The catalpa sphynx moth, attracts predatory wasps, which lay their eggs on the catalpa worms, (caterpillars). The eggs hatch and the wasp larvae consume the catalpa worm from the inside. There's little you can do to get rid of the wasps, as they just fly in.
Usually this is a good thing, (wasps attacking caterpillars) like on your tomatoes.
The ants are more than likely "farming" aphids. You can get a product called Tanglefoot, that you put around the tree trunk, and they won't cross it. I doubt the ants are killing your catalpa worms, but it's possible.