Composition and predicted function of the gut microbiome of a lepidopteran fruit feeder, the grape berry moth, Paralobesia viteana

The grape berry moth (GBM) Paralobesia viteana (Lepidoptera: Tortricidae), is an important pest of cultivated grapes in eastern North America. The larvae damage grape clusters by direct feeding and by increasing susceptibility to fungal and bacterial pathogens. We sequenced the V3-V4 region of 16S-rRNA and V4 region of 18S-rRNA to characterize the composition and diversity of GBM gut bacterial and fungal communities of larvae fed on immature and mature Concord grapes. Using QIIME2, downstream analyses included taxonomic composition, differential abundance, phylogenetic, functional, and alpha/beta-diversity. Results of 16S-rRNA showed that gut-associated bacteria did not differ between larvae fed on immature and mature grapes. Ninety-six percent of the bacterial communities belonged to Proteobacteria, and some may play roles in amino acid and carbohydrate (cellulose and hemicellulose) metabolism in the insect gut. Analyses of 18S rRNA showed significant differences in fungal communities between larvae grown at different grape ripening stages. Ascomycota (99%) was the dominant phylum in the gut of larvae fed on mature grapes, while larvae fed on immature grapes mainly contained fungi in the Cryptomycota (51%). Larvae fed on ripe grapes had a higher abundance of yeasts (Saccharomycetales) compared with those fed on immature grapes. Several gut-associated fungal genera identified are commonly found in rotten grapes, suggesting that some yeasts might be transient insect residents that are ingested with the diet. In conclusion, diet type affects GBM gut-associated fungal communities but not bacterial communities. The results of this study contributes to basic knowledge of gut-associated microbes of fruit-feeding insects.