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Are legume-feeding herbivores buffered against direct effects of elevated carbon dioxide on host plants? A test with the sulfur butterfly, Colias philodice

Global change biology 2007 v.13 no.10 pp. 2045-2051
C3 plants, Colias philodice, Melilotus albus, Trifolium pratense, butterflies, carbon, carbon dioxide, carbon dioxide enrichment, digestion, herbivores, host plants, instars, larvae, leaves, legumes, nitrogen, nitrogen content, pupae, sulfur
When grown under elevated atmospheric carbon dioxide (CO₂), leaf nitrogen content decreases less for legumes than for nonlegume C₃ plants. Given that elevated CO₂ adversely affects insect herbivores primarily through dilution of plant nitrogen, it is reasonable to expect that legume-feeding herbivores will be relatively buffered against CO₂-induced reduction in performance. However, despite their ecological and economic importance, very few studies have addressed the effects of elevated CO₂ on legume-feeding herbivores. Unlike the responses of the vast majority of nonlegume C₃ plants, when the legumes Trifolium pratense and Melilotus alba were grown under elevated (742 ppm) CO₂, leaf nitrogen and carbon contents and C : N ratios did not change. For Colias philodice larvae fed T. pratense, elevated CO₂ had little or no effect on consumption, digestion, or conversion of whole food or nitrogen and, consequently, no effect on growth rate, instar duration, or pupal weight. For larvae fed M. alba, elevated CO₂ had little or no effect on consumption of whole food or nitrogen, increased digestion but decreased conversion of both and, consequently, had no effect on growth rate, instar duration or pupal weight. These results suggest that, relative to herbivores of nonlegume C₃ plants, legume-feeding herbivores will be less affected as atmospheric CO₂ continues to rise.