Tell me what works and what doesn't, and HURRY!!
how reliable is your ID.. and your diagnosis ...
any reason you can't take a cutting to a local nursery, for an onsite opinion ???
any suggestions of any chemical remedy on these words alone.. is malpractice [same with organic remedy, if any]
pix might help ...
First, calm down!!!! You are over-reacting to a potential problem. Even if the ants eat all the leaves off of a healthy tree, it probably would not kill the tree. Only prolonged leaf removal would likely cause the tree to die.
Second, as Ken stated, make sure your diagnosis is correct and that the problem is really significant enough to be a problem. Removal of a third of the leaves is probably not even worth worrying about.
If leaf cutter ants are the issue AND they are removing a majority of the tree's leaves, a combination of measures might be a good idea. Diatomaceous earth (the type produced for use in gardening, not the stuff used for filters) sprinkled around the base of the tree should help and will be harmless to the tree. There are also many other recommendations available with a quick Google check. Just avoid the ones that sound stupid, like the one that came up when I just checked, that said to dig a 1' deep trench around the base of the tree and fill with soapy water (I have no idea what that idiot was thinking).
Here is a link that might be useful: Example of Online Solutions
My pest guy came out and showed me the little grey/white aphids all over the tree. I felt relieved, yet sheepish.
Then he bombed it with conventional spray and a systemic, for which I will no doubt go to gardener's hell, where all there are to grow are ligustrum and variegated pittosporum.