The photo lacks the detail to be certain, but it suggests that your concern about insect damage is justified. When borer activity under the bark is extensive, trees begin to die and the bark falls off or is removed by birds or other animals that feed on the borers. Trees under stress from factors such drought or flooding are especially susceptible to borer damage.

The following website discusses this problem and explains what to do about it:
http://www.dnr.state.mn.us/treecare/forest_health/barkbeetles/index.html

Also, consider asking a forester or certified arborist to evaluate the trees' health onsite and suggest a course of action.

This information may useful if you decide to hire an arborist:

How to hire a professional arborist to help care for your landscape trees
http://www.extension.umn.edu/garden/yard-garden/trees-shrubs/how-to-hire-a-professional-arborist/