Bacteria Endosymbiont, Wolbachia, Promotes Parasitism of Parasitoid Wasp Asobara japonica

Wolbachia is the most widespread endosymbiotic bacterium that manipulates reproduction of its arthropod hosts to enhance its own spread throughout host populations. Infection with Wolbachia causes complete parthenogenetic reproduction in many Hymenoptera, producing only female offspring. The mechanism of such reproductive manipulation by Wolbachia has been extensively studied. However, the effects of Wolbachia symbiosis on behavioral traits of the hosts are scarcely investigated. The parasitoid wasp Asobara japonica is an ideal insect to investigate this because symbiotic and aposymbiotic strains are available: Wolbachia-infected Tokyo (TK) and noninfected Iriomote (IR) strains originally collected on the main island and southwest islands of Japan, respectively. We compared the oviposition behaviors of the two strains and found that TK strain females parasitized Drosophila melanogaster larvae more actively than the IR strain, especially during the first two days after eclosion. Removing Wolbachia from the TK strain wasps by treatment with tetracycline or rifampicin decreased their parasitism activity to the level of the IR strain. Morphological and behavioral analyses of both strain wasps showed that Wolbachia endosymbionts do not affect development of the host female reproductive tract and eggs, but do enhance host-searching ability of female wasps. These results suggest the possibility that Wolbachia endosymbionts may promote their diffusion and persistence in the host A. japonica population not only at least partly by parthenogenesis but also by enhancement of oviposition frequency of the host females.沃尔巴克氏体（Wolbachia）是分布最为广泛的内共生细菌，其通过操控节肢动物宿主的生殖过程，以提升自身在宿主种群中的传播效率。感染沃尔巴克氏体会促使诸多膜翅目（Hymenoptera）昆虫完全进行孤雌生殖，仅产生雌性后代。目前学界已对沃尔巴克氏体介导的这类生殖操控机制开展了大量研究，但针对沃尔巴克氏体共生对宿主行为性状的影响，相关探究仍较为匮乏。 寄生蜂日本索氏茧蜂（Asobara japonica）是开展此类研究的理想昆虫模型，因为该物种已被成功构建出有共生菌与无共生菌两个品系：分别为采自日本主岛的感染沃尔巴克氏体的东京（TK）品系，以及采自日本西南诸岛的未感染沃尔巴克氏体的西表岛（IR）品系。 我们对两个品系的产卵行为进行了对比分析，结果发现TK品系的雌蜂相较于IR品系，会更积极地寄生黑腹果蝇（Drosophila melanogaster）幼虫，这一差异在羽化后的最初两天尤为显著。通过四环素（tetracycline）或利福平（rifampicin）处理去除TK品系蜂体内的沃尔巴克氏体后，其寄生活性会降至与IR品系相当的水平。 对两个品系蜂的形态学与行为学分析显示，沃尔巴克氏体内共生菌并不会影响宿主雌性生殖管道与虫卵的发育，但可显著提升雌蜂的寄主搜寻能力。 上述结果表明，沃尔巴克氏体内共生菌或可通过至少两种途径促进自身在日本索氏茧蜂种群中的扩散与存留：其一，至少部分借助孤雌生殖；其二，增强宿主雌蜂的产卵频率。