Juvenile hormone (JH)

Definition

A family of sesquiterpenoid hormones synthesized by the corpora allata and circulating in the hemolymph of insects and some other arthropods. Juvenile hormone maintains larval or nymphal characteristics during molting; its decline or absence permits metamorphosis to the adult stage. JH also regulates reproduction, diapause, caste differentiation in social insects, and polyphenism.

Etymology

From its role in maintaining juvenile morphology; first isolated and named by Carroll Williams and colleagues in the 1960s.

Example

In the tobacco hornworm (Manduca sexta), high titers of JH during the final larval instar delay the prepupal molt; a precipitous drop in JH allows ecdysteroid-triggered metamorphosis to proceed.

Synonyms

• neotenin
• JH I
• JH II
• JH III
• JH 0

Related Terms

• Ecdysone
• corpus allatum
• Metamorphosis
• ecdysteroid
• allatectomy
• pupal commitment
• Diapause
• Polyphenism
• sesquiterpenoid

Usage Notes

Specialists distinguish JH homologs (JH I–III, JH 0, 4-methyl-JH I) by alkyl side-chain differences; JH III is most widespread. The term is sometimes used loosely for any juvenilizing factor, but strictly refers to the farnesol-derived sesquiterpenoids. Contrast with ecdysteroids, which trigger molting, whereas JH determines the developmental outcome of that molt.