It's not likely that a "borer" will directly cause a tree to die, at most it
will cause a weakness for decay to take a foothold, but that could take many
years and that kind of damage is almost always easily repairable. *When you
say your tree is "dying" you've given no description of what causes you to
say that... and you still haven't said where you're located nor have you
posted pictures of your tree... until you do so all anyone can offer you is
wild speculation.

Okay, I do not have a digital camera, so I cannot post a picture.

I live in Pittsburgh, PA.

The clump has three trunks. I constantly check for leaf miners as I
had troubles with those for many years but there have been no signs in
my two trees in about 4-5 years, thankfully. One day, the trunk
farthest to the right looked like it was wilting, with the lower
branches showing some yellow leaves but the entire thing looking like
it was wilting--from top to bottom. No place looked better or worse.
Then, within two days, the entire trunk was D-E-A-D. The leaves were
brown and, well, dead. But the other two trunks looked perfectly
fine.

I was going to cut the dead trunk down over this past weekend when I
noticed BOTH the other trunks showing the same signs: some yellowing
of the leaves on the lower branches and every leaf on the tree
wilting.

I cut a piece of a lower branch off and noticed the long hickey-doo
that holds the seeds(?) was all dry (I am sorry, I do not know the
name of this thing). I do not think this thing should be dry until
the fall.

Now, we are having a drought this year and it has been quite cool all
summer. In fact, we are about four inches below normal in rainfall.
BUT...I live on an old farm homestead and where this tree is planted
run five underground springs that always have some water running
through them. (In fact, whenever I added an addition onto the house
12 years ago, we were in a worst drought than we are experiencing now
and I broke ground the last week of July. All five springs were
pouring water out so fast that there was almost four feet of water in
a 15x25 hole overnight.)

So, I don't suspect lack of water BUT the tree seems like it is
exhibiting drought damage and shutting itself down to save itself. I
saw the sawdust afterwards and thought maybe the borers have been in
it foe a while and was clogging up the veins of the tree. (Do trees
have veins? What are the things called that carry sap and water
throughout the trees??) I thought maybe that is where the borers
larva live? And they were blocking the arteries like cholesterol
blocks our arteries and kills us.

That is about the best that I can describe what is happening.