Answer: Based on your description, I suspect that the caterpillars are a pest called rose slug. These can be controlled using a product containing carbaryl (the active ingredient in Sevin, for example.)
Ants would not damage the plants or buds, but aphids might be feeding at the tips of the new growth and attracting the ants. Aphids can be knocked off with a spray of water from the garden hose, or can be sprayed with insecticidal soap. If you see ladybugs on your roses, they will control the aphids for you. Carbaryl will also control aphids.
Be sure to read and carefully follow all of the label directions. I hope this helps.
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