Ge Si-Xun, Li Jia-Xing, Jiang Zhuo-Heng, Zong Shi-Xiang, Ren Li-Li
Beijing Key Laboratory for Forest Pest Control, Beijing Forestry University, Beijing, China.
School of Science, Westlake University, Hangzhou, China.
Insect Sci. 2023 Aug;30(4):1165-1182. doi: 10.1111/1744-7917.13148. Epub 2022 Dec 7.
The Japanese pine sawyer, Monochamus saltuarius, as a beetle vector of Bursaphelenchus xylophilus (pine wood nematode), is an economically important forest pest in Eurasia. To feed on the phloem and xylem of conifers, M. saltuarius needs to overcome various stress factors, including coping with entomopathogenic bacteria and also various plant secondary compounds (PSCs). As an important adaptation strategy to colonize host trees, M. saltuarius deposit eggs in oviposition pits to shield their progeny. These pits harbor bacterial communities that are involved in the host adaptation of M. saltuarius to the conifers. However, the composition, origin, and functions of these oviposition pit bacteria are rarely understood. In this study, we investigated the bacterial community associated with M. saltuarius oviposition pits and their ability to degrade PSCs. Results showed that the bacterial community structure of M. saltuarius oviposition pits significantly differed from that of uninfected phloem. Also, the oviposition pit bacteria were predicted to be enriched in PSC degradation pathways. The microbial community also harbored a lethal strain of Serratia, which was significantly inhibited. Meanwhile, metatranscriptome analysis indicated that genes involved in PSCs degradation were expressed complementarily among the microbial communities of oviposition pits and secretions. In vitro degradation showed that bacteria cultured from oviposition pits degraded more monoterpenes and flavonoids than bacteria cultured from uninfected phloem isolates. Disinfection of oviposition pits increased the mortality of newly hatched larvae and resulted in a significant decrease in body weight in the early stages. Overall, our results reveal that M. saltuarius construct oviposition pits that harbor a diverse microbial community, with stronger PSCs degradation abilities and a low abundance of entomopathogenic bacteria, resulting in the increased fitness of newly hatched larvae.
日本松墨天牛（Monochamus saltuarius）作为松材线虫（Bursaphelenchus xylophilus）的甲虫传播媒介，是欧亚大陆一种具有重要经济意义的森林害虫。为了取食针叶树的韧皮部和木质部，日本松墨天牛需要克服各种压力因素，包括应对昆虫病原细菌以及各种植物次生化合物（PSC）。作为在寄主树上定殖的一种重要适应策略，日本松墨天牛会在产卵坑中产下卵来保护其后代。这些坑中含有参与日本松墨天牛适应针叶树寄主过程的细菌群落。然而，这些产卵坑细菌的组成、来源和功能却鲜为人知。在本研究中，我们调查了与日本松墨天牛产卵坑相关的细菌群落及其降解PSC的能力。结果表明，日本松墨天牛产卵坑的细菌群落结构与未感染韧皮部的细菌群落结构显著不同。此外，预计产卵坑细菌在PSC降解途径中富集。微生物群落中还含有一种致死性的沙雷氏菌菌株，该菌株受到显著抑制。同时，宏转录组分析表明，参与PSC降解的基因在产卵坑和分泌物的微生物群落之间互补表达。体外降解实验表明，从产卵坑培养的细菌比从未感染韧皮部分离物培养的细菌降解更多的单萜和黄酮类化合物。对产卵坑进行消毒会增加新孵化幼虫的死亡率，并导致早期体重显著下降。总体而言，我们的结果表明，日本松墨天牛构建的产卵坑中含有多样化的微生物群落，具有更强的PSC降解能力且昆虫病原细菌丰度较低，从而提高了新孵化幼虫的适应性。
