Juvenile hormone (JH) synthesis by the corpora allata (CA) does not occur during the pupal stage in both
male and female Bombyx mori but begins shortly before adult ecdysis and thereafter only in females. JH
biosynthesis in female adults was prevented by allatotropin (AT) through the corpora cardiaca (CC) and
the tightly attached oesophagus before adult ecdysis, but after ecdysis, removal of the CC had little effect
and only the oesophagus was necessary for AT to prevent JH synthesis. AT could not prevent JH synthesis
by the CA alone in either stage. Short neuropeptide F (sNPF) acted directly on the CA, preventing JH biosynthesis
without preventing the JH biosynthetic enzymes before adult ecdysis, but had little effect after
ecdysis, indicating that the action of AT was not via sNPF. The inhibition of JH synthesis by AT was indirect.
Both AT and a factor(s) from the AT-stimulated oesophagus through the CC were necessary for the
inhibitory action, which was due to the prevention of some of the JH biosynthetic enzymes. These results
clearly show that AT prevents JH synthesis in adult CA in B. mori, although AT stimulates JH biosynthesis
by the CA in several insect species.