Cassava leaf harvesting management and positive impact on growth and yields of Eri silkworm

Abstract

Cassava is one of the major host plants for eri silkworm rearing, especially in Thailand. The representatives for extension and popular varieties, Kasetsart 50 (KU50) and Rayong 11, were used in field experiments to determine the effect of cassava leaf harvest management and rearing eri silkworm. Cassava leaves were harvested three times (in batches) with cassava aged 6, 8 and 10 months. Each time, 30% of the leaves were harvested per plant using two methods, harvesting every day and every other day. The experiments were conducted using a randomized complete block design (RCBD) comprising four treatments and three replicates with ten plants/replicate. It was found that the average number of Rayong 11 cassava leaves, harvested every other day (68,534.40 leaves/rai) was higher than KU50 (45,758.40 leaves/rai). Also for every day harvested, Rayong 11 (63,883.20 leaves/rai) were still in greater numbers than KU50 (52,195.20 leaves/rai). The harvested leaves were used as food material for rearing three batches of eri silkworm with leaf harvesting three times. The life cycle (egg–adult) of all batches fed with KU50 and Rayong 11 were similar (between 41–68 days). For survival of larval stages (1^st–5^th instar), larva (1^st‑5^th instar) and adults for the 1^st and 2^nd batches, Rayong 11 was higher but not significantly different than KU50. Whereas in the 3^rd batch, KU50 showed a maximum survival percentage of the 1^st–5^th instar (91%) and no significant difference than when feeding with Rayong 11 (89.33%). For larva (1^st–5^th instar) – adult, KU50 still gave a higher survival rate (75%) and was significantly different (P<0.05) from Rayong 11 (60%). Considering the average cocoon and egg yields, in the 1^st batch, all cocoon yields obtained from feeding with KU50 were the higher values. Only fresh cocoon weight, pupa weight, shell weight and total shell weight were significantly different (P<0.05) when compared to Rayong 11. For egg yields, Rayong 11 exhibited higher average yields than KU50, but these values were not significantly different. For the 2^nd batch, all cocoon yields were similar irregardless of the cassava variety fed and they were not significantly different. However, feeding with KU50 yielded higher fresh cocoon weights (2.0563 g), pupa weights (1.7650 g) and fresh cocoon weights/10,000 larvae (18.85 kg). Feeding with Rayong 11 gave higher yields based on shell weight (0.2830 g), %shell (14.02%) and total shell weight (26.04 g). Moreover, Rayong 11 fed to eri silkworms showed higher and statistically significant (P<0.05) differences in the total number of eggs and hatchability than feeding with KU50. In the 3^rd batch, yields from KU50 were higher for fresh cocoon weight (2.1980 g), pupa weight (1.9156 g) and fresh cocoon weight/10,000 larvae (20 kg). When feeding with Rayong 11 the highest yields were for shell weight (0.2870 g), %shell (13.13%) and total shell weight (25.63 g). Feeding with KU50 gave significantly higher (P<0.05) yields for the total number of eggs and total hatchability compared to feeding with Rayong 11. The results of this research revealed that the method, frequency, timing and variety for cassava leaf harvesting management is very useful to improve the benefits for cassava plantations and eri silkworm rearing as a whole.