Influence of leaf chemistry of Lotus corniculatus (Fabaceae) on larval development of Polyommatus icarus (Lepidoptera, Lycaenidae):: effects of elevated CO2 and plant genotype

1. Four Lotus corniculatus genotypes differing in cyanoglycoside and condensed tannin concentrations were grown in either low (350 ppm) or high (700 ppm) atmospheric CO2 environments. Larval performance, consumption and conversion efficiency of Polyommatus icarus feeding on this plant material were measured. 2. Plants grown under elevated CO2 contained less cyanoglycosides, more condensed tannins and more starch than control plants. However, water concentration, nitrogen and protein as well as nitrogen concentration in relation to carbon concentration did not differ between CO2 treatments. 3. The four genotypes differed significantly in condensed tannins, cyanoglucoside, leaf water and leaf nitrogen but no genotype-CO2 interaction was detected, except for total phenolics and condensed tannins in which two plant genotypes showed stronger increases under elevated CO2 than the other two. 4. Larvae of P. icarus consumed more plant material and used and converted it more efficiently from plants grown at high atmospheric CO2. 5. Larvae developed significantly faster and were significantly heavier when fed plant material grown under elevated CO2. The observed difference in mass disappeared in the pupal and adult stages. However, lipid concentration of adults from the elevated CO2 treatment was marginally significantly higher than of controls. 6. It is concluded that the higher carbohydrate concentration of L. corniculatus plants grown at elevated CO2 renders leaves more suitable and better digestible to P. icarus. Furthermore, differences in allelochemicals might influence the palatability of L. corniculatus leaves for this specialist on Fabaceae.