Investigation of the fall armyworm (Spodoptera frugiperda) gut microbiome and entomopathogenic fungus-induced pathobiome

The gut microflora plays an important role in insect development and physiology. The gut bacterial microbiome of the fall armyworm (FAW), Spodoptera frugiperda, in both cornfield and laboratory-reared populations was investigated using a 16S metagenomic approach. The alpha- and beta-diversity of the cornfield FAW populations varied among sampling sites and were higher than those of the laboratory-reared FAW population, indicating that different diets and environments influence the gut bacterial composition. To better understand the interaction between the microbiome and entomopathogenic fungi (EPF), FAWs from organic and conventionally managed corn fields and from the laboratory-reared colony were inoculated with Beauveria bassiana NCHU-153 (Bb-NCHU-153). A longer median lethal time (LT50) was observed in the Bb-NCHU-153-infected cornfield FAW population than in the laboratory-reared FAWs. In terms of the microbiome, three Bb-NCHU-153-infected FAW groups showed different gut bacterial compositions compared to noninfected FAW. Further investigation of the cooccurrence network and linear discriminant analysis (LDA) of effect size (LEfSe) revealed that the enriched bacterial genera, such as Enterococcus, Serratia, Achromobacter, and Tsukamurella, in the gut might play the role of opportunistic pathogens after fungal infection; in contrast, some gut bacteria of Methylobacterium, Marinomonas, Paenochrobactrum, Pseudomonas, Acinetobacter, Delftia, Dietzia, Gordonia, Leucobacter, Paracoccus, and Stenotrophomonas might be probiotics against EPF infection. These results indicated that EPF infection can change the gut bacterial composition and lead to a pathobiome in the FAW and that some bacterial species might protect the FAW from EPF infection. These findings could be applied to the design of pathobiome-inducing biocontrol strategies.