Abstract:  【Aim】 To investigate the effects of Bursaphelenchus xylophilus in Monochamus alternatus on the bacteria in the gut and trachea of M. alternatus.【Methods】The whole gut and trachea were isolated from the collected M. alternatus adults carrying B. xylophilus in the field to extract DNA for sequencing and splicing of the 16S rDNA gene. The composition, structure, abundance and diversity of bacteria in the gut and trachea of M. alternatus adults carrying B. xylophilus were analyzed by bioinformatics methods. 【Results】A total of 15 phyla, 26 classes, 66 orders, 110 families, 201 genera, 296 species and 444 operational taxonomic units (OTUs) of bacterial flora in the gut and trachea of M. alternatus adults carrying B. xylophilus were detected. There was no significant change in the dominant bacterial flora in the gut between M. alternatus adults carrying B. xylophilus and M. alternatus adults without carrying B. xylophilus, and their dominant bacterial flora were Proteobacteria and Enterobacterales. Proteobacteria and Enterobacterales were the dominant bacterial flora in the trachea of M. alternatus adults carrying B. xylophilus, while Firmicutes and Lactobacillales were the dominant bacterial flora in the trachea of M. alternatus adults without carrying B. xylophilus. The diversity and abundance of bacteria in the trachea of M. alternatus adults carrying B. xylophilus were higher than those of M. alternatus adults without carrying B. xylophilus, and the bacterial community structure in the trachea of M. alternatus adults carrying B. xylophilus was significantly different from that of M. alternatus adults without carrying B. xylophilus. Serratia and Enterobacter were enriched in the gut and trachea of M. alternatus adults carrying B. xylophilus. 【Conclusion】The introduction of B. xylophilus has significant effects on the composition, structure, abundance and diversity of bacterial flora in the trachea of M. alternatus adults. Serratia and Enterobacter in the trachea of M. alternatus adults may be closely related to the B. xylophilus-M. alternatus complex. The increase of Serratia in the trachea of M. alternatus adults carrying B. xylophilus may be associated with the suppressed tracheal immunity of M. alternatus. This study provides a theoretical basis for the study of bacterial diversity in the gut and trachea of M. alternatus, and a new direction for the prevention and control of B. xylophilus.

Key words: Monochamus alternatus, Bursaphelenchus xylophilus, gut bacteria, tracheal bacteria, bacterial diversity