Over a yeat ago a kind person on this forum sent some advice about this which I have followed, and it does seem to have helped . The advice was to burn the fallen leaves, which is where the moth larvae over wimter, so I raked up and burnt as many as I could and the tree did seem a bit healthier and happier as a result. I am not sure that this could ever be a cure but it could prolong the life of a lovely tree. Having said that I have also been advised that horse chestnuts have a tendancy to drop their branches suddenly. Our tree is in a courtyard and although we love it for its beauty and the lovely shade it gives I am increasingly concerned about this possibility, which I imagine is most likely in a diseased tree. Lets hope a cure is found....