A feasibility study towards cryopreservation of silkworm eggs: response of non-diapause silkworm eggs to low temperature.

Insect embryos are very sensitive to chilling temperatures and vary with species and their developmental stages. Insect eggs are small and can supercool to temperatures ranging from -5 degrees C to -40 degrees C. In general, insects rely on a variety of ecological and physiological adaptations to survive low temperatures, making cryopreservation technique significantly complex. Mulberry silkworm (Bombyx mori L., Lepidoptera: Bombycidae) eggs are cleidoic with chorion (approximately 20-25 μm thick). Preservation of non-diapause eggs to a limited period is practiced usually to delay hatching. The advantage of early embryonic periods having resistance to low temperature is utilized for chilling of eggs and preservation for long periods. However, technique for cryopreservation of silkworm eggs is not yet developed and the identification of precise embryonic stage and chill sensitivity is necessary for effective silkworm cryopreservation. The paper reports the chill-sensitivity and tolerance of non-diapause silkworm embryos of mulberry silkworm at various embryonic stages. Silkworm embryo of 48h-age are relatively chill-sensitive as compared to other embryonic ages. This is vital information for the development of cryopreservation protocol for silkworm eggs.