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Photo: Scott Bauer, USDA ARS, Bugwood.org
- Monsanto's Cry3Bb1 rootworm trait, while proven effective on 99% of acres according to the company, is the first trait with confirmed resistance among field populations primarily due to overuse of the trait in consecutive years of continuous corn, and in areas of high rootworm populations that can overwhelm any trait. Visit refuge calculator: http://ncga.com/irm-calculator.
- Unacceptable root injury (due to high beetle populations, and escalated by a warm, dry spring and subsequent drought) has also been noted with other single rootworm traits, such as mCry3A in Agrisure 3000GT, Cry34/35 in Herculex Xtra and even pyramided traits (Cry 34/35+Cry3Bb1 in SmartStax RIB), according to University of Minnesota Entomologist Ken Ostlie.
- In a March 2012 letter of concern to the EPA, signed by 22 public sector scientists, they question the durability of the dual rootworm traits in the SmartStax pyramid (Cry3Bb1 + Cry 34/35Ab1), especially in light of the decreased non-Bt refuge requirements (from 20% down to 5%). Entomologists have concerns that smaller refuge size in problem rootworm areas would likely have the opposite effect of hastening evolution of resistance to Cry 34/35Ab1. The letter states that it is crucial to preserve the effectiveness of the Cry 34/35Ab1 trait, because it is approved in pyramid with mCry3A and is the common toxin in two different pyramids from two companies, with a third seeking to register mCry3A + Cry 34/35Ab1.
- To help you keep the traits straight between hybrids, download the "Handy Bt Trait Table" here: http://bit.ly/Vtqp85.
- Fortunately, some next-generation higher-dose Bt-RW traits may be coming to market. Syngenta's new Agrisure Duracade rootworm trait, that features the new high-dose eCry3.1Ab protein in a pyramid stack with the mCry3A rootworm trait, has been shown to reduce beetle emergence by 99.79% in a University of Missouri study. And by the end of the decade, several companies may introduce a truly unique technology trait that is not a protein like current traits. It is an RNAi technology that interferes differently within the gut of pests once ingested, which dramatically improves control. But due to its uniqueness, it will take longer to receive EPA approval.