I have this mature oak about three feet in dia at the base. I noticed some of the bark was falling off near the base. At a closer look there was an area of about 2 feet in dia where the bark was undermined and hollow beneath. I found bronze, winged insects about 1/2 inch long working under the bark. I could see tree dust below. The questions are, how do I get rid of them, do I remove the loose bark to see if there is any more, can I cover the wound with a tar or substance to prevent entry into the main body of the tree? There are some cracks in the main body of the tree. You can see where the tree has started to grow back around the perimeter of the wound. Our area has alot of very old oak trees.

HI Ken, loose bark often occurs from an old wound. the insects you are seeing may or may not have anything to do with the intiial cause. often insects find loose bark a nice place to hang out. I would suggest contacting your local extension office. you could send them picutres or take in a sample. please use this website to find the one nearest you. http://www.msue.msu.edu/portal/