Can interactions between Bt proteins be predicted and how should effects on non-target organisms of GM crops with multiple Bt Proteins be assessed?

Genes expressing Bacillus thuringiensis (Bt) toxins have been incorporated into genetically modified (GM) plants to render these resistant to certain insect pests. Of particular interest have been the genes encoding Cry (Crystal) proteins, but also the gene encoding the vegetative insecticidal protein Vip3Aa has been incorporated into crop plants. Over the last decennium, GM events have been crossed through traditional breeding, resulting in stacked GM events expressing several Bt insect resistance genes. Experiments demonstrate that interactions between two or more toxins can either enhance or decrease their activity. It is thus possible that interactions between Bt proteins produced by GM plants occur and thereby influence their effect on non-target invertebrates compared to GM plants expressing just a single Bt gene. This report has been drafted as a response to a call of the Netherlands Commission of Genetic Modification (COGEM) to address two main questions: (1) can interactions between Bt proteins be predicted and (2) to what extent are studies on interactions relevant for risk/safety assessment of GM crops. The questions were tackled from an eco-toxicological angle, in particular taking into account those types of information that are relevant for risk/safety assessment of GM crops. Answering the questions was done by reviewing and considering the current knowledge on the specificity of Bt proteins, on known interactions between Bt proteins and the methods to assess these interactions, and available guidance for risk/safety assessment of GM crops combining multiple Bt proteins. Also the information reviewed in a parallel project addressing the same questions, but from a biochemical and toxicological perspective (Eco¿tat, 2014), was taken into account when formulating conclusions.