Box 2: Field-evolved resistance to Bt corn with reduced efficacy reported
Field-evolved resistance of S. frugiperda (fall armyworm) to Bt corn producing Cry1F occurred in 3 years in the United States territory of Puerto Rico75, 76 (Tables 1 and 2). This is the fastest documented case of field-evolved resistance to a Bt crop with reduced efficacy reported and is consistent with worst-case scenarios envisioned in 1997 by some experts32, 68. It is also the first case of resistance leading to withdrawal of a Bt crop from the marketplace. High levels of resistance persisted in Puerto Rico in 2011, 4 years after Cry1F corn had been voluntarily withdrawn from sales76.
Field-evolved resistance to Bt corn producing Cry1Ab occurred in B. fusca (maize stem borer) in South Africa in 8 years21, 101 (Tables 1 and 2) and has some striking parallels with S. frugiperda resistance to Cry1F corn. In both cases, proactive resistance monitoring was not conducted and anecdotal evidence of reduced efficacy in the field preceded documentation of resistance with bioassays73, 74, 75, 76, 101, 102, 107.
Bt corn producing Cry3Bb to kill beetles, particularly D. v. virgifera (western corn rootworm), was first registered in the United States in 2003 (ref. 108). By 2009, farmers planted Cry3Bb corn on 13 million ha, which was 36% of all corn in the United States100, 109. Field and laboratory data show that control problems in the field during 2009 and 2010 were associated with resistance to Cry3Bb in some Iowa populations of D. v. virgifera110, 111, 112. In 'problem' fields, which had severe damage to Cry3Bb corn caused by rootworms, Cry3Bb corn had been planted for 3–7 years110, 111. A 2011 field study of two of the problem fields identified in 2009 found that D. v. virgifera emergence did not differ significantly between Cry3Bb corn and non-Bt corn112.
Department of Entomology, University of Arizona, Tucson, Arizona, USA.
- Bruce E Tabashnik &
- Yves Carrière
Centre de coopération Internationale en Recherche Agronomique pour le Développement, UPR 102, Montpellier, France.
- Thierry Brévault
Competing financial interests
B.E.T. is coauthor of a patent on engineering modified Bt toxins to counter pest resistance, which is related to published research (Nat. Biotechnol. 29, 1128–1131, 2011). Dow AgroSciences, Monsanto and Bayer CropScience did not provide funding to support this work, but may be affected financially by publication of this paper and have funded other work by B.E.T.
Bruce E Tabashnik