anesr:

Ants in dead pear and apple branches are not the cause of branch dieback. They are there as opportunistic foragers, eating the dead wood. The branch dieback can be caused by a wide variety of factors, including several diseases, but in this case may simply be old age. Branch breakage of overloaded limbs is another matter, and can be reduced or eliminated by thinning the fruit before it reaches the overload point.

Full-size apple trees on seedling rootstocks are capable of living beyond 40-50 years, but will suffer some branch losses along the way. To reinvigorate an older tree, first remove all of the dead wood, then prune back even living branches to induce the growth of healthy new wood.

So have a crack at it, and try pruning down both the apples and pears to see if you can't stimulate some healthy new growth. It will either work or won't work, and if it doesn't you can consider planting some new trees. I am always a fan of planting a few new fruit trees whether you need them or not. Meanwhile, the ant, termites, or whatever they are, are not the cause but an effect of the dead branches, since they are not interested in healthy, living wood.

Don Yellman, Great Falls, VA