Make a spray with tomato leafs it helps me with most bugs.
:>

Pick the caterpillars up and MOVE them onto the incarnata vines. If you are adamant about them not feeding on the other passis maybe you can net them to keep the mama fritillaries off the vines. A net designed for keeping birds off would probably work.
spidewoman

That's what I do, just move them. They have done a real number on a small "Lavendar Lady" (most probably Amethyst), so I just move them to another one that can handle the nibbles.

Debbie