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Effects of Elevated CO2 on the Effectiveness of Transgenic Bt Cotton
Chen, F., Wu, G., Ge, F., Parajulee, M.N. and Shrestha, R.B.  2005.  Effects of elevated CO2 and transgenic Bt cotton on plant chemistry, performance, and feeding of an insect herbivore, the cotton bollworm.  Entomologia Experimentalis et Applicata 115: 341-350.

What was done
The authors grew well watered and fertilized cotton (Gossypium hirsutum L.) plants of two varieties - GK-12, expressing Cry1A (c) genes from Bacillus thurigiensis Berliner var. kurstaki and Simian-3, a non-transgenic cultivar from the same recurrent parent - in pots placed within open-top chambers maintained at either 376 or 754 ppm CO2 in Sanhe County, Hebei Province, China from planting in mid-May to harvest in October.  Several immature bolls collected throughout the experiment were analyzed for various chemical characteristics, while others were stored under refrigerated conditions for later feeding to larvae of the cotton bollworm, Helicoverpa armigera (Hubner), while various parameters related to their growth and development were monitored.

What was learned
The elevated CO2 treatment increased immature boll concentrations of condensed tannins by approximately 22% and 26% in transgenic and non-transgenetic cotton, respectively (see Tannins in our Subject Index for a discussion of the significance of this observation).  In addition, the authors report that elevated CO2 slightly decreased the body biomass of the cotton bollworm and reduced moth fecundity.  The Bt treatment was even more effective in this regard; and in the combined Bt-high-CO2 treatment, the negative cotton bollworm responses were expressed most strongly of all.

What it means
Chen et al. conclude that the expected higher atmospheric CO2 concentrations of the future will "either not change or only slightly enhance the efficacy of Bt technology against cotton bollworms."

Reviewed 24 August 2005