From The Ortho Home Gardener’s Problem Solver: "Analysis: Borers are the larvae of beetles or moths. Many kinds of borer attack fruit and nut trees. Females lay their eggs in bark crevices throughout the summer. The larvae feed by tunneling through the bark or wood. Borer tunnels stop the flow of nutrients and water in an area by damaging the conducting vessels; branch and twig dieback result. Sap flow may act as a defense against borers if the tree is healthy. When the borer burrows into the wood, tree sap fills the hole and drowns the insect. Trees weakened by mechanical injuries, disease, poor growing conditions, or insect infestations are susceptible to borer attack."

"Solution: Cut out and destroy all dead and dying branches. Remove severely infested young trees. Spray or paint the trunk and branches of remaining trees with an insecticide containing lindane to kill young larvae before they burrow into the wood. Contact the local cooperative extension office to determine the appropriate time to apply the insecticide in your area. Make sure your tree is listed on the product label. Maintain tree health and vigor by watering and applying fertilizer regularly."

Obviously, that “solution” is not totally organic. I’d once used an open paper clip to poke inside the holes, hoping to crush the insect, eggs or larvae. I lost several tees anyway as I’d spotted the problem too late. They’d actually pushed ‘saw dust’ out the holes.

The rest of my trees I painted with white semi-gloss ‘interior’ latex paint, so the first bite from any borer beetle would be latex paint. And, tried to keep the trees well fed, mulched and watered. I’ve not had borer problems since. But for the meantime, I’ve given up on raspberries, so have no experience or suggestions regarding borers. Perhaps that’s what done them in …and I just never noticed the holes..?