Without a better description or an image, it will be difficult to help you. Perhaps aphids? Spider mites are almost microscopic, but can be seen with the naked eye. They do remove chlorophyll from the cells. Plain water is all you can use since these plants are to be sacrificed for the caterpillars. That and your bare hands for squishing.

If you can see spider mites, then you can see them move. You can also tap tap tap some of the leaves onto a piece of white paper and inspect any tiny specks of 'debris'. If they move, you have mites. Do you see any very tiny webbing?

Thanks, rhizo. I did the white paper test and I am sure that is the problem. I suppose this will be a recurring problem next year? I did remove all the damaged foliage from one plant (there are a few leaves coming out at the bottom) and plan to try keeping that one plant "mite free" with water as you suggested. It is so late in the season I know it would be useless to try to do much, so this one will be my test!! Thanks again.

Spider mites like it hot and dry so try to water or mist to discourage them. Water works pretty well on spider mites, if you could just move the cats and spray hard you should clean em out-you will probably have to do this a couple times. Hold the back of the plant so you don't break it with the water sprayer (I broke some mums that way-but then parsley is bendier).