Please help restore this sycamore tree

[meriil]

Hi,
I believe the tree is 35-40 years old. This summer it was harshly attacked by wood-eating pests . Judging by the severity of the attack, this cannot be the first year, but I have no idea when it exactly began.
The symptoms include severe leaf dropping (the tree lost 85% of its leaves in about 2-3 weeks), and visible sawdust along the cracks of the tree bark.

please also see the following picture. I took it after removing the bark (which came off easily) and cleaning the saw-dust:

I am not sure whether the larva belong to a family of moths or some beetle (both of which are common in my area).
I haven't found any worms in the tunnels yet, only their artifact is visible (((

So, I was thinking, maybe at this stage remedies like "injecting" pesticides into the cracks could be pointless. I was considering removing
the bark at the affected areas and cleaning the mess (like the second set of pictures) and covering the trunk with protective trunk paint afterwards,
therefore preventing the pest (whatever it might be) from laying eggs on the tree cracks, where they will be hard to hunt.
Do you find it a subtle way of prevention? Your ideas and experience are welcome! Thank you!

 

[Sheal]

Looking at the inner layer of bark I suspect the tree was already dying before the insect attack. I think they have taken advantage of the decaying wood.

 

[Chuck]

Research a disease called Canker Stain. It is killing sycamores all over Texas and the disease is world wide. The wood is valuable when milled.