Host Diet and Species Interact to Shape the Bacterial and Fungal Microbiome in the Regurgitant of Four Spodoptera Species

Abstract

The gut microbiome of Lepidopteran insects is highly dynamic, influenced by both host diet and phylogeny. While microbial communities are thought to facilitate host adaptation to diverse diets and environments, the existence of a core microbiome shared among closely related herbivores remains largely untested. In this study, we examined the microbial communities in the regurgitant of four Spodoptera species (S. exigua, S. frugiperda, S. latifascia, and S. littoralis) across different diets (artificial diet, cotton, maize, and squash). Using a high-throughput sequencing, we characterized bacterial and fungal community composition and diversity. Bacterial communities were shaped by both diet and host species, indicating species-specific bacterial selection. In contrast, fungal communities were exclusively structured by diet, with lower diversity and dominance of a few key taxa. Notably, no operational taxonomic units were consistently shared across all species or diets, challenging the concept of a conserved core microbiome in these generalist herbivores. Understanding how microbial communities shape generalist herbivores' ability to feed on diverse plants may offer potential strategies for microbiome-based pest management.

Keywords: 16S rDNA sequencing; Foregut microbiome; Gut bacteria; Gut fungi; ITS rDNA sequencing; Microbial community; Microbiota.

Fig. 1

Non-metric multidimensional scaling (NMDS) ordination plots based on Bray–Curtis distances of Hellinger-transformed relative abundances of Spodoptera regurgitant microbial communities. (a) Bacterial and (b) fungal communities in Spodoptera regurgitant grouped by diet. (c) Bacterial and (d) fungal communities in Spodoptera regurgitant grouped by species. Each point represents one regurgitant sample. Each treatment combination of Spodoptera species and diet was replicated three times (n = 3), with each replicate consisting of pooled regurgitate collected from 10–11 individuals. Ellipses represent 95% confidence intervals around the group mean (diet or species). Different letters indicate significant differences among treatments (pairwise posthoc analysis). NMDS stress values (goodness of fit): bacteria = 0.118; fungi = 0.121

Fig. 2

Bacterial community profiles of regurgitant collected from caterpillars of four species of Spodoptera (S. exigua, S. frugiperda, S. latifascia, and S. littoralis) fed on four different diets (artificial diet, cotton, maize, or squash plants). The bacterial taxa shown represent the 35 most prevalent ASVs identified at the genus level (full list is shown in Table S2). Colours represent the average prevalence (%) of bacterial taxa within each group, with white indicating absence

Fig. 3

Fungal community profiles of regurgitant collected from caterpillars of four species of Spodoptera (S. exigua, S. frugiperda, S. latifascia, and S. littoralis) fed on four different diets (artificial diet, cotton, maize, or squash plants). The fungal taxa shown represent the 30 most prevalent ASVs identified at the genus level (full list is shown in Table S3). Colours represent the average prevalence (%) of fungal taxa within each group, with white indicating absence

Fig. 4

Shannon diversity indices of bacteria (a, c) and fungi (b, d) in Spodoptera regurgitant, grouped by diet (a, b) and species (c, d). Each treatment combination of Spodoptera species and diet was replicated three times (n = 3), with each replicate consisting of pooled regurgitate collected from 10–11 individuals. Grey dots represent individual raw data points (jittered for clarity), while black dots represent outliers included in the analyses. Different letters indicate significant differences among treatments (p < 0.05, Tukey’s HSD)

Fig. 5

Shannon diversity indices of bacteria and fungi in the regurgitant of four Spodoptera species (S. exigua, S. frugiperda, S. latifascia and S. littoralis) fed on four different diets (artificial diet, cotton, maize and squash). Each treatment combination of Spodoptera species and diet was replicated three times (n = 3), with each replicate consisting of pooled regurgitate collected from 10–11 individuals. Grey dots represent individual data points (jittered for clarity), and the black dot indicates an outlier included in the analysis. Asteriks indicate significant differences between bacterial and fungal diversity (p < 0.001, Tukey’s HSD)