Sycamore ace bugs are sucking insects. They do not eat the leaf tissue, they suck out the juices. Their feeding causes the leaves to become progressively faded, eventually turning a tannish color. They also produce the dark colored spots on the back of the leaves.
Leaves that are eaten and look like lace (this is called skeletonizing) are likely being damaged by caterpillars, generally a minor problem.
You cannot take away the damage that has already happened, but treatment now should prevent additional damage. Next year, treat in early summer (May) to prevent damage from occurring. Systemic insecticides available for use against lace bugs include dinotefuran (Safari) and imidacloprid (Bayer Advanced Tree & Shrub Insect Control, Merit). These are applied to the roots and are absorbed by the tree, move into the foliage and control the lace bugs.
Consumer Horticulture Specialist
The LSU AgCenter and the LSU College of Agriculture