卵巢线虫(Contortylenchus genitalicola)在中国松褐天牛上的分布与作用研究

目的]日本学者Kosaka与Ogura发现松褐天牛成虫除携带松材线虫外,雌成虫卵巢内还携带有另一种线虫,他们将其命名为卵巢线虫,并认为这种线虫是松褐天牛成虫的寄生性线虫。我国对该种线虫的研究迄今未见报道。为了证明这种线虫在我国是否存在和分布,开展了本项研究。方法]分期分批捕获刚羽化的松褐天牛雌雄成虫,采用解剖松褐天牛成虫松树木质部及感病的松褐天牛幼虫等方法,调查卵巢线虫的存在与分布。结果]通过调查研究,发现我国的松褐天牛成虫体内有该卵巢线虫存在,分布于松褐天牛成虫、幼虫体内和松树木质部3个部位;在松褐天牛成虫体内的卵巢线虫通过松褐天牛雌成虫产卵而接种、进入寄主树木木质部中。同时,木质部的卵巢线虫也有一部分进入松褐天牛幼虫体内寄生,另一部分仍在木质部生活,当松褐天牛幼虫再次发育为成虫时,在木质部中的卵巢线虫和已被寄生的松褐天牛幼虫体内的卵巢线虫再次进入松褐天牛成虫体内,完成循环。卵巢线虫在松褐天牛雌、雄虫体内均有分布,携带率为44.4%,其中松褐天牛雌成虫携带率为43.8%,松褐天牛雄成虫携带率为45.0%,两者间无显著差异;每头松褐天牛成虫平均携带卵巢线虫574条,其中雌成虫平均携带816条,雄成虫平均携带308条,具显著差异。初步研究表明,卵巢线虫在松褐天牛成虫体内只能完成产卵到1~4龄的幼虫阶段,不能完成一个完整的世代;在松褐天牛幼虫体内寄生和在木质部生活的卵巢线虫能完成一个完整世代,但具体过程尚不清楚;调查中未观察到卵巢线虫对松褐天牛成虫有寄生致病或致死的现象,但对松褐天牛幼虫有寄生致死的能力;卵巢线虫常与松材线虫同时存在,而且侵入松树及离开松树的方式与松材线虫相同。结论]我国松褐天牛体内也发现有卵巢线虫存在;目前尚不能证明该线虫对松褐天牛成虫具有寄生致死性,但对松褐天牛幼虫具有一定的寄生致死性;卵巢线虫的生活史与松材线虫相似,是否与松材线虫一样对松树具有危害性以及其病理作用还有待于进一步研究。

Distribution and Function of the Ovarian Nematode Contortylenchus genitalicola (Tylenchida: Allantonematidae) on Monochamus alternatus (Coleoptera: Cerambycidae) in China

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.