Chunhui Guo

Rickettsia is an endosymbiotic bacterium that infects various arthropods, affecting the host's biology, ecology, and evolution. Leptocybe invasa is an invasive pest that severely damages eucalyptus plants. A comprehensive investigation of Rickettsia in 313 female L. invasa individuals from 17 Chinese populations revealed a 100% infection prevalence. Sequencing of three host molecular markers—mitochondrial COI , nuclear ITS , and 28S —led to the identification of a novel L. invasa haplotype, designated Haplotype 1 × 2, which exhibits mito‐nuclear discordance. Concurrently, sequencing of four Rickettsia genes ( 16S rRNA, gltA , atpA , rpmE ) revealed two distinct strains, termed STRiA and STRiB. These strains demonstrated a specific association with the host lineages, where STRiA was exclusively associated with lineage A (comprising Haplotype 1 and Haplotype 1 × 2), and STRiB was linked to lineage B. Phylogenetic analysis of the multigene datasets from both the host and Rickettsia revealed a high degree of topological congruence between their inferred trees. Correlation analysis further demonstrated a moderate positive association ( r = 0.307). The significance of this relationship was supported by a Mantel test ( p < 0.005), suggesting coevolution. Low‐dose tetracycline treatment effectively eliminated Rickettsia from L. invasa . L. invasa treated with tetracycline exhibited a significantly higher proportion of male offspring, reduced Rickettsia expression, and decreased body length and lifespan in female offspring. Transcriptome analysis comparing Rickettsia ‐free and Rickettsia ‐infected L. invasa following antibiotic treatment identified 178 differentially expressed genes (122 up‐regulated, 56 down‐regulated). These genes were enriched in GO terms related to metabolic processes, cellular processes, cellular components, binding functions, and catalytic activities. KEGG pathway analysis revealed enrichment of differentially expressed genes primarily in metabolic pathways, insect hormone biosynthesis, and thermogenesis. Additionally, enrichment was observed in key signaling pathways, including Ras, MAPK, NF‐κB, TGF‐β, TNF, and Apelin. These findings elucidate the coevolutionary relationship and functional roles of Rickettsia in L. invasa , providing a foundation for symbiont‐mediated biological control.

The study aimed to investigate the effect of soil textural or soil mineral fraction substrates (loam and gravel) from karst desertification areas on the rhizospheric and root-associated bacterial community structure of Dalbergia odorifera (an N-fixing tree), using high-throughput sequencing techniques, based on treatment methods of whole-root and two-chambered split-root systems. Further, this study determined the relative importance of the plant and substrate properties on the rhizospheric, non-rhizospheric and endospheric bacteria composition. The type of substrate exerts a significant influence on both rhizospheric and non-rhizospheric bacterial communities, whereas endophytic communities within the root system are predominantly determined by plant species rather than substrate type. The analysis revealed that endospheric bacterial diversity was considerably lower than that of rhizospheric and non-rhizospheric communities. Cluster analysis indicated that endospheric bacterial samples formed a distinct cluster, while rhizospheric and non-rhizospheric bacteria in the soil substrate grouped into one branch, and those in the gravel substrate formed another branch. In comparison to the gravel treatments, a reduced bacterial abundance was observed in the rhizosphere and non-rhizosphere of nitrogen-fixing plants in soil, potentially due to the interplay of lower nutrient availability and increased porosity in gravel treatments. Proteobacteria, which are involved in the nitrogen cycle, exhibited the highest abundance. In contrast, Acidobacteria, Firmicutes and other bacterial phyla involved in nutrient cycling demonstrated higher abundance, with their presence being more pronounced in extreme environments, such as gravel treatments, compared to soil substrates. These results suggest that nitrogen-fixing plants can respond to extreme environments by increasing bacterial abundance. The findings of this study provide a theoretical basis for the use of D. odorifera for ecosystem recovery and vegetation restoration.

Microorganisms within insects play a vital role in maintaining the basal physiological functions of the insects, with olfactory signals as critical components of insect survival strategies. Leptocybe invasa (L. invasa), an invasive alien pest inflicting significant damage to eucalyptus trees, harbors a rich and varied bacterial community within its body. However, the impact of its endogenous bacteria and their microbial Volatile Organic Compounds (mVOCs) on the behavioral preferences of L. invasa remains unexplored to date. This study focused on nine cultivable and dominant endogenous bacterial strains within L. invasa. Using a Y-tube olfactometer, we investigated the behavioral responses of female L. invasa to the mVOCs emitted by these bacteria. Concurrently, gas chromatography–mass spectrometry (GC–MS) was employed to quantify the mVOCs produced by these endogenous bacteria. Our findings revealed that Staphylococcus sp. exhibited the highest attractiveness of L. invasa, whereas Microbacterium sp. and E. cloacae exerted the most significant avoidance effects. The analysis of the mVOCs further highlighted the significance of aldehyde compounds, notably 2,3,6-trichlorobenzaldehyde, and alkane compounds, such as eicosane, in mediating the repellency and attraction effects. These results contribute to a deeper understanding of the invasion mechanism of L. invasa and provide a scientific basis for developing novel biopesticides or elicitors.