Common substitution mutation F348Y of acetylcholinesterase gene contributes to organophosphate and carbamate resistance in Cimex lectularius and C. hemipterus

Identification of a Novel Inhibitor of Cimex lectularius Acetylcholinesterase

Acetylcholinesterase (AChE) stands as a primary target of commercial insecticides, notably organophosphates and carbamates. Despite their widespread use in agricultural and indoor pest control, concerns over their high toxicity and the emergence of resistance have restricted their efficacy. In this study, we conducted high-throughput virtual screening against both wild-type (WT) and resistant Cimex lectularius AChE utilizing a library encompassing 1 270 000 compounds. From this screening, we identified 100 candidate compounds and subsequently assessed their inhibitory effects on purified AChE enzymes. Among these candidates, AE027 emerged as a potent inhibitor against both WT and resistant AChE, exhibiting IC50 values of 10 and 43 μM, respectively. Moreover, the binding of AE027 significantly stabilized AChE, elevating its melting temperature by approximately 7 °C. Through molecular docking and molecular dynamics simulation, we delineated the binding mode of AE027, revealing its interaction with a site adjacent to the catalytic center, which is distinct from known inhibitors, with differing poses observed between WT and resistant AChE. Notably, the resistance mutation F348Y, positioned at a site directly interfacing with AE027, impedes ligand binding through steric hindrance. Furthermore, we evaluated the toxicity and pharmacokinetic properties of AE027 utilizing bioinformatics tools. These findings lay a crucial foundation for the development of a novel generation of insecticides that can combat both WT and resistant pest populations effectively and safely.

S431F mutation on AChE1 and overexpression of P450 genes confer high pirimicarb resistance in Sitobion miscanthi

Sitobion miscanthi is a destructive wheat pest responsible for significant wheat yield losses. Pirimicarb, one of the most important representatives of N, N-dimethylcarbamate insecticides, is widely used to control wheat aphids. In present work, heterozygous S431F mutation of acetylcholinesterase 1 (AChE1) was identified and verified in three pirimicarb-resistant S. miscanthi populations (two field populations (HA and HS, >955.8-fold) and one lab-selected population (PirR, 486.1-fold)), which has not been reported in S. miscanthi yet. The molecular docking results revealed that AChE1 containing the S431F mutation of S. miscanthi (SmAChE1S431F) showed higher free binding energy to three insecticides (pirimicarb, omethoate, and methomyl) than wild-type AChE1 of S. miscanthi (SmAChE1). Enzyme kinetic and inhibition experiments showed that the recombinant SmAChE1S431F was more insensitive to pirimicarb and omethoate than the recombinant SmAChE1. Furthermore, two overexpression P450 genes (CYP6K1 and CYP6A14) associated with pirimicarb resistance of S. miscanthi were verified by RNAi. These results suggested both target alteration and enhanced metabolism contributed to high pirimicarb resistance of S. miscanthi in the field and laboratory. These findings lay a foundation for further elucidating the mechanism of pirimicarb resistance in S. miscanthi, and have important implications for the resistance management of S. miscanthi control.

Bed Bug Infestation: An Updated Review

In the past decade, there has been a global resurgence of bed bug infestations, especially in developed countries. Proper awareness and identification of bed bug infestations are essential to guide treatment and eradication. The purpose of this article is to familiarize physicians with bed bug bites so that they can effectively diagnose, treat, and address questions about bed bug bites and infestations. Bed bug bites are often painless. Typical reactions include pruritic, erythematous maculopapules occurring in clusters or in a linear or curvilinear distribution in exposed areas of the body. A small red punctum may be visualized at the center of the bite mark. Lesions that appear three in a row and papules on the upper eyelid associated with erythema and edema are highly suggestive of bites from bed bugs. Exaggerated local reactions such as vesicles, urticarial wheals, urticarial perilesional plaques, diffuse urticaria, bullae, and nodules may occur in previously sensitized individuals. Reactions to bed bug bites are self-limited. As such, treatment is mainly symptomatic. Topical pramoxine and oral antihistamines can be used to alleviate pruritus. Topical corticosteroids can be used for significant eruptions to control inflammation and pruritus, and to hasten resolution of the lesions. Integrated pest management, an approach for the eradication of bed bugs, includes monitoring devices (active monitors include the use of heat or carbon dioxide attractants and passive monitors include the use of sticky pads for trapping), and judicious use of nonchemical and chemical treatments known to be effective. Nonchemical interventions include keeping affected areas clean and free of clutter, vacuuming, washing linens with hot water, caulking wall holes and cracks where bugs can hide, proper disposal of highly infested items, and placement of bed bug traps/interceptors at the base of beds and furniture. Chemical interventions involve the use of insecticides such as synthetic pyrethroids, silicates, insect growth disruptors, carbamates, organophosphates, neonicotinoids, diethyl-meta-toluamide, chlorfenapyr, fipronil and plant essential oils. Insecticides should be used with caution to prevent over-exposure and toxicity (in particular, cardiovascular and neurologic toxicity), especially if there are young children around. It is important to note that multiple mechanisms of insecticide resistance exist and as such, chemical treatment should only be undertaken by trained professionals who understand the current literature on resistance. Both nonchemical and chemical technologies should be combined for optimal results. Bed bug infestations may cause diverse dermal reactions, stigmatization, poor self-esteem, emotional stress, anxiety, significant adverse effect on quality of life, and substantial socioeconomic burden to society. As such, their rapid detection and eradication are of paramount importance. Consultation with a professional exterminator is recommended to fully eradicate an infestation.

A masked gene concealed hand in glove in the forkhead protein crocodile regulates the predominant detoxification CYP6DA1 in Aphis gossypii Glover

Cytochrome P450-mediated metabolism is an important mechanism of insecticide resistance, most studies show upregulated transcript levels of P450s in resistant insect strains. Our previous studies illustrated that some upregulated P450s were associated with cyantraniliprole resistance, and it is more comprehensive to use the tissue specificity of transcriptomes to compare resistant (CyR) and susceptible (SS) strains. In this study, the expression profiles of P450s in a CyR strain compared with a SS strain in remaining carcass or midgut were investigated by RNA sequencing, and candidate genes were selected for functional study. Drosophila melanogaster bioassays suggested that ectopic overexpression of CYP4CK1, CYP6CY5, CYP6CY9, CYP6CY19, CYP6CZ1 and CYP6DA1 in flies was sufficient to confer cyantraniliprole resistance, among which CYP6DA1 was the predominant contributor to resistance (12.24-fold). RNAi suppression of CYP4CK1, CYP6CY5, CYP6CY9 and CYP6DA1 significantly increased CyR aphid sensitivity to cyantraniliprole. The CYP6DA1 promoter had two predicted binding sites for crocodile (CROC), an intron-free ORF with bidirectional transcription yielding CROC (+) and CROC (-). Y1H, RNAi and EMSA found that CROC (-) was a transcription factor directly regulating CYP6DA1 expression. In conclusion, P450 genes contribute to cyantraniliprole resistance, and the transcription factor CROC (-) regulates the expression of CYP6DA1 in A. gossypii.

Development of Sustainable Insecticide Candidates for Protecting Pollinators: Insight into the Bioactivities, Selective Mechanism of Action and QSAR of Natural Coumarin Derivatives against Aphids

Plants employ abundant toxic secondary metabolites to withstand insect attack, while pollinators can tolerate some natural defensive compounds. Coumarins, as promising green alternatives to chemical insecticides, possess wide application prospects in the crop protection field. Herein, the bioactivities of 30 natural coumarin derivatives against Aphis gossypii were assessed and revealed that 6-methylcoumarin exhibited potent aphicidal activity against aphids but displayed no toxicity to honeybees. Additionally, using biochemical, bioinformatic, and molecular assays, we confirmed that the action mode of 6-methylcoumarin against aphids was by inhibiting acetylcholinesterase (AChE). Meanwhile, functional assays revealed that the difference in action site, which located in Lys585 in aphid AChE (equivalent to Val548 in honeybee AChE), was the principal reason for 6-methylcoumarin being toxic to aphids but safe to pollinators. This action site was further validated by mutagenesis data, which uncovered how 6-methylcoumarin was unique selective to the aphid over honeybee or mammalian AChE. Furthermore, a 2D-QSAR model was established, revealing that the central structural feature was H3m, which offers guidance for the future design of more potent coumarin compounds. This work provides a sustainable strategy to take advantage of coumarin analogues for pest management while protecting nontarget pollinators.

The first recent case of Cimex hemipterus (Hemiptera: Cimicidae) with super-kdr mutations in the Republic of Korea

With the increase in international travel and trade, in conjunction with the development of insecticide resistance, infestations of Cimex lectularius (L.) and Cimex hemipterus (F.) (Hemiptera: Cimicidae) have resurged globally in the last 2 decades. Recently, it was reported that C. hemipterus was also found in temperate regions, indicating the possibility of its expansion outside tropical regions. Cimex hemipterus has not been officially recorded in Korea since its initial description in 1934. Here, we report the first recent case of C. hemipterus in Korea based on morphological and molecular identification. Partial sequencing of the voltage-sensitive sodium channel gene revealed super-kdr mutations (M918I and L1014F) that are associated with pyrethroid resistance. This case report serves as a warning to intensify the bed bug surveillance system in Korea regarding the presence of C. hemipterus and to prepare effective alternative insecticides for pyrethroids.

Morphometrics of the Tropical Bed Bug (Hemiptera: Cimicidae) From Cape Coast, Ghana

Bed bugs, Cimex lectularius (L.) (Hemiptera: Cimicidae) and Cimex hemipterus (F.), have become established worldwide in recent years largely due to the development of insecticide resistance. However, limited attention has been given to ongoing morphological and macroevolutionary changes within the species and their populations, which could have implications for their control. Here, we evaluated whether bed bugs of the species C. hemipterus inhabiting different communities in Cape Coast, Ghana are undergoing segregation, which could lead to possible speciation. We also aimed to provide a morphometric description of all nymphal stages. Nine-bed bug populations of C. hemipterus were field-collected in Cape Coast and were subjected to geometric morphometric analysis. The multivariate parameters applied distinguished various populations from each of the locations, indicating the presence of morphologically distinct subpopulations of C. hemipterus. Shape-based segregation and shape changes associated with the insect pronotum (which is an important taxonomic character in the Cimicidae) were evident across the populations. Through this comparative study of C. hemipterus, we showed that possible subpopulations of this bed bug are being spread from Ghana. The nymphal stages (first-fifth) of C. hemipterus were distinguished by the length of the last three antennal segment and pronota width; such information contributes to the taxonomic knowledge of the species.

Associations between acetylcholinesterase-1 mutations and chlorpyrifos resistance in beet armyworm, Spodoptera exigua

Control of the beet armyworm, Spodoptera exigua depends heavily on chemical insecticides. Chlorpyrifos, an acetylcholinesterase (AChE) inhibitor, has been used in beet armyworm control for many years in China. Here we describe high level resistance to chlorpyrifos in a S. exigua strain, FX19-R, which was developed from a field-collected Chinese strain (FX) by selection with chlorpyrifos in the laboratory. FX19-R showed 1001-fold resistance to chlorpyrifos compared with the laboratory reference strain WH-S. The esterase inhibitor triphenyl phosphate (TPP) provided significant but small synergism (only 3.5-fold) for chlorpyrifos and neither of the glutathione s-transferase depletor diethyl maleate and the cytochrome P450s inhibitor piperonyl butoxide provided any detectable synergism, indicating that AChE insensitivity may play the major role in the resistance in FX19-R. Consistent with this, an amino acid substitution, F443Y (F331Y in standard Torpedo californica numbering) in AChE1 was identified in the FX19-R strain and shown to be tightly linked to chlorpyrifos resistance. Precisely homologous substitutions have been associated with organophosphate resistance in other pest species. A novel amino acid substitution, G311S (or G198S in standard numbering), was also identified in the reference strain WH-S. Recombinantly expressed AChE1 proteins carrying the G311S and F443Y substitutions were about 4.2-fold and 210-fold less sensitive to inhibition by chlorpyrifos oxon than wild-type AChE1, respectively. These results enhance our understanding of the mechanisms of chlorpyrifos resistance and provide a basis for resistance management based on monitoring the F443Y and G311S substitutions.

Multiple Mechanisms Conferring Broad-Spectrum Insecticide Resistance in the Tropical Bed Bug (Hemiptera: Cimicidae)

The modern resurgence of the common (Cimex lectularius L.) and tropical bed bugs (C. hemipterus [F.]) is thought to be primarily due to insecticide resistance. While there are many reports on insecticide resistance mechanisms in C. lectularius, such information in C. hemipterus is limited. We examined dichloro-diphenyl-trichloroethane (DDT), malathion, deltamethrin, permethrin, lambda-cyhalothrin resistance, and the underlying mechanisms in several C. hemipterus strains (Australia: Queensland [QLD-AU]; Malaysia: Kuala Lumpur [KL-MY], Tanjung Tokong [TT-MY], Christian [CH-MY], and Green Lane [GL-MY]). We used a surface contact method, synergism studies (utilizing piperonyl butoxide [PBO], S,S,S-tributyl phosphorotrithioate [DEF], and diethyl maleate [DEM]), and molecular detection of kdr mutations. Results demonstrated that all C. hemipterus strains possessed high resistance to DDT and the pyrethroids and moderate to high resistance to malathion. Synergism studies showed that deltamethrin resistance in all strains was significantly (P < 0.05) inhibited by PBO. In contrast, deltamethrin resistance was not affected in DEF or DEM. Similar findings were found with lambda-cyhalothrin resistance. Malathion resistance was significantly (P < 0.05) reduced by DEF in all strains. Resistance to DDT was not affected by DEM in all strains. Multiple kdr mutations (M918I, D953G, and L1014F) were detected by molecular analyses. TT-MY strain was found with individuals possessing three kdr mutation combinations; D953G + L1014F (homozygous susceptible: M918), M918I + D953G + L1014F (heterozygous resistant: I918), and M918I + D953G + L1014F (homozygous resistant: I918). Individuals with M918I + D953G + L1014F (homozygous resistant: I918) survived longer on deltamethrin (>12 h) than those (≤1 h) with other combinations. M918I + L1014F mutations most likely conferred super-kdr characteristic toward pyrethroids and DDT in C. hemipterus.