I really like butterflies. But butterfly larva really likes my lettuce, carrots, brassicas, etc. So as I have gardened more and more, I provide more and more habitat, as in food, for butterfly larva. So I get more caterpillar pressure. That is, the butterflies find my garden easier.

The best method to save my crop is not to spray, but to simply but up a physical barrier. In the cooler months, fleece over the plants works best. But in the warmer months, fleece is too warm, and then a low tunnel of mesh is a simple and very effective solution.