Combined use of lipopolysaccharide-binding protein dsRNA and Gram-negative bacteria for pest management of Coptotermes formosanus

miR-571 manipulating termite immune response to fungus and showing potential for green management of Copotermes formosanus (Blattodea: Isoptera)

Termites are not merely social insects; they are also globally important insect pests. MicroRNAs (miRNAs) are potential molecular targets for the biological control of termites. However, their role in termite resistance to pathogens, particularly their impact on termite social immune behaviour, remains unclear. In this study, we identified 50 differentially expressed miRNAs in Coptotermes formosanus, a globally economically important termite pest, in response to Metarhizium anisopliae infection. Injecting miR-571 agomir, one of significantly upregulated miRNAs, significantly increased termite mortality without or with M. anisopliae infection (compared to that with M. anisopliae infection alone). Meanwhile, termites infected with M. anisopliae exhibited a significant reduction in the avoidance, trophallaxis, and grooming behaviors. Subsequently, we identified POP5 as a target gene of miR-571 and found that miR-571-POP5 inhibits the termite immune response to M. anisopliae by inhibiting the expression of downstream genes, trypsin-like serine protease and serine protease. Finally, we confirmed that the ingestion of miR-571 agomir also increased the mortality of M. anisopliae-infected termites. Our findings enhance knowledge regarding miRNA role in insect social immunity, pathogen manipulation mechanisms, and optimizing pathogen effectiveness through insect miRNAs. This offers new molecular targets for the biological control of termites.

RNAi-mediated silencing of transferrin promotes entomopathogens lethality in Odontotermes formosanus (Shiraki)

Transferrin (Tsf) is a highly conserved multifunctional protein involved in insect physiology, defense and development that has been developed as a novel RNA interference (RNAi)-based target for pest control. The function study of the Tsf gene in Odontotermes formosanu (Shiraki) was evaluated for synergistic control of this agroforestry pest with Serratia marcescens (SM1), Bacillus thuringiensis (Bt) or Beauveria bassiana (Bb). The Tsf gene of O. formosanus was identified and characterized. Real-time fluorescent quantitative PCR (qPCR) analysis demonstrated that OfTsf was most highly expressed in the male dealate of O. formosanus, and OfTsf was highly expressed in the hemolymph. OfTsf expression was considerably elevated after SM1, Bt or Bb infection. Furthermore, dsOfTsf treatment was effective in increasing the virulence of entomopathogens to O. formosanus. In addition, OfTsf expression was markedly upregulated in O. formosanus fed with oxidative stress inducers; reactive oxygen species (ROS) levels were significantly increased after dsOfTsf treatment. Therefore, OfTsf gene played an important role in defending against entomopathogen infection and antioxidant stress. Most importantly, our work suggested OfTsf as a potential RNAi target for the control of O. formosanus.

Molecular mechanism of Serratia marcescens Bizio infection in Reticulitermes chinensis Snyder based on full-length SMRT transcriptome sequencing

Reticulitermes chinensis Snyder is an important pest in forestry and construction and is widely distributed in China. We found that Serratia marcescens Bizio strain SM1 has insecticidal activity to R. chinensis, but the pathogenic mechanism of SM1 to R. chinensis is not clear. Therefore, full-length transcriptome sequencing was performed on R. chinensis infected with SM1 and the control group. A total of 230 differentially expressed genes were identified by comparing SM1 infection group and the control group, among which 103 were downregulated and 127 were upregulated. We found downregulated genes in nine metabolic pathway categories, among which carbohydrate metabolism had the most downregulated genes, followed by energy metabolism and amino acid metabolism. We also found that some downregulated genes were related to pattern recognition receptors, cellular immunity, and humoral immunity, indicating that R. chinensis immunity was negatively affected by SM1 infection. In addition, some genes in signal transduction and genetic information processing pathways were downregulated. In this study, high-throughput full-length transcriptome analysis was used to analyse the pathogenic mechanism of SM1 to R. chinensis. The results of this study provide useful information for exploring the relationship between SM1 and R. chinensis, and provide theoretical support for the future application of SM1 and the prevention and treatment of R. chinensis.