The Diversity of Bacterial Symbionts in Major Agricultural Lepidopteran Pests in Australia

Lepidopteran pests are among the most destructive insects in agriculture, causing major yield losses across a wide range of crops worldwide. With growing emphasis on reducing chemical pesticide use, there is increasing interest in understanding their associated microbiomes and endosymbiotic bacteria. These microbial associates can influence host physiology, fitness, and pesticide/thermal resistance traits, and may provide novel opportunities for developing sustainable pest management strategies. Here, we characterized the diversity and distribution of various endosymbionts and other microbiota in agriculturally important lepidopteran pest species in Australia. In total, we screened 21 field-collected and one commercially reared species of Lepidoptera. Our results indicate that endosymbiont infections were relatively rare and polymorphic in Australian Lepidoptera species. Wolbachia was the most prevalent endosymbiont in field-collected and commercially available pest species. This symbiont can manipulate host reproduction through mechanisms such as cytoplasmic incompatibility and sex-ratio distortion, with potential relevance for pest control. Our MLST analysis suggested that the Wolbachia belonged to Supergroups A and B. Targeted microbiota were present across various species, with a particularly high abundance of Enterococcus mundtii in Spodoptera frugiperda (Smith); this gut bacterium may play a role in pesticide resistance. Distance-based compositional principal component analysis conducted on selected species (Plutella xylostella and Helicoverpa spp.) showed that there was no significant difference in bacterial composition between the Helicoverpa species, or between the host crops/geographic locations where these taxa were collected. These findings provide a basis for future investigations on the phenotypic effects of endosymbionts and gut microbiota in local pests, with long-term potential to suppress pest populations sustainably.