Systematic reviews follow predefined standards to ensure unbiased, comprehensive, transparent, repeatable, and robust evidence synthesis including statistical meta-analyses. For various stakeholders, such systematic reviews help to address uncertainties regarding environmental impacts of genetically modified (GM) plants. The current work, following the stringent standards of the Collaboration for Environmental Evidence (CEE), addressed the question: “Does the growing of Bt maize change abundance or ecological function of non-target animals compared to the growing of non-GM maize?”. Literature was searched and screened systematically until August 2019. More than 7200 records on invertebrate abundance, activity density, or predation/parasitism rates were stored in a custom-made database. A critical appraisal scheme for field studies on non-targets in GM crops was developed to capture issues associated with internal and external validity of all primary data. Our meta-analyses on different taxonomic levels revealed few and often non-robust significant effect sizes when comparing Bt maize (GM to produce insecticidal Cry proteins from Bacillus thuringiensis) and untreated non-Bt maize, largely corroborating earlier meta-analyses. When untreated Bt maize was compared with conventional maize sprayed with insecticides, predator populations in particular were lower after the application of broad-spectrum pyrethroids. Bt maize thus represents a highly selective pest control technology with relatively few negative consequences for non-target invertebrates, especially when compared with the use of broad-spectrum insecticides for managing Bt-targeted pests. One shortcoming of the present and all prior reviews, however, is the limited availability of data. To facilitate future meta-analyses, we strongly encourage researchers to publish full datasets along with scientific articles.
