Cross Pathogenicity of Metarhizium rileyi Isolates from Spodoptera frugiperda or Spodoptera litura against Both Host Species（Lepidoptera: Noctuidae）

In 2020, many fall armyworms（FAW; Spodoptera frugiperda）infested with an entomopathogenic fungus were collected from maize fields in Southern Kyushu. In this study, three isolates of FAW fungus and one from common cutworm（CCW; Spodoptera litura）were identified by DNA sequencing as Metarhizium rileyi（formerly Nomuraea rileyi）and found to be closely related to each other. Three fungal isolates from FAW in Kashiwabaru, Satsuma Town; Kinpo, Minamisatsuma City; and Nonomitani, Miyakonojo City, as well as one isolate from CCW in Korimoto, Kagoshima City, were inoculated onto third instar FAW and CCW larvae. The LC50 value ratios of FAW to CCW were 1.14, 0.049, 1.91, and 13.94, respectively, indicating either similar virulence against both species or greater virulence against CCW; only the Kinpo isolate was more virulent against FAW. The LC50 against FAW was 9.7×103 to 9.6×105 conidia*ml−1. These three strains, other than the Kimpo isolate, were more virulent to CCW, but would also be expected to contribute to FAW mortality in the field.