species of soil bacteria. The plant uses it to produce a poison whose effects are fatal to the principal cotton pests – voracious caterpillars. However, certain types of bugs and other pests begin to spread across cotton fields instead, as is the case in China. The decline in the use of chemical pesticides may be partly responsible for this development, but it is probably not the only factor.
Spoiling their appetites A team of researchers led by Jörg Romeis from the Agroscope Reckenholz-Tänikon Research Station has now identified a biological mechanism that offers an additional explanation for the increase in new pests in Bt cotton fields (*). Cotton plants have a sophisticated defence system. When caterpillars begin to nibble on them, they form defensive substances, so-called terpenoids. This spoils the appetite of not only the caterpillars, but of many other nibblers as well.
Also helpful against bugs? Cotton aphids generally do not cause severe agricultural damage because they succumb to their natural enemies out in the open. His results are therefore not relevant to farming, says Romeis. However, he has for the first time revealed an indirect effect of Bt cotton: the killing of the caterpillars also affects other plant-eating insects because the plants' defence system remains inactive. Romeis now wants to investigate whether this effect is relevant to aphids only or also to the bugs that are creating problems for cotton farmers in China and in other cotton-growing regions of the world.
(*) Steffen Hagenbucher, Felix Wäckers, Felix Wettstein, Dawn Olson, John Ruberson and Jörg Romeis (2013). Pest tradeoffs in technology: Reduced damage by caterpillars in Bt cotton benefits aphids. Proceedings of the Royal Society B online. doi: 10.1098/rspb.2013.0042 (PDF available from the SNSF; e-mail: com@snf.ch)
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Steffen Hagenbucher, Felix Wäckers, Felix Wettstein, Dawn Olson, John Ruberson and Jörg Romeis (2013). Pest tradeoffs in technology: Reduced damage by caterpillars in Bt cotton benefits aphids. Proceedings of the Royal Society B online. doi: 10.1098/rspb.2013.0042 (PDF available from the SNSF; e-mail: com@snf.ch) (PDF beim SNF erhältlich; E-Mail: com@snf.ch) (PDF disponible aupres du FNS, e-Mail: com@snf.ch)
Pest tradeoffs in technology: reduced damage by caterpillars in Bt cotton benefits aphids
Steffen Hagenbucher, Felix L. Wackers, Felix E. Wettstein, Dawn M. Olson, John R. Ruberson and Jorg Romeis
ABSTRACT The rapid adoption of genetically engineered (GE) plants that express insecticidal Cry proteins derived from Bacillus thuringiensis (Bt) has raised concerns about their potential impact on non-target organisms. This includes the possibility that non-target herbivores develop into pests. Although studies have now reported increased populations of non-target herbivores in Bt cotton, the underlying mechanisms are not fully understood. We propose that lack of herbivore-induced secondary metabolites in Bt cotton represents a mechanism that benefits non-target herbivores.We showthat, because of effective suppression of Bt-sensitive lepidopteran herbivores, Bt cotton contains reduced levels of induced terpenoids.We also showthat changes in the overall level of these defensive secondary metabolites are associated with improved performance of a Bt-insensitive herbivore, the cotton aphid, under glasshouse conditions. These effects, however,were not as clearly evident under field conditions as aphid populations were not correlated with the amount of terpenoids measured in the plants. Nevertheless, increased aphid numbers were visible in Bt cotton compared with non-Bt cotton on some sampling dates. Identification of this mechanism increases our understanding of how insect-resistant crops impact herbivore communities and helps underpin the sustainable use of GE varieties.