Identification of entomopathogenic fungus Cordyceps cicadae isolated from soil using common cutworm Spodoptera litura (Lepidoptera: Noctuidae) as bait and its high virulence comparable to generalist Metarhizium anisopliae complex

Abstract

The common cutworm (Spodoptera litura, Lepidoptera: Noctuidae) is one of the most widespread pest insects affecting various crops in Asian countries. To screen promising biological control agents for this pest, we isolated 49 potential entomopathogenic fungal isolates from 25 soil samples using S. litura and four additional insect species as baits. The results revealed a high occurrence (24 %) of Cordyceps cicadae in soil through the bait method with all five insect baits, following the Metarhizium anisopliae complex (52 %), despite Cordyceps cicadae generally being known as a specialist entomopathogenic fungus of cicada nymphs. Molecular phylogenetic analysis demonstrated that Cordyceps cicadae isolates from soil and natural cicada nymphs clustered together at a terminal node with previously reported Cordyceps cicadae from cicada nymphs and C. lepidopterorum from lepidopteran larvae. Virulence assays against last-instar larvae of S. litura revealed significant variability in virulence among C. cicadae strains derived from soil and cicada nymphs. Among these, C. cicadae S17, isolated from soil using S. litura as bait, exhibited virulence comparable to the most virulent strains of the M. anisopliae complex and was also virulent against third-instar larvae and pupae. Our findings indicate that C. cicadae exhibit a broader host range than previously recognized, with potential applications in biological control for larvae and pupae of S. litura.