Impact of Bt corn on the diplopod Allajulus latestriatus

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Summary The application of transgenic crops has expanded enormously since their introduction to agriculture in the 1990s. Despite increased research activity in the area of non-target effects, the impact on many groups of soil organisms still remains unclear. In this study, laboratory feeding experiments were conducted to detect possible effects of Bt corn on the detritophagous Allajulus latestriatus (Diplopoda, Julidae). We tested the transgenic corn N4640Bt (expressing the Bt protein Cry1Ab), the corresponding non-transgenic isoline, and two further conventional corn varieties. Furthermore, a toxicity test was performed, in which purified Cry1Ab was added to a corn leaf diet in different concentrations. Cry1Ab concentrations in corn leaves, corn leaf diet, faeces and diplopods were quantified, applying an enzyme-linked immunosorbent assay (ELISA). We performed bioassays using the European Corn Borer Ostrinia nubilalis to test the insecticidal activity of different samples. No significant differences in mortality, consumption of corn leaves, or weight gain were found when animals were fed on N4640Bt compared to its isoline and the other two varieties. However, faeces production per diplopod was significantly increased when animals were kept on Bt corn compared to the isoline and to another corn variety. In the toxicity test, no significant differences were found for mortality, consumption, weight gain or faeces production between diets, not even at Cry1Ab concentrations more than 100 times higher than in Bt leaves. Bioassays proved that the Bt protein in transgenic leaves and in faeces of diplopods was still insecticidal. The toxicity test indicated that Cry1Ab excretion in the faeces is linearly correlated to the Cry1Ab uptake through the diet. Our findings suggest that Bt corn and Cry1Ab will not harm A. latestriatus . However, this diplopod excretes considerable amounts of Bt protein with its faeces. The Bt protein is still insecticidally active and, thus, becomes available to other soil organisms.