Table_1_Secondary symbionts affect aphid fitness and the titer of primary symbiont.docx

Bacterial symbionts associated with aphids are important for their ecological fitness. The corn leaf aphid, Rhopalosiphum maidis (Fitch), is one of the most damaging aphid pests on maize and has been reported to harbor Hamiltonella defensa and Regiella insecticola while the effects of the secondary symbionts (S-symbionts) on host ecology and primary symbiont Buchnera aphidicola remain unclear. Here, four aphid strains were established, two of which were collected from Langfang - Hebei Province, China, with similar symbiont pattern except for the presence of H. defensa. Two other aphid strains were collected from Nanning - Guangxi Province, China, with the same symbiont infection except for the presence of R. insecticola. Phylogenetic analysis and aphid genotyping indicated that the S-symbiont-infected and free aphid strains from the same location had identical genetic backgrounds. Aphid fitness measurement showed that aphid strain infected with H. defensa performed shortened developmental duration for 1st instar and total nymph stages, reduced aphid survival rate, offspring, and longevity. While the developmental duration of H-infected strains was accelerated, and the adult weight was significantly higher compared to the H-free strain. Infection with R. insecticola did not affect the aphid’s entire nymph stage duration and survival rate. As the H-strain does, aphids infected with R. insecticola also underwent a drop in offspring, along with marginally lower longevity. Unlike the H-infected strain, the R-infected strain performed delayed developmental duration and lower adult weight. The B. aphidicola titers of the H-infected strains showed a steep drop during the aphid 1st to 3rd instar stages, while the augmentation of B. aphidicola titers was found in the R-infected strain during the aphid 1st to 3rd instar. Our study investigated for the first time the effect of the S-symbionts on the ecology fitness and primary symbiont in R. maidis, indicating that infection with secondary symbionts leads to the modulation of aphid primary symbiont abundance, together inducing significant fitness costs on aphids with further impact on environmental adaptation and trophic interactions.

与蚜虫共生的细菌对宿主的生态适应性至关重要。玉米叶蚜虫，即 Rhopalosiphum maidis (Fitch)，是玉米上最具破坏性的蚜虫害虫之一，已知其体内携带 Hamiltonella defensa 和 Regiella insecticola，而次级共生菌（S-共生菌）对宿主生态及主要共生菌 Buchnera aphidicola 的影响尚不明确。在本研究中，建立了四种蚜虫菌株，其中两种菌株来自中国河北省廊坊市，两者共生菌模式相似，但存在 H. defensa。另外两种蚜虫菌株来自中国广西壮族自治区南宁市，两者共生菌感染情况相同，但存在 R. insecticola。系统发育分析和蚜虫基因分型表明，同一地点的S-共生菌感染蚜虫菌株和未感染菌株具有相同的遗传背景。蚜虫适应性测量显示，感染 H. defensa 的蚜虫菌株1龄若虫和总若虫阶段的发育时间缩短，蚜虫的存活率、后代数量和寿命降低。而H-感染菌株的发育时间加快，成年蚜虫体重显著高于未感染H菌株。R. insecticola 的感染并未影响蚜虫整个若虫阶段的持续时间及存活率。与H-感染菌株类似，感染 R. insecticola 的蚜虫后代数量减少，寿命略有降低。与H-感染菌株不同，R-感染菌株的发育时间延迟，成年蚜虫体重降低。B. aphidicola 的滴度在蚜虫1龄至3龄若虫阶段急剧下降，而在R-感染菌株中，B. aphidicola 的滴度在蚜虫1龄至3龄若虫阶段增加。本研究首次探讨了S-共生菌对R. maidis的生态适应性和主要共生菌的影响，表明次级共生菌的感染导致蚜虫主要共生菌数量的调节，进而对蚜虫的适应性产生显著的成本，并进一步影响环境适应和营养交互作用。