Mamuang is a much better at finding the borers than I. I always had trouble finding them.
You mentioned you are also using insecticides. If you do use insecticides to treat borers, it’s been my experience you wouldn’t have to dig them out. I will put a qualifier on that statement, which is I use Lorsban as a trunk spray and let it puddle a little at the base of the tree, so I am using a different insecticide than you are using.
I don’t think the insecticides we are discussing have any penetrant activity, nor are they systemic. But I think they work because they are so lethal to the insect, it doesn’t take very many molecules (relatively speaking) of the compound to kill the insect. I think they wash in the holes when it rains.
I’ve read that Imidan has kickback activity on plum curculio not because it’s systemic, but because it’s so lethal to the larva, relatively few molecules are required to kill it. Enough of the chemical washes in the egg laying hole to kill the grub.
Whenever I see borer goo, I apply some Lorsban at the base of the tree and the borers are done.