ENRICHED ATMOSPHERIC CO2 AND DEFOLIATION - EFFECTS ON TREE CHEMISTRY AND INSECT PERFORMANCE

We examined the effects of CO2 and defoliation on tree chemistry and p erformance of the forest tent caterpillar, Malacosoma disstria. Quakin g aspen (Populus tremuloides) and sugar maple (Acer saccharum) trees w ere grown in open-top chambers under ambient or elevated concentration s of CO2. During the second year of growth, half of the trees were exp osed to free-feeding forest tent caterpillars, while the remaining tre es served as nondefoliated controls. Foliage was collected weekly for phytochemical analysis. Insect performance was evaluated on foliage fr om each of the treatments. At the sampling date coincident with insect bioassays, levels of foliar nitrogen and starch were lower and higher , respectively, in high CO2 foliage, and this trend persisted througho ut the study. CO2-mediated increases in secondary compounds were obser ved for condensed tannins in aspen and gallotannins in maple. Defoliat ion reduced levels of water and nitrogen in aspen but had no effect on primary metabolites in maple. Similarly, defoliation induced accumula tions of secondary compounds in aspen but not in maple. Larvae fed fol iage from the enriched CO2 or defoliated treatments exhibited reduced growth and food processing efficiencies, relative to larvae on ambient CO2 or nondefoliated diets, but the patterns were host species-specif ic. Overall, CO2 and defoliation appeared to exert independent effects on foliar chemistry and forest tent caterpillar performance.