It might be coddling moths in your pears, I know they affect apples in the way you describe. We put a pheromone trap in the tree, it attracts and traps the males so they can't breed and infest the fruit, and it does seem to work. The cherries might be being eaten by birds. This year I had lots of blossom and lots of little cherries. I noticed they were starting to ripen but sadly left it a few days to get round to putting a net over it. One morning they were all gone