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Background: Selenium has shown effectiveness in protecting plants from herbivores. However, some insects have evolved adaptability to selenium., Results: Selenium accumulation in host plants protected them against spider mite feeding. Selenium showed toxic effects on spider mites by reducing growth and interfering with reproduction. After 40 generations on selenium-rich plants, a Tetranychus cinnabarinus strain (Tc-Se) developed adaptability to selenium, with an increased rate of population growth and enhanced ability for selenium metabolism. The high expression of two genes (GSTd07 and SPS1) in the selenium metabolism pathway might be involved in selenium metabolism in spider mites. After GSTd07 and SPS1 were silenced, the selenium adaptability decreased. Recombinant GSTd07 protein promoted the reaction between sodium selenite and glutathione (GSH) and increased the production of sodium selenite metabolites. The results indicated that GSTd07 was involved in the first step of selenium metabolism., Conclusion: Plants can resist spider mite feeding by accumulating selenium. Spider mites subjected to long-term selenium exposure can adapt to selenium by increasing the expression of key genes involved in selenium metabolism. These results elucidate the mechanism of the interaction between mites and host plants mediated by selenium. This study of the interaction between selenium-mediated host plants and spider mites may lead to the development of new and less toxic methods for the prevention and control of spider mites. © 2021 Society of Chemical Industry., (© 2021 Society of Chemical Industry.)

Selenium is a trace element necessary for living organisms. It exists mainly in the form of selenite in nature. In plants, selenium can enhance defenses against pests. In this study, transcriptome sequencing technology was used to analyze the response mechanism of Tetranychus cinnabarinus to plant-mediated selenium treatment. We tested four sodium selenite treatments (5, 20, 50, and 200 μM) that were the same for short (2 d) and long (30 d) treatment durations. The results showed that the number of differentially expressed genes (DEGs) in the short-term treatment was greater than in the long-term treatment. This indicated that the gene expression of spider mites gradually stabilized during the selenium treatment. Regardless of the long-term and short-term conditions, spider mites had the largest response to the 20 μM sodium selenite treatment. The functional annotation classification of DEGs showed no significant difference under different concentrations and treatment durations. A total of 25 genes were differentially expressed in all eight treatments, including four down-regulated cytochrome P450 genes and one up-regulated chitinase gene. We speculate that selenium may have the potential to enhance the activity of chemical acaricides. Transcriptome sequencing of sodium selenite treatment at different concentrations and different times revealed the response mechanism of spider mites under plant-mediated selenium treatment. At the same time, it also provides new clues for the development of methods for preventing and controlling spider mites with selenium., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The γ-aminobutyric acid receptor (GABAR) has been identified as a target site of some commonly used insecticides. Our pervious study documented an interesting phenomenon, i.e. GABA accumulation was involved in abamectin resistance in the carmine spider mite, Tetranychus cinnabarinus. However, the mechanism of this phenomenon remains to be clarified. In this study, we investigated the interaction between abamectin and GABAR. Firstly, an artificial increase of GABA content was conducted in T. cinnabarinus and toxicity assays showed that GABA accumulation could indeed increase the tolerance of T. cinnabarinus to abamectin in vivo. Subsequently a GABAR of T. cinnabarinus, RDL2, was expressed in Xenopus oocytes and its sensitiveness to abamectin was detected. The results revealed that RDL2 showed significant responses to a series of GABA concentrations and GABA inhibited the effect of abamectin in vitro, providing direct evidence of the abamectin resistance mediated by GABA content. Our data confirmed that GABAR is the action target of abamectin and the GABA accumulation is one of the mechanisms of abamectin resistance in spider mites., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Tetranychus cinnabarinus (Boisduval), i.e., carmine spider mite, is a worldwide pest that can cause serious damage to plants. Problems of resistance have arisen since abamectin usage in the control of T. cinnabarinus. Unfortunately, there are only limited data on the extent of this problem. To understand the development of abamectin resistance in the carmine spider mite, we prokaryotically expressed an intradiol ring-cleavage dioxygenase (ID-RCD) gene sequence, TcID-RCD1, which had a significant upregulated expression of over 7.7 times in an abamectin-resistant strain (AbR) when compared with that of a susceptible strain (SS). The crude enzyme activity also indicated that the AbR had a higher activity than that exhibited in SS. When susceptible individuals were treated with abamectin, TcID-RCD1 was also overexpressed. Furthermore, using the RNA interference (RNAi) technique, TcID-RCD1 was successfully knocked down, with the expression level decreasing significantly to approximately 39% in the SS strain compared with the control. And the mortality of mites feeding on dsTcID-RCD1 increased significantly when treated with abamectin. These results strongly suggest that TcID-RCD1 is involved in abamectin resistance in T. cinnabarinus., (© The Author(s) 2019. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)