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Herbivores vs. Oak Trees in a CO2-Enriched Atmosphere
Reference
Knepp, R.G., Hamilton, J.G., Zangerl, A.R., Berenbaum, M.R. and DeLucia, E.H. 2007. Foliage of oaks grown under elevated CO2 reduces performance of Antheraea polyphemus (Lepidoptera: Saturniidae). Environmental Entomology 36: 609-617.

Background
Antheraea polyphemus is a leaf-chewing generalist lepidopteran herbivore that represents the most abundant feeding guild in the hardwood trees that grow beneath the canopy of the unmanaged loblolly pine plantation that is home to the Forest Atmosphere Carbon Transfer and Storage (FACTS-1) research site in the Piedmont region of North Carolina, USA, where it possesses the capacity to consume 2-15% of forest net primary production in any given year.

What was done
Focusing their attention on two species of oak tree - Quercus alba L. (white oak) and Quercus velutina Lam. (black oak) - the authors examined host plant preference and larval performance of A. polyphemus when fed foliage of the two tree species that had been grown in either ambient or CO2-enriched air (to 200 ppm above ambient) in this long-running FACE experiment.

What was learned
Knepp et al. report that "growth under elevated CO2 reduced the food quality of oak leaves for caterpillars," and that "consuming leaves of either oak species grown under elevated CO2 slowed the rate of development of A. polyphemus larvae." In addition, they report that feeding on foliage of Q. velutina grown under elevated CO2 led to reduced consumption by the larvae and greater mortality.

What it means
The researchers opine that "reduced consumption, slower growth rates, and increased mortality of insect larvae may explain [the] lower total leaf damage observed previously in plots of this forest exposed to elevated CO2," as documented by Hamilton et al. (2004) and Knepp et al. (2005), which finding bodes well indeed for the growth and vitality of such forests in the years and decades ahead, as the air's CO2 content continues to rise.

References
Hamilton, J.G., Zangerl, A.R., Berenbaum, M.R., Pippen, J.S., Aldea, M. and DeLucia, E.H. 2004. Insect herbivory in an intact forest understory under experimental CO2 enrichment. Oecologia 138: 566-573.

Knepp, R.G., Hamilton, J.G., Mohan, J.E., Zangerl, A.R., Berenbaum, M.R. and DeLucia, E.H. 2005. Elevated CO2 reduces leaf damage by insect herbivores in a forest community. New Phytologist 167: 207-218.

Reviewed 7 November 2007