A risk assessment of genetically modified organisms: Potential effects of Bt maize on spiders

Concerns have been raised that genetically modified Bt maize expressing the Cry1Ab protein of the soil bacterium Bacillus thuringiensis (Bt toxin) may harm non-target organisms. Spiders can be exposed to the Bt toxin by active Bt maize pollen feeding, by ingesting their pollen-dusted webs, and by preying on herbivorous or pollen-collecting prey. In this thesis, the risk potentially arising from Bt maize for foliage-dwelling spiders was assessed by the investigation of exposure pathways of Bt maize to spiders and by assessing the actual Bt effects on foliage-dwelling spiders on laboratory and field scale. The investigations showed that spiders are potentially exposed to Bt maize pollen and Bt-contaminated prey. No lethal effect of Bt maize on spiders on laboratory as well as on field scale was found. Thus a high risk of Bt maize event 176 to spiders can not be confirmed. However, high variation as well as small effect sizes may have masked existing effects and further studies on different temporal and spatial scales as well as studies on potential sublethal or longterm effects are required to allow general statements.