Dispersal of the Japanese pine sawyer, Monochamus alternatus (Coleoptera: Cerambycidae), in mainland China as inferred from molecular data and associations to indices of human activity.

Shao-Ji Hu,Hui Ye,Robert A Haack,Zhen Zhang,Xue-Yu Ma,De-Dao Chen,Da-Ying Fu,Tiao Ning,Wenjun Li

doi:10.1371/journal.pone.0057568

Abstract

The Japanese pine sawyer, Monochamus alternatus Hope (Coleoptera: Cerambycidae), is an important forest pest as well as the principal vector of the pinewood nematode (PWN), Bursaphelenchus xylophilus (Steiner et Buhrer), in mainland China. Despite the economic importance of this insect-disease complex, only a few studies are available on the population genetic structure of M. alternatus and the relationship between its historic dispersal pattern and various human activities. The aim of the present study was to further explore aspects of human activity on the population genetic structure of M. alternatus in mainland China. The molecular data based on the combined mitochondrial cox1 and cox2 gene fragments from 140 individuals representing 14 Chinese populations yielded 54 haplotypes. Overall, a historical (natural) expansion that originated from China’s eastern coast to the western interior was revealed by the haplotype network, as well as several recent, long-distant population exchanges. Correlation analysis suggested that regional economic status and proximity to marine ports significantly influenced the population genetic structure of M. alternatus as indicated by both the ratio of shared haplotypes and the haplotype diversity, however, the PWN distribution in China was significantly correlated with only the ratio of shared haplotypes. Our results suggested that the modern logistical network (i.e., the transportation system) in China is a key medium by which humans have brought about population exchange of M. alternatus in mainland China, likely through inadvertent movement of infested wood packaging material associated with trade, and that this genetic exchange was primarily from the economically well-developed east coast of China, westward, to the less-developed interior. In addition, this study demonstrated the existence of non-local M. alternatus in new PWN-infested localities in China, but not all sites with non-local M. alternatus were infested with PWN.

Highlights

The Japanese pine sawyer, Monochamus alternatus Hope (Coleoptera: Cerambycidae), is a major pest of coniferous forests, especially pines (Pinus spp.), and is the key vector of the exotic pinewood nematode (PWN), Bursaphelenchus xylophilus (Steiner et Buhrer) (Nematoda: Aphelenchoididae), in eastern Asia [1]
M. alternatus could be transported long distances within China via logs and lumber, we believe that wood packaging material such as pallets and crating that are used in the transportation of commercial products is the most likely pathway for long-distance humanassisted transport of M. alternatus across mainland China as well as internationally [8,13]
A 3D multidimensional scaling (MDS) analysis [56] based on the K2P (Kimura two-parameter) distances was performed using SPSS 13.0 and a haplotype network was constructed using median joining method in Network 4.6 (Fluxus Technology Ltd., Clare, Suffolk, UK) with the 14 populations categorized by both the geographical regions of mainland China (Table 1) and the indices having significant correlations based on the analyses described above

Summary

Introduction

The Japanese pine sawyer, Monochamus alternatus Hope (Coleoptera: Cerambycidae), is a major pest of coniferous forests, especially pines (Pinus spp.), and is the key vector of the exotic pinewood nematode (PWN), Bursaphelenchus xylophilus (Steiner et Buhrer) (Nematoda: Aphelenchoididae), in eastern Asia [1]. Given the long life cycle of M. alternatus and that some larvae and pupae can survive the milling process, wood products made from infested trees, especially the sapwood portion, could serve as a pathway by which M. alternatus is moved within China. M. alternatus could be transported long distances within China via logs and lumber, we believe that wood packaging material such as pallets and crating that are used in the transportation of commercial products is the most likely pathway for long-distance humanassisted transport of M. alternatus across mainland China as well as internationally [8,13]. Given that the modern logistics network of roads, railways, and inland waterways has been associated with human-mediated spread of PWN in China, it is logical that it was associated with the dispersal of M. alternatus in China

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