We don't know a lot about the mechanisms involved, but we do know that cultural conditions wind up being at the root of why the trees are susceptible to beetle kill. Bark beetles that attack conifers, at least here in the western U.S., are drawn to weaker individuals in the stand.
Prevention begins with maximizing tree vigor and health.
Prophalactic sprays with carbaryl or clorpyriphos get expensive, and are risky in residential settings especially considering that beetles tend to attack trees near their tops, and work their way down. Trap trees may be a solution for larger tracts, that is, using a doomed tree as an attractant for resident beetle populations, and using a good insecticide such as the above to nix the emerging adults as they hatch from the trap tree. I guess you could also chip the tree and get them too. If there is something you can change for the better - soon, there may be a chance of the tree pulling through it. One thing is for sure, if nothing is done, the tree will die.