Host plant affects the larval gut microbial communities of the generalist herbivores Helicoverpa armigera and Spodoptera frugiperda

Investigations on symbiotic associations between Lepidoptera and bacteria have been inconclusive as to whether these microorganisms represent transient or persistent associations. One reason for this is that most studies have sampled the microbiota from only a few species and frequently from laboratory-reared animals. We sequenced the 16S rRNA gene to profile the gut microbiome of the field collected, agricultural pests Helicoverpa armigera and Spodoptera frugiperda. We found that variation in the structure of bacterial communities is in great part associated with their host diet. Moreover, Enterococcus, among a few other taxa, is consistently present in all samples regardless of the plant hosts were collected. The larval gut bacteria composition matches previously published data in the same or related species, indicating that associations with bacteria taxa such as Enterococcus are persistent despite geographical variation and sampling techniques. Based on our phylogenetic analysis it is not clear, however, if Enterococci associated with Lepidoptera are necessarily different from environmental bacteria. We conclude that to fully understand the nature of Lepidoptera - gut bacteria associations it will be necessary to conduct larger sampling efforts and combine them with identification methods of bacterial strains that go beyond screening of the 16S rRNA gene.