Vol. 3, Issue 1 (2018)
Hatching patterns in the silkworm, Bombyx mori L. under ‘black-boxing’ system: A photoperiodic perspective
Author(s): B Srinath, MA Shanthan Babu, P Lakshminarayana Reddy, B Sujatha, S Sankar Naik
Abstract: Conventional methods of silkworm (Bombyx mori L.) hatching include incubation, exposure to light dark cycles etc., were in practice. As a recent technology for silkworm egg hatching, use of black-boxing method coupled with incubation is advocated in the contemporary Indian sericulture industry to get economical hatching of over 95%, in a single day with quick hatching. In the present study, an attempt is made to compare the photoperiodic way and the black-boxing method of hatching for better understanding the scientific principles behind the black-boxing method. For the studies, the DFLs of CSR2 x CSR4 were introduced into natural solar day condition, LD 12:12, continuous dark (DD) and continuous light (LL) on the third day of oviposition and continued till the completion of hatching experiments. For studies on black-boxing, the DFLs were initially maintained under LD 12:12 up to pin-head stage and introduced into black-boxing (DD) at 06.00 h on the pin-head stage. The DFLs were watched for stray-hatching on the penultimate day of hatching and after confirming stray-hatching, the dark phase in black-boxing is disrupted, exposing the eggs to light on the ultimate day of hatching at 06.00 h. Hatching, in CSR2 x CSR4 bivoltine hybrid occurred very close to dawn under natural solar day, LD 12:12 conditions. Further, light-on phase is taken by Bombyx mori as signal for hatching. Hatching occurred for two consecutive days, with stray hatching on the first day and maximum on the second day. Intervals between two hatching peaks were around 24 h, hence, circadian. When the eggs are driven under continuous conditions (DD/LL) the hatching occurred for 2 consecutive days. Under continuous dark (DD), the hatching occurred for two consecutive days with advancement in peak hatching implying a free-running nature of hatching rhythm following ‘gating’ phenomenon. Hatching on the first day was highest with narrow hatching activity period. Under LL too, hatching occurred for two consecutive days, with low hatching on the first day and maximum on the second day. Further, hatching rhythm delayed with broadened of hatching under LL, indicating a near damp-out expression. When the eggs are kept under ‘black-boxing’ condition, the hatching rhythm was distinct, occurring immediately after interruption of darkness of black-boxing. Hatching was restricted to a single day with narrow hatching activity, measuring 2 h of hatching duration only. Hatching occurred at or after lights on phase indicating that the hatching rhythm is diurnal and lights-on is taken straightly as a signal for hatching. Hatching durations are more under continuous conditions (DD/LL) and less in LD 12:12 and black-boxing conditions.