Objective Japanese scholars found that the pine sawyer Monochamus alternatus carried not only pine wood nematode (Bursaphelenchus xylophilus), but also an another nematode, which was identified as a new specie and named as ovarian nematode, Contortylenchus genitalicola Kosaka et Ogura (Tylenchida:Allantonematidae). It was recognized that the nematode was parasitic in the ovary of M. alternatus. This new ovarian nematode has not been reported in China till now. This study is to determine whether this nematode existing in China and its function in the cerambycid.

Method Capturing emergent M. alternatus in batches and groups, dissecting the beetle, the dead larvae of M. alternatus, and the infected pine wood to find the nematode.

Result It was found that M. alternatus adults in China carried the ovarian nematode indeed. The nematode has 3 niches. It existed in the cerambycid adult and larva of M. alternatus, as well as in the xylem of the infected pine trees. The 4th instar larvae of the ovarian nematode inoculated into the xylem of pine tree when the female M. alternatus laying eggs. Then some of the 4th instar nematode in the xylem parasitized the larvae of M. alternatus as host, while some still lived in the xylem. While the cerambycid developed from egg to larvae and to pupa, the ovarian nematode in xylem could move to the body of the cerambycid adult, finishing and restarting the life cycles among the niches. It was found in the investigation that 44.4% of the cerambycid adults carried this ovarian nematode, in which 43.8% of female adults and 45.0% male adults with the nematode respectively and the data showed no significant difference. The average quantity of nematodes carried by one cerambycid adult was 574, in which each female carried 816 and each male carried 308 in average, and the data showed significant differences. The preliminary study on the ovarian nematode life history indicated that the nematode could only develop stages from egg to 1st-4th instar larva, but did not complete the whole life history in the adult body of the cerambycid. However, in the cerambycid larva and the xylem of infested tree, it was able to finish the whole life history.

Conclusion The ovarian nematode is unable to kill the adults of M. alternatus although it could parasitic in the adult body, however it could kill the cerambycid larvae as a parasitic nematode. It is also found that the ovarian nematode often coexists with pine wood nematode and has a similar way with the pine wood nematode living in the infested pine trees. It is necessary to confirm whether the ovarian nematode has a pathological effect to infested pine tree similar as the pine wood nematode.