Molecular identification and pathogenicity assay on Metarhiziumagainst Octodonta nipae (Coleoptera: Chrysomelidae)

Key Words：Octodonta nipae, Metarhizium anisopliae var. anisopliae, ITS sequence analysis, virulent bioassays

Abstract：        High adult and larval mortality due to infection with a pathogenic fungus was observed when rearing Octodonta nipae (Maulik) under laboratory conditions. ITS sequence analysis identified the fungus as Metarhizium anisopliae var. anisopliae. The effect of inoculating 3rd instar larvae and adults of O. nipae with six different concentrations of M. anisopliae var. anisopliae was investigated.Doseresponse bioassays showed that M. anisopliae var. anisopliae had a high level of toxicity to both larvae and adults. At concentrations ranging from 1.0×10⁵ cfu·mL^-1to 1.0×10¹⁰ cfu·mL^-1, the virulence equations on the 10th day after infection were y =-4.335 + 5.368 x and y =-4.992 + 5.623x for larvae and adults, respectively. The estimated logarithm of median lethal concentration was 6.420 and 7.721 for larvae and adults, respectively. These results indicate that M. anisopliae var. anisopliae was highly virulent against O. nipae larvae and adults and that the degree of virulence increased with increasing concentration. The infection rate was higher in larvae than in adults at the same concentration. These results indicate that M. anisopliae var. anisopliae could be a potential biological control agent for O. nipae.