Thanks Alison - I could not ID this one, but now you have, I came across a list of host species https://www.entsocnsw.org.au/wp-content/uploads/2023/12/GAE-51-11-17-Webb-Scolecobrotus-host.pdf Blue Gums aren't on the list, but Yellow Box are, so maybe a new host tree or it has flown in from a nearby tree.