Answer: It's nearly impossible to diagnose an insect problem without inspecting the plant so I can only offer some general advice. Sycamore trees are deciduous and will lose their leaves in the fall. Even though the leaves look as though something has been munching on them, the pests are probably long gone by now and all that's left is the damage. Since the leaves will be falling anyway, the best thing you can do is to rake them up and remove them from the garden. Next spring your tree should produce healthy new leaves.
Best wishes with your landscape!
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