Abstract
Influence of circadian photoperiods on the larval growth of the silkworm, Bombyx mori L. was studied under an asceptic condition with artificial diet.
1) In 18 hr-photoperiod the larval duration was shorter in 4L14D (249/24 days), than in 1L17D (24.5 days) and 7L11D (about 25 days), The other photoperiodic regimes with longer photophase made the larval duration 1 to 3 days longer.
2) In 20 hr-photocycle the larval growth was fastest in 4L16D and 7L13D (247/24 days), and next in 1L19D and 10L10D (2418/24 days). The larval growth, however, delayed more 1 to 3 days in the other long-day photoperiods.
3) In 22 hr-photoperiod the larval duration was shortest in 5L17D and 8L14D (23 days), and next in 2L20D (24 days) and 11L11D (246/24 days). But, about 25 to 26 days were requested to complete the larval growth in the other photoperiodic regimes with longer photophase.
4) In normal 24hr-photoperiod the fastest larval growth was seen in 6L18D (22 days), and next in 9L15D (22.5 days), 3L21D (23 days) and 12L12D (23 days). The larval duration ranged 24 to 25 days in the other long-day photoperiods with exception of 15L9D (239/24 days).
5) In 26 hr-photocycle the larval duration was shortest in 4L22D, 7L19D and 10L16D (23.5 days), and next in 1L25D (24 days) and 13L13 D (246/24 days). The other photoperiods with longer photophase resulted in more delayed growth which took 26 to 29 days.
6) In 28 hr-photoperiod the larval duration was shortest in 8L20D and 11L17D (23.5 days), and next in 5L23D (24 days), 2L26D (248/24 days) and 14L14D (24.5 days). The duration became longer and ranged 26 to 27 days in the other long-day photocycles.
7) In normal 24 hr-photoperiod the shortest larval duration appeared when the ratio between photophase and scotophase periods was 1:3 (6L18D). This fact, however, was not applicable to any other photoperiods, in which the ratio became larger when one photocycle was longer than 24 hours, but smaller when it was shorter than 20 hours.
8) When the photoperiodic regime in which the larval growth was greatly hastened was compared with the other ones, the qualitative differences in the coccon were hardly recognizable between them, except that the cocoon weight was slightly heavier in the latter than in the former.
