Functional Characterization of Knockdown Resistance Mutation L1014S in the German Cockroach, Blattella germanica (Linnaeus)

Alanine to glycine substitution in the PyR2 confers sodium channel resistance to Type I pyrethroids

BACKGROUND

Aedes aegypti is a primary urban vector of dengue, yellow fever, Zika and chikungunya worldwide. Pyrethroid insecticides are the most effective insecticides for controlling Ae. aegypti. However, pyrethroid resistance has developed due to the long-term overuse of the insecticides, and many knockdown resistance (kdr) mutations have been identified in the resistant populations. A1007G, an alanine to glycine substitution, was found in resistant Ae. aegypti from Vietnam and Malaysia, which has always co-existed with F1534C and V1016G. However, the role of A1007G in pyrethroid resistance and the linkage of A1007G and F1534C or V1016G remain unknown.

RESULTS

In this study, we examined the effects of mutations on the sodium channel gating properties and pyrethroid sensitivity in Xenopus oocytes. We found mutations A1007G, A1007G + F1534C and A1007G + V1016G + F1534C shifted the voltage dependence of activation in the depolarizing direction. Mutations A1007G + F1534C and A1007G + V1016G + F1534C shifted the voltage dependence of inactivation in the depolarizing direction. Both mutations A1007G and F1534C reduced the channel sensitivity to two Type I pyrethroids, permethrin and bifenthrin, and synergistic effects were observed between mutations A1007G and F1534C. However, none of the mutations, A1007G, F1534C and A1007G + F1534C affected the channel sensitivity to two Type II pyrethroids, deltamethrin and cypermethrin. Furthermore, triple mutations A1007G + V1016G + F1534C significantly reduced the channel sensitivity to both Type I and Type II pyrethroids.

CONCLUSION

We identified A1007G had a distinct effect on sodium channel sensitivity to Type I, but not to Type II pyrethroids, also A1007G exhibited synergistic effects with F1534C to Type I pyrethroids, which will provide a fundamental insight into the distinct molecular interactions between insect sodium channel and Type I or Type II pyrethroids. © 2024 Society of Chemical Industry.

Role of mutation G255A in modulating pyrethroid sensitivity in insect sodium channels

A voltage-gated sodium channel (VGSC) plays a crucial role in insect electrical signals, and it is a target for various naturally occurring and synthesized neurotoxins, including pyrethroids and dichlorodiphenyltrichloroethane. The type of agent is typically widely used to prevent and control sanitary and agricultural pests. The perennial use of insecticides has caused mutations in VGSCs that have given rise to resistance in most insects. These mutations are located among the two pyrethroid receptors, i.e., PyR1 and PyR2, as predicted by previous studies. The two binding regions are relatively symmetrical, and here we focus on the linkers between S4 and S5 of Domains I and II. The S4-S5 linker can promote a rapid increase in sodium current and the onset of action potential. By predicting mutations in 19 other amino acids at all the amino acids on S4-S5 linkers, their harmfulness is analyzed, and whether they affect protein stability and drug binding is determined. Through molecular docking and based on docking scores, four mutations were predicted to affect the binding of sodium channels to pyrethroids. Mutations G255V, G255A, A906V, and A906T were introduced into the VGSC of Blattella germanica (BgNav1-1), and their effects on channel gating and pyrethroid sensitivity in Xenopus oocytes were studied. The treatment of VGSCs with two types of pyrethroids (1 nM), Types I (permethrin, bifenthrin) and II (deltamethrin, λ-cyhalothrin), produced tail currents. Among the four, mutant G255A exhibited a certain degree of increased sensitivity to the two types of pyrethroids. This finding was in contrast with the three other mutations, which demonstrated a certain degree of sensitization to one or two pyrethroids. We predicted and validated the critical mutation G255A on the insect VGSC Domain I S4-S5 linker using by electrophysiological technology. In generally, under the pressure of many insecticides, gene modifications, such as transcriptional changes and point mutations in the coding region make insects resistant to insecticides. This phenomenon leads to a higher detoxification rate of insecticides and makes the target site insensitive. However, we found that G255A mutation could promote the combination of pyrethroid and VGSCs by changing the binding force with insecticides. This finding has potential application value in reversing insect resistance. The discovery of mutation G255A exhibits considerable significance for the current use of gene editing and gene drive technology to control pests and delay their resistance development.

The hygienic insecticide dimefluthrin induced neurodevelopmental deficits and behavioral disorders in zebrafish (Danio rerio) larvae

Hygienic insecticides are applied directly to the living environment and are closely related to human life. Dimefluthrin (DIM) is one of the most widely used hygienic insecticides globally. However, with increasing mosquito resistance, both the concentration and duration of DIM usage have risen, prompting public concerns regarding its neurotoxic risks, especially for immunocompromised children. Therefore, this study evaluated DIM's neurotoxic risk from multiple perspectives using zebrafish larvae as a model, which was valuable for the future risk control of sanitary insecticides. The findings indicated that DIM induced neurodevelopmental damage, impaired neurotransmitter transmission, and led to changes in locomotor behavior. Observations using transgenic Tg (elavl3: eGFP) and Tg (flk: eGFP) zebrafish suggested DIM-induced impairments in olfactory bulb and peripheral nerve development, imaging of Tg (flk: eGFP) larvae displayed damage to the blood-brain barrier by DIM. Further exploration declared reduced activity of acetylcholinesterase (AChE) post-exposure, dysregulated mRNA expression levels of the syn2a. Behavioral monitoring results showed that DIM significantly suppressed larval swimming behavior, which were rescued by the dopamine receptor agonist Bromocriptine (BRO). In summary, this study proved that DIM had a health risk associated with neurotoxicity, which highlighted the need for further research on the safety of sanitary insecticides, particularly for children in neuro-sensitive period.

Molecular Detection of kdr and superkdr Mutation Sites and Analysis of the Binding Modes of Pyrethroid Insecticides with Voltage-Gated Sodium Channels in the Plant Bug Lygus pratensis (Hemiptera: Miridae)

This study identified genetic mutations linked to resistance to pyrethroid insecticides in the plant pest Lygus pratensis. The voltage-gated sodium channel (VGSC) gene was cloned, revealing two mutations (Met918Thr and Leu1014Phe) in laboratory strains and field populations from Inner Mongolia, resulting in variable pyrethroid resistance. A 3D model of LpVGSC was created using homology modeling, and pyrethroid binding patterns were analyzed via molecular docking. Molecular dynamics simulations confirmed structural stability changes and binding stability of pyrethroids to VGSC sites. Mutation frequencies of homozygous and heterozygous genotypes did not exceed 40 and 20%, respectively. Toxicity tests showed high resistance to λ-cyhalothrin (LC50:401.31 ng/cm2). The kdr (L1014F) and superkdr (M918T) mutations weakened interaction forces, reducing pyrethroid binding. M918T and L1014F mutations are predicted to reduce Type I pyrethroid affinity, suggesting Type II pyrethroids may be more effective against resistant strains. These findings aid in resistance management and insecticide design.

A tiny sample rapid visual detection technology for imidacloprid resistance in Aphis gossypii by CRISPR/Cas12a

Insecticide resistance monitoring is essential for guiding chemical pest control and resistance management policies. Currently, rapid and effective technology for monitoring the resistance of tiny insects in the field is absent. Aphis gossypii Glover is a typical tiny insect, and one of the most frequently reported insecticide-resistant pests. In this study, we established a novel CRISPR/Cas12a-based rapid visual detection approach for detecting the V62I and R81T mutations in the β1 subunit of the nAChR in A. gossypii, to reflect target-site resistance to imidacloprid. Based on the nAChR β1 subunit gene in A. gossypii, the V62I/R81T-specific RPA primers and crRNAs were designed, and the ratio of 10 μM/2 μM/10 μM for ssDNA/Cas12a/crRNA was selected as the optimal dosage for the CRISPR reaction, ensuring that Cas12a only accurately recognizes imidacloprid-resistance templates. Our data show that the field populations of resistant insects possessing V62I and R81T mutations to imidacloprid can be accurately identified within one hour using the RPA-CRISPR/Cas12a detection approach under visible blue light at 440-460 nm. The protocol for RPA-CRISPR detection necessitates a single less than 2 mm specimen of A. gossypii tissues to perform RPA-CRISPR detection, and the process only requires a container at 37 °C and a portable blue light at 440-460 nm. Our research represents the first application of RPA-CRISPR technology in insecticide resistance detection, offers a new method for the resistance monitoring of A. gossypii or other tiny insects, helps delay the development of resistance to imidacloprid, improves the sustainability of chemical control, and provides theoretical guidance for managing pest resistance.

Cardiotoxicity risk induced by sanitary insecticide Dimefluthrin

Dimefluthrin (DIM) is a commonly utilized sanitary insecticide, predominantly employed for indoor pest management within residential and public environments directly interacting with human habitation. However, the usage of DIM is escalating with increasing mosquito resistance, prompting concerns about its health risks. Here, using zebrafish as a research model, we systematically evaluated DIM's impact on human health. Findings revealed significant health hazards during embryonic development, including reduced hatching rates, shortened body lengths, and organ malformations, notably affecting the heart. It was explored the mechanism of DIM-induced cardiotoxicity in zebrafish, and histopathological analyses revealed that DIM resulted in ventricular linearization in zebrafish embryos. Antioxidant enzyme activities were reduced and cardiac reactive oxygen species (ROS) accumulated after DIM exposure, suggesting clear signs of oxidative stress. Additionally, acridine orange (AO) staining and caspase-3 immunofluorescence demonstrated cardiac apoptosis in Tg (kdrl: EGFP) zebrafish. qPCR analysis implied that DIM induced apoptosis via the p53/Caspase pathway by up-regulating the expression levels of p53, cytochrome C (cyto-C), caspase-9, and caspase-3. Together, our work provided a systematic perspective on the cardiotoxicity of sanitary pesticides, which could offer opportunities for future risk management.

Population genetics as a tool to understand invasion dynamics and insecticide resistance in indoor urban pest insects

Many indoor urban pest insects now show a near-global distribution. The reasons for this may be linked to their cryptic behaviors, which make unintentional transport likely, tied to their reliance on human-mediated dispersal that can result in spread over potentially long-distances. Additionally, numerous species exhibit an array of mechanisms that confer insecticide resistance. Using population genetics, it is possible to elucidate the genetic characteristics that define globally successful indoor urban pest insect species. Furthermore, this approach may be used to determine the frequency and distribution of insecticide resistance. Here, I review the recent literature that utilizes population genetic analyses in an effort to identify the characteristics that help explain the success of indoor urban pests.