Scanning electron microscopy and pathogenicity of Beauveria bassiana infection with Hylurgus ligniperda

Beauveria bassiana was screened and its pathogenicity on larvae and adults of Hylurgus ligniperda was investigated, the infection process of B. bassiana on larvae and adults of H. ligniperda was verified.

1) Morphological identification and molecular biology identification were used to determine the strain of the selected strains; 2) The cumulative corrected mortality rate was calculated using Excel 2016 and the SPSS 26.0 was used for ANOVA and the virulence regression equation and LC50 were calculated; 3) Electron microscopy scanning was used to observe the infection of larvae and adults of H. ligniperda.

1) Through bioassay, it was found that 4 strains of B. bassiana were not the same virulence to the larvae and adults of H. ligniperda, named Bbz1, Bbz2, Bbz3 and Bbz4; 2) Among them, the strain Bbz4 had the best poisoning effect on larvae, after inoculation for 5 days, the killing effect of 1×10⁸ spores/mL concentration of spore suspension on the larvae of H. ligniperda reached 100%, LC₅₀ was 3.68×10⁵ spores/mL. The best poisoning effect on the adult of H. ligniperda was the strain Bbz1. After inoculation for 5 days, the killing effect of 1×10⁸ spores/mL concentration of spore suspension on the alduts of H. ligniperda reached 100%, and the LC₅₀ was 3.27×10⁶ spores/mL; 3) Scanning electron microscopy was performed on the infection of larvae and adults of H. ligniperda used strain Bbz4 and strain Bbz1, and it was found that the conidia of these strains touched and attached to the body surface of H. ligniperda during 0-12 h after inoculation. When inoculated for 18 h, spore germination was found and bud tubes were produced; At 36 h, there was mycelium penetrating the body wall; When inoculated for 72 h, hyphae appeared on the surface of the worm; At 96-120 h of inoculation, the entire body was covered with hyphae.

It was determined that four different strains of B. bassiana were isolated from the body of H. ligniperda, among which strains Bbz4 and Bbz1 were the most pathogenic to the larvae and adults of H. ligniperda, and determined their infection process on H. ligniperda at different time points after inoculation.