Date: 01.08.2017

Stacked Bt maize and arthropod predators – Exposure to insecticidal Cry proteins and potential hazards

The publication reports results from experiments with stacked Bt maize, two herbivores and three generalist predators with different modes of feeding. No acute lethal or sublethal effects of stacked Bt maize on predators was revealed. In addition, no evidence of synergistic interactions between individual Cry proteins that could affect beneficial non-target species was provided. Our study suggests that examined stacked Bt maize could improve agricultural production in a sustainable way.

Figure 1. Median concentrations (µg g-1 dry weight) of (a) Cry1A.105, (b) Cry1F, (c) Cry2Ab2, (d) Cry3Bb1 and (e) Cry34Ab1 in SmartStax maize leaves and pollen, in spider mites and aphids feeding on whole maize plants, and in lacewings, ladybeetles and spiders feeding on maize pollen, aphids or spider mites. Arrow thickness represents the percentage of Cry protein in the higher compared with the next lower trophic level.

Commercialized insect-resistant genetically engineered (GE) crops express genes from the bacterium Bacillus thuringiensis (Bt) that encode crystalline (Cry) proteins. Cry proteins provide protection against certain Lepidoptera or Coleoptera pests. GE crops with stacked insecticidal traits expose arthropods to multiple Cry proteins. One of them is SmartStax maize that combines six insect-protection genes and two herbicide-tolerance genes and provides the unique opportunity to study the flow and fate as well as potential non-target effects of multiple Cry proteins simultaneously because the different Cry proteins may interact and lead to unexpected adverse effects on non-target species. Those include natural enemies that help to control herbivores in crop fields and thus contribute to sustainable pest management.

Bi- and tri-trophic experiments with SmartStax maize, herbivorous spider mites (Tetranychus urticae), aphids (Rhopalosiphum padi), predatory spiders (Phylloneta impressa), ladybeetles (Harmonia axyridis) and lacewings (Chrysoperla carnea) were conducted. Our results showed that Cry proteins moved in a similar pattern through the arthropod food chain, although the transfer efficiency differed. While spider mites contained Cry protein concentrations exceeding the values in leaves (except Cry2Ab2), aphids contained only traces of some Cry protein. Among the different predators, ladybeetle larvae showed higher concentrations than lacewing larvae and juvenile spiders (Figure 1). Acute negative effects of SmartStax maize on predator survival, development and weight were not observed. The study thus provides evidence that the different Cry proteins do not interact in a way that poses a risk to the investigated non-target species under controlled laboratory conditions.

Svobodová Z., Shu Y., Skoková Habuštová O., Romeis J., Meissle M. (2017) Stacked Bt maize and arthropod predators – Exposure to insecticidal Cry proteins and potential hazards. Proceedings of the Royal Society B 284: 20170440. DOI: 10.1098/rspb.2017.0440

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