Abstract: As an important entomogenous fungus, Metarhizium has been extensively utilized in the biological control of agricultural and forestry pests. This study aimed to screen the most infective strain against E. grisescens from 7 preserved strains and verify its infectivity at different doses. Subsequently, the taxonomic status of the strain was determined through observation of morphological characteristics and methods for multigene phylogenetic tree analysis. Finally, the optimal culture medium, temperature and pH value for strain growth were investigated. The results indicate that the seven tested strains exhibited different control effects on the 3rd instar larvae of E. grisescens, with strain Ma54 exhibiting the highest virulence, achieving a corrected mortality rate of 81.67% after 10 d of treatment and an LT₅₀ (lethal time for 50% mortality) of 4.93 d. The mortality rate of E. grisescens shows a dose-response relationship with the spore concentration of strain Ma54. After 7 d of treatment under a high concentration of Metarhizium (1.0×10⁸ spores·mL^-1), the mortality rate reached 98.33%, and the LT₅₀ value was 4.09 days. Seven days after strain Ma54 infected E. grisescens, the cadavers were covered with mycelia and turned dark green. After 14 days of growth on PDA medium, the conidia further spread and appeared dark green. The phylogenetic trees of the ribosomal transcription factor, β-tubulin, and the largest subunit of RNA polymerase Ⅱ of strain Ma54 all clustered with Metarhizium anisopliae. The colony diameter, spore production per unit area, and spore germination rate of strain Ma54 were optimal under conditions of a PPDA medium, a temperature of 25 ℃, and a pH value of 7.0. This study obtained the Ma54 strain with high virulence against E. grisescens, authenticated it as M. anisopliae, and preliminarily clarified its growth conditions of the strain, laying a foundation for its subsequent utilization in the biological control of E. grisescens.

Key words: Ectropis grisescens, Metarhizium anisopliae, high virulence, taxonomic status, growth conditions