Evaluation of multivoltine x bivoltine hybrids of mulberry silkworm, Bombyx mori L. tolerant to disease and high yield at various generation for end users

This study was conducted in the Sericulture Research Laboratory of Melkassa Research Center. Four bivoltine and one polyvoltine silkworm were involved in the crossing experiment and laid out in complete randomized design with four replications. Data was collected on fecundity, pupation rate (%), number of diseased larvae, survival rate (%), cocoon weight (g), cocoon shell weight (g), cocoon shell ratio (%) and filament length (m). Uniform and non-significant numbers of eggs produced by adults and cocooning percentages were recorded for both hybrid and parents in all the generations. Average larval weight significantly (P<0.01) reduced for F1, F2, F3 and F4 generations hybrids than parents but increased in F5, F6 and F7 generations hybrids. Silk ratios and survival rates significantly (P<0.01) increased for all hybrids than parent bivoltine in all hybrid generations. Larval period significantly (P<0.01) reduced in F5, F6 and F7 generations hybrid than parent bivoltines. Filament length significantly (P<0.01) reduced in F1, F2, F3 and F4 generations hybrids than parent bivoltine but significantly increased in F5, F6 and F7 generations hybrids than parent bivoltines. It can be concluded that instead of using parent polyvoltine and bivoltine mulberry silkworms separately for silk production, the farmers can use F5 and above generations hybrids of multivoltine x bivoltine for relatively higher disease resistance and maximum silk productions.   Key words: Polyvoltine silkworm, bivoltine silkworm, hybrids.