Dealing with woodworms
I believe you should contact a licensed exterminator.
My experience with hard to reach burrowing insects or worms  was  dealt with by  an exterminator who has access to products we do not.
For example we have had problems with carpenter bees which travelled long distances through the beams.
With a puff of  some powder"  which the creature carries back to the queen,
they were eliminated.
(we had also tried many things ourselves with no luck)