Background: Herbivorous insects acquire their gut microbiota from diverse sources, and these microorganisms play significant roles in insect hosts’ tolerance to plant secondary defensive compounds. Camellia weevil (Curculio chinensis) (CW) is an obligate seed parasite of Camellia oleifera plants. Our previous study linked the CW’s gut microbiome to the tolerance of the tea saponin (TS) in C. oleifera seeds. However, the source of these gut microbiomes, the key bacteria involved in TS tolerance, and the degradation functions of these bacteria remain unresolved. Results: Our study indicated that CW gut microbiome was more affected by the microbiome from soil than that from fruits. The soil-derived Acinetobacter served as the core bacterial genus, and Acinetobacter sp. was putatively regarded responsible for the saponin-degradation in CW guts. Subsequent experiments using fluorescently labeled cultures verified that the isolate Acinetobacter sp. AS23 can migrate into CW larval guts, and ultimately endow its host with the ability to degrade saponin, thereby allowing CW to subsist as a pest within plant fruits resisting to higher concentration of defensive chemical. Conclusions: The systematic studies of the sources of gut microorganisms, the screening of taxa involved in plant secondary metabolite degradation, and the investigation of bacteria responsible for CW toxicity mitigation provide clarified evidence that the intestinal microorganisms can mediate the tolerance of herbivorous insects against plant toxins.

Bacteria often play important roles in the host adaptation of phytophagous insects. Beetles of the genus Curculio (Coleoptera: Curculionidae) include pest species that bore into the seeds of trees in the family Fagaceae and damage the cotyledons. At present, there are few studies of the taxonomic diversity and functional effects of symbiotic bacteria involved in changes in host ranges and host adaptation of Curculio. Here, we used 16S rRNA gene Illumina and metagenomic sequencing to compare the composition and functions of the bacterial communities of three species of host plants and several Curculio species combinations: Curculio bimaculatus feeding on Castanopsis sclerophylla, C. bimaculatus feeding on Castanopsis tibetana, and Curculio davidi feeding on Ca. tibetana. The host plants influenced the diversity of symbiotic bacteria, while the Curculio species influenced the community structure of the symbiotic bacteria. Functional predictions showed that symbiotic bacteria contributed to the metabolism of the hosts. However, consistent with the variation in bacteria, the major metabolism-related bacterial genera varied among the treatment groups. Comparisons of metabolic enzymes based on KEGG (Kyoto Encyclopedia of Genes and Genomes) annotation revealed differences in the enzymes involved in insect development and detoxification of plant secondary compounds among the three groups, and the patterns were influenced by the dominance of the Curculio species on the host plants. This study provides valuable insights into the possible role of symbiotic bacteria in Curculio as host insects.

The tree species of Toona sinensis has been cultivated in China for over 2,000 years with multiple purposes. In 2022, leaf spots were detected on the leaves of T. sinensis in a germplasm resource nursery in Zhejiang Province, China. Symptomatic leaves were collected and fungal isolation was conducted. Four fungal isolates resembling Alternaria were isolated from the diseased leaves. These isolates were identified as Alternaria alternata, combining the morphological characteristics and multigene phylogenetic analysis. To fulfill Koch’s postulates, pathogenicity of the selected isolate YKHH was tested on 2-year-old container seedlings of T. sinensis. Disease symptoms basi-cally consistent with those observed in the field developed 12 days after inoculation (DAI) when either conidia or mycelia were used as the inoculum. Nevertheless, no visible symptoms devel-oped on the leaves of the control groups. The fungi were reisolated from the diseased leaves, and both the morphological characteristics as well as the three gene sequences (GAPDH, RPB2, and TEF1-α) of the reisolated fungi were consistent with those of the original YKHH isolate. Suscepti-bility trial results showed that family 55 of T. sinensis (F55) had the highest susceptibility to A. al-ternata, while family 28 of T. sinensis (F28), family 52 of T. sinensis (F52), and Toona ciliata var. pu-bescens (TCP) exhibited equal susceptibility to A. alternata. To the best of our knowledge, this is the first report of leaf spot disease caused by A. alternata on T. sinensis in China.

The leaf roller, Eumorphobotys obscuralis, is a highly destructive pest that causes severe defoliation, ultimately reducing plant vigor, leading to culm death, and resulting in significant economic and ecological losses. Despite its substantial impact, effective prevention and control strategies remain lacking, further exacerbating the damage caused by this species. To address the critical gap in genomic resources, we generated a high-quality chromosome-scale genome assembly for E. obscuralis using a combination of Illumina short reads, PacBio HiFi long reads, and Hi-C chromatin interaction data. The final assembly spans 701.9 Mb across 31 chromosomes, including the single sex chromosome Z. Key assembly metrics include a contig N50 of 1.73 Mb and a scaffold N50 of 23.70 Mb, with an estimated genome completeness of 96.7%. Genome annotation identified 15,855 protein-coding genes and revealed that repetitive sequences account for 58.9% of the genome. This genomic resource lays a solid foundation for exploring the genetic mechanisms underlying the pest’s biology and adaptation, and serves as a valuable reference for the development of targeted pest management strategies.