Cao Qingjie, Zhao Yu, Koski Tuuli-Marjaana, Li Huiping, Sun Jianghua
College of Forestry, Hebei Agricultural University, Baoding, Hebei Province, China.
State Key Laboratory of Integrated Management of Pest Insects and Rodents, Institute of Zoology, Chinese Academy of Sciences, Beijing, China.
Insect Sci. 2024 Feb;31(1):225-235. doi: 10.1111/1744-7917.13210. Epub 2023 May 24.
Bark beetles are an economically and ecologically important insect group, with aggregation behavior and thus host colonization success depends on pheromone-mediated communication. For some species, such as the major invasive forest pest in China, red turpentine beetle (Dendroctonus valens), gut microbiota participates in pheromone production by converting tree monoterpenes into pheromone products. However, how variation in gut microenvironment, such as pH, affects the gut microbial composition, and consequently pheromone production, is unknown. In this study, we fed wild caught D. valens with 3 different pH media (main host diet with natural pH of 4.7; a mildly acidic diet with pH 6 mimicking the beetle gut pH; and highly acidic diet with pH 4), and measured their effects on the gut pH, bacterial community and production of the main aggregation and anti-aggregation pheromone (verbenone). We further tested the verbenone production capacity of 2 gut bacterial isolates in different pH environments (pH 6 and 4). Compared to natural state or main host diet, feeding on less acidic diet (pH 6) diluted the acidity of the gut, whereas feeding on highly acidic diet (pH 4) enhanced it. Both changes in gut pH reduced the abundance of dominant bacterial genera, resulting in decreased verbenone production. Similarly, the highest pheromone conversion rate of the bacterial isolates was observed in pH mimicking the acidity in beetle gut. Taken together, these results indicate that changes in gut pH can affect gut microbiota composition and pheromone production, and may therefore have the potential to affect host colonization behavior.
小蠹虫是一类在经济和生态方面都很重要的昆虫群体，具有聚集行为，因此其对寄主的定殖成功与否取决于信息素介导的通讯。对于某些物种，比如中国主要的入侵性森林害虫微红梢斑螟（Dendroctonus valens），肠道微生物群通过将树木单萜转化为信息素产物来参与信息素的产生。然而，肠道微环境的变化，如pH值，如何影响肠道微生物组成，进而影响信息素的产生，目前尚不清楚。在本研究中，我们用3种不同pH值的培养基（天然pH值为4.7的主要寄主食物；pH值为6的微酸性食物，模拟甲虫肠道pH值；pH值为4的高酸性食物）喂养野外捕获的微红梢斑螟，并测量它们对肠道pH值、细菌群落以及主要聚集和抗聚集信息素（马鞭草烯酮）产生的影响。我们还进一步测试了2种肠道细菌分离株在不同pH环境（pH值为6和4）下的马鞭草烯酮产生能力。与自然状态或主要寄主食物相比，食用酸性较低的食物（pH值为6）会稀释肠道酸度，而食用高酸性食物（pH值为4）则会增强肠道酸度。肠道pH值的这两种变化都降低了优势细菌属的丰度，导致马鞭草烯酮产量下降。同样，在模拟甲虫肠道酸度的pH值下观察到细菌分离株的最高信息素转化率。综上所述，这些结果表明肠道pH值的变化会影响肠道微生物群组成和信息素产生，因此可能有潜力影响寄主定殖行为。
