BIOLOGICAL SCIENCES / AGRICULTURAL SCIENCES
Farm-scale evaluation of the impacts of transgenic cotton on biodiversity, pesticide use, and yield
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*,||
*Department of Entomology, University of Arizona, 410 Forbes Building, P.O. Box 210036, Tucson, AZ 85721-0036; Graduate Interdisciplinary Program in Insect Science, University of Arizona, 225 Life Sciences South, Tucson, AZ 85721; Arizona Remote Sensing Center, Office of Arid Lands Studies, University of Arizona, 1955 East Sixth Street, Tucson, AZ 85710; Arizona Research and Protection Council, 3721 East Weir Avenue, Phoenix, AZ 85040-2933; and ¶Department of Plant Science, Macdonald Campus, Raymond Building, McGill University, St-Anne-de-Bellevue, QC, Canada H9X 3V9
Edited by May R. Berenbaum, University of Illinois at Urbana-Champaign, Urbana, IL, and approved April 6, 2006 (received for review September 22, 2005)
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.
agricultural sustainability | environmental impact | transgenic crops
PNAS May 16, 2006, vol. 103, no. 20, 7571-7576. OPEN ACCESS ARTICLE.
The increasing world population and changes in consumption patterns may necessitate significant agricultural intensification in the next 50 years (1, 2). Unless crop yield is improved and release of fertilizers and pesticides from croplands is reduced, such intensification could augment contamination and perturbation of managed and natural ecosystems, ultimately harming biodiversity and public health (1–4). It was proposed that transgenic Bacillus thuringiensis (Bt) crops could be valuable tools for increasing agricultural productivity while minimizing the environmental impacts of agriculture (1, 2). However, the potential effects of transgenic crops on nontarget arthropods have caused concern, especially in regions where agricultural land is important to sustain biodiversity (5–7).
Although Bt crops are grown extensively worldwide (8), no large-scale studies had been performed to simultaneously test whether they have favorable agricultural effects and minimal impacts on nontarget arthropods. Here, we report results of a 2-year farm-scale evaluation of the effects of transgenic cotton on biodiversity, pesticide use, and yield. We studied 81 commercial fields in a region of 6,600 km2 in Arizona, where Bt cotton represented 48% and 62% of the cotton planted in the first and second year of the study, respectively. Forty fields were planted to nontransgenic (nonTr) cotton, 21 fields to transgenic cotton producing the Bt toxin Cry1Ac (Bt), and 20 fields to cotton with Bt protein and herbicide resistance (BtHr). Bt cotton with Cry1Ac controls the pink bollworm (Pectinophora gossypiella), a major insect pest of cotton (9, 10).