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Update:December 7, 2020

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Two species of Bursaphelenchus nematodes have been detected from a cerambycid beetle obtained in the pine-wilt frontline area

Article title

Occurrence of two species of Bursaphelenchus (Nematoda: Aphelenchoididae) in the reproductive organs of Monochamus saltuarius (Coleoptera: Cerambycidae)

Author (affiliation)

Sota Ozawa (a), Noritoshi Maehara (b), Takuya Aikawa (a), Kenichi Yanagisawa (c), Katsunori Nakamura (a)

(a) Tohoku Research Center, FFPRI, Morioka, Iwate, Japan.

(b) Department of Forest Entomology, FFPRI, Tsukuba, Ibaraki, Japan.

(c) Nagano Prefecture Forestry Research Center, Shiojiri, Nagano, Japan.

Publication Journal

Nematology, BRILL, September 2020 DOI:10.1163/15685411-bja10054( External link )

Content introduction

Bursaphelenchus xylophilus is the pathogen of pine wilt disease. In Japan, it is carried by Monochamus alternatus to healthy pine trees, where it can cause damage. Although B. xylophilus originated in North America, it has now been spread around the world. How it has adopted indigenous beetles as new carriers has been a mystery.

M. saltuarius, which is indigenous to Japan, has been a vector insect of B. mucronatus, which normally does not cause pine disease. In this study, we investigated the species composition of the Bursaphelenchus nematodes carried by M. saltuarius obtained at the frontline of pine wilt disease spread in Nagano Prefecture, and found that the insects mainly harbored B. mucronatus, but could sometimes harbor B. xylophilus or both. This means that M. alternatus carrying B. xylophilus had newly invaded this area and transmitted B. xylophilus to the dead pine trees accompanying with laying eggs, and that M. saltuarius that originally utilized such trees in this area is turning to be a new carrier of B. xylophilus.

Furthermore, it was also found that these nematodes commonly invade the reproductive organs of male and female adults of M. saltuarius. It appears that nematodes that have invaded reproductive organs have a greater chance of infesting pine trees when it is done in conjunction with the egg-laying behavior of their carrier, M. saltuarius. These findings will provide important knowledge for understanding the process by which pine disease is spread to areas that have not previously been infested.


Photo 1: Nematodes scattering from the reproductive organ

Photo 1: Nematodes scattering from the reproductive organ (spermatheca) of an adult female Monochamus saltuarius. The linearly objects spreading out of the organ are the nematodes of the genus Bursaphelenchus.


Photo 2: Male adults of Monochamus saltuarius

Photo 2: Male adults of Monochamus saltuarius (left) and M. alternatus (right).
M. saltuarius is a smaller species than M. alternatus.