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Abstract Background The primary method utilized by orchard owners to combat Cydia pomonella is the application of various chemical insecticides. However, this has resulted in the development of resistance. The resistance mechanisms to insecticides from different chemical classes are diverse but interconnected. Therefore, it is crucial to comprehend the commonalities in these mechanisms to effectively develop strategies for managing resistance. Materials and methods To determine whether target-site insensitivity to LCT and AM plays a role in resistance, the sequences of voltage-gated sodium channel (VGSC) and glutamate-gated chloride channel (GluCl) containing the mutation domains were detected. To validate whether similar mechanisms were involved in the detoxification process of lambda-cyhalothrin (LCT) and abamectin (AM) at sublethal doses (specifically LD10 and LD30), cytochrome P450 monooxygenases (P450), glutathione S-transferases (GST), and carboxylesterases (CarE) activities were evaluated after insecticides exposure; synergistic experiments were conducted using piperonyl butoxide (PBO), diethyl maleate (DEM), and triphenyl phosphate (TPP) as inhibitors of P450, GST, and CarE respectively. RNA-sequencing (RNA-Seq) was performed to compare the expression levels of detoxification-related genes between susceptible (SS) and resistant strains. Results The best known target-site mutations caused by LCT and AM, including L1014F in VGSC and V263I, A309V, I321T, and G326E in GluCl were not occurred. We observed that PBO had a strong synergistic effect on LCT and AM, while DEM on LCT. The activities of detoxification enzymes increased after insecticide exposures, indicating that the detoxification of LCT was primarily carried out by P450 and CarE enzymes, while P450 and GST enzymes played a major role in the detoxification of AM. A total of 72 P450 genes and 75 CarE genes were identified in the C. pomonella transcriptome, with 43 of these genes (including 11 P450, 3 GST, 10 CarE, 11 ABC transporters, and 8 UDP-glycosyl transferases) being over-expressed in response to both insecticides Interestingly, ABC transporters were predominantly induced by AM treatment, while GST showed higher induction levels with LCT treatment. Furthermore, LCT-resistant strains of C. pomonella exhibited higher levels of induction of detoxification-related genes compared to susceptible strains. Conclusion The up-regulation of these detoxification genes is a common metabolic mechanism employed by C. pomonella to counteract the effects of insecticides, although the extent of gene expression change varies depending on the specific insecticide.

The codling moth Cydia pomonella (Lepidoptera: Tortricidae) is a major invasive pest of pome fruits and walnuts worldwide. Lambda-cyhalothrin (LCT) and abamectin (AM) have been frequently used in C. pomonella control, but control of this pest is very difficult because shortly after hatching, larvae of this insect bore tunnels and hide inside host plant fruit. In this study, a simulated field spray bioassay method was developed against neonate larvae of C. pomonella and concentration-response bioassays were conducted to evaluate the susceptibility of the neonate larvae to LCT and AM. Exposure of neonate larvae to sublethal concentration (LC30) of LCT or AM significantly reduced the survival rate of larvae (4th and 5th instars), lowered the mean weight of larvae and pupae, and decreased the daily maximal number of eggs laid and the total number of eggs laid (fecundity) per female. The sublethal effects, including reduced body mass, mean fecundity and net reproductive rate, extended mean generation time, and shortened oviposition period, were also found in transgenerational offspring. Furthermore, the transgenerational maternal effects were more obvious for AM than LCT, in comparison to the control. Additionally, the estimated population size was decreased by exposure to LC30 of LCT and AM, and the observed reduction of fecundity and population size within and across generations was likely the result of the downregulation of the reproduction-related vitellogenin gene (CpVg) after exposure to LC30 of LCT and AM. These results provide a better understanding of the overall effects of LCT and AM on C. pomonella and the transgenerational effects which should be taken into consideration when using insecticides in order to control C. pomonella.

The codling moth Cydia pomonella L. (Lepidoptera: Tortricidae) is one of the most notorious pests of pome fruits and walnuts worldwide, which has developed resistance to almost all classes of insecticides, including abamectin (ABM). ATP-binding cassette (ABC) transporters are thought to play a vital roles in insecticide detoxification by reducing the toxic concentrations of insecticides in an organism tissues. Despite the tremendous progress in understanding the detoxification mechanisms at the molecular level, the physiological functions of ABC transporters in insects have been poorly investigated. In this study, we found that the ABC inhibitor verapamil synergized significantly the toxicity of ABM, suggesting a potential role of ABC in detoxification. A total of 54 ABC genes were identified in the third-instar larvae of C. pomonella after treatment with sublethal doses (LD10 and LD30) of ABM. The expression profile of these genes in ABM-treated larvae at different time points (24, 48, 72 hr) using transcriptomic analysis (RNA-seq) was also investigated. The results showed that the expression of about 30 ABC genes was significantly co-upregulated after treatment. Several specific genes were up-regulated at 48 hr after treatment of larvae with LD10 ABM. Among these up-regulated genes, we found that the relative expression level of the CPOM19553 was 29.7-fold and 16.0-fold higher when larvae were exposed to ABM at the LD10 and LD30 doses compared to control, respectively. Unlike other ABC genes, only CPOM08323 exhibited significant expression levels in the head and cuticle of the third-instar larvae of C. pomonella exposed to the two sublethal doses of ABM, with no expression was observed in the detoxification tissues such as midgut and Malpighian tubule. This study suggests that these up-regulated genes may be involved in ABM resistance in C. pomonella. Our findings will provide an additional information required for further analysis of ABC transporter genes associated with xenobiotic metabolism in C. pomonella.