Bacterial Communities Associated with the Pine Wilt Disease Insect Vector Monochamus alternatus (Coleoptera: Cerambycidae) during the Larvae and Pupae Stages.

Hongjian Chen,Zhiqiang Wei,Lujie Wang,Dejun Hao,Tao Lin

doi:10.3390/insects11060376

Abstract

Monochamus alternatus is an important insect pest in pine forests of southern China and the dispersing vector of the pine wood nematode, Bursaphelenchus xylophilus, which leads to pine wilt disease (PWD). Microbiome of M. alternatus may contribute to survival of larvae in the host pine trees. In order to investigate the intestinal bacterial structure of M. alternatus during the larvae and pupae stages in host trees, and infer the function of symbiotic bacteria, we used 16S rRNA gene Illumina sequencing to obtain and compare the bacterial community composition in the foregut, midgut, and hindgut of larvae, pupal intestines, larval galleries, and pupal chambers of M. alternatus. The diversity of the bacterial community in larval intestines and pupal intestines were similar, as well as was significantly greater in larval galleries and pupal chambers. Although there were differences in bacterial compositions in different samples, similar components were also found. Proteobacteria and Firmicutes were the two most dominant phyla in all samples, and genera Enterobacter, Raoultella, Serratia, Lactococcus, and Pseudomonas were dominant in both the intestinal samples and plant tissue samples. Enterobacter was the most abundant genus in larval intestines, and Serratia was dominant in pupal intestine. The functions of these dominant and specific bacteria were also predicted through metagenomic analyses. These bacteria may help M. alternatus degrade cellulose and pinene. The specific role of symbiotic bacteria in the infection cycle of PWD also warrants further study in the future.

Highlights

The sawyer pine beetle, Monochamus alternatus Hope, causes serious damage to pine forests in southern China and is regarded as a forest pest in Asia due to vectoring an invasive pathogenic nematode, Bursaphelenchus xylophilus (Steiner et Buhrer) Nickle, which is known to cause pine wilt disease (PWD) [1,2,3]
Our research based on high-throughput sequencing adds to the understanding of intestinal bacteria in M. alternatus, and some interesting results were obtained
The results of metagenomic inference showed that some intestinal symbiotic bacteria played an important role in digesting lignocellulose to obtain nutrients and degrade terpenes toxic to beetles secreted by conifers when M. alternatus fed on host pine trees

Summary

Introduction

The sawyer pine beetle, Monochamus alternatus Hope, causes serious damage to pine forests in southern China and is regarded as a forest pest in Asia due to vectoring an invasive pathogenic nematode, Bursaphelenchus xylophilus (Steiner et Buhrer) Nickle, which is known to cause pine wilt disease (PWD) [1,2,3]. At the beginning of the 20th century, PWD was first detected in Japan and subsequently spread to other Asian countries including China and Korea [4]. PWD has been reported successively in Portugal, Spain and the Portuguese island of Madeira in Europe [5]. PWD is considered to be one of the most serious diseases affecting conifers in the world. Throughout the larval and pupal stages, M. alternatus grows and develops entirely in host trees. The 1st and 2nd instar larvae feed on the phloem and cambium, and later instars tunnel into the xylem forming a characteristic

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Results

Conclusion