Abstract
Beauveria bassiana and Verticillium lecanii have been isolated from the diseased pupae of the silkworm, Bombyx mori L., and both fungi were demonstrated to be pathogenic to the silkworm. The production of a toxic substance in the dead pupae infected with each fungus was confirmed through a bioassay by use of artificial diets containing powder prepared from the dead pupae. The toxic substance was also detected in the fungus bodies of both fungi cultivated in surface culture on chemically-defined media. The toxic substance was lethal to silkworm larvae by oral administration and caused atonic symptoms in the larval bodies at less than lethal doses. A toxin named bassianolide has been isolated from the fungus bodies of both fungi which accounted for the lethality and toxicity accompanying the atonic symptom detected in the dead pupae infected with each fungus.
