The responses of soil nematode communities to Bt maize cultivation at four field sites across Europe

Transgenic maize expressing the Bacillus thuringiensis (Bt) insecticidal crystal (Cry1Ab) protein is poisonous to lepidopterans including the European Corn Borer (Ostrinia nubilalis). In many European countries, commercial cultivation of Bt maize is not allowed. One major reason is the potential variation of the environmental risk across different biogeographical regions. The aim of this study was to collect data about soil nematode communities as bioindicators of unintended effects across geographically diverse maize growing regions in Europe by sampling field sites in Denmark, Slovakia, and Sweden during 2013–2014, and in Spain during 2013. DKC3872YG (Bt maize line MON810) and its near-isogenic line DKC3871 were grown at the sites in Slovakia, Denmark, and Sweden and hybrids DKC6451YG (Bt maize line MON810) and its near-isogenic line DKC6450 were cultivated at the site in Spain. Dominating nematode genera in the maize fields regardless of the field site or maize variants were bacterial feeders Rhabditis, Acrobeloides; root-fungal feeders Filenchus; fungal feeders Aphelenchoides, Aphelenchus; and omnivores Eudorylaimus. A significant effect of the field site location on the total nematode abundance, nematode abundance in trophic groups, diversity of nematode genera, and ecological and functional nematode indices was detected. Significant annual variation was found in the Plant parasite and Structure indices. There were significant differences in the abundances of omnivores and root-fungal feeders and in the Maturity, Channel, and Enrichment indices between Bt and non-Bt maize plots in Denmark in 2013, and in the abundance of fungal feeders in Sweden (2013). On the other hand, no difference was found between the Bt and non-Bt plots at the sites in Spain and Slovakia or at any of the sites in 2014. The effect of the field site location and season on the soil nematode community was more pronounced than that of the Bt genetic modification. We conclude that Bt maize had only a limited or no effect on soil nematode communities.