关键词: 球孢白僵菌, 华北大黑鳃金龟, 致病力, rDNA-ITS序列分析, 分离鉴定

Abstract: 【Aim】 Holotrichia oblita is an important insect pest of various crops such as peanuts, fruit forests and nurseries, and it has been mainly controlled by chemical control for a long time. In this study, the pathogenicity of Beauveria bassiana strain JCF to the larvae and adults of H. oblita was determined to provide fungal resources for the biological control of H. oblita. 【Methods】 The parasitic fungi on the dead body of the diseased H. oblita were isolated and rejoined, and the pathogenic strain JCF was isolated and purified. The morphological characteristics of the strain were observed by light microscope. The rDNA-ITS sequence of JCF was amplified by PCR and then sequenced, and the phylogenetic tree of JCF was constructed for molecular identification. The virulence of the JCF strain to the adults and larvae of H. oblita was determined by immersion method and field simulation test. 【Results】 The colony of the strain JCF with colorless back is white fluffy at the initial stage, then becomes yellow or light yellow flocculent at the late stage. The conidiogenous cells are clustered on the conidiophore in a bottle shape, and the conidiophore is spike-shaped and attached to the vegetative hypha. Conidia are solitary, transparent, subglobose, and (2.0-3.5) μm×(1.5-2.0) μm in diameter. The molecular identification of rDNA-ITS sequence showed that the strain JCF was B. bassiana. The medium lethal concentration (LC₅₀) value of B. bassiana strain JCF against H. oblita adults was 2.124×10⁷ conidia/mL, and the medium lethal time (LT₅₀) values of this strain at the concentrations of 2×10⁸, 1×10⁸ and 5×10⁷ conidia/mL against H. oblita adults were 6.267, 6.852 and 7.455 d, respectively. The LC₅₀ values of B. bassiana strain JCF against the 1st, 2nd and 3rd instar larvae of H. oblita were 5.47×10⁶, 1.59×10⁸ and 2.50×10⁸ conidia/mL, respectively. The LT₅₀ values of B. bassiana strain JCF at the concentration of 1×10⁸ conidia/mL against the 1st and 2nd instar larvae of H. oblita were 8.6 and 18.6 d, respectively, and those of B. bassiana strain JCF at the concentration of 5×10⁸ conidia/mL against the 2nd and 3rd instar larvae were 10.3 and 13.2 d, respectively. In the field simulation test, the spore suspension of B. bassiana strain JCF (2×10⁸ conidia/mL) exhibited good pathogenic effects on both adults and larvae of H. oblita.【Conclusion】 The B. bassiana strain JCF has high pathogenicity to the adults and larvae of H. oblita, providing a new strain resource for the development of B. bassiana formulations to control Melolonthidae pests. And it has potential application value for biological control of Melolonthidae pests.

Key words: Beauveria bassiana, Holotrichia oblita; pathogenicity, rDNA-ITS sequence analysis, isolation and identification