Double-strand RNAs targeting MaltRelish and MaltSpz reveals potential targets for pest management of Monochamus alternatus.

Overcoming the innate immunity of insects is a key process to improve the efficiency of biological control. Antimicrobial peptides (AMPs) are important effectors in insect innate immunity, usually mediating resistance to pathogenic microorganisms through Toll and IMD signaling pathways. This study investigated the effect of key genes on upstream immune recognition receptor (GNBP3 ) and downstream effectors (AMPs) by RNAi technology. The transcriptome KEGG enrichment analysis and differential gene annotation results showed that the immune response genes MaltSpz and MaltRelish are important regulators of Toll and IMD signaling pathways, respectively. Both dsSpz and dsRelish could affect AMP gene expression and increase the expression of the immune recognition receptor MaltGNBP3 . Moreover, they significantly reduce the survival rate of Monochamus alternatus and promote hyphal growth after Beauveria bassiana infection. This helps to improve the biological control effect of B. bassiana, control the population of vector insects and cut off the transmission route of pine wood nematode. The combined MaltSpz and MaltRelish knockdown increased the infection rate of M. alternatus larvae from 20.69% to 83.93%, achieving the best efficiency in synergistic B. bassiana infection. Our results showed important roles of MaltRelish- and MaltSpz-mediated regulation of AMP genes function in insect entomopathogenic fungi tolerance and induced significant mortality in larvae. Based on this study, MaltSpz and MaltRelish could represent candidate gene targets for the biological control of M. alternatus by RNAi.