Changes in bacillus thuringiensis tolerance levels due to hybridization of Bt-tolerant and susceptible silkworm populations

Males and females of a bt-tolerant mulberry silkworm (bombyx mori l.) population were crossed with females and males of a bt-susceptible population,to produce bt-tolerant silkworm hybrids,and to determine the expression of the bt-tolerance pattern in the fl hybrids. it was observed that when a bt-tolerant (42% larval mortality) female (btt ♀) silkworm was crossed with a bt-susceptible (85% larval mortality) male (bts ♂,the resultant fl offspring showed lower levels of bt-tolerance (87% larval mortality). on the other hand,when a bt-tolerant male (btt ♂ was crossed with a bt-susceptible female (bts ♀,the f1 hybrid showed higher levels of bt-tolerance (35% larval mortality) characteristic. the probit statistics showed that both hybrids expressed bt-tolerance or susceptible levels similar to their male parents. these different patterns of bt-tolerance in fl hybrids might be due to the transferring of a bttolerant gene,from the parents to offspring,through the homozygotic male (zz) silkworm.