Answer: Sounds like a bark borer of some type. Adults lay their eggs just beneath the bark by making a little hole in the bark. When the egg hatches the larvae tunnels beneath the bark, feeding and growing until it works its way out and becomes an adult. It is difficult to control the adults because they fly away and almost impossible to control the larvae because they spend their lives hiding beneath the bark. Since one section has already died, I'd strongly recommend removing it from the garden. In doing so you may prevent the next generation of borers. Wish I had something more positive to offer, but if borers are attacking your plant, there's not much you can do.
Q&A Library Searching Tips