抄録
Twenty-two strains of silkworm, Bombyx mori (Linnaeus) (Lepidoptera: Bombycidae), were investigated to determine their susceptibilities to an isolate of entomopathogenic fungus, Beauveria brongniartii (Sacc.). Most strains showed resistance to B. brongniartii, but some were extremely susceptible. When second instar larvae were infected by dipping in a conidial suspension of B. brongniartii (1.9×109 c.f.u./ml), the differences in susceptibility between the resistant strains and susceptible strains were large: mortality rate of strain Akako was 100% and that of strain Japanese No.1 was 11.0±9.0%. When fifth instar larvae were infected by injection of the conidial suspension, the maximum difference in LD50 values among the strains was about 500-fold. F1 progenies from the cross of the susceptible strain and the resistant strain were resistant, a half of the backcrossed hybrids to the susceptible parent strain was resistant and a half of them was susceptible. Those results indicate that the susceptible strain possesses a recessive gene conferring high susceptibility to B. brongniartii isolate. Silkworm strains may be useful model insects to study the mechanisms and genes related to the resistance of lepidopteran pests against entomopathogenic fungi.
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