Sometimes the damage occurs in the bud and shows up in various ways as the leaf grows out.
You could try Safer's Insecticidal Soap or Neem Oil. Test both in one area of the tree first before soaking it.
It won't help the already damaged leaves though.
You might also look here:
http://www.ip-sys.com/~bonsai/forum...tid=751#post751
Regards,
Matt