Performance of adult psyllids in no-choice experiments on juvenile and adult leaves of Eucalyptus globulus

The presence of glaucous juvenile leaves and glossy adult leaves in the can opy of the heteroblastic plant Eucalyptus globulus Labill., is a source of within-tree variation that affects herbivory by three psyllid species (Cten arytaina eucalypti Maskell, C. spatulata Taylor and Glycaspis brimblecombei Moore) (Homoptera, Psyllidae). In no-choice field experiments with adult f emale psyllids in clip-on cages, we compared (1) leaf-settling, honeydew pr oduction, and survival of the Ctenarytaina species on juvenile and adult le aves of E. globulus, (2) leaf-settling and survival of G. brimblecombei on juvenile and adult leaves, (3) leaf-settling and survival of the three spec ies on waxy (untreated) juvenile leaves and de-waxed (rubbed) juvenile leav es, and (4) leaf-settling and survival of C. spatulata on juvenile leaves f rom which wax was repeatedly removed. Leaf-settling by C. eucalypti was sig nificantly greater on juvenile than adult leaves, however, honeydew product ion and survival were equal on both leaf types. In contrast, leaf-settling, honeydew production, and survival by C. spatulata were significantly great er on adult than juvenile leaves. Similarly, leaf-settling and survival by G. brimblecombei were significantly greater on adult than juvenile leaves. Wax removal from juvenile leaves significantly increased leaf-settling and survival of C. spatulata and G. brimblecombei. Although wax removal decreas ed leaf-settling by C. eucalypti, it did not affect survival. Repeated remo val of regenerating wax from juvenile leaves did not affect leaf-settling o r survival of C. spatulata. These results suggest that the epicuticular wax of juvenile leaves plays a role in resistance to C. spatulata and G. brimb lecombei, however other unknown factors are probably also involved.