Effects of Isaria cateniannulata on Enzyme Activities and Chitinase Genes in Tetranychus urticae

Tetranychus urticae is a globally important economic pest mite. Isaria cateniannulata can infect the mite through its conidial penetration of the cuticle, ultimately leading to host mortality; however, the immune mechanisms involving enzyme activity systems and chitinase genes of T. urticae during this process remain unclear. In this study, T. urticae infected with I. cateniannulata was used as experimental material to analyze changes in antioxidant and detoxification enzyme activities during infection. In addition, the expression patterns of six chitinase genes were analyzed, and significantly upregulated genes were selected for bioinformatics analysis and functional verification. The results showed that infection with I. cateniannulata enhanced the activity of defense-related enzymes in T. urticae, with Catalase (CAT) and mixed function oxidase (MFO) playing dominant roles. All six chitinase genes were activated, among which TuCHT7 and TuCHT12 were significantly upregulated at 24 h post-infection, and then TuCHT7 gradually declined. Whereas TuCHT12 maintained a sustained and stable induction pattern, TuCHT10 was suppressed, while the other genes exhibited transient expression. Feeding dsTuCHT12 suppressed the expression of this gene within 72 h, with significant suppression observed at 48 h. At this time, the expression levels of TuCHT8, TuCHT9 and TuCHT10 genes were activated, whereas TuCHT7 and TuCHT11 were suppressed. The combined application of dsCHT12 and I. cateniannulata increased the mortality of T. urticae by 3.19-fold and reduced egg production by 52.8%. This study preliminarily revealed the defense response mechanism of T. urticae against I. cateniannulata infection and provides a theoretical basis for eco-friendly pest control based on the combined application of RNAi and arthropodpathogenic fungi.