Efficiency of mulberry leaf conversion into cocoons and cocoon shells was determined for seven exotic bivoltine pure lines of Bombyx mori L. strains (J-99, J-101, 205-MKD, 206-MKD, 206-PO, 207-PO and 208-PO) during spring and autumn seasons. Eight quantitative traits viz., total food ingestion (Tl), Total food digestion (TD), cocoon weight, shell weight, efficiency of conversion of ingested food into cocoon (ECIC) & shell (ECIS), efficiency of conversion of digested food into cocoon (ECDC) & shell (ECDS) were measured. Rearing was carried out at 24±1°C and 75±5%RH during spring and 28±1°C and 75±5%RH during autumn. The strains J-99, J-101 and 205-MKD were the most efficient to convert ingested and digested food into cocoon and cocoon shell The maximum Tl (4080.25 mg/larva), TD (2031.25 mg/larva), single cocoon weight (1233.75mg), shell weight (291.5mg), ECIC (32.6%), ECIS (7.15%), ECDC (67.75%) and ECDS (15 03%) were recorded in J-101, J-101, J-99, J-101, J-99, J-101& 205-MKD, 205-MKD and 205-MKD, respectively during spring. Similarly minimum Tl (3325.98 mg/larva), TD (1543.93 mg/larva), cocoon weight (938.75 mg), shell weight (183.75 mg), ECIC (28 73%), ECIS (5.50%) and ECDS (11.98%) were found in 207-PO while ECDC (60 60%) was in 206-PO. During autumn the total ingestion and digestion of mulberry leaf were approximately the same as in spring however, cocoon and shell weights ECIC, ECIS, ECDC and ECDS were lower in all test strains. Based on these results it is recommended that more profitable and efficient strains like J-99, J-101, 205-MKD, etc. should be reared at 24±1°C with 75±5% RH. In addition, training of mulberry plants should be carried out before the autumn rearing to get young nutritious leaves.

Key words: Silkworm, Bombyx mori, Rearing, Efficiency, Mulberry leaf.