Hemimetabolous and holometabolous insects have evolved morphologically distinct larval (or nymphal) and adult forms, enabling them to disperse and occupy different habitats. Hemimetaboly comprises nymphal and adult stages, whereas holometaboly comprises larval, pupal, and adult stages. Similar to holometabolous insects, hemimetabolous development is regulated by ecdysteroids and juvenile hormones (JHs)Juvenile hormone (JH). In the embryonic development of hemimetabolous insects, JH biosynthesis starts in the middle of the embryonic stage, and events such as nymphal cuticle formation are regulated by JH. In postembryonic development, JH is secreted from the corpora allata into the hemolymph during the nymphal stage but disappears in the final nymphal instar as they prepare for metamorphosis to adulthood, indicating that JH has anti-metamorphic action to prevent precocious adult metamorphosis. The signaling pathway of JH, including the JH receptor Methoprene-tolerant (Met)-Taiman, the early JH-response gene Krüppel homolog 1 (Kr-h1), and the adult specifier ecdysone-induced protein 93F (E93), is conserved in hemimetabolous insects. In contrast, the function of Broad is different from that in Holometabola; Broad is essential for progressive wing development in Hemimetabola. A comparison of the expression profiles of transcription factors in hormonal signaling among insect species has provided insights into the evolution of metamorphosis in thrips, which develop from larvae to adults through nonfeeding and quiescent stages. In addition to regulating embryonic and postembryonic development, JH is involved in polyphenism in aphids and sexual dimorphism in scale insects.