Effect of high temperature environment on the cocoon colour sex-limited breed 'Nandi' of the silkworm, Bombyx mori L.

摘要

In India, the bulk of the production of raw silk is from the polyvoltine x bivoltine silkworm breeds. Generally, for the production of cross breeds, the females of polyvoltine are crossed with the males of bivoltine. Therefore, to prepare correct hybrids, the males and females are to be separated. Generally, the sex separation is carried out at the pupal stage based on the abdominal markings. However, this method is highly laborious and costly to produce millions of hybrid layings. In this context, the cocoon colour sex-limited breeds are of paramount relevance. Accordingly, two cocoon colour sex-limited bivoltine breeds, namely CSR8 and CSR2 (SL) (Nandi), have been developed. It is also imperative to have knowledge on the performance of the new breed Nandi and its hybrids with polyvoltine breeds under high temperature environment. The results indicate that the performance of Nandi is better than normal CSR2 under high temperature environment as evident from the higher pupation rate of Nandi (32.4% at 36+or-1 degrees C and 50+or-5% RH and 20.6% at 36+or-1 degrees C and 85+or-5% RH) versus the lower pupation rate for normal CSR2 (26.6% at 36+or-1 degrees C and 50+or-5% RH and 15.7% at 36+or-1 degrees C and 85+or-5% RH). Besides, the hybrids of Nandi with all the polyvoltine breeds also performed better than the hybrids with normal CSR2 as evident from the higher pupation rate of all the hybrids of Nandi [PM x CSR2 (SL):85.7 and 72.7%; Nistari x CSR2 (SL):88.1 and 80.9%; ND7 x CSR2 (SL):86.9 and 77.7%, respectively, for the two treatments] as against lower pupation rate for the hybrids with normal CSR2 (PM x CSR2:85.0 and 71.6%; Nistari x CSR2:85.2 and 79.8%; ND7 x CSR2:83.2 and 76.7%, respectively). Therefore, Nandi can be utilized throughout the year as a better male component than normal CSR2.