Biological Activity of Cry1Ab Toxin Expressed by Bt Maize Following Ingestion by Herbivorous Arthropods and Exposure of the Predator Chrysoperla carnea

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 (Hu¨bner); 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.

Biologia comparada e comportamento de Tetranychus urticae Koch (Acari: Tetranychidae) e Phytoseiulus macropilis (Banks) (Acari: Phytoseiidae) em algodoeiro bollgardTM e Isolinha não-Transgênica

“…Rhizoglypus robini (Claparède) (Acari: Acaridae) também não foi afetada pela toxina Cry3Bb1 presente no milho Bt, em relação à sobrevivência de adultos e imaturos coletados em armadilhas no milho Bt e em quatro isolinhas não-Bt (Carter et al 2004). Similar aos resultados encontrados para P. macropilis, Obrist et al (2006a) verifi caram que a toxina Cry1Ab no milho Bt, não afetou seu predador Neoseiulus cucumeris Oudemans (Acari: Phytoseiidae). No entanto, fêmeas de N. cucumeris alimentadas com pólen Bt apresentaram cerca de 9% de prolongamento no tempo de desenvolvimento e cerca de 17% de redução de fecundidade.…”

“…Essas toxinas são produzidas constitutivamente pela planta, mas predominantemente nas folhas. Ao serem expressas continuamente, as toxinas fi cam expostas aos demais herbívoros não-alvos e, consequentemente, aos seus inimigos naturais (Dutton et al 2002, Obrist et al 2006a, Torres et al 2006, Torres & Ruberson 2008. Entretanto, nenhum dos trabalhos realizados até o momento avaliaram os possíveis efeitos subletais das toxinas Cry ao longo de gerações ou indiretos, através da planta e comportamentais, na biologia e comportamento de T. urticae, praga não-alvo do algodoeiro Bt, mas que apresenta considerável exposição à toxina.…”

Ecological compatibility of GM crops and biological control

“…Less-susceptible prey species, on the other hand, may provide prolonged exposure to predators. Intake of transgene toxins by herbivores (targets and nontargets) has been well documented, with variations among taxa (Dutton et al, 2002;Obrist et al, 2005Obrist et al, , 2006b). In some cases, such as spider mites, herbivores concentrate the toxins at levels significantly exceeding the titers present in plants (Dutton et al, 2002;Obrist et al, 2006a).…”

Setting the record straight: a rebuttal to an erroneous analysis on transgenic insecticidal crops and natural enemies

“…These results strongly indicate that the effects observed by Hilbeck et al (1998a) were due to C. carnea feeding on poor quality (sick or dying) lepidopteran prey. Additional studies with aphids (which do not ingest Cry1Ab) and spider mites [which contain high concentrations of biologically active Cry1Ab (Obrist et al 2006)], neither of which is affected when feeding on Bt maize, demonstrated that, when these herbivores fed on Bt maize and were in turn consumed by C. carnea, the predator was not harmed (Dutton et al 2002). These results emphasize that care must be taken when designing laboratory studies to assess the potential effects of Cry proteins and other insecticidal factors on predators; otherwise the results can easily be misinterpreted.…”