PHOTOSENSITIVITY IN THE CIRCADIAN HATCHING RHYTHM OF THE CAROTENOID-DEPLETED SILKWORM, BOMBYX-MORI

Silkworms (Bombyx mori) were reared on a carotenoid-deprived artificia l diet, and the carotenoid-depleted eggs of the next generation were i ncubated so that we could observe the effect of the depletion on the c ircadian rhythm of hatching. The phototactic response curves of newly hatched larvae showed that the visual photosensitivity in ocelli of la rvae from the carotenoid-depleted eggs was at least 4 log units lower than that of a carotenoid-rich control group. However, the phase-shift experiment revealed that carotenoid depletion did not reduce the phot osensitivity in the hatching rhythm. When the hatching rhythm was gene rated by exposure to a single light pulse in constant darkness, the fi rst peak in the rhythm of the carotenoid-depleted silkworms occurred s ignificantly earlier than that of the carotenoid-rich group, but the f ollowing second peaks of both groups were found at the same time. Thes e results suggest that for the silkworm, carotenoid is not involved in photoreception for the hatching rhythm, but is involved in the timing of hatching.