The large carpenter ants are on the leaves due to aphids. Curling leaves are a characteristic of leaves fed on by aphids as well. If the tree is for aesthetics and not for eating, I'd suggest doing nothing. The leaf damage is cosmetic, and beneficial insects will find the aphids and attack them. If you really wanted to treat the issue, you could apply neem oil or horticultural oil if temperatures are below 85 F but it wont fix the curled leaves.