草地贪夜蛾病原微孢子虫的鉴定及其致病力分析

为明确从田间采集草地贪夜蛾 Spodoptera frugiperda幼虫体内发现的一种微孢子虫的分类地位和致病性，利用传统形态学观察和分子生物学技术对该微孢子虫进行鉴定，同时采用室内生物活性测定法对其致病性进行分析。结果显示，该微孢子虫的形态学特征与家蚕微孢子虫 Nosemabombycis相近，具有典型微孢子虫超微组成结构，孢子壁厚度为195.00~205.15 nm，极丝盘旋于孢子后极内侧10~12圈；其基因组的基因间隔区（intergenic spacer， ITS）和小亚基核糖体RNA（smallsubunit ribosomal RNA， SSU）序列与已报道的家蚕微孢子虫相关序列的相似度分别达94.34%和99.50%，系统发育树显示该微孢子虫属于微孢子虫属 Nosema，与家蚕微孢子虫亲缘关系最近。该微孢子虫侵染草地贪夜蛾1龄和2龄幼虫5 d时的LC50分别为2.51×10⁷孢子/mL和2.48×10⁷孢子/mL；侵染3龄幼虫10 d时的LC₅₀为3.79×10⁷孢子/mL；侵染4龄幼虫15 d时的LC50为3.98×10⁷孢子/mL；且当微孢子虫浓度为1.0×10⁸孢子/mL时，草地贪夜蛾1至4龄幼虫的LT₅₀分别为3.04、 3.86、 7.47和10.43 d。表明该微孢子虫隶属微孢子虫属，对草地贪夜蛾不同龄期幼虫均有较强的致病力，具有良好的开发应用潜力。

Identification and pathogenicity of an entomopathogenic microsporidium collected from fall armyworm Spodoptera frugiperda

In order to clarify the classification status and pathogenicity of a microsporidia found in fall armyworm Spodoptera frugiperda larvae collected from corn fields, the microsporidium was identified by traditional morphology and modern molecular techniques, and the pathogenicity of the microsporidia was determined by bioassay. The results showed that the morphological characteristics of the microsporidia were similar to those of Nosema bombycis, with a typical ultrastructure of microsporidia. The thickness of its spore wall ranged from 195.00 nm to 205.15 nm, and the polar filaments circled 10- 12 turns inside the posterior pole of the spore. The intergenic spacer (ITS) and small subunit ribosomal RNA (SSU) sequences shared 94.34% and 99.50% similarity to the reported corresponding sequence of N. bombycis. Phylogenetic analysis showed that the microsporidia belonged to the genus Nosema,which was closely related to N. bombycis. The LC₅₀ values of the 1st and 2nd instar larvae of S. frugiperda infected by the microsporidia were 2.51×10⁷ spores/mL and 2.48×10⁷ spores/mL at day 5, respectively. The LC50 value of the 3rd instar larvae was 3.79×10⁷ spores/mL at day 10 after infection, and the LC₅₀ value of the 4th instar larvae was 3.98×10⁷ spores/mL at day 15 after infection. When the concentration of this microsporidia was 1.0×10⁸ spores/mL, the LT₅₀ value of the 1st to 4th instar larvae of S. frugiperda was 3.04, 3.86, 7.47 and 10.43 days, respectively. The results indicated that the microsporidia belonged to the genus Nosema, and had a strong virulence against different instars of S. frugiperda, which has good potential for development and application for S. frugiperda control.