Analysis of glutathione S-transferases (GSTs) gene expression in an insecticide-resistant strain of Cydia pommnella using real-time quantitative PCR is a key step towards more mechanism studies that requires suitable reference genes with stable expression. Here, nine commonly used reference genes were selected and their expression stabilities were analyzed. Results showed that EF-1α was the most stable reference gene in all of the experimental sets. The combination of EF-1α and 18S, EF-1α and RPL12, and EF-1α and GAPDH were sufficient for normalization of gene expression analysis accurately in developmental stages, tissues, and larvae exposed to sublethal dose (LD10) of λ-cyhalothrin, respectively. Additionally, the suitability of particular reference genes was verified by analyzing the spatiotemporal and insecticide-induced expression profiles of CpGSTe3, CpGSTd3, and CpGSTd4, which wereover-expressed in a λ-cyhalothrin-resistant population from northeast China. These genes were used to confer the practicability of reference genes chosen in this study.

The oriental fruit fly, Bactrocera dorsalis (Hendel), is a widespread agricultural pest that has evolved resistance to many commonly used insecticides including malathion. Glutathione S‐transferases (GSTs) are multifunctional enzymes that metabolize insecticides directly or indirectly. The specific mechanism used by GSTs to confer malathion resistance in B. dorsalis is unclear. BdGSTd9 was identified from B. dorsalis and was expressed at twice the level in a malathion‐resistant strain (MR) than in a susceptible strain (MS). By using RNAi of BdGSTd9, the toxicity of malathion against MR was increased. Protein modelling and docking of BdGSTd9 with malathion and malaoxon indicated key amino acid residues for direct binding in the active site. In vitro assays with engineered Sf9 cells overexpressing BdGSTd9 demonstrated lower cytotoxicity of malathion. High performance liquid chromatography (HPLC) analysis indicated that malathion could be broken down significantly by BdGSTd9, and it also could deplete the malathion metabolite malaoxon, which possesses a higher toxicity to B. dorsalis. Taken together, the BdGSTd9 of B. dorsalis could not only deplete malathion, but also react with malaoxon and therefore enhance malathion resistance. BdGSTd9 is a component of malathion resistance in B. dorsalis. It acts by depleting both malathion and malaoxon.

The European red mite, Panonychus ulmi (Koch), is one of the major pests of apple trees worldwide. Cyclic keto-enol compounds such as spirodiclofen and spiromesifen are frequently used to control phytophagous spider mites in agricultural crops, including P. ulmi on apple trees. Spider mites, however, can rapidly develop resistance against acaricides and, in this study, multiple P. ulmi populations from apple orchards in Iran were monitored for spirodiclofen and spiromesifen resistance. The Urmia and Shahin Dej population showed the highest spirodiclofen resistance ratio (more than 150-fold) compared to the susceptible Ahar population. Toxicity bioassays also revealed the presence of moderate cross-resistance between spiromesifen and spirodiclofen, but not towards the chitin synthase inhibitor etoxazole. As a first step towards elucidating spirodiclofen resistance mechanisms, the role of detoxification enzymes (cytochrome P450 monooxygenases, carboxyl/choline esterases and glutathione S-transferases) was investigated by in vivo synergism and in vitro enzyme assays. PBO pretreatment synergized spirodiclofen toxicity in the populations of Urmia and Shahin Dej to a higher extent than in the susceptible Ahar population. Furthermore, enzyme activity measurements showed relatively higher activity of detoxifying enzymes in the resistant populations. In conclusion, increased detoxification is most likely underlying spirodiclofen resistance and results in limited cross-resistance to spiromesifen.

The sweet potato (cotton) whitefly Bemisia tabaci is a major agricultural pest in various fields and vegetable crops worldwide. It causes extensive damage by direct feeding on plants, reducing quality, secreting honeydew and transmitting plant viruses. B. tabaci is known for its genetic diversity and considered a complex of biotypes or, as suggested, a complex of distinct cryptic species. Management of whiteflies relies mainly on the use of insecticides; however, its ability to develop resistance to major insecticide classes creates a serious challenge to farmers and pest control specialists. Among the cryptic species of B. tabaci, MED is considered more resistant than the MEAM1 to insecticides such as pyriproxyfen and neonicotinoids; however, in recent years there are other species of B. tabaci including MEAM1, Asia I and Asia II-1 that have developed high resistance to various groups of insecticides. Advanced methods based on molecular and gene sequence data obtained from resistant and susceptible field-collected B. tabaci populations resulted in a better understanding of resistance mechanisms in this pest. Several components of IPM-IRM (Integrated Pest Management-Insecticide Resistance Management) programs such as selective and biorational insecticides, insecticide rotation with different modes of action and nonchemical control methods are among the countermeasures of insecticide resistance management for this pest. In the current review, we concentrate on insecticide resistance and resistance management of B. tabaci, focusing on reports published mainly over the past 10 years.

Laboratory studies were conducted during 2018-2019 in the Department of Agricultural Entomology, College of Horticulture, Vellanikkara, Kerala Agricultural University, Thrissur, to evaluate the susceptibility of different populations of Tribolium castaneum Malathion (Herbst) (Coleoptera: Tenebrionidae) collected from five FCI godowns of Kerala viz., Thikkodi, Olavakkode, Mulangunnathukavu, Angamaly and Valiyathura to malathion with respect to the laboratory maintained susceptible strain from IARI, New Delhi. Residual film bioassay was carried out using technical grade malathion. Angamaly population of T. castaneum showed 13.34 fold resistance with the highest LC50 value of 6949.80 ppm, while the IARI strain had the lowest LC50 of 520.76 ppm. Resistance ratios for Mulangunnathukavu, Valiyathura, Olavakkode and Thikkodi population were 11.82, 11.27, 10.99 and 10.95, respectively. Resistance to malathion in all field collected populations were uniform and homogenous.