imago (n.)

"final or adult stage of an insect," 1797, from Latin imago "an image, a likeness," from stem of imitari "to copy, imitate" (from PIE root *aim- "to copy"). "The name is due to the fact that such an insect, having passed through its larval stages, and having, as it were, cast off its mask or disguise, has become a true representation or image of its species." [Century Dictionary]