Tanglefoot applied to the trunk is effective at stopping ants, if you are careful not to allow any alternate paths onto the tree.
Leafcutter ants are really interesting, the wikipedia article claims they will avoid plants that harm the fungus they farm, so applying a fungicide might help... but it also says they can defoliate a whole tree in a day so they probably won't learn fast enough to save the plant.
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Unfortunately Tanglefoot is not available in Brazil. But I have tried two alternatives using this Principle of isolating the access.
a) I use broad adhesive tape about 4" broad and circle the trunk. Then I apply roller bearing grease in the middle of the tape keeping half inch from each side of the breath of the tape. This works to a certain extent for small trees and deters ants from climbing and cutting.
b) I collect discarded car tyres which do not have steel belts. Using a circular saw I cut the tyre in the middle. Each half I put around the tree bark burying a part of the tyre. Then fill the crevice with water. This also deters access of ants to the tree leaves.
What I was looking for was for more effective insecticides in powder form to pump inside the holes and kill and DESTROY the cutter ant colonies.