Biosafety research into Diabrotica resistant Bt-maize: indicator organisms and monitoring methods

The genetic modification of crop plants holds many possibilities for the improvement of different plant characteristics, or for the simplification of agricultural practices. The most common modifications are resistances against different insect pests on the basis of Bacillus thuringiensis proteins, as well as tolerances against the herbicidal compounds glyphosate and glufosinate. EU directive 2001/18/EC and regulation 1829/2003/EC stipulate an environmental risk assessment for and a monitoring of genetically modified plants. In each single case, a tiered case-by-case assessment has to be carried out, before a GM-plant can be marketed. A development with future relevance for the European market are GM-maize varieties with resistance against the Western corn rootworm Diabrotica virgifera virgifera. This chrysomelid beetle has been introduced from the United States and poses a dire threat to the maize production in Europe. The resistance of maize plants is based on the expression of the Bt-protein Cry3Bb1 in all green tissued. This protein is supposed to be specific against leaf beetles (Chrysomelidae). The potential impact of the cultivation of the Bt-maize variety MON88017 on non-target arthropods in the maize herb-layer was assessed. The non-deregulated MON88017, its near-isogenic line DKC5143 and the two conventional hybrids DK315 and Benicia were cultivated on a field-release site. Sweep netting, sticky traps, cob and panicle samples were used to survey the herb layer fauna, and were evaluated for their applicability in the context environmental monitoring. The exposure of selected arthropods to Cry3Bb1 was assessed with an immunological assay (DAS-ELISA). A very diverse community of arthropods was found in the herb layer, which in part could be identified as being bound to maize based on published data. Two herbivorous arthropods were of special interest because of their high densities during the 3 field seasons: the maize leafhopper Zyginidia scutellaris and the rice leaf bug Trigonotylus caelestialium. Both species are considerably exposed to the Bt-proteins expressed in genetically modified maize, because of their mode of feeding. This and their wide distribution over the whole of Europe make them candidates for surrogate non-target species in future assessments of genetically modified maize. The statistical analyses showed no negative impact of MON88017 on the selected non-target organisms. For T. caelestialium, a strong and consistent varietal effect could be shown, however: the two conventional maize lines DK315 and Benicia were significantly different with regard to the observed field densities of T. caelestialium. This underlines the necessity for ecologically meaningful baselines as references in the assessment of the enviromental impacts of the cultivation of genetically modified plants. This is a challenge for future biosafety research. The methods employed are all suitable for monitoring and surveillance purposes, however, some special aspects need to be considered and merit attention