Lecture 23

Abstract

The postembryonic, or juvenile, development of insects begins with hatching and extends through the periods of growth, which are separated by molts. Juvenile development is indirect development, or metamorphosis: in the series of juvenile stages, the characters of the sexually mature adult stage stem from changes in external morphology and from the transformation of the internal organs. In insects with incomplete metamorphosis (Hemimetabola) the adult organs appear without a profound transformation of the larval organization. Certain larval structures are dismantled, the rudiments of adult organs, wings, genital appendages, etc., grow quite gradually (e.g., Odonata, Heteroptera), or nymphal stages with sheathed external wing rudiments differentiate from completely wingless larvae. In the Holometabola early development ends in a nonfeeding pupal stage. In the molt leading to the pupa (pupal molt) the larva’s internal rudiments of wings, other extremities, and genital appendages are everted; and in the pupa, the last major process of metamorphosis is carried out. The demolition of larval organs proceeds simultaneously with the growth and differentiation of adult parts.