Background
Lotus corniculatus is a cyanogenic plant that produces foliar cyanoglycosides to deter against herbivory by insects.  The Common Blue Butterfly (Polyommatus icarus), however, regularly feeds upon this plant, for it possesses an enzyme that detoxifies these cyanide-containing defensive compounds.

What was done
Four genotypes of Lotus corniculatus, differing in cyanoglycoside and tannin concentrations, were collected near Paris, France, and grown in controlled environmental chambers receiving atmospheric CO2 concentrations of 350 and 700 ppm.  The effects of elevated CO2 on leaf quality were determined prior to allowing larvae of the Common Blue Butterfly (Polyommatus icarus) to feed upon leaves.  Thus, the authors studied whether CO2-induced changes in leaf quality can influence larval development in this butterfly species.

What was learned
Elevated CO2 significantly increased leaf tannin and starch contents in a genotypically-dependent and -independent manner, respectively, while decreasing leaf cyanoglycoside contents, regardless of genotype.  Atmospheric CO2 enrichment did not significantly affect leaf water, sugar, protein, or nitrogen contents.  Thus, these CO2-induced changes in leaf chemistry (higher starch and tannin and lower cyanoglycoside concentrations) increased its palatability, as indicated by greater leaf dry weight consumption of CO2-enriched leaves by butterfly larvae.  In addition, increased leaf consumption (of CO2-enriched leaves) led to greater larval biomass and shorter larval developmental times, indicating that atmospheric CO2 enrichment affected leaf quality to positively influence larvae of the Common Blue Butterfly.  Moreover, larval mortality was lower when feeding upon CO2-enriched, rather than ambiently-grown, leaves.

What it means
As the CO2 content of the air rises, it is likely that Lotus corniculatus plants will increase their photosynthetic rates and differentially invest their additional carbon gains in storage, structural, and defensive compounds.  Specifically, it is anticipated that atmospheric CO2 enrichment will increase leaf starch and tannin contents and decrease cyanoglycoside contents, without affecting sugar, protein, water, and nitrogen contents.  Collectively, these chemical changes act to improve the palatability of Lotus corniculatus leaves to the Common Blue Butterfly larvae.  Thus, as the atmospheric CO2 concentration continues to increase, such larvae will likely exhibit less mortality, greater biomass, and quicker developmental times, as demonstrated in this paper, which indicates that this butterfly species will likely thrive in the CO2-enriched air of the future.