Schedotrioza apicobystra galls on a eucalyptus tree- Eucalyptus camaldulensis.

Old and young galls,induced by psyllids.
Psyllids are tiny sap-sucking insects that feed on the nutrient rich liquids inside leaves and transport tissues (xylem & phloem). Most species of psyllid will only feed on one specific host plant, however some species are known to broaden their preferences to plant varieties within the same family. (Info sourced from Wikipedia)