Abstract:  【Aim】 The pea aphid, Acyrthosiphon pisum, is an important agricultural pest in the world and causes great economic losses to legume crops. In this study, based on the previous screening of the pathogen Lecanicillium longisporum strain TF-2 of A. pisum, the virulence effect and infection mode of conidia of this pathogen on A. pisum were detected, so as to provide a theoretical basis for the control of A. pisum by entomogenic fungi. 【Methods】 The pathogenicity of L. longisporum strain TF-2 to A. pisum adults dipped into serial concentrations of conidial suspension (1.0×10³-1.0×10⁷ conidia/mL) of L. longisporum strain TF-2 was assayed by feeding method with detached leaves in the laboratory. The external infection symptoms and process of L. longisporum strain TF-2 to A. pisum adults infected with the TF-2 strain (1.0×10⁷ conidia/mL) were observed under scanning electron microscope (SEM) and stereoscopic microscope (SM). 【Results】 The pathogenicity of different concentrations of conidia of L. longisporum strain TF-2 to A. pisum adults gradually enhanced with the increase of conidial concentration. The medium lethal concentration (LC₅₀) of the TF-2 strain to A. pisum adults at 6 d after treatment was 3.26×10⁴ conidia/mL, and the medium lethal time (LT₅₀) of this strain at the highest treatment concentration (1.0×10⁷ conidia/mL) was 2.92 d. The results of SEM observation showed that the conidia of L. longisporum strain TF-2 germinated and bud tubes and appressorium formed on the epidermis of A.pisum adults at 24 h after inoculation. Bud tubes elongated and a network structure formed in compound eyes, the base of antennae, the basal segment of legs, the end of the abdomen reproductive segment, etc. of A.pisum adults, at 48 h after inoculation. At 96 h after inoculation, hyphae covered the whole body of A. pisum adults and new conidia produced. 【Conclusion】 L. longisporum strain TF-2 has a strong pathogenicity to A. pisum adults, and the SEM observation revealed the infection process of its conidia. These results provide the theoretical basis and references for the further application of entomogenous fungi in biological control.

Key words: Lecanicillium longisporum; Acyrthosiphon pisum, conidia, infection, pathogenicity, SEM