关键词: 昆虫病原真菌, 球孢白僵菌, 油松毛虫, 扫描电镜, 组织病理学

Abstract: In order to well understand the pathogenesis of entomopathogenic fungus, Beauveria bassiana to pine caterpillar, Dendrolimus tabulaeformis Tsai et Liu, and to provide the scientific guidance for biological pest control in northern China, in the present study, B. bassiana strain No.1573 was used to infect the pine caterpillar, D. tabulaeformis. The fungal infection process and the host hisopathological changes were observed using light microscopy (LM) and scanning electron microscopy (SEM). The results showed that the pathogenic fungus generally infected the pine caterpillar by penetrating the integument. At 24 h after inoculation, the attached conidia were found on the vertex and the regions around ocellis, antenna and mouthpart on the head, while on the thorax and abdomen, they adhered on verrucas, tufts, the acanthae and intersegments. At 36 h after infection, the conidia germinated into hypha on the cuticle, and then the hyphal tip differentiated into appressoria and penetration pegs to penetrate the cuticle. At 48 h, hyphae penetrated the integument depending on both the mechanical pressure and degradation action from hyphal extracellular enzymes, causing cuticular rupture and melanism. At about 72 h after infection, the hyphae had entered the body cavity and infected hemolymph, fat body, muscle, alimentary canal, silk gland and nerve tissue. By utilizing the nutrition of haemolymph and internal organs and tissues, the fungus massively proliferated. The insect body showed swelling and dark. At 96 h after infection, as hyphae occupied the haemocoel, the internal tissue structure of the pine caterpillar was totally destroyed and the insects died. At last, the hyphae broke through the cuticle and released new conidia on the cadaver surface. This study revealed that the strain No.1573 of B. bassiana is an effective pathogen to the pine caterpillar, D. Tabulaeformis. It is a series of infection in the integument and inner tissues that causes the host insect to die.

Key words: Entomopathogenic fungus, Beauveria bassiana, pine caterpillar (Dendrolimus tabulaeformis), scanning electron microscopy, histopathology