The mothers of a lot of borers are attracted by the the chemicals emitted by the trees under stress or dying. So they may have laid their eggs inside even before you noticed that the tree was in serious trouble. The adult form can bore the bark to get out when the limb/ tree is still alive. The modalities vary with the species of course. But a hole in the bark is a wound and the living bark try to block it by filling the void with pitch. That's the droplets seen in your pics. I bet that you can find a hole under each of them (or at the source if it has flown down).I guess my reason for posting about it again was trying to figure out if it was burnt or bugs. I don’t see bug holes…