Heteroblasty describes plants whose juvenile and adult vegetative shoots differ morphologically. In Eucalyptus, heteroblasty is a common source of within-plant variation and an expression of ontogenetic aging that affects the within-tree distribution of psyllids. Using Eucalyptus globulus Labillardiere as a model system, we studied the reproductive behavior of adults of two Australian psyllid species (Ctenarytaina eucalypti Maskell and C. spatulata Taylor) on the glaucous, simple-shaped juvenile leaves and the glossy, sickle-shaped adult leaves under field conditions. We compared the ovipositional preferences and mating site preferences of the psyllids in caged pairs of juvenile and adult shoots, as well as the behavior of the psyllids after they landed on both types of shoots. Ctenarytaina eucalypti oviposited only on juvenile shoots and C. spatulata oviposited only on adult shoots. Ctenarytaina eucalypti mated primarily (88% of the time) on juvenile shoots, and C. spatulata mated only on adult shoots. After landing on both shoot types, C. eucalypti remained longer than C. spatulata on juvenile shoots, but C. spatulata remained longer than C. eucalypti on adult shoots. This is the first experimental evidence that heteroblasty in Eucalyptus affects insect reproductive behavior. These results are discussed in relation to subsequent studies on psyllid performance in this system that found that the epicuticular wax (present only on the juvenile leaves) plays a primary role in the preferences of these psyllid species for the juvenile versus adult shoots.