I had read pyrethrum (spelling?) daisy was the best plant companion to prevent bronze bettle but I have no experience of same.
We have very old pear trees and they suffer from the same thing - we are not able to water them and I believe water stress may lead to bronze bettle infestation. We like the pear trees for leaf coverage in the summer as sun protection so the bettle damage is a secondary factor and i would prefer not to spray the trees.
Pigeon Valley - picture shows the pear trees in blossom