I had the same problem with a pear tree from which for well over a decade we have not had a single fruit grow past the size of a small plumb seed/stone. Working on the theory that the insects pupate after the attacked/dead fruit embryos fall off (i.e. on/under the ground right blow the tree), I laid out and weighed down some good plastic sheet on top of the ground and out beyond a radius equal to the height of the tree. I have now pulled off and disposed of all the flower buds that have appeared over the past two years. I will soon remove the plastic sheet to see what happens next summer. We have apple trees growing maybe some 30 metres distant - they have not so far been affected.