Abstract: 【Aim】To further investigate the entomopathogenic nematode(EPN) resources in Gansu Province, northwestern China, and screen native EPNs with high virulence against Spodoptera frugiperda. 【Methods】A survey of EPN resources was conducted in Dingxi City, Baiyin City, Qingyang City, Lanzhou City, Wuwei City and Jiuquan City of Gansu Province by using Galleria mellonella as the bait from July 2023 to April 2024. The morphological indicators of EPN infective juveniles isolated from Gansu Province, including body length, maximum body width, distance from anterior end to excretory pore, distance from anterior end to nerve ring, distance from anterior end to the base of pharynx, tail length and anal body width, were measured and analyzed. Molecular biology methods were also used to amplify, compare and analyze the sequences of ITS gene and D2-D3 region of 28S rDNA gene of each EPN strain for taxonomic identification. The virulence of nine EPN strains (200 IJs/ind.) screened in the preliminary experiment (Steinernema feltiae 0819B, S. feltiae 0931L, S. hebeiense 0847H, S. everestense 0821S, Heterorhabditis megidis 0853BH, H. megidis 0872L, H. beicherriana 0817H, H. beicherriana 0861H and H. beicherriana 0415L) was determined using laboratory bioassay. The sensitivity of different instar larvae (3rd, 4th and 5th instar larvae, and mature larvae) of S. frugiperda to a high virulence EPN strain H. megidis 0872L strain and the effects of different infestation dosages (50, 100, 150, 200, 250, 300 and 350 IJs/ind.) and ambient temperatures (13, 17, 21, 25, 29 and 33 ℃) on the virulence of H. megidis 0872L strain were also evaluated.【Results】A total of 20 EPN strains were obtained in this survey, including three species of the genus Steinernema, namely S. feltiae, S. hebeiense and S. everestense, of which S. everestense was the first recorded species in China, and two species of the genus Heterorhabditis, i.e., H. megidis and H. beicherriana. The results of the laboratory bioassay showed that H. megidis 0872L strain was the most virulent to the 3rd instar larvae of S. frugiperda, causing the corrected mortality rate of the 3rd instar larvae of S. frugiperda of 79.63% after 96-h infestation. Further investigation of single factors affecting virulence revealed that the 5th instar larvae of S. frugiperda were the most susceptible to H. megidis 0872L strain, and the optimal infestation dosage of H. megidis 0872L strain against the 3rd instar larvae of S. frugiperda was 250 IJs/ind. and the optimal infestation temperature was 25 ℃.【Conclusion】There are abundant EPN resources in Gansu Province, they have high virulence against S. frugiperda, and the H. megidis 0872L strain shows promising potential for biological control.

Key words: Entomopathogenic nematodes; Spodoptera frugiperda, isolation, identification, virulence