Biological Activity of Cry1Ab Toxin Expressed by Bt Maize Following Ingestion by Herbivorous Arthropods and Exposure of the Predator Chrysoperla carnea |
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Authors: | L B Obrist A Dutton J Romeis F Bigler |
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Institution: | (1) Agroscope FAL Reckenholz, Swiss Federal Research Station for Agroecology and Agriculture, Reckenholzstr. 191, 8046 Zurich, Switzerland;(2) Syngenta Crop Protection AG, 4332 Stein, Switzerland |
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Abstract: | A major concern regarding the deployment of insect resistant transgenic plants is their potential impact on non-target organisms,
in particular on beneficial arthropods such as predators. To assess the risks that transgenic plants pose to predators, various
experimental testing systems can be used. When using tritrophic studies, it is important to verify the actual exposure of
the predator, i.e., the presence of biologically active toxin in the herbivorous arthropod (prey). We therefore investigated
the uptake of Cry1Ab toxin by larvae of the green lacewing (Chrysoperla carnea (Stephens); Neuroptera: Chrysopidae) after consuming two Bt maize-fed herbivores (Tetranychus urticae Koch; Acarina: Tetranychidae and Spodoptera littoralis (Boisduval); Lepidoptera: Noctuidae) by means of an immunological test (ELISA) and the activity of the Cry1Ab toxin following
ingestion by the herbivores. Moreover, we compared the activity of Cry1Ab toxin produced by Bt maize to that of purified toxin
obtained from transformed Escherichia coli, which is recommended to be used in toxicity studies. The activity of the toxin was assessed by performing feeding bioassays
with larvae of the European corn borer (Ostrinia nubilalis (Hübner); Lepidoptera: Crambidae), the target pest of Cry1Ab expressing maize. ELISA confirmed the ingestion of Bt toxin
by C. carnea larvae when fed with either of the two prey species and feeding bioassays using the target pest showed that the biological
activity of the Cry1Ab toxin is maintained after ingestion by both herbivore species. These findings are discussed in the
context of previous risk assessment studies with C. carnea. The purified Cry1Ab protein was more toxic to O. nubilalis compared to the plant-derived Cry1Ab toxin when applied at equal concentrations according to ELISA measurements. Possible
reasons for these findings are discussed. |
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Keywords: | biological activity Chrysopidae ELISA Neuroptera non-target effects risk assessment transgenic plants |
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