Gypsy moth feeding in the canopy of a CO₂‐enriched mature forest

Abstract

Abstract Rising atmospheric carbon dioxide (CO 2 ) concentration is expected to change plant tissue quality with important implications for plant–insect interactions. Taking advantage of canopy access by a crane and long‐term CO 2 enrichment (530 μ mol mol −1 ) of a natural old‐growth forest (web‐free air carbon dioxide enrichment), we studied the responses of a generalist insect herbivore feeding in the canopy of tall trees. We found that relative growth rates (RGR) of gypsy moth ( Lymantria dispar ) were reduced by 30% in larvae fed on high CO 2 ‐exposed Quercus petraea , but increased by 29% when fed on high CO 2 ‐grown Carpinus betulus compared with control trees at ambient CO 2 (370 μ mol mol −1 ). In Fagus sylvatica , there was a nonsignificant trend for reduced RGR under elevated CO 2 . Tree species‐specific changes in starch to nitrogen ratio, water, and the concentrations of proteins, condensed and hydrolyzable tannins in response to elevated CO 2 were identified to correlate with altered RGR of gypsy moth larvae. Our data suggest that rising atmospheric CO 2 will have strong species‐specific effects on leaf chemical composition of canopy trees in natural forests leading to contrasting responses of herbivores such as those reported here. A future change in host tree preference seems likely with far‐ranging consequences for forest community dynamics.