Tetranychus truncatus (Acari: Tetranychidae) has caused serious economic losses on some crops (soybean, corn, and cotton) in China, and has developed resistance to most acaricides. Our laboratory study found that T. truncatus was resistant to pyridaben and also adapted to high temperature (34–40 °C). High temperature stress may cause arthropods to produce a large amount of reactive oxygen species (ROS), causing oxidative damage. Antioxidant enzymes, as the main antioxidants, can reduce the damage caused by excessive ROS in arthropods. In order to study the adaptation mechanism of the pyridaben-resistant strain of T. truncatus to high temperature and the role of antioxidant enzyme genes under high temperature stress, four antioxidant enzyme genes, TtSOD, TtPOD3, TtPOD4, and TtGSTs2, were screened according to the transcriptome sequencing data of pyridaben-susceptible and -resistant strains in T. truncatus. Firstly, the phylogeny and structure analyses of these four genes were carried out. Then, real-time quantitative PCR (RT-qPCR) technology was used to analyze the gene expression patterns of antioxidant enzymes in two strains of T. truncatus at three different high temperature ranges (34 °C, 38 °C, and 42 °C). The results showed that the expression levels of four antioxidant enzyme genes of two strains of T. truncatus were induced by high temperature stress, and the expression levels of antioxidant enzyme genes were significantly different in each development state. The gene expression of antioxidant enzyme genes in resistant strains at the adult stage was significantly higher than that in susceptible strains. After the TtSOD and TtPOD4 genes of adult mites of the resistant strain were silenced by RNA interference (RNAi) technology, the mortality rate of mites with TtPOD4 gene silencing reached 41.11% after 96 h at 34 °C, which was significantly higher than that of the control and TtSOD gene silencing. It has been confirmed that the TtPOD4 gene plays a key role in the adaptation of pyridaben-resistant strain of T. truncatus to high temperature. It lays a theoretical foundation for revealing the thermal adaptation mechanism of T. truncatus.

Carboxylesterases (CarEs) are detoxification enzymes that play important roles in xenobiotic metabolism and host adaptation in the polyphagous spider mite Tetranychus truncatus. However, the specific carboxylesterase proteins involved in host plant detoxification in Tetranychus truncatus remain poorly characterized. In this study, we investigated the activities of glutathione S-transferase (GST), carboxylesterase (CarE), and cytochrome P450 (CYP450) in T. truncatus reared on three host plants—common bean, cucumber, and jujube. CarE activity was significantly higher in mites fed on jujube, while CYP450 content increased in mites fed on cucumber. GST activity did not differ significantly among the three host plants, indicating that different hosts induce distinct detoxification responses in T. truncatus. Expression profiling of 24 CarE genes revealed that the carboxylesterase gene TtCarE-4 exhibited the strongest host-specific response, with expression levels 8-fold and 160-fold higher on jujube than on bean and cucumber, respectively, consistent with changes in total CarE enzyme activity. RNAi-mediated silencing of TtCarE-4 reduced its transcript abundance by 32.8%, significantly increased mite mortality, and decreased female fecundity. Off-target analysis indicated that the gene is specifically targeted to T. truncatus and is safe for non-target organisms such as natural enemies. This study provides new insights into the physiological mechanisms of host adaptation in spider mites and identifies the carboxylesterase gene TtCarE-4 as a potential RNAi target for sustainable pest management.