The relationship between corpus allatum (CA) and prothoracic gland (PG) activities has been examined during postfeeding larval and prepupal stages of en-silkworm, Philosamia ricini (Dru.). Using the isolated larval abdomen technique, the critical period of ecdysone (MH) was determined. It was 114 hr immediately after the beginning of cocoon spinning at 20 ± 2°C. To study the CA activity a histometric method was used. CA volumes suddenly increased at the prepupal stage. From these data a clear positive correlation between CA and PG activities was recognized.

Brainless Ph. ricini pupae, a highly reliable bioassay organism for detecting prothoracicotropic (PTTH)-like effects, were produced. The debraination of Ph. ricini larvae after the critical period of PTTH, produced brainless pupae. This bioassay organism was used for studying the action of juvenile hormone (JH) and MH in the metamorphic endocrine centres during the absence of the brain.

Injection of 5 μg altozar (JHA) into debrained Ph. ricini larvae accelerated pupation (12.24 ± 0.36 instead of 16.51 ± 0.19 days). Moreover the produced brainless pupae moulted to second brainless pupae. The injection of 5 μg JHA into brainless pupae or isolated larval abdominae of Ph. ricini did not show any effects. Brainless Ph. ricini moths were obtained after injecting the brainless pupae with MH (10 μg-40 μg/p). The injection of high concentrations of MH (≥ 70 μg/p) into brainless pupae activated the CA and produced pupal-adult intermediates. The present data reveal that the PTTH at low concentrations, permits the action of a JHA in the PG. Also it shows that the MH at high levels activates the CA.