Large Yellow Moth Identification

[Little Pua]

I am an expert gardener, but a novice when it comes to butterflies and moths...
though I do my best of providing them a good home. I need help identifying a
large moth that is in my Nashville, Tennessee, USA garden now.

large (6 inch wing span), about the size of a luna moth. It has 2 larger, outer
wings and 2 seperate smaller wings in closer to its lower body
sulfer yellow color with a single magenta stripe on each wing and some magenta
speckling.
large body, about the diameter of my index finger, with some magenta ridges on
its back.

I found it during the day as it was struggling to get an inch worm off its
back... I used tweezers to remove the worm. It looks like the worm did attack
it for a while and I am now watching to see if it survives.

Can anyone tell me anything about this moth. If you need more information about
it first, just let me know. 

Thanks,
Sherry