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Status Report for the PPDC: Resistance Management For Bt-crop

Information provided for informational purposes only

Note: This information is provided for reference purposes only. Although the information provided here was accurate and current when first created, it is now outdated.


There are currently 8 registered Bacillus thuringiensis (Bt) plant-pesticides. There is one registration each for Bt potatoes, Bt cotton, and Bt popcorn; and there are 5 registrations for Bt field corn. One of these Bt field corn products (Novartis' Event 11) is also registered for processed sweet corn.

Resistance management for Bt-crops was one of the first issues brought to the Pesticide Program Dialog Committee (PPDC). At the time of that meeting, resistance management for Bt crops already was an issue being discussed by EPA, registrants, and public interest groups at Scientific Advisory Panel (SAP) meetings. In addition, registrants were conducting research on the biology and ecology of affected insects and crops to better understand long-term resistance management of Bt-crops to slow or halt the development of insect resistance. Of special consideration were the microbial forms of Bt used in Integrated Pest Management (IPM) programs because of their importance to sustainable agriculture and organic farming. That first PPDC cautioned EPA not to require resistance management plans for all pesticides, while acknowledging that Bt was a special case ("in the public good") and worthy of extra protection.

Subsequent to registration of the first Bt crops in 1995, a great deal has been learned which has been helpful in better understanding the need for and refining resistance management plans. A USDA organization known as NC (North Central) 205 issued a report in 1997 for Bt corn which recommended refuges or set-asides using non-Bt corn acreage as a major component of resistance management plans. EPA has also received a detailed, final report from the February 9, 1998 SAP Subpanel meeting on Bt resistance management; and the International Life Sciences Institute (ILSI) is in the process of finalizing their report which focuses on Bt resistance management for corn. In January of this year, in preparation for another SAP meeting on Bt crops and resistance management, EPA released a report summarizing our current understanding of this topic. Shortly afterwards, the Union of Concerned Scientists published their report entitled: Now or Never, Serious New Plans to Save a Natural Pest Control. Additional knowledge on Bt resistance has been garnered from annual research reports on Bt resistance submitted to EPA by registrants of Bt plant-pesticides; Agency hearings and participation in regional and national workshops; and extensive literature review on Bt resistance conducted by EPA scientists.

A significantly larger rate of adoption of Bt plant-pesticides technology has occurred than what was expected by registrants and by EPA at the time the initial Bt products were registered. This is especially true for Bt-corn. Although the 1998 data is not yet available, preliminary estimates have Bt-based plant-pesticides representing 15 to 17 percent of the field corn crop in the US, and adoption of Bt-based plant-pesticides rising to a high of 25 percent in 1999. Surprisingly, in 1995 it was estimated that the adoption of Bt-based plant-pesticides would be about five percent by the year 2001.

Mindful of the accelerated adoption rate, EPA and USDA have agreed to re-examine Bt crop resistance and resistance management strategies. EPA and USDA intend to use a public dialog process to include researchers, registrants, growers, public interest groups, and government agencies to identify reasonable approaches to resistance management. The PPDC meeting is not intended to discuss the exact size and location of refuges or set-asides that government agencies and growers would support, but rather to present and discuss the general framework and process for enhancing the knowledge base on Bt resistance and management of plant-pesticides. In addition, EPA and USDA are jointly authoring a working paper to serve as the central discussion piece for a planned workshop in early March aimed at exploring ways of designing and implementing resistance management programs that are flexible and can accommodate rapidly changing technology (e.g., gene stacking or adding additional Bt proteins, and adding new non-Bt genes to crop plants).

EPA is also actively considering changes to existing registrations, especially for Bt potatoes and certain Bt corn registrations, to stipulate similar refuges or set-asides as those listed in the registrations for Bt cotton. The size, location, and time frame for implementing these set-asides would be a major focus of the proposed March workshop. EPA and USDA would like to have consistent refuge or set-aside requirements for similar Bt crop registrations where appropriate; however, some Bt-proteins may turn out to be so unique that refugia or set-aside acreage could be reduced or even eliminated for those products. In addition, regional differences in climate, pest/crop combinations, and pest biology may call for different resistance management plans, e.g., the pink bollworm control program in Arizona.

In the long-term, a regional approach to resistance management for plant-pesticides is gaining support. USDA is considering the development of "virtual centers" around the country to be staffed by commodity experts from the USDA and grant partners. While the centers would serve a number of functions, one role discussed has been development of regional resistance management plans for Bt-based crops. These regional centers could help establish appropriate regional resistance management strategies for the Bt crops grown in that area.

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