A challenge for the seed mixture refuge strategy in Bt maize: impact of cross-pollination on an ear-feeding pest, corn earworm.

Fei Yang,Graham P Head,Fangneng Huang,Ronnie Levy,B Rogers Leonard,Ying Niu,David L Kerns,Raul Narciso Carvalho Guedes

doi:10.1371/journal.pone.0112962

Fei Yang, Graham P Head + Show 6 more

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https://doi.org/10.1371/journal.pone.0112962

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Abstract

To counter the threat of insect resistance, Bacillus thuringiensis (Bt) maize growers in the U.S. are required to plant structured non-Bt maize refuges. Concerns with refuge compliance led to the introduction of seed mixtures, also called RIB (refuge-in-the-bag), as an alternative approach for implementing refuge for Bt maize products in the U.S. Maize Belt. A major concern in RIB is cross-pollination of maize hybrids that can cause Bt proteins to be present in refuge maize kernels and negatively affect refuge insects. Here we show that a mixed planting of 5% nonBt and 95% Bt maize containing the SmartStax traits expressing Cry1A.105, Cry2Ab2 and Cry1F did not provide an effective refuge for an important above-ground ear-feeding pest, the corn earworm, Helicoverpa zea (Boddie). Cross-pollination in RIB caused a majority (>90%) of refuge kernels to express ≥ one Bt protein. The contamination of Bt proteins in the refuge ears reduced neonate-to-adult survivorship of H. zea to only 4.6%, a reduction of 88.1% relative to larvae feeding on ears of pure non-Bt maize plantings. In addition, the limited survivors on refuge ears had lower pupal mass and took longer to develop to adults.

Highlights

Transgenic crops expressing Bacillus thuringiensis (Bt) proteins were planted on .72 million hectares for pest control in the world in 2013 [1]
Qualitative ELISA tests (Figure S1) showed that all 150 individual kernels sampled from 30 ears of pure Bt maize plantings in three field trials expressed all four Bt protein groups in SmartStax (Table 1)
All kernels from 30 ears sampled from pure non-Bt plantings were free of Bt protein expression, suggesting that there was no cross-pollination among the trial fields

Summary

Introduction

Transgenic crops (maize and cotton) expressing Bacillus thuringiensis (Bt) proteins were planted on .72 million hectares for pest control in the world in 2013 [1]. In 2012– 2013, field and laboratory studies were conducted to assess the intensity of Bt protein contamination in a RIB planting of 5% nonBt and 95% Bt maize containing the SmartStax trait and the corresponding effect of the cross-pollination on survival, growth, and development of H. zea.

Results

Conclusion