The design and implementation of insect resistance management programs for Bt crops

Abstract

Cotton and corn plants with insect resistance traits introduced through biotechnological methods and derived from the bacterium Bacillus thuringiensis (Bt) have been widely adopted since they were first introduced in 1996. Because of concerns about resistance evolving to these Bt crops, they have been released with associated IRM programs that employ multiple components and reflect the input of academic, industrial and regulatory experts. This paper summarizes the current status of Bt crop technologies in cotton and corn, the principles of IRM for Bt crops and what they mean for the design of IRM programs. It describes how these IRM programs have been implemented and some of the key factors affecting successful implementation. Finally, it suggests how they may evolve to properly steward these traits in different geographies around the world. The limited number of reported cases of resistance after more than 15 years of intensive global use of Bt crops suggest that this exercise has been broadly successful. Where resistance issues have been observed, they have been associated with first generation technologies and incomplete or compromised IRM programs (i.e., inadequate structured refuge). Next generation technologies with multiple pyramided modes of action, together with the implementation of IRM strategies that are more dependent upon manufacturing and less dependent upon grower behavior, such as seed mixes, should further enhance IRM programs for Bt crops.

Scientific Opinion on an application from Pioneer Hi‐Bred International and Dow AgroSciences LLC (EFSA‐GMO‐NL‐2005‐23) for placing on the market of genetically modified maize 59122 for food and feed uses, import, processing and cultivation under Regulation (EC) No 1829/2003

“…Insect resistance management strategies are designed to minimise the selection pressure associated with Bt-crops, in order to prevent or at least delay resistance evolution in the target insect pests and to extend the durability of Bt-crops Alcalde et al, 2007;Andow, 2008;MacIntosh, 2010;Head and Greenplate, 2012). As currently implemented for several Bt-crops in several countries, the insect resistance management plan proposed by the applicant relies on the high dose/refuge strategy (Gould, 1998;Glaser and Matten, 2003;MacIntosh 2010).…”

Resistance to Bacillus thuringiensis Toxin Cry2Ab in Trichoplusia ni Is Conferred by a Novel Genetic Mechanism

“…Cry1Ab and Cry1Ac are the primary insecticidal proteins expressed in the current commercial transgenic Bt maize and Bt cotton varieties to target Lepidoptera pests in the field (21). Resistance to Cry1Ac and Cry1Ab has been observed in both laboratory-selected and field-evolved populations of insect pests (5,6,8).…”

“…To delay the development of resistance to Bt toxins in insect populations, the toxin Cry2Ab has been used to pyramid with Cry1Ac in the new generation of Bt crops (1,6,21), as Cry2Ab is known not to share the same binding sites with Cry1Ab or Cry1Ac in insects (22)(23)(24). The gene pyramiding strategy to combine Cry1Ac and Cry2Ab has proven to be effective in delaying the development of insect resistance to Bt toxins (25,26).…”

Analysis of resistance to Cry1Ac in field-collected pink bollworm,Pectinophora gossypiella(Lepidoptera:Gelechiidae), populations

“…The 2013 Bt cotton acreage was 11 million ha constituting >95 % of the total cotton area but with very low proportion of non-Bt refuge planting. The near-absence of structured refuge with large acreages of Bt cotton has placed the Bt technology at great risk of resistance development in bollworms 24 and resistance to Cry1Ac in Bollgard was reported in 2010 from Gujarat, western India. Many reasons could be ascribed to the Cry1Ac-resistance in PBW.…”