Virulence assay of eight entomopathogenic fungi to larvae and pupae of Solenopsis invicta Buren

【Objective】 To screen out the entomopathogenic fungi with high pathogenicity to the larvae and pupae of Solenopsis invicta Buren， which could provide candidate strains for the biological control of Solenopsis invicta Buren. 【Method】 Taking four strains of Beauveria bassiana （ZG5， HHY-B， Bb040， CP728）， and two strains of Purpureocillium lilacinum （HHY-M， LYC1）， one strain of Metarhizium anisopliae （ZG30）， and one strain of Metarhizium rileyi （CDTNN2） as the research materials， and the larvae and pupae of Solenopsis invicta Buren as the research objects， the pathogenicity of each strain against the larvae and pupae of Solenopsis invicta Buren were determined respectively by the immersion method at concentrations of 1.0×10⁴， 1.0×10⁵， 1.0×10⁶， 1.0×10⁷， and 1.0×10⁸ spore/mL in the laboratory. The lethal concentration effect and lethal time effect of each strain to the larvae and pupae of Solenopsis invicta Buren was analyzed. 【Result】 Eight strains of entomopathogenic fungi were pathogenic to both the larvae and pupae of Solenopsis invicta Buren， and the corrected mortality rates of larvae and pupae of Solenopsis invicta Buren gradually increased with the increase of the spore concentration of the strains. Among them， four strains of Beauveria bassiana （ZG5， HHY-B， Bb040， CP728） had strong virulence to the larvae and pupae of Solenopsis invicta Buren. The corrected mortality rates of larvae of Solenopsis invicta Buren were 100.00%， 95.19%， 92.75%， and 93.46%， infection rates were 93.33%， 94.35%， 89.26%， and 85.56%，median lethal concentration （LT₅₀） were 2.14， 1.86， 2.32， and 3.20 d respectively， after treated with 1.0×10⁸ spores /mL for 10 d. And the corrected mortality rates of pupae of Solenopsis invicta Buren were 100.00%， 97.35%， 96.84%， and 95.57%， infection rates were 95.44%， 96.61%， 91.48%， and 85.56%， LT₅₀ were 2.15， 1.54， 2.12， and 2.98 d respectively. Dose-effect analysis indicated that median lethal concentration （LC₅₀） of Beauveria bassia-na ZG5， HHY-B， Bb040， and CP728 against Solenopsis invicta Buren larvae was 0.22×10⁵， 8.05×10⁵， 1.52×10⁵， and 2.83×10⁵ spore/mL， the LC₅₀ for pupae was 0.14×10⁵， 0.31×10⁵， 1.48×10⁵， and 1.38×10⁵ spore/mL respectively. 【Conclusion】 Beauveria bassiana strains ZG5， HHY-B， Bb040 and CP728 all exhibits strong pathogenic activity against the larvae and pupae of Solenopsis invicta Buren. They have high potential for application in the biological control of Solenopsis invicta Buren and can be regarded as potential bacterial resources for the biological control of Solenopsis invicta Buren.