Very nice pics again Phillinsydney ... I always enjoy viewing your photos.
Per chance picked up an old Australian Geographic (June 2007 #86) in a waiting-room today ... with an brief article on the culprit moth(s).
The CSIRO in Canberra has identified that "individual Scribbly Moth species have their own scribble types and their own preferred species". They identified "4 species of moth in E.rossii in Canberra ... but only two different scribble types" ... and suspect that some Moth-larvae may mine much deeper than others.
Scribbly gums: interpreting their scribbles (Fact Sheet) Scribbly Gum Moth
To all non-aussies
... they ARE harmless to the tree.