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[SANET-MG] Bt cotton does not imporve yield



In the article below Bt is Cry1Ac for pink boll worm control and BtHr is Bt roundup ready cotton.
Published online before print May 4, 2006
Proc. Natl. Acad. Sci. USA, 10.1073/pnas.0508312103

Agricultural Sciences
Farm-scale evaluation of the impacts of transgenic cotton on biodiversity, pesticide use, and yield
( agricultural sustainability | environmental impact | transgenic crops )

Manda G. Cattaneo *, Christine Yafuso *, Chris Schmidt *, Cho-ying Huang , Magfurar Rahman , Carl Olson *, Christa Ellers-Kirk *, Barron J. Orr , Stuart E. Marsh , Larry Antilla , Pierre Dutilleul ¶, and Yves Carrière *||

Higher yields and reduced pesticide impacts are needed to mitigate the effects of agricultural intensification. A 2-year farm-scale evaluation of 81 commercial fields in Arizona show that use of transgenic Bacillus thuringiensis (Bt) cotton reduced insecticide use, whereas transgenic cotton with Bt protein and herbicide resistance (BtHr) did not affect herbicide use. Transgenic cotton had higher yield than nontransgenic cotton for any given number of insecticide applications. However, nontransgenic, Bt and BtHr cotton had similar yields overall, largely because higher insecticide use with nontransgenic cotton improved control of key pests. Unlike Bt and BtHr cotton, insecticides reduced the diversity of nontarget insects. Several other agronomic and ecological factors also affected biodiversity. Nevertheless, pairwise comparisons of diversity of nontarget insects in cotton fields with diversity in adjacent noncultivated sites revealed similar effects of cultivation of transgenic and nontransgenic cotton on biodiversity. The results indicate that impacts of agricultural intensification can be reduced when replacement of broad-spectrum insecticides by narrow-spectrum Bt crops does not reduce control of pests not affected by Bt crops.

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