title: Impact of stacked Bt maize on aquatic non-target arthropods
Creators: name: Chen, Yi
Publisher: name: Universität Bern
Year: 2021
Subjects: subject: 580 Plants (Botany)

description: Material from genetically engineered (GE) maize that produces insecticidal Cry proteins from Bacillus thuringiensis (Bt) may enter aquatic ecosystems and affect non-target organisms. In this thesis, two aquatic arthropods, the water flea Daphnia magna (Crustacea, filter-feeder) and the midge Chironomus riparius (Insecta, collector-gatherer), were selected as surrogates to assess the potential environmental risk of stacked GE maize (SmartStax). This GE maize produces a total of six Cry proteins and thus provides a worst-case exposure condition for non-target organisms.

Previous studies about effects of Bt plants on the life table parameters of D. magna reported ambiguous results. In the first part of this thesis, the suitability of three different maize materials, i.e., flour, leaf and pollen, from five diverse conventional maize lines, as exclusive food for D. magna, was tested. The experiments reveald that maize material is a suboptimal food for D. magna causing nutritional stress. By calculating the 95% confidence interval for all measured parameters of D. magna performance for each maize line, the natural range of variation was captured, which can be informative for future risk assessment studies.

Flour, leaves, and pollen of SmartStax maize in two different plant backgrounds (SmartStax; SmartStax+RR) were used for the second part of the thesis. Most of the significant differences in D. magna life table parameters were observed between the two Bt maize lines and their respective non-Bt comparators when fed flour, but not for leaf or pollen material. Due to the fact that flour was made directly from original grains that had been produced in different locations, years, and with potentially different management, observed effects could be caused by the way of production rather than by the Bt trait. An in-study natural range of variation (IRV) and an external range of variation (ERV) based on the first part of this thesis were applied to interpret differences between Bt and non-Bt comparators in the context of differences among conventional maize lines. Most of the measured D. magna parameters in SmartStax hybrids were within the IRV and the ERV. Furthermore, when fed leaves, which contained the highest amounts of Cry protein, no significant adverse effects on D. magna compared with their respective non-Bt comparators were observed. This indicates that D. magna is not sensitive to the six Cry proteins produced by SmartStax maize under realistic worst-case exposure conditions.

Experiments with SmartStax leaves and C. riparius were conducted in the third part of this thesis. A significant difference in C. riparius performance was only observed for the female development time when fed with the two Bt maize lines compared to their respective non-Bt controls. Female C. riparius fed with SmartStax or SmartStax+RR maize leaves showed significantly shorter development time than those fed with the two non-Bt comparator maize lines, which is not considered an adverse effect. All measured C. riparius parameters in the two SmartStax maize lines were within the natural range of variation, which indicates no effects of SmartStax maize leaves on C. riparius.

This thesis emphasized the importance of using the natural range of variation for interpretating observed effects between Bt and non-Bt comparators, and using different plant materials with different plant background to disentangle potential plant background effects from Bt effects in the environmental safety assessment for aquatic ecosystems.