Characterization of entomopathogenic fungi from invasive fall armyworm in China and their risk to native pests

The role of pathogens in the successful invasion of pests has received increasing attention. Previous hypotheses on parasite-related invasion mainly focus on the lack of parasites against invasive pests or the introduction of parasites with a higher risk to native pests. Fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), is a new invasive pest in China. Here, we investigated pathogen infection in eight natural populations of FAW in China, isolated and characterised the pathogens, and then evaluated the infection risk of the pathogens to native pests. The pathogen infection frequencies in FAW were very low (0.32%); only two individuals were found to have typical symptoms of fungal infection, and the fungi were identified as Beauveria bassiana and Metarhizium rileyi. Internal transcribed spacer sequence-based analysis showed that among 44 B. bassiana isolates worldwide, the SFJS01 isolate was genetically different from only 3 isolates. Among all 13 isolates of M. rileyi from FAW, including the SFGX01 isolate, there was no significant differentiation. Comparison of the mortality caused by B. bassiana SFJS01 or M. rileyi SFGX01 against S. frugiperda, Spodoptera litura, Bemisia tabaci, Laodelphax striatellus and Nilaparvata lugens showed that the new isolates all had the highest virulence to S. frugiperda and the lowest virulence to S. litura, a native pest closely related to FAW. The findings indicated that pathogens isolated from FAW did not pose a high risk to native pests and that they did not play a key role in the successful invasion of the FAW in China.