Improvement of eri silkworm (Samia ricini D.) tolerance to high temperature and low humidity conditions by discontinuous regime

Improvement of eri silkworm tolerance to high temperature was carried out under high temperature (42±1°C) and low relative humidity (50±5% R.H., relative humidity). Eri silkworm rearing at normal temperature (25±2°C; 80±5% R.H.) served as control treatment and was compared to rearing at high temperatures. Directional selection was undertaken with the batches reared at 42±1°C and 50±5% R.H. until the 5th generation. From 6th, 8th, 10th and 12th generations, rearing was conducted as normal rearing (25±2°C; 80±5% R.H.), while for 7th, 9th, and 11th generations directional selection was done as 1st – 5th generations. Various parameters were used as indexes for high temperature tolerance. When the silkworms were reared until to F12 (12th generation), the survival rate of larva (1st–5th instar) (95.33%) and larva (1st–5th instar) – adult (69.33%) including cocooning rate (80.67%) of F12 were the highest compared to F1 and F11. For cocoon yields among F1, F11, and F12, the highest values of fresh cocoon weight (2.7144 g), pupa weight (2.3490 g), shell weight (0.3671 g), shell ratio(13.53%), total cocoon shell weight(17.01 g), and fresh cocoon/10,000 larvae (25. 16 kg) were achieved from F12, which were significantly different (P< 0.05) to F1 and F11. In the same manner for egg yields, F12 provided the maximum numbers in case of eggs/moth (311.33 eggs), total eggs (6,693.33 eggs) and total hatching eggs (4,842.67 eggs) except hatching eggs (73.15%). Of these evaluations between F11 and F1, it was found that F11 was higher than F1 and statistically different (P<0.05) in all parameters excluding the percentage of hatching eggs, which was not significant difference. These results indicate that the property of high temperature tolerance was improved and heat tolerant property of eri silkworm (SaKKU1) is heritable. This is a first to report on heat tolerance improvement of eri silkworm. Although it is a first trial that was carried out in a laboratory, it can be applied on eri silkworm rearing in the future to cope with recent global warming trends.