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Cotton Bolls vs. Cotton Bollworms in a CO2-Enriched World
Reference
Wu, G., Chen, F.-j., Sun, Y.-c. and Ge, F. 2007. Response of successive three generations of cotton bollworm, Helicoverpa armigera (Hubner), fed on cotton bolls under elevated CO2. Journal of Environmental Sciences 19: 1318-1325.

What was done
The authors examined the growth, development and consumption of three successive generations of cotton bollworms -- Helicoverpa armigera (Hubner) -- that were reared on cotton bolls grown under ambient (370 ppm) and close to double-ambient (750 ppm) atmospheric CO2 concentrations in an open-top chamber experiment in which they also documented CO2-induced changes in a number of cotton-boll properties.

What was learned
The four Chinese researchers report that "significant decreases in the protein, total amino acid, water and nitrogen content by 15.8%, 17.7%, 9.1% and 20.6% and increases in free fatty acid by 16.1% were observed in cotton bolls grown under elevated CO2." When fed with the cotton bolls, they say that the larval survival rate of H. armigera "decreased by 7.35% in the first generation, 9.52% in the second generation and 11.48% in the third generation under elevated CO2 compared with ambient CO2." In addition, they observed that "the fecundity of H. armigera decreased by 7.74% in the first generation, 14.23% in the second generation and 16.85% in the third generation," while noting that "fecundity capacity is likely to be reduced even further in the next generation."

The synergistic effects of these several phenomena, in the words of Wu et al., "resulted in a potential population decrease in cotton bollworm by 18.1% in the second generation and 52.2% in the third generation under elevated CO2," with the result that "the potential population consumption of cotton bollworm decreased by 18.0% in the second generation and 55.6% in the third generation ... under elevated CO2 compared with ambient CO2."

What it means
In light of these several findings, Wu et al. conclude that "the potential population dynamics and potential population consumption of cotton bollworm will alleviate the harm to [cotton] plants in the future rising-CO2 atmosphere."

Yes, as the atmosphere's CO2 concentration continues to climb, it looks like the cotton bolls are definitely on their way to a big win over the cotton bollworms, handing one of mankind's major crop-destroying opponents a loss from which they may never fully recover.

Reviewed 9 April 2008