Hi, 

The insect does appear to be a Redheaded Ash borer. Removing the dead branches will help with the borers being attracted to the decaying wood. Usually borers are a secondary cause of death so the cracked or damaged tree most likely attracted the boring insects to help the wood decay. They are native insects so just doing their job.

Crapemyrtles can re-grow easily after being cut down, so if wanted to save the tree, you could remove all the broken, cracked or dead branches and move away from the stump to see if it helps control the borers and regrows with healthy branches. 

'Treating the wound' is not a common practice anymore with the thought being that it can possibly seal in an disease but also most trees can callus over cut areas naturally. 

If you are trying to keep the tree or have it regrow after you trim it down, you should add a mulch ring around the tree to help keep the soil moist, add organic material as it decomposes, and to protect the trunk or new shoots from lawn mowing and trimming. 

If you wanted to just remove the tree and replant a flowering tree, we would suggest trying a native alternative as Crapemyrtle, while beautiful with blooms, exfoliating bark, and nice fall color, have been overplanted and we are dealing with a bark scale insect that is very difficult to control. 

Let us know if you have additional questions. 

Emily