Borers are secondary insects in nature with the express intent to expedite mortality in stressed /dead or dying plants. This particular picture is a Juniper borer trying to escape a fireplace mantel that had been drying in a hybrid kiln for over a year, milled down to the dimensions of a typical mantel. It was in the process of being sanded and finished with an epoxy application when we came across him.
Now full disclosure we were aware of activity in the wood after it was milled so it was also sprayed with an insecticide 2 to 3 months before this picture was taken to try and halt the damage. Typically, the advice we give people is if you store infected wood on your property it is best: to tarp the wood with a black poly (if possible in direct sunlight) or debark the wood to expose these guys and let exposure in colder months take care of them and/or spray the wood with an insecticide.
If conditions continue, these little guys can do a vast amount of damage to our urban trees. We have always struggled with the top three here, IPS, Elm Bark beetle, and Shothole borer. The new kid on the block is Emerald Ash Borer. The difference with EAB is the other three are associated with stress in a plant. EAB doesn't care, healthy or stressed Ash trees are a target.
Hydration, Hydration, Hydration. Winter watering is huge in times of drought for our plant material to maintain vigor.
Preventive sprays and injections; this has to be done preventively with borers, once they are in the plant the odds of gaining control are low.
Sanitation of infected plants. Remove infected trees immediately, Don't store infected wood on your property ie: Ash/Spruce, and as we see in the picture Juniper either.