Exposure of arthropod predators to Cry1Ab toxin in Bt maize fields

Abstract.  1. To assess the risks of an insect-resistant transgenic plant for non-target arthropods, it is important to investigate the exposure of non-target species to the transgene product. Exposure of predators in the field depends on the toxin levels in food sources, their feeding ecology and that of their prey.
2. To verify the transmission of Cry1Ab toxin through the food chain, and thus exposure of predators in the field, samples from different plant tissues, herbivores, and predators in Bt maize fields in Spain (Event 176) were collected at different periods over the season and the toxin content was measured using ELISA. Complementary laboratory studies were performed with the omnivorous predator Orius majusculus to assess the toxin uptake and persistence after feeding on variable Bt-containing food sources.
3. Field results revealed that toxin content in some herbivores was negligible (aphids, thrips, leafhoppers) compared with those in spider mites. The latter herbivore only occurred after pollen shed and contained three times greater toxin levels than Bt maize leaves.
4. Data confirmed that the Bt toxin can be transferred to predators, that is to say to Orius spp., Chrysoperla spp., and Stethorus sp. This only applied when Bt maize pollen or spider mites were available. The passage of Bt toxin to O. majusculus via these two food sources was also confirmed in the laboratory. Contrastingly, some predators in the field (hemerobiids, Nabis sp., Hippodamia sp., Demetrias sp.) contained no or negligible toxin levels even when pollen or spider mites were present.
5. Besides essential information for exposure assessment of numerous arthropod predators, this study provides an insight into the feeding ecology of different arthropods in the maize system.