How will earth's butterflies respond to the twin evils of the climate-alarmist crowd, i.e., atmospheric CO2 enrichment and global warming? We here explore what has been learned about the question over the past few years, beginning with a review of studies that focus on carbon dioxide and concluding with studies that focus on temperature.
In a study of Lotus corniculatus (a cyanogenic plant that produces foliar cyanoglycosides to deter against herbivory by insects) and the Common Blue Butterfly (Polyommatus icarus, which regularly feeds upon L. corniculatus because it possesses an enzyme that detoxifies cyanide-containing defensive compounds), Goverde et al. (1999) collected four genotypes of L. corniculatus differing in their concentrations of cyanoglycosides and tannins (another group of defensive compounds) near Paris, France. They then grew them in controlled-environment chambers maintained at atmospheric CO2 concentrations of 350 and 700 ppm, after which they determined the effects of the doubled CO2 concentration on leaf quality and allowed the larvae of the Common Blue Butterfly to feed upon the plants' leaves. This work revealed that elevated CO2 significantly increased leaf tannin and starch contents in a genotypically-dependent and - independent manner, respectively, while decreasing leaf cyanoglycoside contents independent of genotype. These CO2-induced changes in leaf chemistry increased leaf palatability, as indicated by greater dry weight consumption of CO2-enriched leaves by butterfly larvae. In addition, the increased consumption of CO2-enriched leaves led to greater larval biomass and shorter larval development times, positively influencing the larvae of the Common Blue Butterfly. Hence, it is not surprising that larval mortality was lower when feeding upon CO2-enriched as opposed to ambiently-grown leaves.