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The Upside of a CO2-Induced Decrease in Plant Nutritive Value
Yin, J., Sun, Y. and Ge, F. 2014. Reduced plant nutrition under elevated CO2 depresses the immunocompetence of cotton bollworm against its endoparasite. Scientific Reports 14: 10.1038/srep04538.

The authors set the stage for their report on the subject by noting that "decreased foliar nitrogen and protein concentrations under elevated CO2 reduce plant nutritional quality," diminishing the value of the foliage as a resource for insect herbivores, as described by the studies of Mattson (1980) and Johns and Hugher (2002). And in support of this statement, they go on to report that most such previous studies have discovered that "decreases in plant nutritional quality under elevated CO2 result in increased development times, mortality and [are] always associated with reduced food conversion efficiency, adult weight and population fitness of herbivore insects," citing the work of Stiling et al. (1999), Wu et al. (2006) and Chen et al. (2007).

What was done
Yin et al. investigated the immune response of the larvae of the much-hated cotton bollworm (Helicoverpa armigera) - which they describe as "a major agricultural pest worldwide (Fitt, 1989; Wu and Guo, 2005)" - to attack by its chief parasitoid (Mecroplitis mediator) in both ambient and CO2-enriched air (375 and 750 ppm, respectively).

What was learned
The three Chinese scientists discovered that elevated CO2 decreased the immunity of the cotton bollworm larvae to attacks by M. mediator - the latter of which was not impacted by the CO2-enriched air - as a result of the reduced nutritional quality of the wheat that had been grown in the CO2-enriched air and upon which the cotton bollworms had feasted.

What it means
Quoting the concluding words of Yin et al., "our results suggest that lower plant nutritional quality under elevated CO2 could decrease the immune response of herbivorous insects against their parasitoid natural enemies," which could prove to be a huge boon to agriculture the world over.

Chen, F., Wu, G., Parajulee, M.N. and Ge, F. 2007. Impacts of elevated CO2 and transgenic Bt cotton on performance and feeding of three generations of cotton bollworm in a long-term experiment. Entomologia Experimentalis et Applicata 124: 27-35.

Fitt, G.P. 1989. The ecology of Heliothis species in relation to agroecosystems. Annual Review of Entomology 34: 17-53.

Johns, C.V. and Hugher, L. 2002. Interactive effects of elevated CO2 and temperature on the leaf-miner Dialectica scalariella Zeller (Lepidoptera: Gracillariidae) in Paterson's Curse, Echium plantagineum (Boraginaceae). Global Change Biology 8: 142-152.

Stilling, P., Cattell, M., Moon, D.C., Rossi, A., Hungate, B.A., Hymus, G. and Drake B. 1999. Decreased leaf-miner abundance in elevated CO2 lowers herbivore abundance, but increases leaf abscission rates. Global Change Biology 8: 658-667.

Wu, G., Chen, F. and Ge, F. 2006. Response of multiple generations of cotton bollworm Helicoverpa armigera Hubner, feeding on spring wheat, to elevated CO2. Journal of Applied Entomology 131: 2-9.

Wu, K.M. and Guo, Y.Y. 2005. The evolution of cotton pest management practices in China. Annual Review of Entomology 50: 31-52.

Reviewed 25 June 2014