PHYSIOLOGY OF INSECT DIAPAUSE. XV. THE TRANSMISSION OF PHOTOPERIOD SIGNALS TO THE BRAIN OF THE OAK SILKWORM, ANTHERAEA PERNYI

¹ The Biological Laboratories and the Division of Engineering and Applied Physics, Harvard University, Cambridge, Massachusetts

1. The pupal diapause of Antheraea pernyi is sustained by exposure of cocoons to short-day conditions (daily photophases of 4 to 12 hours) and terminated after exposure to daily photophases of 15 to 18 hours.

2. The photoperiod signal is conveyed by the direct action of violet, blue, and blue-green light (398-508 mµ) on the brain itself. This finding implicates a pink brain pigment in the absorption of the effective wave-lengths.

3. Despite its opacity, the cocoon functions as a light-integrating sphere in the collection of scattered light—especially of blue light ranging from 440 mµ to 510 mµ.

4. After its collection within the cavity of the cocoon, the blue "haze" penetrates the pupal cuticle to act on the brain. The brain's photoperiod mechanism is "saturated" by less than 1 foot-candle of blue light.