Answer: What an interesting observation. Ants often 'herd' aphids, protecting them from predators and milking them for the sticky 'honeydew' they excrete. I suspect that the leaves are curling because aphids are sucking the juices from the leaves. The ants you found were probably gathering the honeydew left by the aphids. I wouldn't spray anything at this point; the dogwood leaves will be shed in just a few weeks. Rake the leaves up and remove them from the garden to remove the potential of overwintering aphid eggs.
Holes in the leaves are usually associated with the feeding of caterpillars or beetles. If you found none of these insects on the leaves, there's no point in spraying to eradicate them.
Ants in themselves are considered beneficial in the garden and are usually just left alone.
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