The ovarian development and oviposition response of two vector beetles of pine wood nematode, Monochamus alternatus and M. saltuarius, was investigated. The ovary structure of two beetles was investigated by means of light microscopy. The ovary of both beetles was composed of two ovaries that are connected by a common oviduct. Each of the two ovaries was consisted of twelve ovarioles, the functional units of female oogenesis. The ovary type was meroistic telotrophic with nurse cells and oocytes in the tropharium. Ovarian development of two vector beetles was completed at 12-14 days after maturation-feeding pine twigs. Aspect of accumulation of vitellogenins in the ovary of two vectors showed difference in developmental stages and major yolk proteins, differently from vitellogenin. To investigate oviposition performance of two vector beetles, we provided P. thunbergii and P. koraiensis bolts for egg laying and collected emerged adults from each pine bolts in the next year. M. saltuarius females made more oviposition wounds and entrance hole of larvae than M. alternatus on pine bolts. We also investigated whether two beetles can transmission of Bursaphelenchus xylophilus and the European type of B. mucronatus via oviposition to noninfected dead pines. 48-83% from newly emerged adults of two beetles were carried two species nematode. This results suggested that two species beetles can transmit nematodes through oviposition performance and transmitted nematodes successfully propagate in non-infected dead pines.

A survey was conducted in the northern conifer forests of Korea from February to May in 2009 for the Monochamus species vectored Bursaphelenchus species. Dead pine trees infested with bark beetle larvaes were collected from Pinus densiflora and P. koraiensis located in the following target areas: Pocheon, Yeongi, Jincheon, Chuncheon, and Bonghwa. A cerambycid beetle, M. saltuarius was only found from sampled log piles in target areas. Bursaphelenchus species carried by M. saltuarius was only isolated in Pocheon, Gyeonggi province. The nematodes recovered from 17 (71%) of 24 beetles from P. koraiensis and 12 (75%) of 16 beetles from P. densiflora. The average number of nematode per adult was 1,974 and 11,823 from P. koraiensis and P. densiflora, respectively. The nematode was also recovered from the inner bark of both Pinus species infested with M. saltuarius larvae. Bursaphelenchus species identification was performed by morphological characters and molecular analysis with ITS-RFLP patterns and sequences of ITS and D2D3 region. Both morphological and molecular characters match well with the original description of the European type of B. mucronatus. This is the first report of M. saltuarius species as a vector of the European type of B. mucronatus on both P. densiflora and P. koraiensis in Korea.

Since pine wilt disease was first reported in Busan in 1988, this disease has become a serious threat to pine forests in Korea. A general survey for Bursaphelenchus xylophilus group (B. xylophilus, B. mucronatus) nematodes were carried out to determine their geographic range, host tree species and insect vectors, Monochamus species. Based on the survey results, B. xylophilus were found over 57 cities or district and a similar nematode, B. mucronatus also has been isolated over 30 cities or district including Jeju and Pocheon. The Asian type of B. mucronatus was founded from Pinus thunbergii and P. densiflora, generally associated with M. alternatus as its insect vector. The European type of B. mucronatus which was limited distribution to the central areas, such as Yeongwol, Bonghwa, Yeongdeok, was also found on P. koraiensis and P. desiflora associated with M. saltuarius. Both Monochamus species transmitted both Bursaphelenchus species and co-existed in Muju and Yeongdeok predicted as their range margin. Their range margins shifted northwards compared to 2006, seemingly as a result of climate change. Recently, the European type of B. mucronatus has been identified in other several areas since it was first reported in Pocheon in 2008. Several reports indicate the potential pathogenicity of European type of B. mucronatus and other species, B. sexdentati and B. lenoni in Europe. Therefore, sustainable survey and the study for the newly invading Bursaphelenchus species as well as the member of B. xylophilus group should be performed to protect Korean forests.