JUVENILE HORMONE IN RELATION TO THE LARVAL-PUPAL TRANSFORMATION OF THE CECROPIA SILKWORM

¹ Biological Laboratories, Harvard University, Cambridge, Massachusetts 02138

1. Pupae retaining larval integumentary structures were formed after topical applications of Cecropia juvenile hormone or a mixture of juvenile hormone analogues to fifth instar Cecropia larvae prior to the initiation of spinning. Even daily applications of high doses did not result in a supernumerary larval molt.

2. The integument was most sensitive to juvenile hormone (JH) two to four days prior to spinning.

3. During the period of cocoon spinning, both the larval integument and viscera were insensitive to exogenous JH.

4. During the prepupal period, the integument remained insensitive but the larval-pupal transformation of the viscera was retarded by topical application of JH.

5. Juvenile hormone applied during the prepupal period prevented the normal "shutting-off" of the prothoracicotropic activity of the brain prior to pupal ecdysis. Consequently, the pupae did not diapause but initiated adult development within 5 days. The subsequent adults were normal externally but retained pupal or pupal-adult viscera with occasional retention of larval characters.

6. Unlike the epidermis, the viscera are sensitive to JH not only at the reported time of DNA synthesis, but also during the following period of tissue histolysis and reorganization.