What about orange oil for drywood termites?

Orange oil is the name given to extracts from the peel of citrus.  Mostly this is near pure d-limonene.  It is a general solvent.  You have probably used it in bathroom or hand cleaners.  It kills insects.  I used it as the recommended cleanup solvent for the Blockaid non-toxic termite barrier as it was much less of an OH&S risk than mineral turpentine.

In the USA it is being used as an injectable anti-termite treatment, mostly in California as heavily promoted by a bloke who writes for the usually high quality SFGate. In 2007 the Californian Structural Pest Control Board commissioned  research on the spot treatment of drywood termites and has available, for free download, excellent reports of the work headed by Drs Vernard Lewis and Mike Rust.  If you must do spot treatments for drywoods, then read these reports!

So long as you can get it to soak through the at-risk timber, a good dose of limonene should kill the termites but as for any residue providing long-term deterrence. well don't hold your breath.  You'd probably need to seal the holes and put a quality coating system over it (filler and paint or varnish).  If the timber is more than slightly damaged, replacement may be advisable.

I've also had great success using d-limonene as a fire starter.  A small amount will help even the stubborn logs light.  Makes a lot of smoke (good for Hawaiian bbq?).  So, while I'm sure the chemical can kill termites, beetles, ants and maybe even some fungi, I'd hesitate to use it myself anywhere that there was a risk of fire but perhaps that's because I live in a high fire risk zone

The usual proviso with drywoods also applies, depending on your situation.  You may never find all the colonies, so fumigating the whole structure may be a safer alternative to spot treatments.