You can hand pick the caterpillars off of your plants. Neem oil can also be used.
Oh.. need oil? Please tell me more about using neem oil in my garden. How can it benefit and what ways do I need to be careful with it?
Neem oil is a naturally occurring pesticide. You can find out more from searching neem oil on the site, npic.orst.edu. It has a Bitter taste and a garlic/sulfur smell.