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Bacillus thuringiensis (Bt) Plant-Incorporated Protectants - page 10 / 30





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Bt Plant-Incorporated Protectants October 15, 2001 Biopesticides Registration Action Document

Francis' Satyr butterfly and Kern Primrose Sphinx moth) are not going to be exposed to Cry1Ac protein because their habitats do not overlap with cotton fields.

Limited data do not indicate that Cry proteins have any measurable effect on microbial populations in the soil. Horizontal transfer from transgenic plants to soil bacteria has not been demonstrated. Purified microbially produced Cry1Ac protein produced a DT50 (Degradation Time) of 9.3-20.2 days. Ground, lyophilized Cry1A(c) cotton line 931tissue produced a DT50 of 41 days. Based upon estimates of 60,000 plants per acre, a total of 1.44 grams of Cry protein per acre would enter the soil when the cotton plants are incorporated after harvest.

3. Insect Resistance Management

Available data indicate that after six years of commercialization, no reported insect resistance has occurred to the Bt toxins expressed either in Bt potato, Bt corn, or Bt cotton products. The Agency believes that the existing IRM plan for Bt potato is adequate to mitigate Colorado potato beetle resistance. The existing IRM plan for Bt corn which had been strengthened for the 2000 growing season) was strengthened to further mitigate European corn borer, corn earworm, and southwestern corn borer. The existing IRM plan for Bt cotton (already strengthened for the 2001 growing season) was further strengthened to mitigate tobacco budworm, cotton bollworm, and pink bollworm resistance including requiring additional data to more closely examine the effectiveness of the 5% external, unsprayed refuge option.

The issue of insect resistance management has generated more data, meetings, and public comments than all of the other sections covered in this BRAD. Insect resistance management (IRM) is the set of practices aimed at reducing the potential for insect pests to become resistant to a pesticide. Bt IRM is of great importance because of the threat insect resistance poses to the future use of Bt plant- incorporated protectants and Bt technology as a whole. EPA considers protection of insect (pest) susceptibility of Bt to be in the “public good.” EPA has determined that development of resistant insects would constitute an adverse environmental effect. In order to delay the development of insect resistance to Bt corn and cotton plant-incorporated protectants, EPA has mandated specific IRM requirements to strengthen the existing IRM programs as part of the terms and conditions of the registrations.

a. Bt Corn

The Agency has determined that the 20% non-Bt field corn refuge requirements for Bt corn grown in the Corn-Belt and the 50% non-Bt corn refuge requirements for Bt corn grown in cotton-growing areas are scientifically-sound, protective, feasible, sustainable, and practical to growers. Models have been developed by scientists in academia to predict the estimated time that insect resistance


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