First up. Caterpillars are baby butterflies (and moths, but moths are important too). Know that by killing the caterpillars you are killing the flitty, floaty things most people love in their garden.

But they can decimate a plant in minutes (ok maybe hours).

Hand pick if possible. Even consider moving them to a less precious plant (make sure it is still a food source for them). Many plants will recover with even better growth - citrus in particular. If you do spray, bacteria based sprays such as Dipel and Success target caterpillars (they will need to eat a little more leaf to ingest the poison).

For brassicas (broccoli etc) and dealing with the cabbage white butterfly. A) don’t grow them in summer. B) net your plants.