PREVENTION OF PUPAL DIAPAUSE BY THE APPLICATION OF JUVENILE-HORMONE ANALOG TO THE LAST INSTAR LARVAE OF MAMESTRA-BRASSICAE

When JHA (ZR-515) was applied to late last instar larvae of Mamestra brassicae destined for pupal diapause, some of the resulting pupae failed to enter diapause. The roles of the brain and the prothoracic glands in these pupae continuing adult development were examined. Extirpation of the brain within 10 hr after pupal ecdysis did not prevent adult development, but ablation of the prothoracic glands at the same stage disrupted metamorphosis. These results suggest that the brain does not play an important role in the prevention of pupal diapause by JHA application. Brains from JHA-treated pupae which failed to enter the diapause had enough prothoracicotropic hormone (PTTH) activity to cause pupation of dauer larvae. Brains with no PTTH activity could not be activated by in vivo culture in the haemocoel of isolated pupal abdomens to which JHA was then applied. However, the pupal inactive brains did acquire PTTH activity when β-ecdysone was injected into the pupae. It is proposed, based on these results, that an increase in the PTTH activity of the brain is elicited by ecdysone from prothoracic glands activated by JHA. It is concluded from these results that JHA applied to the last instar larvae are maintained even at the pupal stage and activates the pupal prothoracic glands to secrete ecdysone, which the ecdysone plays an important role to prevent to enter the pupal diapause. Furthermore, the ecdysone also activates the diapause pupal brain to secrete PTTH which in turn activates the prothoracic glands; probably this hormone secreted in this way takes part in the induction of diapause prevention. © 1979, JAPANESE SOCIETY OF APPLIED ENTOMOLOGY AND ZOOLOGY. All rights reserved.