Sicherheitsforschung zum Anbau von transgenen Pflanzen: Prüfung der Nebenwirkungen von Bt-Mais auf Mikrohymenopteren der Gattung Trichogramma (Hym., Trichogrammatidae). | Risk assessment of culturing transgenic crops: testing of side effects of Bt corn on Microhymenoptera of the genus Trichogramma (Hym., Trichogrammatidae).

Transgenic Bt maize carries a Bacillus thuringiensis toxin which is effective against larva of the European corn borer, Ostrinia nubilalis. The objective of using Bt maize is to reduce the use of pesticides and to develop sustainable pest control methods against O. nubilalis. The evaluation of potential side effects of transgenic crops on beneficial nontarget organisms such as parasitoid hymenopterans is of growing importance. The species Trichogramma brassicae is a naturally occurring enemy of the European corn borer. The effects of transgenic maize plant food sources were tested on adults of T. brassicae. The experiments followed the principles of the IOBC/WPRS testing guidelines with minor modifications. The following maize cultivars were tested and compared in the laboratory: Pactol CB (Bt 176) and Novelis (Mon 810) and the respective non-transformed cultivars Pactol and Nobilis. Groups of T. brassicae were exposed to the different maize food sources into glass cages: pollen, honeydew from Sitobion avenae aphids and phloem sap. The rate of parasitism of the European corn borer by T. brassicae was calculated as eggs per female and comparisons were made between Bt, non-Bt food sources and control. With pollen, the parasitism per female was 18.923.36 eggs for control, 22.562.24 eggs for Pactol CB (Bt 176), 18.622.27 eggs for Pactol (non-Bt), 15.543.15 eggs for Novelis (Mon 810) and 24.531.93 eggs for Nobilis (non-Bt). When exposed to phloem sap from stem tissue, parasitism was 22.464.60 eggs for control, 16.985.82 for Pactol CB (Bt 176), 14.072.54 for Pactol (non-Bt), 14.924.08 for Novelis (Mon 810) and 14.341.88 for Nobilis (non-Bt). The highest parasitism with maize food sources was reached with honeydew on leaves, with 25.733.62 eggs for control, 30.342.43 for Pactol CB (Bt 176), 34.533.67 for Pactol (non-Bt), 29.682.44 for Novelis (Mon 810) and 35.503.33 for Nobilis (non-Bt). In all the experiments, no significant differences were found between Bt and non-Bt maize. There was no reduction of parasitism. The tested Bt maize cultivars Bt176 and Mon810 can be classified as "harmless" (category 1) to T. brassicae parasitoid wasps. In the present study, the testing method and the indicator organism of the genus Trichogramma were shown to be suitable for future risk assessment and monitoring of transgenic crops.