Identification of a microspordium isolated from Megacopta cribraria (Hemiptera: Plataspidae) and characterization of its pathogenicity in silkworms.

A new microsporidium isolated from Megacopta cribraria was characterized by both biological characteristics and phylogenetic analysis. Moreover, its pathogenicity to silkworms was also studied. The spores are oval in shape and measured 3.64 ± 0.2 × 2.20 ± 0.2 μm in size. Its ultrastructure is characteristic of the genus Nosema: a diplokaryon, 13-14 polar filament coils and posterior vacuole. Its life cycle includes meronts, sporonts, sporoblasts and mature spores, with a typical diplokaryon in each stage and propagation in a binary fission. A phylogenetic tree based on SSU rRNA and rRNA ITS gene sequence analysis further indicated that the parasite is closely related to Nosema bombycis and should be placed in the genus Nosema and sub-group 'true' Nosema. Furthermore, the microsporidium heavily infects lepidopteran silkworm insect and can be transmitted per os (horizontally) and transovarially (vertically). Our findings showed that the microsporidium belongs to the 'true' Nosema group within the genus Nosema and heavily infects silkworms. Based on the information obtained during this study, we named this new microsporidium isolated from M. cribraria as Nosema sp. MC.