Improvement of Eri Silkworm (Samia ricini D.) Tolerant to High Temperature and Low Humidity Conditions by Continuously Regime

Improvement of eri silkworm tolerant to high temperature condition was carried out by selection and continuous rearing (1 – 12 generation) under high temperature (42±1 °C) and low relative humidity (50±5%R.H.). The eri silkworm rearing at a normal temperature (25±2 °C; 80±5%R.H.) served as control treatment. The result revealed that eri silkworm was continuously tolerant to high temperature of 42±1˚C with low relative humidity (50±5%R.H.) up to 12 generations. Among treated generations with high temperature, the silkworm survived from larva stage (1st – 5th instar) to adult in all generations ranking 16.67 – 54.17%. Between F12 and F1, survival rate of larva – adult stage of F12 was 43.33% less than F1 (54.17%), but not significantly different (P<0.05). For cocoon yields, fresh cocoon weight, pupa weight and cocoon shell weight of F12 were lower than F1. Shell ratio of F12 (11.84%), total cocoon shell weight (5.72g) and fresh cocoon/10,000 larvae (9.39 kg) were not significantly different to F1(11.61 %, 5.72 g and 10.55 kg, respectively). It was clearly, if the egg yields were considered, egg laying/moth, hatchability, total egg laying and total hatchability increased from F1 to F12. The result indicates that the thermotolerant property of eri silkworm SaKKU1 is heritable by high temperature up to F12. This study is a first report on continuously heat tolerant improvement of eri silkworm in Thailand and elsewhere.