So if the required native plants are not present in an area, nearly all butterfly and moth species will die out in that area along with much of the other animal life that depends on them. For example, 96% of terrestrial bird species rely on insects to feed their young, and fat juicy caterpillars are the most important part of that diet. Terrestrial birds, predator/beneficial insects and a large part of the rest of the food chain depend either directly or indirectly on native plant - caterpillar pairs.
Native plants and caterpillars are a key foundation of our whole native ecosystem. This is the primary reason why native landscapes support 35x more caterpillar biomass than non-native landscapes.
However, 90% of caterpillar species cant get past the chemical and structural defenses of other than a handful of native plants with which they coevolved. Butterflies often have preferences for native nectar sources, but they can usually make do with non-native nectar. Non-native plants can seldom be host plants for native butterfly or moth species.
If a given species of butterfly or moth cant find their particular host plants in an area, it will die out in that area. These plants are called "host plants" for that species of butterfly or moth. The caterpillars of most butterfly and moth species have evolved to eat the leaves of just a small number of plant species native to their geographic range, sometimes in just one genus of plants.