Beautiful photo. The only one I know vaguely like that is Hyblaea puera, see http://lepidoptera.butterflyhouse.com.au/hybl/puera.html but that is in a tropical family. It's relative Hyblaea ibidias is known down to Taree, see http://www.lepbarcoding.org/australia/species.php?region=1&id=69357 with a larva that has been found on Pandorea jasminoides, BIGNONIACEAE, but I do not know what it's larva is like, and whether it would eat MYRTACEAE.
Ah-ha: found better matches: Epipaschiinae, like Salma pyrastis http://lepidoptera.butterflyhouse.com.au/pyra/pyrastis.html and especially Spectrotrota fimbrialis http://lepidoptera.butterflyhouse.com.au/pyra/fimbrialis.html
Web moths (Pyralidae) can be serious pests of Myrtaceae, especially narrow-leaved species such as Astartea, Kunzea, Leptospermum. also of some Proteaceae such as Acacia, Indigofera. The host range of each species is often not precisely known.