Why do some adult moths lack working mouthparts?

In many species of Lepidoptera, adult mouthparts have become reduced or vestigial through independent evolutionary processes. While the larval stage is dedicated to nutrition and growth, the adult stage in these specific groups is focused entirely on reproduction and dispersal.12

Because these adults do not feed, they rely exclusively on the fat stores accumulated during their time as caterpillars to survive their short adult lifespans. For example, the atlas moth emerges as an adult with reduced mouthparts and typically lives for only one to two weeks, using its remaining energy reserves solely to seek a mate. This evolutionary strategy allows the insect to bypass the need for adult feeding, shifting all nutritional requirements to the larval phase.321