Isolation, identification, and screening of highly pathogenic Beauveria spp. against Lasioderma serricorne larvae

To screen for entomopathogenic fungi with high pathogenicity against Lasioderma serricorne larvae, cadavers of naturally infected L. serricorne and Ephestia elutella were collected from tobacco storage facilities. Entomopathogenic fungi were isolated and purified via the tissue separation method, and their taxonomic positions were clarified based on morphological characteristics and homology analysis of the rDNA-ITS region sequences. The growth rate and sporulation yield of the isolated strains on SDAY plate (26 ℃, 80%RH) cultivated for 10 days were determined using the cross measurement method and hemocytometer counting method, respectively. Finally, the bioactivity of each isolated strain against L. serricorne larvae was assayed in vitro by the dipping method, and their biocontrol potential was evaluated. The results showed that 15 Beauveria bassiana strains (Bb001-Bb015) were isolated and identified. The growth rates of these strains ranged from 2.59 to 4.59 mm·d^-1, and the sporulation quantity varied from 1.54×10⁷ to 5.75×10⁷ spores per square centimeter. Bioactivity assay results showed that at a concentration of 1×10⁸ spores per millilitre, strains Bb001 and Bb013 exhibited the strongest toxicity against L. serricorne larvae, with corrected mortality rates of 91.38% and 84.48% 10 days after the inoculation. Gradient dosage tests revealed that larval mortality rate increased with the elevation of spore concentration, and the survival time of L. serricorne larvae inoculated with Bb001 was shorter than that of those inoculated with Bb013 at the same concentration. The median lethal concentration (LC₅₀) of Bb001 was 4.52×10⁴ spores per millilitre, which was lower than that of Bb013 (1.02×10⁵ spores per millilitre).