The silkworm, Bombyx mori is a domesticated insect sensitive to temperature challenges. In India, high temperature prevails during summer season. Rearing silkworms at such temperature leads to poor silk productivity. Developing a silkworm breed tolerant to high temperature is the most effective measure to perpetuate silk productivity. Choosing the right segregating population in which to initiate selection and successive crosses is one of the most important steps for development of new breeds. In this study, two multivoltine (Nistari and Cambodge) and a bivoltine (CSR2) breed, their F1s, F2s and backcross populations without reciprocal crosses were reared at 25 and 36°C. Data on commercially important rearing traits were collected. The rearing traits were significantly (P < 0.05) decreased in the breeds, hybrids, F2s and backcross populations at 36°C. Backcross populations performed better than the F2s at 36°C. Higher cocoon shell percent was also recorded with backcross populations with CSR2 as a female component. Similarly, the backcross populations with Nistari or Cambodge as a female component showed higher survival. At 36°C, CSR2 x (Nistari x CSR2) was the better performer in terms of silk yield and quality, whereas, Nistari x (Nistari x CSR2) was more stable with least percentage reduction over control in larval weight, cocoon yield / 10,000 larvae by number and weight and cocoon weight, and second lowest percentage reduction in cocoon shell weight and cocoon shell percent. The information generated by this study would be valuable in selecting the cross to initiate breeding for increasing silk productivity at high temperature conditions.
