Study shows Bt crop technology unsustainable
In order to prevent pest resistance to Bt toxins, maize farmers in the US are required to plant "refuges" of non-Bt maize near the Bt fields. The idea is that the refuges will sustain populations of pests that are susceptible to Bt toxins.
However, previous studies have shown that refuges do not work well, for three reasons: farmers don't comply with refuge requirements, pests are able to live and reproduce in Bt maize fields, and the non-Bt refuge plants become contaminated by cross-pollination with Bt toxin-producing genes (see "Refuge concept breaking down" in GMO Myths and Truths).
Poor compliance by farmers in planting refuges has led to seed companies selling seed mixtures, known as "refuge-in-a-bag", which contain a percentage of non-Bt seeds mixed in with the Bt seeds. Now a study part-funded by Monsanto and the USDA confirms that "refuge-in-a-bag" does not work because the non-Bt maize becomes contaminated with Bt toxin genes through cross-pollination. The study found that over 90% of maize kernels expressed at least one Bt protein. In addition, the surviving pests on the refuge plants did not thrive, meaning that no viable Bt-susceptible pest populations survived.
A Challenge for the Seed Mixture Refuge Strategy in Bt Maize: Impact of Cross-Pollination on an Ear-Feeding Pest, Corn Earworm
Yang F, Kerns DL, Head GP, Leonard BR, Levy R, et al. (2014) PLoS ONE 9(11): e112962. doi:10.1371/journal.pone.0112962
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.