Diet-associated variation in the midgut bacterial communities of Loxostege sticticalis larvae fed botanically...

Gut microbiota can influence insect physiology and ecological interactions, but how botanically distinct host plants affect gut bacterial communities in polyphagous insects remains poorly understood.

We investigated the midgut bacterial communities of Loxostege sticticalis larvae fed three host plants from different genera or an artificial diet using 16S rRNA gene sequencing. Bacterial diversity, community composition, differential taxa, and predicted functional profiles were compared among dietary treatments.

Dietary treatments were associated with differences in gut bacterial community structure. The MS group exhibited higher bacterial richness and diversity, whereas the CA group showed a relatively simplified bacterial community. Bray-Curtis-based PCoA and PERMANOVA indicated significant overall variation in community composition among dietary treatments, although exact pairwise PERMANOVA tests were not significant. Bacillota and Pseudomonadota were dominant across treatments, while the MS group showed increased representation of Actinomycetota-associated taxa. LEfSe identified Actinomycetota-related taxa as characteristic features of the MS group and Bacillota-related taxa as features of the AD group. PICRUSt2 suggested differences in predicted functional potential among dietary treatments, including pathways related to amino acid metabolism, metabolism of cofactors and vitamins, and xenobiotics biodegradation and metabolism.

The results demonstrate diet-associated variation in the gut bacterial communities of L. sticticalis and provide a descriptive basis for further investigation of diet-microbiota interactions. Because the study included only three pooled biological replicates per treatment and did not characterize plant-associated microbiota or plant chemistry, the observed associations and predicted functions should not be interpreted as evidence of specific microbial mechanisms or host adaptation.