Insecticide resistance in mosquitoes: impact, mechanisms, and research directions

Synthesis of Benzo[h]quinoline derivatives and evaluation of their insecticidal activity against Culex pipiens L. larvae

A new series of pyrrolinone and hydrazone derivatives containing a benzo[h]quinoline core was synthesized and evaluated for their insecticidal activity against Culex pipiens larvae. The synthesis involved condensation of acid hydrazide, obtained from a 2(3H)-furanone, with a variety of carbonyl compounds leading to the desired candidates. The larvicidal bioassays of the prepared compounds revealed that several derivatives exhibited potent activity, with pyrrolinone 6 showing the highest efficacy (LC50 = 0.4 μg/mL), surpassing the reference insecticide chlorpyrifos. Molecular docking and molecular dynamics (MD) simulations supported these findings, showing strong and stable binding of the synthesized compounds, particularly compound 6, to key mosquito neuroreceptors such as acetylcholinesterase (AChE). The structure-activity relationship (SAR) analysis highlighted the impact of functional groups on insecticidal potency. Additionally, in silico pharmacokinetic predictions indicated favorable ADME profiles for several derivatives, emphasizing their potential as effective mosquito control agents. It is hoped that this study might provide insights into the design of new benzo[h]quinoline-based insecticides contributing to addressing the challenge of insecticide resistance in mosquito populations by forming structures that could target multiple neuroreceptors.

Comparative transcriptomics reveals different profiles between diflubenzuron-resistant and -susceptible phenotypes of the mosquito Culex pipiens

BACKGROUND

Chitin-synthesis inhibitors (CSIs) represent a major tool in vector control. The intensive use of these compounds has led to the evolution of resistance against several CSIs, including diflubenzuron (DFB). DFB resistance has been associated to a target-site mechanism; however, studies investigating the gene expression profile of resistant phenotypes are limited, preventing a full understanding of DFB resistance. Here, we analyzed the constitutive gene expression of susceptible and DFB-resistant individuals of the mosquito Culex pipiens, a major disease vector in temperate areas.

RESULTS

Comparative gene expression analysis between susceptible and DFB-resistant individuals identified 527 differentially expressed genes (i.e., 432 up-regulated and 95 down-regulated genes). Among the up-regulated genes, 87 genes belong to gene families associated with insecticide resistance in arthropods, such as cytochrome P450s, glutathione-S-transferases, UDP-glucuronosyltransferases, heat shock proteins and cuticular proteins (CPs). Interestingly, the CP transcripts were the most abundant among up-regulated genes (73 of 87), and furthermore they constitute 11 of the 20 most over expressed genes. The enrichment of transcripts associated with cuticle synthesis was also identified by the Gene Ontology (GO) enrichment analysis.

CONCLUSIONS

Adaptation to insecticides can involve transcriptional changes in genes encoding for multiple defense mechanisms. Our results identified the over-expression of transcripts associated with detoxification and cuticle synthesis in DFB-resistant individuals of Cx. pipiens. Multiple mechanisms, beyond the known target-site mechanism, may therefore contribute to the DFB-resistant phenotype. Together these findings corroborate the complexity underpinning the resistant phenotypes and provide important information for the implementation of effective control strategies against mosquito vectors. © 2025 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Assessing pyrethroid resistance mechanisms in individual Culex tarsalis (Diptera: Culicidae)

The evolution of pyrethroid insecticide resistance in Culex tarsalis Coquillett, a vector for West Nile and St. Louis encephalitis viruses, is a growing concern in Northern California. Common mechanisms of resistance include the target-site mutation, kdr, and increased levels of detoxification enzymes, such as mixed-function oxidases, GSTs, and esterases. The goal of this study was to compare the prevalence of kdr mutations (L1014F and L1014S) and detoxification enzymes between pyrethroid susceptible and resistant Cx. tarsalis individuals. Individual mosquitoes, categorized by resistance status from permethrin bottle bioassays, were prepared for both molecular and enzymatic testing by separating the legs of a mosquito from the remaining body. Legs were used to test for the presence of kdr mutations, while the bodies were used to test for the activity of detoxification enzymes. The number of phenylalanine (F) alleles present at the kdr target-site as well as levels of GST were increased in mosquitoes that survived the bottle bioassay compared to those that were knocked down. Individuals with 2 F alleles and an active GST level greater than or equal to 0.052 µg/ml showed a higher survival rate than either mechanism independently demonstrating resistance to pyrethroids in Cx. tarsalis is likely the result of multiple resistance mechanisms acting collectively. Further work is needed to determine the interplay of multiple resistance mechanisms to achieve phenotype resistance in this mosquito species.

Genome wide population genetics and molecular surveillance of insecticide resistance in Anopheles stephensi mosquitoes from Awash Sebat Kilo in Ethiopia

Since the detection of the Asian mosquito Anopheles stephensi in Dijbouti in 2012, it has spread throughout the Horn of Africa. This invasive vector continues to expand across the continent and is a significant threat to malaria control programs. Vector control methods, including insecticide-treated nets and indoor residual spraying, have substantially reduced the malaria burden. However, the increasing prevalence of mosquitoes resistant to insecticides, including An. stephensi populations, undermines ongoing malaria elimination efforts. Understanding population structure, gene flow between populations, and the distribution of insecticide resistance mutations is essential for guiding effective malaria control strategies. Here, we generated whole genome sequencing data for An. stephensi sourced from Awash Sebat Kilo, Ethiopia (n = 27) and compared with South Asian populations (n = 45; India and Pakistan) to assess genomic diversity, population structure, and uncovering insecticide resistance mutations. Population structure analysis using genome-wide single nucleotide polymorphisms (n = 15,533,476) revealed Ethiopian isolates clustering as a distinct ancestral group, separate from South Asian isolates. Three insecticide resistance-associated SNPs (gaba gene: A296S and V327I; vgsc L1014F) were detected. Evidence of ongoing selection was found in several loci, including genes previously associated with neonicotinoids, ivermectin, DDT, and pyrethroid resistance. This study represents the first whole genome population genetics study of invasive An. stephensi, revealing genomic differences from South Asian populations, which can be used for future assessments of vector population dispersal and detection of insecticide resistance mechanisms.

A progress report in advancements of heterocyclic compounds as novel antimalarial agents over the last 5 years

Malaria, caused by Plasmodium parasites and transmitted by Anopheles mosquitoes, remains a significant global health challenge, especially in tropical and subtropical regions where the disease is endemic. The complex Plasmodium lifecycle, involving stages in both the liver and bloodstream, leads to symptoms such as high fever, anemia, and, in severe cases, life-threatening complications, particularly P. falciparum infections. While historical treatments such as quinine and modern therapies such as artemisinin-based combination therapies (ACTs) have been effective, the growing issue of drug and insecticide resistance undermines these efforts. This resistance has spurred the need for new antimalarial drugs and strategies. Among the promising areas of research are heterocyclic compounds, which, due to their diverse and versatile chemical structures, are being investigated for their ability to disrupt the Plasmodium lifecycle. These compounds have potential as novel therapeutic agents that could enhance current treatment options. Understanding the mechanisms underlying drug resistance and advancing these therapeutic innovations are crucial for maintaining effective malaria control and treatment, highlighting the importance of on-going research in this field.

The synergism between metabolic and target-site resistance enhances the intensity of resistance to pyrethroids in Spodoptera exigua

The widespread application of insecticides imposes intense selective pressure on pest populations, driving the evolution of high-level resistance and leading to frequent control failures of pest. Insecticide resistance is primarily mediated through two primary mechanisms: target-site insensitivity and enhanced metabolic detoxification. However, the potential interactions and synergistic effects between these mechanisms remain largely unexplored. In this study, we demonstrate a striking cooperative interaction between these two major resistance mechanisms in a field-derived strain of Spodoptera exigua exhibiting extreme resistance (631-fold) to the pyrethroid insecticide lambda-cyhalothrin. Through genetic mapping and linkage analysis, we identified that this resistance phenotype is conferred by the combined effects of overexpression of the P450 CYP9A9 (two copies: CYP9A9a and CYP9A9b) and a target-site mutation (L1014F, kdr) in the voltage-gated sodium channel. Using an introgression approach, we generated two near-isogenic strains: WH-kdr, carrying only the target-site resistance allele (6.2-fold resistance), and WH-CYP9A, harboring only the metabolic resistance genes (79-fold resistance), both compared to the susceptible WH-S strain. CRISPR/Cas9-mediated knockout of both CYP9A9 copies in the QP19 strain dramatically reduced resistance from 631-fold to 19-fold, while transgenic expression of the CYP9A9a variant (containing three amino acid substitutions) from QP19 strain in Helicoverpa armigera conferred 39-fold resistance to lambda-cyhalothrin. These findings provide compelling evidence that target-site resistance can significantly potentiate metabolic resistance, resulting in substantially higher resistance levels than either mechanism alone in S. exigua. These findings enhance the understanding of higher level resistance mechanisms mediated by interactions between resistance genes and provide theoretical basis for devising management strategies of insecticide resistance.

Optimizing dsRNA sequences for RNAi in pest control and research with the dsRIP web platform

BACKGROUND

RNA interference (RNAi) is a tool for studying gene function and has emerged as a promising eco-friendly alternative to chemical pesticides. RNAi relies on delivering double-stranded RNA (dsRNA), which is processed into small interfering RNA (siRNA) to silence genes. However, so far, knowledge and tools for optimizing the dsRNA sequences for maximum efficacy are based on human data, which might not be optimal for insect pest control.

RESULTS

Here, we systematically tested different siRNA sequences in the red flour beetle Tribolium castaneum to identify sequence features that correlated with high efficacy using pest control as a study case. Thermodynamic asymmetry, the absence of secondary structures, and adenine at the 10th position in antisense siRNA were most predictive of insecticidal efficacy. Interestingly, we also found that, in contrast to results from human data, high, rather than low, GC content from the 9th to 14th nucleotides of antisense was associated with high efficacy. Consideration of these features for the design of insecticidal dsRNAs targeting essential genes in three insect species improved the efficacy of the treatment. The improvement was associated with a higher ratio of the antisense, rather than sense, siRNA strand bound to the RNA-induced silencing complex. Finally, we developed a web platform named dsRIP, which offers tools for optimizing dsRNA sequences, identifying effective target genes in pests, and minimizing risk to non-target species.

CONCLUSIONS

The identified sequence features and the dsRIP web platform allow optimizing dsRNA sequences for application of RNAi for pest control and research.

Simulating dynamic insecticide selection pressures for resistance management in mosquitoes assuming polygenic resistance

Insecticide resistance management (IRM) is critical to maintain the operational effectiveness of insecticides used in public health vector control. Evaluating IRM strategies rests primarily on computational models. Most models assume monogenic resistance, but polygenic resistance may be a more appropriate assumption. Conventionally, polygenic models assume selection differentials are constant over successive generations. We present a dynamic method for calculating the selection differentials accounting for the level of resistance and insecticide efficacy. This allows the inclusion of key parameters namely insecticide dosing, insecticide decay and cross resistance, increasing biological and operational realism. Two methods for calculating the insecticide selection differential were compared: truncation (only the most resistant individuals in the population survive) and probabilistic (individual survival depends on their level of resistance). The probabilistic calculation is extendable to multiple gonotrophic cycles, whereby mosquitoes may encounter different insecticides over their life span. A range of IRM strategies of direct policy relevance can be simulated, including the implication of reduced dose mixtures. We describe in detail the calculation and calibration of these models. We demonstrate the ability of the models to simulate a variety of IRM strategies and implications of including these features of the models. In simple IRM strategy evaluations, the truncation and probabilistic models give comparable results to each other and against published polygenic and monogenic models. Analysis of model simulations indicates there is often little difference between sequences or rotations of insecticides. Full-dose mixtures remain the best evaluated IRM strategy. Consistency between models increases confidence in their predictions especially when demonstrating model assumptions do not significantly impact key operational decisions. Using the multiple-gonotrophic cycle model we calculate the age distributions of mosquitoes which provides a framework to link resistance management with disease transmission. Future applications will investigate more scenario-specific evaluations of IRM strategies to inform public health policy.

Mechanisms and genetic mutations of pyrethroid resistance in Aedes albopictus in the context of urbanization: a case study of Hangzhou, China

Background

The Asian tiger mosquito (Aedes albopictus) serves as a globally significant vector for arboviruses such as dengue, chikungunya, and Zika. The extensive application of pyrethroid insecticides has led to a growing resistance in Ae. albopictus populations, thereby compromising mosquito control initiatives. This study examines the mechanisms underlying pyrethroid resistance and the related genetic mutations in Ae. albopictus within the framework of urbanization, with the objective of informing the development of effective control strategies.

Methods

Ae. albopictus larvae were sampled from five districts in Hangzhou, China, each characterized by different levels of urbanization. Resistance to beta-cypermethrin and permethrin were evaluated utilizing the World Health Organization (WHO) tube test methodology. Molecular analyses were conducted to identify mutations in the voltage-gated sodium channel (VGSC) gene, with a specific focus on the F1534S mutation. The data were subjected to statistical analysis using Fisher's exact test, chi-square test, and Pearson correlation to assess the relationship between resistance levels and urbanization.

Results

Populations of Ae. albopictus in Hangzhou demonstrated substantial resistance to pyrethroids, with mortality rates falling below 90%. Notably, the Binjiang District exhibited the lowest mortality rates, with 20.55% for beta-cypermethrin and 21.21% for permethrin, whereas Chun'an County displayed relatively higher mortality rates of 32.00% and 47.28%, respectively. The F1534S mutation was predominantly observed, with homozygous (S/S) mutations constituting 87.78% and 83.29% of the populations exposed to beta-cypermethrin and permethrin, respectively. Chi-square analyses confirmed a significant association between the F1534S mutation and resistance (P < 0.01). Furthermore, no significant correlation was identified between resistance levels and urbanization rates (P > 0.05), indicating that urbanization is not a primary factor contributing to resistance.

Conclusion

The F1534S mutation is pivotal in conferring pyrethroid resistance in Ae. albopictus. To enhance the effectiveness of mosquito control strategies, it is imperative to incorporate resistance monitoring, insecticide rotation, and non-chemical approaches. Additionally, further research is warranted to investigate alternative resistance mechanisms and the influence of urbanization on mosquito ecology.

Dietary L-3,4-dihydroxyphenylalanine (L-DOPA) augments cuticular melanization in Anopheles mosquitos while reducing their lifespan and malaria parasite burden

L-3,4-dihydroxyphenylalanine (L-DOPA), a naturally occurring tyrosine derivative, is prevalent in environments that include mosquito habitats, potentially serving as part of their diet. Given its role as a precursor for melanin synthesis we investigate the effect of dietary L-DOPA on mosquito physiology and immunity to Plasmodium falciparum and Cryptococcus neoformans infection. Dietary L-DOPA is incorporated into mosquito melanin via a non-canonical pathway and has a profound transcriptional effect associated with enhanced immunity, increased pigmentation, and reduced lifespan. Increased melanization results in an enhanced capacity to absorb electromagnetic radiation that affects mosquito temperatures. Bacteria in the mosquito microbiome act as sources of dopamine, a substrate for melanization. Our results illustrate how an environmentally abundant amino acid analogue can affect mosquito physiology and suggest its potential usefulness as an environmentally friendly vector control agent to reduce malaria transmission, warranting further research and field studies.

Exploiting Wolbachia as a Tool for Mosquito-Borne Disease Control: Pursuing Efficacy, Safety, and Sustainability

Despite the application of control measures, mosquito-borne diseases continue to pose a serious threat to human health. In this context, exploiting Wolbachia, a common symbiotic bacterium in insects, may offer effective solutions to suppress vectors or reduce their competence in transmitting several arboviruses. Many Wolbachia strains can induce conditional egg sterility, known as cytoplasmic incompatibility (CI), when infected males mate with females that do not harbor the same Wolbachia infection. Infected males can be mass-reared and then released to compete with wild males, reducing the likelihood of wild females encountering a fertile mate. Furthermore, certain Wolbachia strains can reduce the competence of mosquitoes to transmit several RNA viruses. Through CI, Wolbachia-infected individuals can spread within the population, leading to an increased frequency of mosquitoes with a reduced ability to transmit pathogens. Using artificial methods, Wolbachia can be horizontally transferred between species, allowing the establishment of various laboratory lines of mosquito vector species that, without any additional treatment, can produce sterilizing males or females with reduced vector competence, which can be used subsequently to replace wild populations. This manuscript reviews the current knowledge in this field, describing the different approaches and evaluating their efficacy, safety, and sustainability. Successes, challenges, and future perspectives are discussed in the context of the current spread of several arboviral diseases, the rise of insecticide resistance in mosquito populations, and the impact of climate change. In this context, we explore the necessity of coordinating efforts among all stakeholders to maximize disease control. We discuss how the involvement of diverse expertise-ranging from new biotechnologies to mechanistic modeling of eco-epidemiological interactions between hosts, vectors, Wolbachia, and pathogens-becomes increasingly crucial. This coordination is especially important in light of the added complexity introduced by Wolbachia and the ongoing challenges posed by global change.

Controlling Aedes mosquitoes using densovirus-based biolarvicides: Current status and prospects

Aedes albopictus and Aedes aegypti are the main vectors of emerging arboviruses, such as dengue, chikungunya and Zika viruses. Entomopathogenic viruses, such as densoviruses, might represent more environmentally friendly control methods. Densoviruses are single-stranded DNA viruses belonging to the Parvoviridae family and three species are known to infect mosquitoes: Protoambidensovirus dipteran, Brevihamaparvovirus dipteran 1, and Brevihamaparvovirus dipteran 2. Densoviruses belonging to the Brevihamaparvovirus dipteran 1 and Brevihamaparvovirus dipteran 2 species could be candidates for innovative vector control strategies to limit mosquito-borne diseases. The objective of this review was to analyse the current state of knowledge on mosquito-infecting densoviruses (updated classification/taxonomy, host range, distribution, ecology, co-infection effects, unanswered questions) in view of their use as a biocontrol tool against Aedes mosquitoes.

Friedericia Chica, a Medicinal Plant from the Amazon Region, is Repellent Against Aedes Aegypti: In Vivo and Molecular Docking Evidence

Fridericia chica is widely distributed in Brazil, where it is commonly known as crajiru or pariri in several regions. Despite its popular use for treating inflammations and as an insect repellent, there has been limited assessment of its chemical and biological properties, including its bioinsecticide activities. In this study, we conducted phytochemical analyses and investigated the larvicidal and repellent effects of F. chica against the mosquito Aedes aegypti. The F. chica (HEFc) hydroalcoholic extract was partitioned using column chromatography, and subfractions were analyzed using chromatographic and spectroscopic analyses (ESI-IT-MSn and NMR). In addition, HEFc was evaluated for its larvicidal and repellent activities. Phytochemical analyses revealed the presence of 17 constituents, including 2,4-dihydroxybenzoic and p-coumaric acids, along with umbelliferone, acetovanilone, myricetin-3-O-glucuronide, and cis-isorhapontigenin, which are reported for the first time in this species. Although no larvicidal effect was observed at the doses tested, the HEFc exhibited promising repellent effects against A. aegypti, which aligns with its ethnopharmacological potential. In addition, molecular docking studies demonstrated that the compounds of HEFc interacted efficiently with insect odorant binding proteins (OBPs), providing repellent effects. Consistent with the chemical profile and in silico studies, preparations of F. chica have considerable repellent potential.

Insecticide mixtures-uses, benefits and considerations

Insecticides remain an important tool for the control of many insect pests. There has long been an interest in insecticide mixtures (in-can and tank-mix) as a means to provide the needed efficacy and/or spectrum to control many insect public health, crop pests or crop pest complexes. This aspect has become more important since insecticides developed in the last 30 years tend to be narrower in spectrum with many primarily focused on either sap-feeding or chewing insect pests. Insecticide mixtures are also seen as an important approach to insect resistance management (IRM) with certain requirements for optimal implementation. Additionally, insecticide mixtures can also address certain agronomic, commercial and intellectual property needs and opportunities. This perspective will review some of the drivers and considerations for insecticide mixtures and their potential uses. © 2024 Society of Chemical Industry.

Integrative Analysis of Transcriptomics and Proteomics for Screening Genes and Regulatory Networks Associated with Lambda-Cyhalothrin Resistance in the Plant Bug Lygus pratensis Linnaeus (Hemiptera: Miridae)

The prolonged use of pyrethroid insecticides for controlling the plant bug Lygus pratensis has led to upward resistance. This study aims to elucidate the molecular mechanisms and potential regulatory pathways associated with lambda-cyhalothrin resistance in L. pratensis. In this study, we constructed a regulatory network by integrating transcriptome RNA-Seq and proteome iTRAQ sequencing analyses of one lambda-cyhalothrin-susceptible strain and two resistant strains, annotating key gene families associated with detoxification, identifying differentially expressed genes and proteins, screening for transcription factors involved in the regulation of detoxification metabolism, and examining the metabolic pathways involved in resistance. A total of 82,919 unigenes were generated following the assembly of transcriptome data. Of these, 24,859 unigenes received functional annotations, while 1064 differential proteins were functionally annotated, and 1499 transcription factors belonging to 64 distinct transcription factor families were identified. Notably, 66 transcription factors associated with the regulation of detoxification metabolism were classified within the zf-C2H2, Homeobox, THAP, MYB, bHLH, HTH, HMG, and bZIP families. Co-analysis revealed that the CYP6A13 gene was significantly up-regulated at both transcriptional and translational levels. The GO and KEGG enrichment analyses revealed that the co-up-regulated DEGs and DEPs were significantly enriched in pathways related to sphingolipid metabolism, Terpenoid backbone biosynthesis, ABC transporters, RNA transport, and peroxisome function, as well as other signaling pathways involved in detoxification metabolism. Conversely, the co-down-regulated DEGs and DEPs were primarily enriched in pathways associated with Oxidative phosphorylation, Fatty acid biosynthesis, Neuroactive ligand-receptor interactions, and other pathways pertinent to growth and development. The results revealed a series of physiological and biochemical adaptations exhibited by L. pratensis during the detoxification metabolism related to lambda-cyhalothrin resistance. This work provided a theoretical basis for further analysis of the molecular regulation mechanism underlying this resistance.

Widespread Distribution of chs-1 Mutations Associated with Resistance to Diflubenzuron Larvicide in Culex pipiens Across Italy, Reaching Virtual Fixation in the Venetian Lagoon

Control interventions against mosquito larvae are the primary measure to reduce the adult abundance and risk of arbovirus outbreaks in Europe. One of the most commonly used larvicides in Italy is diflubenzuron (DFB), which targets chitin synthase 1 (chs-1), interrupting the normal development of larvae into adults. Recent studies identified high levels of DFB resistance in Culex pipiens populations from Emilia-Romagna (Italy) associated with I1043L/M/F mutations at position 1043 of the chs-1 gene. The aim of the present study was to assess the circulation of 1043 resistance alleles in Cx. pipiens populations across Italy, outside Emilia-Romagna, with a focus on the Veneto region. Overall, 1032 specimens were genotyped. The 1043L allele was found in all examined Italian regions (Trentino-Alto Adige 19-36%; Veneto 0-91%; Piemonte 11%; Liguria 28%; Lazio 0-8%; Puglia 5%). The highest frequencies (up to >90%) were observed in the Venetian lagoon, where 1043M was also detected (6-11%). Overall, the relatively low frequencies of 1043 mutations despite extensive and longstanding use of DFB in Italy suggest a high fitness cost worthy of further investigations, while their extremely high frequencies in coastal touristic sites point to these sites as the most relevant for resistance monitoring and larvicide rotation.

Properties of "Stable" Mosquito Cytochrome P450 Enzymes

The use of insecticides is widespread in the control of debilitating mosquito-borne diseases. P450 enzymes (CYPs) play essential roles in mosquito physiological function but also in the enzymatic detoxification of xenobiotics. Broadly speaking, CYPs can be classified as "stable", meaning those that have no or very few paralogs, and "labile", constituting gene families with many paralogous members. The evolutionary dichotomy between "stable" and "labile" P450 genes is fuzzy and there is not a clear phylogenetic demarcation between P450s involved in detoxification and P450s involved in essential metabolic processes. In this study, bioinformatic methods were used to explore differences in the sequences of "stable" and "labile" P450s that may facilitate their functional classification. Genomic and sequence data of Anopheles gambiae (Agam), Aedes aegypti (Aaeg), and Culex quinquefasciatus (Cqui) CYPs were obtained from public databases. The results of this study show that "stable" CYPs are encoded by longer genes, have longer introns and more exons, and contain a higher proportion of hydrophobic amino acids than "labile" CYPs. Compared to "labile" CYPs, a significantly higher proportion of "stable" CYPs are associated with biosynthetic and developmental processes.

Distribution and frequency of genetic mutations in three insecticide targets in field populations of Culex tritaeniorhynchus in Mianyang City, Sichuan Province, China

Japanese encephalitis (JE) is an important mosquito borne infectious disease which is mainly transmitted by Culex tritaeniorhynchus Giles (1901) in China. At present, vector control remains an important means to prevent and control vector-borne diseases including JE. The development of insecticide resistance has seriously threatened the effectiveness of insecticide-based vector control programmes. Therefore, understanding insecticide resistance in the target pest is essential to inform evidence-based vector control. In Mianyang City of Sichuan Province of China, Cx. tritaeniorhynchus is the dominant mosquito species, and JE has been documented in this city. Unfortunately, there is little information on the status and underlying mechanisms of insecticide resistance in field populations of Cx. tritaeniorhynchus, the main JE vector in this region. In the study, a total of 314 adults of Cx. tritaeniorhynchus, collected from 6 sites across Mianyang City, were inspected for resistance-conferring mutations in three genes encoding voltage-gated sodium channel (VGSC), Gamma-aminobutyric acid (GABA) receptor Rdl subunit (Rdl), and acetylcholinesterase (AChE) by DNA Sanger sequencing. The results showed that the classical L1014F mutation in VGSC was distributed in all the 6 populations at varying frequencies from 16.98% to 27.78%, and the frequency of F455W mutation in AChE was extremely high (97.06%-100%). Notably, the conserved mutations A296S and V327I previously reported in the Rdl of some other species of mosquitoes were discovered in Cx. tritaeniorhynchus for the first time. The frequency of the resistant Rdl 296S allele was 62.04% to 94.00%, while the V327I mutation was present at a much lower frequency ranging from 0.93% to 1.8%. Overall, the prevalent co-existence of resistance-conferring mutations in multiple insecticide target proteins in Cx. tritaeniorhynchus populations in Mianyang City indicates a worrying status of insecticide resistance, and suggests that it is highly required to monitor the phenotypic resistance of Cx. tritaeniorhynchus on a regular basis.

Histone deacetylases synergistically regulate juvenile hormone signaling in the yellow fever mosquito, Aedes aegypti

Controlling Aedes aegypti mosquitoes is crucial for managing mosquito-transmitted diseases like dengue, zika, chikungunya, and yellow fever. One of the efficient methods to control mosquitoes is to block their progression from the larval to the adult stage. Juvenile hormones (JH) maintain the larval stage and ensure proper developmental timing for transitioning from larval-pupal-adult stages. Our previous studies showed that histone deacetylases (HDACs) regulate JH signaling and metamorphosis in the red flour beetle Tribolium castaneum. However, the role of HDACs in regulating JH signaling in Ae. aegypti mosquito is unknown. To investigate the role of HDACs in JH signaling, we knockdown each HDAC coding gene in Aag-2 cells derived from Ae. aegypti. Knockdown of HDAC1, HDAC4, and HDAC11 increased the expression of the JH primary response gene, Krüppel homolog 1 (Kr-h1), which represses the larval-pupal metamorphosis. Moreover, the simultaneous knockdown of these three HDACs synergistically increased the Kr-h1 promoter activity and its expression, mimicking JH action in inducing Kr-h1. Nevertheless, each HDAC regulates the transcription of different sets of genes, except for a few common genes involved in JH signaling. Furthermore, the knockdown of these HDACs in Ae. aegypti larvae caused different phenotypes apart from delayed pupation: HDAC1 knockdown caused larval growth retardation, body shrinkage, and eventual death; HDAC4 knockdown led to incomplete head capsule shedding after metamorphosis; and HDAC11 knockdown caused higher pupal mortality. Our data demonstrates functional overlap and distinct functions for HDAC1, HDAC4, and HDAC11 in modulating JH signaling, with each HDAC having a unique role in mosquito development.

Neglected impacts of plant protection products on invertebrate aquatic biodiversity: a focus on eco-evolutionary processes

The application of plant protection products (PPPs) may have delayed and long-term non-intentional impacts on aquatic invertebrates inhabiting agricultural landscapes. Such effects may induce population responses based on developmental and transgenerational plasticity, selection of genetic resistance, as well as increased extirpation risks associated with random genetic drift. While the current knowledge on such effects of PPPs is still scarce in non-target aquatic invertebrate species, evidences are accumulating that support the need for consideration of evolutionary components of the population response to PPPs in standard procedures of risk assessment. This mini-review, as part of a contribution to the collective scientific assessment on PPP impacts on biodiversity and ecosystem services performed in the period 2020-2022, presents a brief survey of the current results published on the subject, mainly in freshwater crustaceans, and proposes some research avenues and strategies that we feel relevant to fill this gap.

Trends in insecticide resistance in natural populations of Culex quinquefasciatus and its impact on mosquito fitness in Dschang, West Cameroon

Specific information about the dispersion of Culex quinquefasciatus from Dschang in western Cameroon is scarce, and evidence-based interventions are needed. Common use of larvicides and adulticides conduct to the development of vectors resistance which can lead to deep biological changes, including fitness costs. We assessed the profile of insecticide resistance in field populations of Cx. quiquefasciatus and its potential fitness cost in a lineage selected for deltamethrin and permethrin resistance in the laboratory for two generations. The resistance intensity of the Cx. quinquefasciatus population was moderated when the population was exposed to deltamethrin at 10 × . Preexposure to PBO led to the restoration of full susceptibility to both deltamethrin and permethrin. Compared with that of the control group, female fecundity rates, egg hatchability, and pupation rates were significantly lower in the insecticide exposed groups. Larval development time and adults emergence rates were comparable between insecticide-exposed groups and the control. Insecticide-exposed adults lived longer than control adults did. Our findings suggest that the mechanisms selected for pyrethroid resistance are associated with negative impacts on different life-trait parameters and support the hypothesis that insecticide resistance is related to a high fitness cost.

The southern house mosquito Culex quinquefasciatus in Abu Dhabi, UAE, is developing resistance to deltamethrin insecticide

Culex quinquefasciatus is a widely spread mosquito species that poses a significant public health threat in many countries. This insect vector is present in the United Arab Emirates (UAE), yet no studies have been conducted on its resistance to any insecticide group. Research shows that controlling mosquitoes is crucial to eliminating mosquito-borne diseases, but when these vectors develop insecticide resistance, the situation can escalate dangerously out of control. This study aimed to identify a knockdown resistance (kdr) mutation L1014F using molecular tools. Additionally, it aimed to assess deltamethrin resistance using the Centers for Disease Control and Prevention (CDC) bottle bioassay. We screened Cx. quinquefasciatus adults (N = 174) for the presence of the mutation using allele-specific PCR (AS-PCR) and DNA sequencing. We detected the mutation and found the kdr allele in all the sampled locations. Furthermore, the CDC bottle bioassay revealed deltamethrin resistance from only one sampling location. To our knowledge, this is the first report of insecticide resistance in Cx. quinquefasciatus in the UAE. Our findings show the need for continued insecticide resistance monitoring for effective mosquito control in the UAE.

Endosymbionts as hidden players in tripartite pathosystem of interactions and potential candidates for sustainable viral disease management

The convoluted relationships between plants, viruses, and arthropod vectors housing bacterial endosymbionts are pivotal in the spread of harmful plant viral diseases. Endosymbionts play key roles in: manipulating host responses, influencing insect resistance to pesticides, shaping insect evolution, and bolstering virus acquisition, retention, and transmission. This interplay presents an innovative approach for developing sustainable strategies to manage plant diseases. Recent progress in targeting specific endosymbionts through genetic modifications, biotechnological advancements, and RNA interference shows potential for curbing viral spread and disease progression. Additionally, employing synthetic biology techniques like CRISPR/Cas9 to engineer endosymbionts and disrupt crucial interactions necessary for viral transmission in arthropod vectors holds promise for effective control measures. In this review, these obligate and facultative bacterial cruxes have been discussed to elaborate on their mechanistic involvement in the regulation and/or inhibition of tripartite pathways of interactions. Furthermore, we provide an in-depth understanding of endosymbionts' synergistic and antagonistic effects on: insect biology, plant immunity, and virus acquisition and transmission. Finally, we point out open questions for future research and provide research directions concerning the deployment of genetically engineered symbionts to affect plant-virus-vector interactions for sustainable disease management. By addressing existing knowledge gaps and charting future research paths, a deeper comprehension of the role of endosymbionts in plant-virus-vector interactions can pave the way for innovative and successful disease management strategies. The exploration of antiviral therapies, paratransgenesis, and pathogen-blocking tactics using engineered endosymbionts introduces pioneering solutions for lessening the impact of plant viral diseases and green pest management.

Transcriptome Analysis of Culex pipiens quinquefasciatus Larvae Exposed to a Semi-Lethal Dose of Vermistatin

Culex pipiens quinquefasciatus is a notorious vector transmitting severe diseases such as Zika virus and West Nile virus to humans worldwide. Vermistatin is a type of funicon-like compound and was first isolated from Penicillin vermiculatum in the 1970s. Vermistatin has shown promising activity against Cx. p. quinquefasciatus larvae in our previous research. Here, we conducted a transcriptomic analysis of Cx. p. quinquefasciatus larvae treated with a median lethal concentration of 28.13 mg/L vermistatin. Differential expression analysis identified 1055 vermistatin-responsive genes, with 477 downregulated and 578 upregulated. Gene Ontology annotation and enrichment analysis revealed the metabolic process to be the most significantly affected biological process, the membrane to be the most significantly affected cellular component, and catalytic activity to be the most significantly affected molecular function. Kyoto Encyclopedia of Genes and Genomes pathway analysis classified the differential expression genes into six major categories, with metabolism and organismal systems being the most enriched. Fifty-five pathways were significantly enriched, with the hematopoietic cell lineage, renin-angiotensin system, cholesterol metabolism, and peroxisome proliferator-activated receptor signaling pathways among the top altered pathways. Furthermore, 32 potential detoxification-related genes were differentially expressed, with 3 cytochrome P450s, 2 ABC transporters, and 1 UGT induced by vermistatin. This study provides insights into the molecular mechanisms of vermistatin's action against Cx. p. quinquefasciatus larvae, highlighting potential targets for novel mosquito control strategies.

Consequences of insecticide overuse in Hungary: assessment of pyrethroid resistance in Culex pipiens and Aedes albopictus mosquitoes

BACKGROUND

Mosquitoes, as vectors of various pathogens, have been a public health risk for centuries. Human activities such as international travel and trade, along with climate change, have facilitated the spread of invasive mosquitoes and novel pathogens across Europe, increasing the risk of mosquito-borne disease introduction and their spread. Despite this threat, mosquito control in Hungary still relies predominantly on chemical treatments, which poses the risk of developing insecticide resistance in local populations. While pyrethroid resistance has been documented in several countries, there is no information on this issue from Hungary. This study aims to investigate the presence of resistance in Hungarian mosquito populations by analyzing a native, already known disease vector and a recently established invasive species with public health significance.

METHODS

We assessed the presence of knockdown resistance (kdr) mutations L1014F in Culex pipiens and V1016G and F1534C in Aedes albopictus mosquitoes, which are responsible for pyrethroid resistance. Mosquito specimens were investigated retrospectively, collected from previous years within the framework of local monitoring programs run in urban areas representing five regions of Hungary. The mutations in mosquitoes were detected individually by allele-specific polymerase chain reaction (PCR) and gel electrophoresis, following generally used protocols.

RESULTS

In Cx. pipiens, the kdr mutation was detected across all five collection sites, with resistance allele frequencies ranging from 18.1% to 36.3%. Resistance alleles were identified in homozygosity and heterozygosity with the susceptible allele, resulting in 53% of the investigated mosquitoes showing resistance to pyrethroids in the Hungarian populations. In contrast, for Ae. albopictus, the analyzed individuals were found to carry only the susceptible alleles, indicating a homozygous susceptible genotype across the investigated populations on the basis of V1016G and F1534C genes.

CONCLUSIONS

Our work highlights the consequences of the unilateral and long-term use of chemical treatments on mosquitoes. This indicates an urgent need for a change of concept in mosquito control strategy in Hungary, as well as in countries where mosquito control still relies dominantly on insecticides. The restricted use of chemical treatment is highly recommended to prevent the development of pyrethroid resistance in recently established populations of the invasive Ae. albopictus, and to decrease the public health risk of vector-borne diseases.

Seasonal fluctuation of insecticide resistance mutation frequencies in field populations of Anopheles and Culex species in Korea

Members of the Anopheles Hyrcanus Group, Culex pipiens complex, and Culex tritaeniorhynchus are prevalent vector species in the Republic of Korea (ROK), transmitting Plasmodium vivax and various arboviruses. Extensive use of insecticides to control these mosquitoes has led to insecticide resistance. In this study, we monitored 3 target site mutations associated with insecticide resistance (kdr for pyrethroid resistance, ace1 for organophosphate resistance, and rdl for phenylpyrazole resistance) in these mosquito groups over four consecutive years to understand the seasonal dynamics of resistance in different areas with distinct ecological characteristics. In the Anopheles Hyrcanus Group, the frequencies of kdr and ace1 mutations exhibited seasonal fluctuations in an urban-rural complex area (Humphreys US Army Garrison) (hereafter Humphreys), suggesting an overwintering fitness cost, whereas the rdl mutation frequencies remained constant at nearly saturated levels. These patterns were less clear in rural areas (the demilitarized zone separating Korea), indicating area-specific profiles related to different insecticide usage patterns. The kdr and rdl mutation frequencies associated with the Cx. pipiens complex were relatively constant, but varied by the collection area, with higher rdl frequency in Humphreys and higher kdr frequency in Yongsan, a metropolitan area, suggesting different selection pressures. Overall resistance mutation frequencies were highest in Cx. tritaeniorhynchus, with ace1 and rdl mutations being seasonally saturated, while the kdr mutation frequency varied over time. Our findings demonstrate species- or group-specific seasonal and regional dynamic patterns of insecticide resistance, presenting the need for targeted control strategies and further improving the management of mosquito-borne diseases in the ROK.

The Anthropocene and the biodiversity crisis: an eco-evolutionary perspective

A major facet of the Anthropocene is global change, such as climate change, caused by human activities, which drastically affect biodiversity with all-scale declines and homogenization of biotas. This crisis does not only affect the ecological dynamics of biodiversity, but also its evolutionary dynamics, including genetic diversity, an aspect that is generally neglected. My tenet is therefore to consider biodiversity dynamics from an eco-evolutionary perspective, i.e. explicitly accounting for the possibility of rapid evolution and its feedback on ecological processes and the environment. I represent the impact of the various avatars of global change in a temporal perspective, from pre-industrial time to the near future, allowing to visualize their dynamics and to set desired values that should not be trespassed for a given time (e.g., +2 °C for 50 years from now). After presenting the impact of various stressors (e.g., climate change) on biodiversity, this representation is used to heuristically show the relevance of an eco-evolutionary perspective: (i) to analyze how biodiversity will respond to the stressors, for example by seeking out more suitable conditions or adapting to new conditions; (ii) to serve in predictive exercises to envision future dynamics (decades to centuries) under stressor impact; (iii) to propose nature-based solutions to the crisis. Significant obstacles stand in the way of the development of such an approach, in particular the general lack of interest in intraspecific diversity, and perhaps more generally a lack of understanding that, we, humans, are only a modest part of biodiversity.

Human migrations, anthropogenic changes, and insect-borne diseases in Latin America

Rapid urbanization and migration in Latin America have intensified exposure to insect-borne diseases. Malaria, Chagas disease, yellow fever, and leishmaniasis have historically afflicted the region, while dengue, chikungunya, and Zika have been described and expanded more recently. The increased presence of synanthropic vector species and spread into previously unaffected areas due to urbanization and climate warming have intensified pathogen transmission risks. This review examines recent outbreaks and reemergence of insect-borne diseases through five case studies: (i) malaria transmission linked to political instability and large-scale migration through the Amazon jungle; (ii) the expansion of triatomine bug habitats into overcrowded, substandard urban settlements, increasing Chagas disease incidence; (iii) the influence of movement and ecotourism in the Amazonia on yellow fever transmission in peri-urban areas; (iv) the spread of visceral leishmaniasis driven by deforestation and human-canine movement; and (v) dengue outbreaks in rural Amazon regions, spurred by urbanization and rural development. The findings underscore the complex interactions among vectors, pathogens, and shifting environmental and social conditions, complicating predictability and control. Addressing the social, economic, and political determinants of health is crucial to reducing disease transmission. Key measures include scaling vaccine coverage, especially for dengue and yellow fever; developing vaccines and treatments for neglected diseases; improving housing and sanitation; strengthening vector surveillance and control; fostering community engagement; enhancing data-driven interventions.

Recombinant venom proteins in insect seminal fluid reduce female lifespan

The emergence of insecticide resistance has increased the need for alternative pest management tools. Numerous genetic biocontrol approaches, which involve the release of genetically modified organisms to control pest populations, are in various stages of development to provide highly targeted pest control. However, all current mating-based genetic biocontrol technologies function by releasing engineered males which skew sex-ratios or reduce offspring viability in subsequent generations which leaves mated females to continue to cause harm (e.g. transmit disease). Here, we demonstrate intragenerational genetic biocontrol, wherein mating with engineered males reduces female lifespan. The toxic male technique (TMT) involves the heterologous expression of insecticidal proteins within the male reproductive tract that are transferred to females via mating. In this study, we demonstrate TMT in Drosophila melanogaster males, which reduce the median lifespan of mated females by 37 - 64% compared to controls mated to wild type males. Agent-based models of Aedes aegypti predict that TMT could reduce rates of blood feeding by a further 40 - 60% during release periods compared to leading biocontrol technologies like fsRIDL. TMT is a promising approach for combatting outbreaks of disease vectors and agricultural pests.

Self-assembled co-delivery nanoplatform for increasing the broad-spectrum susceptibility of fall armyworm toward insecticides

INTRODUCTION

Unscientific application of insecticides has led to severe resistance of pests to almost all classes of insecticides. Enhanced detoxification is the most common mechanism for this kind of resistance.

OBJECT

Fall armyworm (FAW) has developed insecticide resistance, which is often linked to the overexpression of detoxification genes. Herein, a multicomponent nano-pesticide is designed to increase its broad-spectrum susceptibility toward insecticides.

METHOD

Regulatory function of nuclear factor erythroid 2-related factor 2 (Nrf2) in detoxification was confirmed using transcriptome sequencing, quantitative real-time PCR and enzyme activity measurement. A star polycation (SPc) was adopted to construct the pesticide/SPc/complex, whose self-assembly mechanism and characterization were examined using isothermal titration calorimetry, dynamic light scattering and transmission electron microscope. The delivery efficiency of SPc-loaded dsRNA was examined in vitro and in vivo using fluorescent tracer technique. A multicomponent nano-pesticide was created through the integration of bacterial expression system and nano-delivery system, and its bioactivity was tested in laboratory and field.

RESULTS

We confirmed the crucial role of Nrf2 in regulating the detoxification in FAW, and silencing Nrf2 could decrease detoxification gene expression and increase insecticide susceptibility. We then applied the SPc to self-assemble a nanoplatform for delivering Nrf2 double-stranded RNA (dsRNA) and pesticide simultaneously. Nano-sized pesticide/SPc/dsRNA complex exhibited high delivery efficiency in vitro and in vivo. Excitingly, the insecticidal activities of pesticide/SPc/dsNrf2 complexes were remarkably improved with the normalized synergistic ratios of 5.43-6.25 for chlorantraniliprole, 4.45-15.00 for emamectin benzoate, and 6.75-15.00 for spinetoram. Finally, we developed a multicomponent nano-pesticide (pesticide/SPc/dsNrf2 complex) using a bacterial expression system and nano-delivery system. This approach exhibited excellent leaf protection and pest control efficacy.

CONCLUSION

The integration between the pesticide nanometerization and insecticide susceptibility improvement offers a promising strategy to increase insecticidal activity. Our study provides a revolutionary and universal strategy to increase insecticidal activity and decease application doses.

Esterase-Mediated Pyrethroid Resistance in Populations of an Invasive Malaria Vector Anopheles stephensi from Ethiopia

BACKGROUND

The swift expansion of the invasive malaria vector Anopheles stephensi throughout Africa presents a major challenge to malaria control initiatives. Unlike the native African vectors, An. stephensi thrives in urban settings and has developed resistance to multiple classes of insecticides, including pyrethroids, organophosphates, and carbamates.

METHODS

Insecticide susceptibility tests were performed on field-collected An. stephensi mosquitoes from Awash Sebac Kilo, Ethiopia, to assess insecticide resistance levels. Illumina RNA-seq analysis was then employed to compare the transcriptomes of field-resistant populations and susceptible laboratory strains (STE2).

RESULTS

An. stephensi populations exhibited high levels of resistance to both deltamethrin (mortality, 39.4 ± 6.0%) and permethrin (mortality, 59.3 ± 26.3%) in WHO tube bioassays. RNA-seq analysis revealed that both field-resistant and field-unexposed populations exhibited increased expressions of genes associated with pyrethroid resistance, including esterases, P450s, and GSTs, compared to the susceptible STE2 strain. Notably, esterase E4 and venom carboxylesterase-6 were significantly overexpressed, up to 70-fold, compared to the laboratory strain. Functional enrichment analysis revealed a significant overrepresentation of genes associated with catalytic activity under molecular functions and metabolic process under biological process. Using weighted gene co-expression network analysis (WGCNA), we identified two co-expression modules (green and blue) that included 48 genes strongly linked to pyrethroid insecticide resistance. A co-expression network was subsequently built based on the weight values within these modules.

CONCLUSIONS

This study highlights the role of esterases in the pyrethroid resistance of an An. stephensi population. The identification of candidate genes associated with insecticide resistance will facilitate the development of rapid diagnostic tools to monitor resistance trends.

Chromobacterium biopesticide overcomes insecticide resistance in malaria vector mosquitoes

Vector mosquito control is an integral part of malaria control. The global emergence of insecticide resistance in malaria-transmitting Anophelines has become an impediment and has created an urgent need for novel mosquito control approaches. Here, we show that a biopesticide derived from the soil-dwelling bacterium Chromobacterium sp. Panama (Csp_P) kills insecticide-resistant Anopheles mosquitoes, regardless of their resistance mechanisms. In addition, sublethal dose of Csp_P acts as a synergist to now used chemical insecticides across multiple classes. Moreover, Csp_P reduces host-seeking behavior and malaria parasite infection in vector mosquitoes in ways that further decrease transmission. Mosquito glutathione S-transferases are essential for Csp_P's mosquito-killing mechanism. Enclosed field trials in Burkina Faso, conducted in diverse ecological settings and supported by a mathematical model, have now demonstrated its potential for malaria control in settings with widespread insecticide resistance.

Field-evolved resistance to neonicotinoids in the mosquito, Anopheles gambiae, is associated with mutations of nicotinic acetylcholine receptor subunits combined with cytochrome P450-mediated detoxification

New insecticides prequalified for malaria control interventions include modulators of nicotinic acetylcholine receptors that act selectively on different subunits leading to variable sensitivity among arthropods. This study aimed to investigate the molecular mechanisms underlying contrasting susceptibility to neonicotinoids observed in wild populations of two mosquito sibling species. Bioassays and a synergist test with piperonyl butoxide revealed that the sister taxa, Anopheles gambiae and An. coluzzii, from Yaounde, Cameroon, both have the potential to develop resistance to acetamiprid through cytochrome P450-mediated detoxification. However, contrary to An. coluzzii, An. gambiae populations are evolving cross-resistance to several active ingredients facilitated by mutations of nicotinic acetylcholine receptors (nAChRs). We sequenced coding regions on the β1 and α6 nAChR subunits where variants associated with resistance to neonicotinoids or to spinosyns have been found in agricultural pests and detected no mutation in An. coluzzii. By contrast, six nucleotide substitutions including an amino acid change in one of the loops that modulate ligand binding and affect sensitivity were present in the resistant species, An. gambiae. Allele frequency distributions were consistent with the spread of beneficial mutations that likely reduce the affinity of An. gambiae nAChRs for synthetic modulators. Our findings provide critical information for the application and resistance management of nAChR modulators in malaria prevention.

Two critical detoxification enzyme genes, NlCYP301B1 and NlGSTm2 confer pymetrozine resistance in the brown planthopper (BPH), Nilaparvata lugens Stål

The brown planthopper (BPH), Nilaparvata lugens Stål, is a notorious pest that infests rice across Asia. The rapid evolution of chemical pesticide resistance in BPH poses an ongoing threat to agriculture and human health. Currently, pymetrozine has emerged as a viable alternative to imidacloprid for managing N. lugens. The detoxification of insecticides in insects includes three major metabolic gene families: cytochrome P450 monooxygenases (P450s), glutathione S-transferases (GSTs), and carboxylesterases (CarEs). In this study, highly resistant strains of BPH to pymetrozine (BPH-R40: 705-fold) were created from the susceptible BPH strain through continuous multi-selection. The activities of detoxifying enzymes, including P450s, GSTs, and CarEs were measured. Notably, P450s and GSTs exhibited significantly higher activity in the pymetrozine-resistance strain than that of the susceptible BPH strain. Hence, we characterized P450s and GSTs genes in N. lugens and revealed their phylogeny, structure, motif analysis, and chromosome location. Subsequently, the expression profiles of 53 P450s and 11 GSTs genes were quantified, and two crucial detoxifying enzyme genes, NlCYP301B1 and NlGSTm2, were identified as being involved in pymetrozine resistance. Furthermore, RNA interference (RNAi)-mediated silencing of NlCYP301B1 and NlGSTm2 gene expression significantly increased larval mortality of BPH in response to pymetrozine. To our knowledge, enhancing the activity of key detoxification enzymes to resist insecticides represents a widespread and vital defense mechanism in insects.

Integrating pyriproxyfen into the incompatible insect technique enhances mosquito population suppression efficiency and eliminates the risk of population replacement

BACKGROUND

The incompatible insect technique (IIT) has been used for Aedes mosquito population suppression to curb the transmission of dengue. However, its wide application is limited owing to the low output of male mosquitoes and the risk of population replacement from the release of fertile Wolbachia-infected females. This study aims to improve IIT efficiency for broader adoption.

RESULTS

We assessed the impact of 10% pyriproxyfen (PPF) sticky powder exposure on Wolbachia (from Culex molestus)-transinfected Aedes albopictus Guangzhou line (GUA line) (GC) mosquitoes. We found that the exposure caused chronic toxicity in adult mosquitoes without affecting the cytoplasmic incompatibility (CI)-inducing capability of males. The PPF-contaminated GC females exhibited significant sterilization and the ability to disseminate lethal doses of PPF to breeding sites. Subsequently, we conducted a field trial combining PPF with IIT aiming to suppress the Ae. albopictus population. This combined approach, termed boosted IIT (BIIT), showed a notable enhancement in population suppression efficiency. The improved efficacy of BIIT was attributed to the dispersion of PPF particles in the field via the released PPF-contaminated male mosquitoes. During the BIIT field trial, no Wolbachia wPip-positive Ae. albopictus larvae were detected, indicating the effective elimination of the risk of Wolbachia-induced population replacement. Additionally, the field trial of BIIT against Ae. albopictus resulted in the suppression of the nontarget mosquito species Culex quinquefasciatus.

CONCLUSION

Our results highlight the remarkable efficiency and feasibility of combining IIT with PPF in suppressing mosquito populations, facilitating the widespread implementation of IIT-based management of mosquito-borne diseases. © 2024 Society of Chemical Industry.

Identification and functional validation of P450 genes associated with pyrethroid resistance in the malaria vector Anopheles sinensis (Diptera Culicidae)

Cytochrome P450 monooxygenases (P450s), a multifunctional protein superfamily, are one of three major classes of detoxification enzymes. However, the diversity and functions of P450 genes from pyrethroid-resistant populations of Anopheles sinensis have not been fully explored. In this study, P450 genes associated with pyrethroid resistance were systematically screened using RNA-seq in three field pyrethroid-resistant populations (AH-FR, CQ-FR, YN-FR) and one laboratory resistant strain (WX-LR) at developmental stages, tissues, and post blood-meal in comparison to the laboratory susceptible strain (WX-LS) in An. sinensis. Importantly, the expression of significantly upregulated P450s was verified using RT-qPCR, and the function of selected P450s in pyrethroid detoxification was determined with RNA interference using four laboratory pyrethroid-resistant strains (WX-LR, AH-LR, CQ-LR, YN-LR). Sixteen P450 genes were significantly upregulated in at least one field-resistant population, and 44 were significantly upregulated in different developmental stages, tissues or post blood-meal. A total of 19 P450s were selected to verify their association with pyrethroid resistance, and four of them (AsCYP6P3v1, AsCYP6P3v2, AsCYP9J10, and AsCYP9K1) demonstrated significant upregulation in laboratory pyrethroid-resistant strains using RT-qPCR. Knockdown of these four genes all significantly reduced pyrethroid resistance and increased the mortality by 57.19% (AsCYP6P3v1 and AsCYP6P3v2 knockdown group), 38.39% (AsCYP9K1 knockdown group) and 48.87% (AsCYP9J10 knockdown group) in An. sinensis by RNAi, which determined the pyrethroid detoxification function of these four genes. This study revealed the diversity of P450 genes and provided functional evidence for four P450s in pyrethroid detoxification in An. sinensis for the first time, which increases our understanding of the pyrethroid resistance mechanism, and is of potential value for pyrethroid resistance detection and surveillance.

Copy number variants underlie major selective sweeps in insecticide resistance genes in Anopheles arabiensis

To keep ahead of the evolution of resistance to insecticides in mosquitoes, national malaria control programmes must make use of a range of insecticides, both old and new, while monitoring resistance mechanisms. The outdoor-biting malaria vector Anopheles arabiensis is of increasing concern for malaria transmission because it is apparently less susceptible to many indoor control interventions, yet knowledge of its mechanisms of resistance remains limited. Furthermore, comparatively little is known in general about resistance to non-pyrethroid insecticides such as pirimiphos-methyl (PM), which are crucial for effective control in the context of globally high resistance to pyrethroids. We performed a genome-wide association study to determine the molecular mechanisms of resistance to the pyrethroid deltamethrin (commonly used in bednets) and PM (widespread use for indoor spraying), in An. arabiensis from 2 regions in Tanzania. Genomic regions of positive selection in these populations were largely driven by copy number variants (CNVs) in gene families involved in metabolic resistance. We found evidence of a new gene cluster involved in resistance to PM, identifying a strong selective sweep tied to a CNV in the carboxylesterase genes Coeae2g - Coeae6g. Using complementary data from another malaria vector, An. coluzzii, in Ghana, we show that copy number at this locus is significantly associated with PM resistance. Similarly, for deltamethrin, resistance was strongly associated with a novel CNV allele in the Cyp6aa / Cyp6p cluster (Cyp6aap_Dup33). Against this background of metabolic resistance, resistance caused by mutations in the insecticide target sites was very rare or absent. Mutations in the pyrethroid target site Vgsc were at very low frequency in Tanzania, yet combining these samples with 3 An. arabiensis individuals from West Africa revealed a startling evolutionary diversity, with up to 5 independent origins of Vgsc-995 mutations found within just 8 haplotypes. Thus, despite having been first recorded over 10 years ago, Vgsc resistance mutations in Tanzanian An. arabiensis have remained at stable low frequencies. Overall, our results provide a new copy number marker for monitoring resistance to PM in malaria mosquitoes, and reveal the complex picture of resistance patterns in An. arabiensis.

Emamectin benzoate-induced stress significantly affects the gut microbiome of adult Zeugodacus cucurbitae

The detoxification mechanisms in insects, which are triggered by insecticides, alter the diversity of their intestinal microorganisms. Emamectin benzoate is an insecticide used to control Zeugodacus cucurbitae (Coquillett), a globally significant pest. In this study, high-throughput sequencing, traditional isolation and culture methods, and single bacterial 16S rDNA sequencing were used to analyze the diversity and functional predictions of intestinal microbial communities in Z. cucurbitae adults exposed to emamectin benzoate. The results showed that the intestinal microorganisms of Z. cucurbitae on Cucumis sativus and Benincasa hispida var. chieh-qua were primarily composed of the phyla Proteobacteria and Bacteroidetes and genera Providencia, Enterobacter, Citrobacter, and Klebsiella. The relative abundances of Citrobacter, Enterobacter, Klebsiella, and Raoultella decreased with the induced stress, whereas those of Providencia and Pectobacterium increased. Diversity analysis revealed significant differences in the midgut flora of Z. cucurbitae before and after stress induction with emamectin benzoate.

Resistance Management for Cancer: Lessons from Farmers

One of the main reasons we have not been able to cure cancers is that treatments select for drug-resistant cells. Pest managers face similar challenges with pesticides selecting for pesticide-resistant insects, resulting in similar mechanisms of resistance. Pest managers have developed 10 principles that could be translated to controlling cancers: (i) prevent onset, (ii) monitor continuously, (iii) identify thresholds below which there will be no intervention, (iv) change interventions in response to burden, (v) preferentially select nonchemical control methods, (vi) use target-specific drugs, (vii) use the lowest effective dose, (viii) reduce cross-resistance, (ix) evaluate success based on long-term management, and (x) forecast growth and response. These principles are general to all cancers and cancer drugs and so could be employed broadly to improve oncology. Here, we review the parallel difficulties in controlling drug resistance in pests and cancer cells. We show how the principles of resistance management in pests might be applied to cancer. Integrated pest management inspired the development of adaptive therapy in oncology to increase progression-free survival and quality of life in patients with cancers where cures are unlikely. These pest management principles have the potential to inform clinical trial design.

Pyriproxyfen, villain or good guy? A brief review

Pyriproxyfen (PPF) acts as a juvenile growth regulator, interfering with normal metamorphosis and blocking the development of insects into adulthood. Although the World Health Organization (WHO) considers the use of PPF at a concentration of 0.01 mg/L as unlikely to pose health risks, recent studies have unveiled potential risks associated with PPF exposure to non-target organisms. Exposure to PPF disrupts insect development primarily by mimicking juvenile hormones; therefore, concerns linger over its impact on unintended species. Studies have highlighted the adverse effects of PPF on aquatic invertebrates, fish, and amphibians and revealed mortality and developmental abnormalities in non-target mosquito species exposed to PPF-treated water. Moreover, PPF may act as an endocrine disruptor, interfering with hormonal pathways crucial for growth, reproduction, and behavior in exposed organisms. Amphibians, for instance, display altered reproductive physiology and developmental abnormalities due to disruptions in endocrine signaling pathways caused by PPF. The ecological ramifications of PPF extend beyond direct toxicity to non-target species. Indirect effects include shifts in food web dynamics and ecosystem functioning. Reductions in insect populations, induced by PPF, can disrupt food availability for higher trophic levels, potentially destabilizing community structure and ecosystem equilibrium. Given mounting evidence of unintended consequences, robust risk assessment and regulatory oversight are imperative. Accurate classification of PPF by regulatory bodies is essential to balancing its role in disease control and pest management benefits with the need to safeguard non-target species and maintain ecosystem health. Future research must prioritize comprehensive assessments of PPF's ecological impact across various habitats and taxa to inform evidence-based policymaking.

Asaia spp. accelerate development of the yellow fever mosquito, Aedes aegypti, via interactions with the vertically transmitted larval microbiome

AIMS

A wide range of vector control programmes rely on the efficient production and release of male mosquito. Asaia bacteria are described as potential symbionts of several mosquito species but their relationship with Aedes aegypti has never been rigorously tested. Here, we aimed to quantify the benefits of three Asaia species on host development in Ae. aegypti, and the ability of these bacteria to form a stable symbiotic association with growing larvae.

METHODS AND RESULTS

In order to disentangle direct and indirect effects of Asaia inoculation on host development, experiments used insects with an intact microbiome and those reared in near-aseptic conditions, while we characterized bacterial communities and Asaia densities with culture dependent and independent methods (16S rRNA amplicon sequencing). Neonate larvae were inoculated with Asaia spp. for 24 h, or left as uninoculated controls, all were reared on sterile food. Aseptic larvae were produced by surface sterilization of eggs. Although all Asaia were transient members of the gut community, two species accelerated larval development relative to controls. The two mutualistic species had lasting impacts on the larval microbiome, largely by altering the relative abundance of dominant bacteria, namely Klebsiella and Pseudomonas. Axenic larvae were dominated by Asaia when inoculated with this species but showed slower development than conventionally reared insects, indicating that Asaia alone could not restore normal development.

CONCLUSIONS

Our results reveal Asaia as a poor mutualist for Ae. aegypti, but with a species-specific positive effect on improving host performance mediated by interactions with other bacteria.

Toxicity and Sublethal Effect of Chlorantraniliprole on Multiple Generations of Aedes aegypti L. (Diptera: Culicidae)

Due to the quick development of insecticide resistance, it is crucial to optimize management programs by understanding the sublethal effects of effective insecticides like chlorantraniliprole on Aedes aegypti L. populations. Using age-stage and two-sex life tables, we investigated the sublethal impacts of chlorantraniliprole on Ae. aegypti. Larval duration in the progeny of exposed parents was reduced by 0.33-0.42 days, whereas, the longevity of male and female adults was decreased by 1.43-3.05 days. Similarly, the egg-laying capacity of F1 and F2 progeny of the exposed parents was significantly reduced from 27.3% to 41.2%. The mean generation time (T) increased up to 11.8% in exposed populations, and the net reproduction rate (Ro) decreased by 51.50-55.60%. After 24 h of chlorantraniliprole treatment, there was a significant increase in cytochrome P450 activity. Contrarily, the activity of glutathione S-transferase (GST) initially declined but started increasing after 48 h of treatment. This research highlights the importance of chlorantraniliprole in mosquito management, as well as the importance of considering sublethal effects when developing strategies to handle them. Having a thorough understanding of the harmful effects of insecticides on mosquito populations can greatly enhance the effectiveness of insecticide-based interventions, while also minimizing the risk of pest resurgence.

Differences in seasonal dynamics and pyrethroid resistance development among Anopheles Hyrcanus group species

BACKGROUND

The Anopheles Hyrcanus group, which transmits Plasmodium vivax, consists of six confirmed species in South Korea. An epidemiological study revealed differences in the seasonal occurrence patterns of each species. Pyrethroid resistance in An. sinensis dates back to the early 2000s, whereas information on pyrethroid resistance in other species is lacking despite their greater significance in malaria epidemiology.

METHODS

Anopheles mosquitoes were collected from two malaria-endemic regions in South Korea for 2 years and their knockdown resistance (kdr) mutations were genotyped. The larval susceptibility to λ-cyhalothrin was compared in six Anopheles species and its seasonal changes in three species were investigated. The full-length sequences of the voltage-sensitive sodium channel (VSSC) were compared across six species to evaluate potential target-site insensitivity. The contribution of the kdr mutation to phenotypic resistance was confirmed by comparing median lethal time (LT50) to λ-cyhalothrin between populations of Anopheles belenrae with distinct genotypes.

RESULTS

The composition and seasonal occurrence of rare species (Anopheles kleini, Anopheles lestri, and Anopheles sineroides) varied considerably, whereas An. sinensis occurs continuously throughout the season. A kdr mutation in the form of heterozygous allele was newly identified in An. belenrae, An. lesteri, An. pullus, and An. sineroides. The baseline susceptibility to λ-cyhalothrin was the highest in An. belenrae, followed by An. lesteri, An. sineroides, An. kleini, An. pullus, and An. sinensis, with median lethal concentration (LC50) values ranging from 6.0- to 73.5-fold higher than that of An. belenrae. The susceptibility of An. sinensis and An. pullus varied by season, whereas that of An. belenrae remained stable. The kdr-heterozygous An. belenare population exhibited 5.1 times higher LT50 than that of the susceptible population. Species-specific VSSC sequence differences were observed among the six species.

CONCLUSIONS

Our findings suggest that the status and extent of pyrethroid resistance vary among Anopheles Hyrcanus group species. While An. sinensis, the predominant species, developed a considerable level of pyrethroid resistance through kdr mutation, the resistance levels of other species appeared to be less pronounced. Large-scale monitoring is crucial to fully understand species-specific seasonal occurrence and resistance status for effective management strategies, considering the ongoing impact of climate change on their vectorial capacity.

Unveiling the Role of Two Rhodopsin-like GPCR Genes in Insecticide-Resistant House Flies, Musca domestica

Insecticide resistance in insects, driven by the overexpression of P450 enzymes, presents a significant challenge due to the enhanced metabolic detoxification of insecticides. Although the transcriptional regulation of P450 genes is not yet fully understood, G-protein-coupled receptor (GPCR) genes have emerged as key regulators in this process. This study is the first to associate GPCR genes with insecticide resistance in Musca domestica. We identified two key rhodopsin-like GPCR genes, ALHF_02706.g1581 and ALHF_04422.g2918, which were significantly overexpressed in the resistant ALHF strain compared to sensitive strains. Notably, both ALHF_02706.g1581 and ALHF_04422.g2918 were mapped to autosome 2, where critical but unidentified regulatory factors controlling resistance and P450 gene regulation are located. This supports our hypothesis that GPCRs function as trans-regulatory factors for P450-mediated resistance. Functional analysis using transgenic Drosophila demonstrated that overexpression of these rhodopsin-like GPCR genes increased permethrin resistance by approximately two-fold. Specifically, ALHF_02706.g1581 overexpression significantly upregulated the Drosophila resistance-related P450 genes CYP12D1, CYP6A2, and CYP6A8, while ALHF_04422.g2918 increased CYP6G1 and CYP6A2 expression, thereby enhancing insecticide detoxification in rhodopsin-like GPCR transgenic Drosophila lines. These findings suggest that these rhodopsin-like GPCR genes on autosome 2 may act as trans-regulatory factors for P450-mediated resistance, underscoring their critical role in insecticide detoxification and resistance development in M. domestica.

A cub and sushi domain-containing protein with esterase-like activity confers insecticide resistance in the Indian malaria vector Anopheles stephensi

Chemical insecticides (organophosphates and pyrethroids) in the form of IRS (Indoor Residual Sprays) and LLINs (Long Lasting Insecticidal Nets) are the cornerstone for vector control, globally. However, their incessant use has resulted in widespread development of resistance in mosquito vectors, warranting continuous monitoring and investigation of the underlying mechanisms of resistance. Here, we identified a previously uncharacterized- Cub and Sushi Domain containing Insecticide Resistance (CSDIR) protein and generated evidence for its role in mediating insecticide resistance in the Anopheles stephensi. A strong binding affinity of the CSDIR protein towards different classes of insecticide molecules-malathion (KD 6.43 μM) and deltamethrin (KD 46.7 μM) were demonstrated using MD simulation studies and Surface Plasmon Resonance (SPR) experiments. Further, the recombinant CSDIR913-1190 protein exhibited potent esterase-like activity (α-naphthyl acetate (α-NA)- 1.356 ± 0.262 mM/min/mg and β-naphthyl acetate (β -NA)- 1.777 ± 0.220 mM/min/mg). Interestingly, dsRNA-mediated gene silencing of the CSDIR transcripts caused >60% mortality in resistant An. stephensi upon 1-h exposure to deltamethrin and malathion insecticides, compared to the control group. A significant reduction in the esterase-like activity was also observed against α-NA (p = 0.004) and β-NA (p = 0.025) in CSDIR silenced mosquitoes compared to the control group. Using computational analysis and experimental data, our results provided significant evidence of the involvement of the CSDIR protein in mediating insecticide resistance in Anopheles mosquitoes. Thereby making the CSDIR protein, a novel candidate for exploration of novel insecticide molecules. These data would also be helpful in further understanding the development of metabolic resistance by the Anopheles vector.

Point mutations in the voltage-gated sodium channel gene conferring pyrethroid resistance in China populations of the Dermanyssus gallinae

BACKGROUND

Dermanyssus gallinae, the poultry red mite (PRM), is a worldwide ectoparasite posing significant economic challenges in poultry farming. The extensive use of pyrethroids for PRM control has led to the emergence of pyrethroid resistance. The objective of this study is to detect the pyrethroid resistance and explore its associated point mutations in the voltage-gated sodium channel (VGSC) gene among PRM populations in China.

RESULTS

Several populations of D. gallinae, namely CJF-1, CJP-2, CJP-3, CSD-4 and CLD-5, displayed varying degrees of resistance to beta-cypermethrin compared to a susceptible field population (CBP-5). Mutations of VGSC gene in populations of PRMs associated with pyrethroid resistance were identified through sequencing its fragments IIS4-IIS5 and IIIS6. The mutations I917V, M918T/L, A924G and L925V were present in multiple populations, while no mutations were found at positions T929, I936, F1534 and F1538.

CONCLUSION

The present study confirmed the presence of extremely high levels of pyrethroid resistance in PRM populations in China, and for the first time detected four pyrethroid resistance mutations in the VGSC gene. Identifying pyrethroid resistance in the field population of PRM in China can be achieved through screening for VGSC gene mutations as an early detection method. Our findings underscore the importance of implementing chemical PRM control strategies based on resistance evidence, while also considering the management of acaricide resistance in the control of PRMs. © 2024 Society of Chemical Industry.

NADPH-cytochrome P450 reductase involved in the lambda-cyhalothrin susceptibility on the green mirid bug Apolygus lucorum

NADPH-cytochrome P450 reductase (CPR) is crucial for the detoxification process catalysed by cytochrome P450, which targets various exogenous xenobiotics, as well as pesticides. In our research, we successfully obtained the complete cDNA sequence of Apolygus lucorum's CPR (AlCPR) using reverse transcription PCR along with rapid amplification of cDNA ends technology. Bioinformatics analysis exhibited that the inferred amino acid sequence of AlCPR is characteristic of standard CPRs, featuring an N-terminal membrane anchor and three conserved FMN, FAD and NADP binding sites. Phylogenetic result revealed that AlCPR was positioned within the Hemiptera cluster, showing a close evolutionary relationship with the CPR of Cimex lectularius. The real-time quantitative PCR results demonstrated widespread expression of AlCPR across various life stages and tissues of A. lucorum, with the most prominent expression in adults and the abdominal region. Injecting double-stranded RNA of AlCPR only significantly increased the lambda-cyhalothrin susceptibility in lambda-cyhalothrin-resistant strain rather than the susceptible strain. These findings suggest a potential link between AlCPR and the P450-dependent defence mechanism against lambda-cyhalothrin in A. lucorum.

Mitochondrial Variation in Anopheles gambiae and Anopheles coluzzii: Phylogeographic Legacy and Mitonuclear Associations With Metabolic Resistance to Pathogens and Insecticides

Mitochondrial DNA has been a popular marker in phylogeography, phylogeny, and molecular ecology, but its complex evolution is increasingly recognized. Here, we investigated mitochondrial DNA variation in Anopheles gambiae and Anopheles coluzzii, in relation to other species in the Anopheles gambiae complex, by assembling the mitogenomes of 1,219 mosquitoes across Africa. The mitochondrial DNA phylogeny of the Anopheles gambiae complex was consistent with previously reported highly reticulated evolutionary history, revealing important discordances with the species tree. The three most widespread species (An. gambiae, An. coluzzii, and Anopheles arabiensis), known for extensive historical introgression, could not be discriminated based on mitogenomes. Furthermore, a monophyletic clustering of the three saltwater-tolerant species (Anopheles merus, Anopheles melas, and Anopheles bwambae) in the Anopheles gambiae complex also suggested that introgression and possibly selection shaped mitochondrial DNA evolution. Mitochondrial DNA variation in An. gambiae and An. coluzzii across Africa revealed significant partitioning among populations and species. A peculiar mitochondrial DNA lineage found predominantly in An. coluzzii and in the hybrid taxon of the African "far-west" exhibited divergence comparable to the interspecies divergence in the Anopheles gambiae complex, with a geographic distribution matching closely An. coluzzii's geographic range. This phylogeographic relict of the An. coluzzii and An. gambiae split was associated with population and species structure, but not with the rare Wolbachia occurrence. The lineage was significantly associated with single nucleotide polymorphisms in the nuclear genome, particularly in genes associated with pathogen and insecticide resistance. These findings underline potential mitonuclear coevolution history and the role played by mitochondria in shaping metabolic responses to pathogens and insecticides in Anopheles.

UGT201H1 overexpression confers cyflumetofen resistance in Tetranychus cinnabarinus (Boisduval)

BACKGROUND

Tetranychus cinnabarinus is one of the most common polyphagous arthropod herbivores, and is primarily controlled by the application of acaricides. The heavy use of acaricides has led to high levels of resistance to acaricides such as cyflumetofen, which poses a threat to global resistance management programs. Cyflumetofen resistance is caused by an increase in metabolic detoxification; however, the role of uridine diphosphate (UDP)-glycosyltransferase (UGT) genes in cyflumetofen resistance remains to be determined.

RESULTS

Synergist 5-nitrouracil (5-Nul) significantly enhanced cyflumetofen toxicity in T. cinnabarinus, which indicated that UGTs are involved in the development of cyflumetofen resistance. Transcriptomic analysis and quantitative (q)PCR assays demonstrated that the UGT genes, especially UGT201H1, were highly expressed in the YN-CyR strain, compared to those of the YN-S strain. The RNA interference (RNAi)-mediated knockdown of UGT201H1 expression diminished the levels of cyflumetofen resistance in YN-CyR mites. The findings additionally revealed that the recombinant UGT201H1 protein plays a role in metabolizing cyflumetofen. Our results also suggested that the aromatic hydrocarbon receptor (AhR) probably regulates the overexpression of the UGT201H1 detoxification gene.

CONCLUSION

UGT201H1 is involved in cyflumetofen resistance, and AhR may regulates the overexpression of UGT201H1. These findings provide deeper insights into the molecular mechanisms underlying UGT-mediated metabolic resistance to chemical insecticides. © 2024 Society of Chemical Industry.

Mechanisms of transcriptional regulation in Anopheles gambiae revealed by allele-specific expression

Malaria control relies on insecticides targeting the mosquito vector, but this is increasingly compromised by insecticide resistance, which can be achieved by elevated expression of detoxifying enzymes that metabolize the insecticide. In diploid organisms, gene expression is regulated both in cis, by regulatory sequences on the same chromosome, and by trans acting factors, affecting both alleles equally. Differing levels of transcription can be caused by mutations in cis-regulatory modules (CRM), but few of these have been identified in mosquitoes. We crossed bendiocarb-resistant and susceptible Anopheles gambiae strains to identify cis-regulated genes that might be responsible for the resistant phenotype using RNAseq, and CRM sequences controlling gene expression in insecticide resistance relevant tissues were predicted using machine learning. We found 115 genes showing allele-specific expression (ASE) in hybrids of insecticide susceptible and resistant strains, suggesting cis-regulation is an important mechanism of gene expression regulation in A. gambiae. The genes showing ASE included a higher proportion of Anopheles-specific genes on average younger than genes with balanced allelic expression.