Maria Fremlin the larvae (grub) borrow into the trunk tissues, creating long tunnels and usually pupating under the bark. Very common in Pacific and Asia. And the larvae is a favorite delicacy that goes well with sago.
Thank you for answering my first question. In fact, since then I was able to see teneral imagos half way up an old palm tree near the surface of the trunk.
What about my second question: How do larval faecal pellets look like?