The immune response of Phytoseiulus persimilis (Acari: Phytoseiidae) to the bacterial pathogen Acaricomes phytoseiuli.

The natural immune system of arthropods is an important defense against pathogen infection. Predatory mites, as a highly commercialized group of natural enemies, suffer the threat of pathogen infection during mass rearing processes. However, there is a lack of research on the immune mechanisms of predatory mites in response to pathogen infection. To explore whether the Phytoseiulus persimilis possesses a natural immune response to pathogen, we selected the typical Gram-positive bacterium Acaricomes phytoseiuli to examine the pathogenic impact on P. persimilis fitness and the potential immune-related genes. The results showed that the survival rate, fecundity and predation of P. persimilis were significantly reduced after infection with A. phytoseiuli. Furthermore, fluorescent in situ hybridization was used to identify the pathogen enriched in the ovary and intestinal tract of P. persimilis. To further investigate the natural immune defense of P. persimilis, we analyzed the expression of twelve immune genes selected from the transcriptome. The results showed that the expression levels of four genes, tok, HPB, DUOX, and Peroxidase, were upregulated after one day of pathogen infection. While the expression of other genes showed no significant differences in either the 1st day or 3rd day. Our study provide preliminary exploration of natural immune mechanism of phytoseiid mites, laying a theoretical foundation for further their disease resistance.