| Abstrakt: |
1. In the oak silkworm,Antheraea pernyi,photoperiod controls not only the onset of pupal diapause (as previously demonstrated by Tanaka) but also the termination of pupal diapause.2. At 25° C., short-day conditions (4-to 12-hour photophases) strongly inhibit the termination of pupal diapause; maximal inhibition is by a 12-hour photophase.3. Long-day conditions (15-to 18-hour photophases) promote the termination of diapause; a 17-hour photophase is the most effective.4. A 14-hour photophase is transitional between short-days which sustain diapause and long-days which terminate diapause.5. By various experimental maneuvers, sensitivity to photoperiod was localized in the head-end of the pupa. Short-day illumination of the head-end inhibited the termination of diapause even when the hind-end was exposed to long-day conditions. In like manner, long-day illumination of the head-end was fully effective even when the abdomen received short-day illumination.6. When the brain was removed from the head and implanted into the tip of the abdomen, the sensitivity to photoperiod was thereby shifted to the hind-end.7. Additional experiments indicated that the brain is the vehicle for the reception and implementation of photoperiod signals. Brainless pupae are insensitive to photoperiod, while normal pupae are sensitive to photoperiod during the period when development is dependent on the secretion of brain hormone. When this period terminates about 60 hours after the initiation of adult development, photoperiod has lost all its effectiveness.8. It is concluded that photoperiod acts directly on the brain, itself, to modulate the secretion of brain hormone and thereby to control the termination of pupal diapause. |
