Abstract: The fall armyworm, Spodoptera frugiperda, is a migratory lepidopteran pest invading China in recent years. The pest causes serious damage to various crops, threatening crop yield in China. S. frugiperda nucleopolyhedtovirus (SfMNPV) is a baculovirus, host-specific virus to the fall armyworm. As an important biocontrol agent, it will contribute to the integrated pest management (IPM). In the present study, an entomo-pathogenic virus strain SfMNPV-Yz01 was isolated from natural dead larvae by enrichment isolation. Based on the morphological features and analysis of the sequences of conservate baculovirus gene Me53 and cg30, the strain SfMNPV-Yz01 was identified in the genus of S. frugiperda nucleopolyhedtovirus. SfMNPV-Yz01 was highly infectious and lethal to the 3^rd instar larvae of S. frugiperda. The LC₅₀ was 7.4910⁴ PIB/mL, and the LT₅₀ were from 5.51―8.02 d at different concentrations. Larvae died within 3―5 d post infection with the strain, with peak mortality occurring at 6―7 d. The survival curves of larvae were significantly different among different concentrations of SfMNPV-Yz01. Sub-lethal treatment of SfMNPV-Yz01 significantly affected the development and reproduction of S. frugiperda, with larval duration extended by 0.95 d, gender ratio changed by 0.265, and oviposition dropped by 42.6%, suppressing the population buildup of S. frugiperda. It was indicated, that SfMNPV-Yz01 is a strain of relatively high virulence to S. frugiperda. Using baculovirus as an eco-regulating agent may play significant role in reducing the expansion and damage of S. frugiperda.

Key words: Spodoptera frugiperda, nucleopolyhedtovirus, infecting effect, sublethal effect