Microbial control of Diamondback Moth, Plutella xylostella, by entomopathogenic fungus, Beauveria bassiana. I. Laboratory studies on pathogenicity of Beauveria bassiana and field experiment.

The pathogenicities of five isolates of Beauveria bassiana to Plutella xylostella were investigated. Treatment of 4th-instar larvae with each isolate resulted in 0%-100% mortalities at 5 days after inoculation. Detailed studies were made on the most virulent isolate, MG-Bb-1, obtained from P. xylostella, to determine its efficacy at different developmental stages of P. xylostella, doses, and humidities. MG-Bb-1 had high pathogenicity to lervae of all instars, but little pathogenicity to eggs, and almost no pathogenicity to pupae. Humidity influenced the virulence to 4th-instar larvae; MG-Bb-1 caused mortality of over 80% at 76% RH or higher levels, but only 30% mortality at 52% RH. A conidial suspension (10(7)/ml) of MG-Bb-1 was sprayed on a cabbage field to control P. xylostella. A single application controlled P. xylostella as well as Flufenoxuron.