Pathogenicity of Metarhizium anisopliae to the chestnut weevil larvae under laboratory and field conditions

We used a baiting method to isolate 65 entomopathogenic fungi with pathogenicity to the chestnut weevil larva from soil samples. Metarhizium anisopliae strain HF293 showed the highest pathogenicity. Under laboratory conditions, the LD50 value of strain HF293 on the 10th day after treatment of newly emerged larvae was 9.9 x 10(3) conidia/larva, and the mortality rate of larvae reached 56% at five weeks after treatment with a conidial dose of 2.0 x 10(2)/larva. Susceptibility of the larvae that had been stored at 6degreesC to strain HF293 gradually. decreased over the first three months of storage but stabilized by the fourth month. The results of a field study of larvae in flowerpots indicated that the survival rate of larvae decreased with increasing doses of conidia of M. anisopliae strain HF293.