Hey Charles,
I thought caterpillars mostly went after brassicas, however, just discovered a few days ago that somehow some of them managed to get into my lettuce seedlings together with endives and kale in their module trays under mesh.
Oddly, it was mostly the lettuce and endives that received the damage from these pesky minute caterpillars! I am guessing that the mesh holes are not tiny enough. And oddly enough my other older brassicas (cabbages and Brussel sprouts – coming along VERY NICELY I gotta say, fingers crossed!) under the same mesh sizes have not had this kind of damage.
Thankfully I have more than enough seedlings. I have been picking these caterpillars off with tweezer as they are quite tiny.