Effect of Temperature under Continuous Darkness Photoperiod on Egg Hatching and Embryonic Development of Eri Silkworm (Samia cynthia ricini)
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Abstract
Background. The eri silkworm (Samia cynthia ricini) is a non-mulberry silkworm with considerable potential for natural silk production. Unlike some silkworm species, S. c. ricini eggs do not undergo obligatory diapause and generally hatch within 8–10 days after oviposition, creating challenges in synchronizing egg hatching with distribution and rearing schedules.
Methods. This study evaluated the effects of temperature under a continuous-darkness photoperiod (24D:0L) on hatching time, hatching delay, hatchability, and embryonic development of S. c. ricini. A total of 1,163 fertile eggs were assigned to four temperature treatments: control, 15 °C, 25 °C, and 30 °C, with three replicates per treatment. Temperature and relative humidity were monitored throughout the experimental period, while hatching performance and embryonic development were observed periodically.
Result. The results showed that temperature significantly affected hatching delay and hatchability (P<0.05). Eggs maintained at 15 °C exhibited the longest hatching period (23.96±0.07 days) and a hatching delay of 15.96±0.07 days, although hatchability was relatively low (9.68±9.13%). At 25 °C, eggs hatched within 10.21±0.76 days with a hatchability of 22.55±19.13%, while embryonic development proceeded normally. In contrast, exposure to 30 °C resulted in extremely low hatchability (0.91%) and considerable embryonic damage. Embryological observations further demonstrated that low temperature temporarily arrested development, whereas high temperature adversely affected embryo survival.
Conclusion. These findings indicate that temperature manipulation under continuous darkness can regulate the timing of eri silkworm egg hatching. A temperature of 15 °C effectively delays hatching, whereas approximately 25 °C provides more favorable conditions for subsequent embryonic development and larval productivity. This approach may improve synchronization of egg distribution, incubation, and eri silkworm production management.
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