Isolation and identification of salivary bacteria of Tuta absoluta and their influence on tomatoes

The tomato leaf miner, Tuta absoluta Meyrick (Lepidoptera), primarily attacks Solanaceae species, particularly tomatoes, significantly affecting both yield and quality. Saliva plays a crucial role in insect-plant interactions which needs direct physical contact. As an important part of insect saliva, it is of significant importance to analyze the role of salivary bacteria in the feeding processes of insects on host plants. In this study, conventional isolation methods were employed to isolate bacteria from the saliva of third-instar larvae of T. absoluta. Species identifications of the isolated strains were performed using 16S rRNA sequence homology analysis. The isolated strains were inoculated into tomato plants, and growth and defense indexes, including chlorophyll, malondialdehyde, peroxidase, superoxide dismutase, soluble sugar, soluble protein, nitrogen, and phosphorus were measured after inoculation. The results showed that the isolated salivary bacteria belonged to three phyla, six genera, and seven species: Enterococcus mundtii and Bacillus amyloliquefaciens (phylum Firmicutes), Enterobacter cloacae and Acinetobacter rhizosphaerae (phylum Proteobacteria), Microbacterium arborescens, Microbacterium oleivorans and Curtobacterium flaccumfaciens (phylum Acinobacteria). Inoculation experiments in vitro demonstrated that M. arborescens and E. mundtii significantly reduced the peroxidase activity of tomato plants which decreased by 62.92% and 76.83% after treatment, respectively. Treatments with A. rhizosphaerae and E. mundtii resulted in a significant increase in malondialdehyde content in the plants (P < 0.05). Soluble protein levels increased significantly after treatment with M. arborescens, E. mundtii, and M. oleivorans (P < 0.05), whereas soluble sugar content decreased significantly after treatment with A. rhizosphaerae and E. cloacae (P < 0.05). Nitrogen levels also exhibited a decreasing trend after treatment with the salivary bacteria. Additionally, chlorophyll content was significantly higher in all treatment groups than that of the control group (P < 0.05). In conclusion, inoculation in vitro with salivary bacteria from T. absoluta leads to peroxidation in tomato plants, and certain strains inhibit the plants' defense mechanisms. This finding indicates that the saliva of T. absoluta plays a role in regulating the growth and defense responses of tomato plants, which may be a factor of facilitating the adaptation of T. absoluta to tomato. This study enriches our understanding of the mechanisms underlying the interaction between T. absoluta and tomato plants and provides a theoretical basis for the prevetion and control of T. absoluta.