Stylet penetration and survival of three psyllid species on adult leaves and 'waxy' and 'de-waxed' juvenile leaves of Eucalyptus globulus

The stylet probing behavior and survival of Ctenarytaina eucalypti Maskell, C. spatulata Taylor and Glycaspis brimblecombei Moore (Homoptera, Psyllida e) on adult leaves and 'waxy' (untreated) and 'de-waxed' (rubbed) juvenile leaves of the heteroblastic plant Eucalyptus globulus Labillardiere were co mpared. Psyllids were confined within clip-on cages and after 15 days the l eaf tissue under each cage was sectioned and stained to characterize and qu antify stylet tracks. Across all leaf treatments and psyllid species 1438 s tylet tracks were observed in 7239 leaf sections and 571 of these stylet tr acks reached the vascular tissue. Survival and the number of stylet tracks of C eucalypti on the different leaf types did not differ, In contrast, C. spatulata survived significantly longer and produced significantly more sty let tracks on adult leaves and 'de-waxed' juvenile leaves than on 'waxy' ju venile leaves. Although G. brimblecombei survived equally on all treatments . it produced more stylet tracks on adult leaves and 'de-waxed' juvenile le aves than on 'waxy' juvenile leaves. For all three psyllid species. there w as a positive correlation between survival and number of stylet tracks reac hing the vascular tissue. Stylet tracks of all species were generally inter cellular from the leaf epidermis to the vascular tissue. Oil glands were av oided by all species, as indicated by the repeated branching and formation of stylet tracks at the periphery of the glands. In 'de-waxed' juvenile lea ves, C. spatulata and G. brimblecombei produced stylet tracks that entered the leaf at the adaxial surface and exited at the abaxial surface. This pat tern was rarely observed on adult leaves, and never occurred with C. eucaly pti in any leaf type. We conclude that ( I) the epicuticular wax on juvenil e leaves reduced stylet probing by C. spatulata and G. brimblecombei, (2) t here were apparently no internal physical barriers in either juvenile or ad ult leaves to prevent the stylets of any of the psyllid species from reachi ng the vascular tissue, (3) the psyllids avoided oil glands in both leaf ty pes, and (4) C. spatulata and G. brimblecombei may lack cues to orient thei r stylets towards the vascular tissue in the juvenile leaves.