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

PLoS One. 2014 Nov 19;9(11):e112962. doi: 10.1371/journal.pone.0112962. eCollection 2014.

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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animal Feed
  • Animals
  • Bacillus thuringiensis / genetics*
  • Decision Making
  • Lepidoptera* / growth & development
  • Pest Control, Biological / methods*
  • Plants, Genetically Modified
  • Pollination*
  • Seeds / genetics*
  • Survival Analysis
  • Zea mays / genetics*
  • Zea mays / physiology*

Grants and funding

F.H. received research funding related to this project from Monsanto, the Louisiana Soybean and Feed Grain Promotion Board, and the hatch funds from the USDA National Institute of Food and Agriculture. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. The authors confirm that a funder (Monsanto) provided support in the form of salaries for a co-author [G.P.H.], but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section. The authors also confirm that this does not alter their adherence to PLOS ONE policies on sharing data and materials.