RESPONSES OF TREE SAP-FEEDING HERBIVORES TO ELEVATED CO2

Five species of sap-feeding homoptera were studied on Fagus sylvatica and Acer pseudoplatanus and exposed to elevated concentrations of carb on dioxide (600 mu L L(-1)). The concentration of total soluble amino acids in foliage of F. sylvatica was unaffected by growing saplings in elevated atmospheric CO2 concentrations. Although experiments on indi vidual aphids indicated poorer performance of Phyllaphis fagi (fewer, smaller nymphs produced), resultant populations did not differ from th ose in ambient (350 mu L L(-1)) conditions. The area of beech foliage stippled by the leafhopper Fagocyba cruenta was similar at ambient and elevated CO2 concentrations. The concentration of total amino acids a nd that of serine of A. pseudoplatanus foliage were significantly lowe r at elevated CO2 concentrations. However, the relative growth rates o f two aphid species Drepanosiphum platanoidis and Periphyllus testudin aceus and one leafhopper Ossiannilssonola callosa were not significant ly different in elevated CO2. No evidence was found that, under the co nditions of these experiments, populations of aphids and leafhoppers w ill change as concentrations of CO2 increase.