How does juvenile hormone affect an insect’s metamorphosis?

In insects, juvenile hormone plays a critical role in regulating development by controlling the retention of larval characteristics during molting. Secreted by the corpora allata glands near the brain, this hormone dictates whether a molt results in another larval stage or a transformation into a pupa or adult.12

The hormone functions primarily by suppressing the genes responsible for expressing adult traits. During early development, high levels of juvenile hormone ensure the insect remains in its larval form. As the insect matures, a reduction in or the total absence of the hormone during subsequent molts allows for the emergence of mature, adult characteristics.21

Beyond its role in metamorphosis, juvenile hormone remains active in many adult insects, where it is often essential for normal egg production in females. Because of its influence on development, synthetic compounds that mimic juvenile hormone are sometimes utilized as insecticides; by disrupting the natural hormonal balance in later life stages, these substances can effectively prevent the insect from reaching maturity.12