Microbiome and electron microscopy analyses of the mechanisms underlying the effects of Bacillus thuringiensis on Dioryctria abietella

[Display omitted] •Bt feeding alters the abundance and composition of the gut microbiota of D. abietella larvae.•Bt ingestion triggers pathways related to cellular metabolism and function in the gut microbiota.•Bt promotes the apoptosis of gut epithelial cells of D. abietella. The ability of the bacteria Bacillus thuringiensis (Bt) to effectively kill target insects is well-established. However, the mechanisms by which Bt interacts with gut microbes to trigger insect cell death is in forest pests remain unclear. Dioryctria abietella is one of the most destructive forest pests for coniferous trees. In the present work, D. abietella was used as a model to investigate the effects of Bacillus thuringiensis subsp. galleriae 05041 strain (Bt05041, 1 × 108 CFU mL−1) on the gut microbiota and midgut cells at different time points after treatment (3, 6, 9, 12, and 24 h). Treatment with Bt05041 significantly enriched the gut bacterial community, altered the composition of the gut microbiota, and resulted in the dysfunction of gut cells. Bt05041 treatment significantly increased the OTUs (operational taxonomic units) compared to the number in the control group. The genera Enterococcus, Wolbachia, Bacillus, and unclassified Enterobacteriaceae had relatively high abundances after Bt05041 treatment. The midgut cells of D. abietella deteriorated significantly in response to Bt05041, as determined by transmission electron microscopy. Changes in cell morphology included the disruption of microvilli, deformation of organelles, and cytoplasmic vacuolation. With the extension of the Bt05041 treatment duration, the basal plasma membrane and septate junction gradually ruptured until cells were completely dissolved. In conclusion, our findings reveal the effects of Bt05041 exposure for various durations on gut microbes and cells, clarify the detailed mechanism underlying Bt-mediated apoptosis, and provide new insights into the use of Bt for forest pest control.