PHOTORECEPTIONS IN THE ECLOSION OF THE SILKWORM, Bombyx mort

When silkworms, Bombyx mori , were kept in a photoperiodic regime of LD 8:16 during pupal development, the moths showed overt bimodal eclosion rhythms with one peak in the dark period, and with the other peak at light-on. When the developing pupae were transferred from the photoperiodic cycle to continuous darkness, the eclosion of the dark period persisted with a free-running circadian rhythm, while the eclosion corresponding to the light-on peak was not shown. Vitamin A-deficiency. which brought about a loss of photoreceptive function in compound eyes, significantly reduced the light-on peak, but did not influence the timing of eclosion in the dark period. Covering compound eyes with black wax also reduced the light-on peak. These results show that the eclosion clock of the silkworm is most likely entrained by an extraretinal photoreceptor, but the eclosion at light-on is evoked by an exogenous light effect that is mediated via compound eyes