Specificity and Combinatorial Effects of Bacillus Thuringiensis Cry Toxins in the Context of GMO Environmental Risk Assessment

Abstract

Stacked GM crops expressing up to six Cry toxins from Bacillus thuringiensis (Bt) are today replacing the formerly grown single-transgene GM crop varieties. Stacking of multiple Cry toxins not only increase the environmental load of toxins but also raise the question on how possible interactions of the toxins can be assessed for risk assessment, which is mandatory for GM crops. However, no operational guidelines for a testing strategy or testing procedures exist. From the developers point of view, little data testing for combinatorial effects of Cry toxins is necessary as the range of possibly affected organisms focuses on pest species and no evidence is claimed to exist pointing to combinatorial effects on non-target organisms. We have examined this rationale critically using information reported in the scientific literature. To do so, we address the hypothesis of narrow specificity of Cry toxins subdivided into three underlying different conceptual conditions (i) "efficacy" in target pests as indicator for "narrow specificity," (ii) lack of reported adverse effects of Cry toxins on non-target organisms, and (iii) proposed modes of action of Cry toxins (or the lack thereof) as mechanisms underlying the reported activity/efficacy/specificity of Cry toxins. Complementary to this information, we evaluate reports about outcomes of combinatorial effect testing of Cry toxins in the scientific literature and relate those findings to the practice of environmental risk assessment of Bt-crops in general and of stacked Bt-events in particular.

Possible health impacts of Bt toxins and residues from spraying with complementary herbicides in genetically engineered soybeans and risk assessment as performed by the European Food Safety Authority EFSA

“…Moreover, truncation and mutagenesis of synthetic toxins might alter their range of toxicity compared with the native toxins”. Some of these uncertainties are summarised by Hilbeck and Otto [19], who come to the conclusion that “there is presently no way of predicting which species may or may not be affected based on the current state of understanding of the proposed modes of action of Cry toxins”.…”

Czech Farmers' Experience with Bt Maize: Fulfilment, and the Opposite, of Monsanto's Promises

“…Moreover, it is generally assumed that the replacement of chemical insecticides with plantbased toxins is beneficial for the environment as their mode of action is believed to be specific for certain species pest (Meissle, Romeis and Bigler, 2011). However, according to a review by Hilbeck and Otto (2015), an increasing body of evidence suggests a significant cross-order activity of Cry toxins. The class of Cry1 proteins (to which the MON810-maize-produced Cry1Ab toxin belongs) has been reported to be toxic against nonlepidopteran non-target organisms (Latham, Love and Hilbeck, 2017).…”

Integration of Plant Defense Traits with Biological Control of Arthropod Pests: Challenges and Opportunities

“…The planting of Bt crops has increased dramatically since their introduction in the mid-1990’s; for example, in the United States, the percentage of Bt maize was only 1% of the total crop grown in 1996 but 81% of all maize grown in 2015 (United States Department of Agriculture National Agricultural Statistics Service, 2015). The ecological interactions between insect-resistant GM crops and biological control are complex and have been addressed in numerous comprehensive reviews (e.g., Obrycki et al, 2004; Lundgren et al, 2009a; Hilbeck and Otto, 2015). Two major categories for how GM crops influence biological control, proposed by Lundgren et al (2009a), are discussed below: (1) toxicity-based pathways, including natural enemy consumption of toxic plant or prey foods; and (2) crop-induced changes to the environment, including unintended alterations to the crop plant and a decrease in prey quality and/or density that alter functional and numerical responses as well as the community ecology of natural enemies.…”