POPULATION ECOLOGY CO2 and O3 Effects on Paper Birch (Betulaceae: Betula papyrifera) Phytochemistry and Whitemarked Tussock Moth (Lymantriidae: Orgyia leucostigma) Performance

Elevated atmospheric concentrations of CO2 and O3 are known to alter the chemical composition of foliage, which in turn may affect the performance of herbivorous insects. We investigated the independent and interactive effects of CO2 and O3 on foliar quality of paper birch (Betula papyrifera Marshall) and the consequences of chemical changes for performance of the whitemarked tussock moth Orgyia leucostigma (J. E. Smith). The experimental design was a 2 by 2 factorial, with ambient and elevated levels of CO2 and O3, respectively. Foliage was analyzed for concentrations of nitrogen, starch, and condensed tannins. CO2 and O3 independently and interactively affected nitrogen concentrations, with the elevated CO2 O3 treatment reducing nitrogen concentrations more than either treatment alone. Elevated CO2 and O3 had no signiÞcant effect on starch and tannin concentrations when administered alone but increased starch concentrations by 17% over ambient when administered together. Larvae were reared on experimental trees from egg hatch through pupation to determine treatment effects on development time and pupalmass. Larval performance measures were not statistically different among fumigation treatments, although females tended to have reduced pupal mass under the elevated CO2 O3 treatment. These results demonstrate that chemical responses of some plant species to elevated levels of CO2 (560 l L ) and O3 (1.5 ambient) may be of insufÞcient magnitude to signiÞcantly alter standard measures of individual insect performance.