关键词: 杨干象, 致病力, 白僵菌, LT₅₀, LC₅₀

Abstract: [Objective] Because larvae of Cryptorrhynchus lapathi bore and feed in tree trunk, it is very difficult to control this pest with chemical pesticides. In this study, we screened fungal strains with high pathogenicity to larvae of C. lapathi, and determined the control effect to provide the basis for biological control the pest. [Method] In this study, 7 entomopathogenic fungal strains were tested for pathogenicity to C. lapathi larvae in laboratory. The strong virulent strains were selected and used for infecting trials in the field. The pathogenic symptoms of infection were observed. [Result] 1)The CFCC8732 conidiospore suspension at the concentration of l0⁸ conidia·mL^-1 was used to infect larvae of C. lapathi. in lab, and the results showed that the adjusted mortality rate of C. lapathi larvae was 93.38%, the quickest median lethal times (LT₅₀) was 3.536 d, and the median lethal concentration (LC₅₀) was 7.0×10³ conidia·mL^-1. In the field experiments, the conidiospore suspension with l0⁸ conidia·mL^-1 was smeared on the tree trunk infested by C. lapathi larvae, and the results showed that the adjusted death rate of C. lapathi larvae caused by infection of strains CFCC87323 was 77.62%. 2) The strain of ACCC30830 at the of concentration of l0⁸ conidia·mL^-1 was used to infect larvae of C. lapathi, and the adjusted death rate of larvae was 81.46%, the LT₅₀ was 4.248 d and the LC₅₀ was 5.43×10³ conidia·mL^-1. In the field experiments, the conidiospore suspension with l0⁸ conidia·mL^-1 was smeared on the infested trunk of C. lapathi larvae, and the adjusted death rate of C. lapathi larvae caused by infection of strains ACCC30830 was 66.06%. 3)The strain of ACCC30830 conidiospore suspension at the concentration of l0⁸ conidia·mL^-1 was used to infect larvae of C. lapathi in lab, and the results showed that the adjusted mortality rate of larvae was 73.51%. In the field experiments, the adjusted mortality rate of larvae was 58.48%. 4)The CFCC87327 conidiospore suspension at the concentration of l0⁸ conidia·mL^-1 was used to infect larvae of C. lapathi in lab, the results showed that the adjusted mortality rate of larvae was 72.85%, In the field experiments, the adjusted mortality rate of larvae was 56.32%. 5)As for the pathogenic symptoms, the time from the appearance of symptoms with infection of the strains CFCC87323 to dead body of C. lapathi larvae took (74.67±2.31) h. From the beginning of infection by C. lapathi larvae to the hypha of strains CFCC87323 covering the whole body took (93.67±3.21) h. [Conclusion] The results indicated that strain CFCC87323 of Beauveria bassiana had strongest pathogenicity to C. lapathi larva and the strain ACCC30830 took the second place. The strains ACCC30830 and CFCC87327 also showed pathogenic effect to C. lapathi larva. This study provided a new way to safely and effectively control the population of C. lapathi and their damages to the plants.

Key words: Cryptorrhynchus lapathi, pathogenicity, Beauveria bassiana, the quickest median lethal times (LT₅₀), the median lethal concentration (LC₅₀)