Cytochrome P450 associated with insecticide resistance catalyzes cuticular hydrocarbon production in Anopheles gambiae

High levels of sinigrin trigger synthesis of fatty acids in Plutella xylostella (L.)

Diamondback moth (Lepidoptera: Plutellidae; Plutella xylostella L.) is a specialist insect of the Brassicaceae family, damaging economically important crops, such as cabbage and cauliflower. Glucosinolates, also known as 'mustard oil bombs' are present in all Brassicaceae members, of which sinigrin (allyl-glucosinolate or 2-propenyl-glucosinolate) is a major aliphatic compound. During herbivory, glucosinolates are converted to toxic isothiocyanates that deter insect pests. P. xylostella possesses glucosinolate sulfatases that desulfate them. Such a conversion renders them unfit for degradation to toxic products. Changes in the larval performance prompted us for RNA sequencing to understand probable adaptation mechanism under sinigrin stress. Differentially expressed genes were found to be related to larval cuticle proteins. Further, gene ontology and KEGG (Kyoto Encyclopedia of Genes and Genomes) analyses depict genes belonging to the categories, integral component of membrane, cellular processes and those involved in biosynthesis of fatty acids. Upregulation of cuticular genes viz. larval cuticle protein-17 (LCP-17), cuticular protein-19 (2CP-19) and ATP binding cassette transporter C7 (ABCC7), ABCC16 was validated by qRT-PCR. Liquid chromatography quadrupole time of flight mass spectrometry analysis of whole larvae feeding on sinigrin and their separated cuticle, depicted abundance of fatty acids. Changes in the topography of the larval cuticle were evident by scanning electron microscopy. Expression of PxABCH1 was corroborated to its role in the transport of cuticular lipids. Notably, molecular docking of PxABCH1 with cuticular fatty acids showed favorable binding interactions. To summarize, integrated transcriptomic and metabolomic analyses suggest that in response to a diet containing a high dose of sinigrin, P. xylostella re-programs metabolic pathways related to fatty acid biosynthesis that directly influence insect development.

NADPH-cytochrome P450 reductase mediates resistance to neonicotinoid insecticides in Bradysia odoriphaga

As a crucial electron transfer partner of the P450 system, NADPH-cytochrome P450 reductase (CPR) plays an influential role in P450-mediated detoxification metabolism of xenobiotics. CPR has been found to be associated with insecticide resistance in several insects. However, the role of CPR in the cross-resistance of Bradysia odoriphaga to clothianidin and neonicotinoid insecticides remains to be elucidated. In this study, the CPR gene (BoCPR) of B. odoriphaga was cloned and characterized. The expression of BoCPR was more abundant in the adult stage and in the midgut and Malpighian tubules of larvae, and BoCPR was significantly overexpressed in the clothianidin-resistant (CL-R) strain compared to the susceptible (SS) strain. Exposure to clothianidin significantly increased BoCPR expression in both the SS and CL-R strains. In addition, knockdown of BoCPR in SS and CL-R strains significantly reduced CPR and P450 enzyme activities, and resulted in a significant increase in larval susceptibility to clothianidin, imidacloprid, and thiamethoxam. These results suggest that BoCPR plays an important role in B. odoriphaga resistance to clothianidin and cross-resistance to neonicotinoid insecticides.

Exploring the metabolic and cuticular mechanisms of increased pyrethroid resistance in Anopheles gambiae S.l populations from Ghana

Increasing insecticide resistance in malaria vectors threatens the efficacy of current control tools, however knowledge of metabolic and cuticular mechanisms is widely lacking in Ghana. We examined the metabolic and cuticular resistance mechanisms in Anopheles gambiae mosquitoes from coastal and sahel zones of Ghana. WHO susceptibility tests and synergist assays were performed on F0 field collected An. gambiae s.l. Gene expression profiles of eight key metabolic and cuticular genes were determined using qRT-PCR. Moderate to high pyrethroid resistance (< 70%) were observed across all the sites. Piperonyl butoxide significantly increased susceptibility to pyrethroids across all sites and insecticides, implicating P450s. Gene expression analysis revealed overexpression of metabolic and cuticular resistance genes in field An. gambiae populations compared to the susceptible Kisumu strain. CYP6M2 and CYP6P3 were the most overexpressed metabolic genes in pyrethroid-resistant mosquitoes, compared to the pyrethroid susceptible mosquitoes in the coastal (FC: 122.28 and 231.86, p < 0.05) and sahel (FC: 344.955 and 716.37, p < 0.001) zones respectively. CYP4G16 (previously associated with cuticular resistance) was significantly overexpressed in only resistant mosquitoes (FC: 3.32-30.12, p < 0.05). Overexpression of metabolic and cuticular resistance genes in local malaria vectors highlights the need to intensify insecticide resistance management strategies to control malaria in Ghana.

A multi-omic meta-analysis reveals novel mechanisms of insecticide resistance in malaria vectors

Malaria control faces challenges from widespread insecticide resistance in major Anopheles species. This study, employing a cross-species approach, integrates RNA-Sequencing, whole-genome sequencing, and microarray data to elucidate drivers of insecticide resistance in Anopheles gambiae complex and An. funestus. Here we show an inverse relationship between genetic diversity and gene expression, with highly expressed genes experiencing stronger purifying selection. Gene expression clusters physically in the genome, revealing potential coordinated regulation, and we find that highly over-expressed genes are associated with selective sweep loci. We identify known and novel candidate insecticide resistance genes, enriched for metabolic, cuticular, and behavioural functioning. We also present AnoExpress, a Python package, and an online interface for user-friendly exploration of resistance candidate expression. Despite millions of years of speciation, convergent gene expression responses to insecticidal selection pressures are observed across Anopheles species, providing crucial insights for malaria vector control.

Bifenthrin resistance in Dalbulus maidis (Hemiptera: Cicadellidae): inheritance, cross-resistance, and stability

BACKGROUND

Pyrethroid insecticides have been a primary strategy for managing Dalbulus maidis (Hemiptera: Cicadellidae) in Brazil. Howeve, failures in the control of D. maidis with pyrethroids have been reported. In this study, we selected a bifenthrin-resistant strain of D. maidis under laboratory cage conditions to investigate the inheritance pattern of resistance, cross-resistance to other insecticides, and resistance stability.

RESULTS

The estimated LC50 of the Bif-R was 2,055.72 μg a.i. mL-1, while that of the susceptible (Sus) strain was 0.64 μg a.i. mL-1, resulting in a 3,170-fold resistance ratio (RR). Reciprocal crosses (H1: Bif-R ♀ × Sus ♂ and H2: Bif-R ♂ × Sus ♀) and backcrosses between heterozygous H1 and H2 with the Sus strain indicated autosomal, incompletely dominant, and polygenic resistance. Potential cross or multiple-resistance was observed between Bif-R and lambda-cyhalothrin, imidacloprid, and acetamiprid, with resistance ratios varying from 300- to 2,000-fold. No cross-resistance was detected between Bif-R and methomyl, carbosulfan or acephate. Cage studies with different proportions of Sus and Bif-R strains revealed that resistance of D. maidis to bifenthrin is unstable. A decrease in the LC50 of the field-collected population from 113.61 to 10.73 μg bifenthrin mL-1 was detected in the absence of selection pressure.

CONCLUSIONS

Our findings provide insights into the evolution of resistance of D. maidis to bifenthrin. This study is the first comprehensive analysis of pyrethroid resistance in D. maidis and will contribute to insect resistance management (IRM) strategies to preserve the efficacy of bifenthrin and other insecticides. © 2025 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

The pore canal protein snsl is required for cuticular lipids transport and cuticle barrier function in the migratory locust, Locusta migratoria

Lipids are important components of the insect cuticle protecting against desiccation and xenobiotic penetration. Delivery of lipids to the cuticular surface occurs through pore canals, which are a nano-canal system formed by the epidermis, running through the procuticle and terminating at the epicuticle, where they ramify as wax-canals. The molecular mechanisms of cuticular lipids deposition in insects are poorly understood. Here, we identified the pore canal protein Snsl (Snustorr snarlik) in the migratory locust Locusta migratoria (LmSnsl) and investigated its function in cuticular lipid transport and cuticle barrier construction. We found that LmSnsl was specifically expressed in the integument and had a high expression level before ecdysis when a new cuticle is formed. Silencing of LmSnsl by RNA interference (RNAi) caused a lethal phenotype during or shortly after molting. In addition, RNAi against LmSnsl resulted in a decrease in cuticular lipids and in the accumulation of internal lipids. The pore canals of dsLmSnsl animals are deformed and contain less luminal material. Furthermore, we found that cuticle permeability to xenobiotics was enhanced in dsLmSnsl-treated nymphs that were, consistently, more susceptible to insecticides. These animals were also prone to pathogen invasion suggesting that cuticle lipids act in pathogen defense. Taken together, our results indicate that the locust Snsl protein is needed for pore canal integrity required for the transport of lipids from the epidermis to the cuticle to constitute a barrier against xenobiotics and pathogens.

Nanocarrier-mediated transdermal delivery of Lmidgf4 dsRNA expedites biological control of locusts by Beauveria bassiana

Locusts have been a major global agricultural pest that poses a serious threat to crop and livestock production. Entomopathogenic fungi (EPF) provide an eco-friendly control method; however, their efficacy usually takes slow and is unstable. To achieve an enhancement of the biocontrol efficacy of Beauveria bassiana (B. bassiana) against locusts, we developed a new strategy by which B. bassiana and nanocarrier-mediated dsRNA are co-applied across the locust cuticle. The nanocarrier star polycation (SPc) effectively delivers Lmidgf4 dsRNA (dsLmidgf4) into the locust, which targets Locusta migratoria imaginal disc growth factor 4 (Lmidgf4). SPc protects dsLmidgf4 from degradation by the hemolymph and enables efficient gene silencing. Furthermore, SPc has no adverse effects on B. bassiana spore germination and growth. Lmidgf4 interference leads to a thinner layer of endocuticle, thus facilitates infection of B. bassiana, and finally reduces the median lethal time of locusts infected with B. bassiana. In conclusion, the combination of B. bassiana and dsRNA/SPc complex overcomes the slow action of fungi, providing a novel strategy for field control of locusts.

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.

Discrimination of inherent characteristics of susceptible and resistant strains of Anopheles gambiae by explainable artificial intelligence analysis of flight trajectories

Understanding mosquito behaviours is vital for the development of insecticide-treated nets (ITNs), which have been successfully deployed in sub-Saharan Africa to reduce disease transmission, particularly malaria. However, rising insecticide resistance (IR) among mosquito populations, owing to genetic and behavioural changes, poses a significant challenge. We present a machine learning pipeline that successfully distinguishes between innate IR and insecticide-susceptible (IS) mosquito flight behaviours independent of insecticidal exposure by analysing trajectory data. Data-driven methods are introduced to accommodate common tracking system shortcomings that occur due to mosquito positions being occluded by the bednet or other objects. Trajectories, obtained from room-scale tracking of two IR and two IS strains around a human-baited, untreated bednet, were analysed using features such as velocity, acceleration, and geometric descriptors. Using these features, an XGBoost model achieved a balanced accuracy of 0.743 and a ROC AUC of 0.813 in classifying IR from IS mosquitoes. SHAP analysis helped decipher that IR mosquitoes tend to fly slower with more directed flight paths and lower variability than IS-traits that are likely a fitness advantage by enhancing their ability to respond more quickly to bloodmeal cues. This approach provides valuable insights based on flight behaviour that can reveal the action of interventions and insecticides on mosquito physiology.

Chemosensory Proteins Protect Nilaparvata lugens from Imidacloprid by Sequestering the Insecticide and Facilitating Metabolic Detoxification

The involvement of chemosensory proteins (CSPs) in binding to insecticides has been implicated. However, our understanding of CSP-mediated insecticide resistance remains limited. Herein, 15 CSP genes were identified and characterized from Nilaparvata lugens. Expression analysis identified six CSPs with overexpression in the imidacloprid-resistant strain, whose involvement in imidacloprid resistance was validated by RNA interference. Among them, four CSPs were successfully expressed using a prokaryotic expression system, and their binding affinities to imidacloprid were confirmed through fluorescence competitive binding assays. Knockdown of them impaired the capacity of N. lugens to metabolize imidacloprid and inhibited the activity of metabolic detoxification pathways, while their overexpression in Escherichia coli enhanced bacterial metabolic efficiency toward imidacloprid. Furthermore, the transcriptional regulation of CSP2 and CSP15 was found to be mediated by AhR/ARNT and CncC/MafK. These findings suggest that the overexpression of CSPs in N. lugens promotes imidacloprid resistance by sequestering the insecticide and enhancing metabolic detoxification.

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.

Oxidative metabolism mechanism of terpenoid compound ZQ-8 by cytochrome P450 enzyme in Helicoverpa armigera

In our previous research, we identified that treatment of Helicoverpa armigera with ZQ-8 led to upregulation of CYP450 genes. To clarify the metabolic pathway of ZQ-8, this study analyzed the expression of CYP450 genes and proteins in H. armigera after ZQ-8 treatment through transcriptomics and proteomics. Molecular docking, recombinant protein expression, and surface plasmon resonance techniques were employed to investigate the interactions between ZQ-8 and P450 proteins. The oxidative reduction related pathways were significantly enriched in H. armigera larvae treated with ZQ-8, with an increase in the expression of CYP6B2 and CYP6B6 genes. The CYP6B2 and CYP6B6 proteins exhibited significant expression following ZQ-8 treatment. ZQ-8 demonstrated rapid binding and stable dissociation characteristics with CYP6B6, characterized by a dissociation constant (KD) of 88.15 μM. In contrast, ZQ-8 also showed rapid binding and dissociation with CYP6B2, but with a lower KD of 74.77 μM indicating that CYP6B2 has a stronger binding affinity for ZQ-8 compared to CYP6B6, and is capable of oxidizing ZQ-8 to the corresponding carboxylic acid. This study provides a reference for the metabolism and mechanism of action of ZQ-8 as a potential drug molecule, laying the foundation for future drug design and optimization, paving the way for environmentally sustainable pest control strategies and reducing reliance on traditional chemical pesticides.

Evaluating the potential of Kalanchoe pinnata, Piper amalago amalago, and other botanicals as economical insecticidal synergists against Anopheles gambiae

BACKGROUND

Synergists reduce insecticide metabolism in mosquitoes by competing with insecticides for the active sites of metabolic enzymes, such as cytochrome P450s (CYPs). This increases the availability of the insecticide at its specific target site. The combination of both insecticides and synergists increases the toxicity of the mixture. Given the demonstrated resistance to the classical insecticides in numerous Anopheles spp., the use of synergists is becoming increasingly pertinent. Tropical plants synthesize diverse phytochemicals, presenting a repository of potential synergists.

METHODS

Extracts prepared from medicinal plants found in Jamaica were screened against recombinant Anopheles gambiae CYP6M2 and CYP6P3, and Anopheles funestus CYP6P9a, CYPs associated with anopheline resistance to pyrethroids and several other insecticide classes. The toxicity of these extracts alone or as synergists, was evaluated using bottle bioassays with the insecticide permethrin. RNA sequencing and in silico modelling were used to determine the mode of action of the extracts.

RESULTS

Aqueous extracts of Piper amalago var. amalago inhibited CYP6P9a, CYP6M2, and CYP6P3 with IC50s of 2.61 ± 0.17, 4.3 ± 0.42, and 5.84 ± 0.42 μg/ml, respectively, while extracts of Kalanchoe pinnata, inhibited CYP6M2 with an IC50 of 3.52 ± 0.68 μg/ml. Ethanol extracts of P. amalago var. amalago and K. pinnata displayed dose-dependent insecticidal activity against An. gambiae, with LD50s of 368.42 and 282.37 ng/mosquito, respectively. Additionally, An. gambiae pretreated with K. pinnata (dose: 1.43 μg/mosquito) demonstrated increased susceptibility (83.19 ± 6.14%) to permethrin in a bottle bioassay at 30 min compared to the permethrin only treatment (0% mortality). RNA sequencing demonstrated gene modulation for CYP genes in anopheline mosquitoes exposed to 715 ng of ethanolic plant extract at 24 h. In silico modelling showed good binding affinity between CYPs and the plants' secondary metabolites.

CONCLUSION

This study demonstrates that extracts from P. amalago var. amalago and K. pinnata, with inhibitory properties, IC50 < 6.95 μg/ml, against recombinant anopheline CYPs may be developed as natural synergists against anopheline mosquitoes. Novel synergists can help to overcome metabolic resistance to insecticides, which is increasingly reported in malaria vectors.

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.

Insecticide resistant Anopheles from Ethiopia but not Burkina Faso show a microbiota composition shift upon insecticide exposure

BACKGROUND

Malaria remains a key contributor to mortality and morbidity across Africa, with the highest burden in children under 5. Insecticide-based vector control tools, which target the adult Anopheles mosquitoes, are the most efficacious tool in disease prevention. Due to the widespread use of these interventions, insecticide resistance to the most used classes of insecticides is now pervasive across Africa. Understanding the underlying mechanisms contributing to this phenotype is necessary to both track the spread of resistance and to design new tools to overcome it.

METHODS

Here, we compare the microbiota composition of insecticide-resistant populations of Anopheles gambiae, An. coluzzii and An. arabiensis from Burkina Faso, and in the latter case additionally from Ethiopia, to insecticide-susceptible populations.

RESULTS

We show that the microbiota composition between insecticide-resistant and -susceptible populations does not differ in Burkina Faso. This result is supported by data from laboratory colonies originating in Burkina Faso across two countries. In contrast, An. arabiensis from Ethiopia demonstrates clear differences in microbiota composition in those dying from and those surviving insecticide exposure. To further understand resistance in this An. arabiensis population, we performed RNAseq and saw differential expression of detoxification genes associated with insecticide resistance and changes in respiration, metabolism and synapse-related ion channels.

CONCLUSIONS

Our results indicate that, in addition to changes in the transcriptome, microbiota can contribute to insecticide resistance in certain settings.

A single mutation G454A in the P450 CYP9K1 drives pyrethroid resistance in the major malaria vector Anopheles funestus reducing bed net efficacy

Metabolic mechanisms conferring pyrethroid resistance in malaria vectors are jeopardizing the effectiveness of insecticide-based interventions, and identification of their markers is a key requirement for robust resistance management. Here, using a field-lab-field approach, we demonstrated that a single mutation G454A in the P450 CYP9K1 is driving pyrethroid resistance in the major malaria vector Anopheles funestus in East and Central Africa. Drastic reduction in CYP9K1 diversity was observed in Ugandan samples collected in 2014, with the selection of a predominant haplotype (G454A mutation at 90%), which was completely absent in the other African regions. However, 6 years later (2020) the Ugandan 454A-CYP9K1 haplotype was found predominant in Cameroon (84.6%), but absent in Malawi (Southern Africa) and Ghana (West Africa). Comparative in vitro heterologous expression and metabolism assays revealed that the mutant 454A-CYP9K1 (R) allele significantly metabolizes more type II pyrethroid (deltamethrin) compared with the wild G454-CYP9K1 (S) allele. Transgenic Drosophila melanogaster flies expressing 454A-CYP9K1 (R) allele exhibited significantly higher type I and II pyrethroids resistance compared to flies expressing the wild G454-CYP9K1 (S) allele. Furthermore, laboratory testing and field experimental hut trials in Cameroon demonstrated that mosquitoes harboring the resistant 454A-CYP9K1 allele significantly survived pyrethroids exposure (odds ratio = 567, P < 0.0001). This study highlights the rapid spread of pyrethroid-resistant CYP9K1 allele, under directional selection in East and Central Africa, contributing to reduced bed net efficacy. The newly designed DNA-based assay here will add to the toolbox of resistance monitoring and improving its management strategies.

Mechanistic exploration of odorant binding protein-mediated chlorpyrifos resistance in Nilaparvata lugens: Insights from insecticide sequestration and transcriptional regulation

The effectiveness and sustainable application of insecticides are severely threatened by the rapid evolution of resistance in agricultural pests. Recent research indicates that odorant binding proteins (OBPs) may be involved in facilitating insecticide resistance, while the specific mechanisms remain poorly understood. Herein, 11 OBPs were identified from Nilaparvata lugens. Among them, OBP5 exhibited high and specific expression in the head, and showed constitutive overexpression in the chlorpyrifos-resistant strain. Knockdown of OBP5 notably restored susceptibility to chlorpyrifos in N. lugens, while overexpression of OBP5 in Escherichia coli significantly enhanced bacterial tolerance to chlorpyrifos. Fluorescence competitive binding assay confirmed the strong binding affinities of OBP5 to chlorpyrifos and its active metabolite chlorpyrifos-oxon. Molecular docking studies proposed a critical interacting amino acid (Lys147) in the binding site, which was further validated by comparative binding studies between wildtype OBP5 and the mutated protein OBP5K147A. Furthermore, Lim1β that also presented overexpression pattern in the resistant strain, was found to regulate expression of OBP5 through a dual-luciferase reporter assay. Our findings demonstrate that the overexpression of OBP5 contributes to chlorpyrifos resistance by binding and sequestering the insecticides, shedding light on the sequestration resistance mechanism conferred by OBPs and offering potential targets for resistance management.

Cuticular composition: An alternative taxonomic approach to differentiate between Argas arboreus and Argas persicus ticks (Acari: Argasidae)

Argas arboreus and A. persicus are blood sucking ectoparasites on domestic birds in Egypt. They cause anemia in birds, in addition to transmitting a variety of pathogens that leads to economical loss in the poultry industry. It is difficult for non-taxonomists to differentiate between these species because of minor morphological characters. Therefore, it is very important to identify tick species for developing a suitable strategy to reduce risks to poultry wealth. This study characterized the female cuticular hydrocarbons of two Argas species using gas chromatography-mass spectrometry. Sixty different hydrocarbons were exclusively identified in A. arboureus, whereas only 51 in A. persicus. Some of the hydrocarbon compounds were stage-specific ones that differentiate between two species. Others shared between all feeding stages of both species that improved they are closely related ones. Genetic variability recorded its maximum value between unfed stages of the two species, and similarity reached only 25 %. The present study provides the first chemotaxonomic data to differentiate between two closely related Argas species according to their cuticular hydrocarbons. Therefore, hydrocarbon composition seems to be a promising tool available as a taxonomic character, in addition improved that feeding stage was the susceptible one to be controlled.

The Dual Resistance Mechanism of CYP325G4 and CYP6AA9 in Culex pipiens pallens Legs According to Transcriptome and Proteome Analysis

Mosquitoes within the Culex pipiens complex play a crucial role in human disease transmission. Insecticides, especially pyrethroids, are used to control these vectors. Mosquito legs are the main entry point and barrier for insecticides to gain their neuronal targets. However, the resistance mechanism in mosquito legs is unclear. Herein, we employed transcriptomic analyses and isobaric tags for relative and absolute quantitation techniques to investigate the resistance mechanism, focusing on Cx. pipiens legs. We discovered 2346 differentially expressed genes (DEGs) between deltamethrin-resistant (DR) and deltamethrin-sensitive (DS) mosquito legs, including 41 cytochrome P450 genes. In the same comparison, we identified 228 differentially expressed proteins (DEPs), including six cytochrome P450 proteins. Combined transcriptome and proteome analysis revealed only two upregulated P450 genes, CYP325G4 and CYP6AA9. The main clusters of DEGs and DEPs were associated with metabolic processes, such as cytochrome P450-mediated metabolism of drugs and xenobiotics. Transcription analysis revealed high CYP325G4 and CYP6AA9 expression in the DR strain at 72 h posteclosion compared with that in the DS strain, particularly in the legs. Mosquitoes knocked down for CYP325G4 were more sensitive to deltamethrin than the controls. CYP325G4 knockdown reduced the expression of several chlorinated hydrocarbon (CHC)-related genes, which altered the cuticle thickness and structure. Conversely, CYP6AA9 knockdown increased CHC gene expression without altering cuticle thickness and structure. P450 activity analysis demonstrated that CYP325G4 and CYP6AA9 contributed to metabolic resistance in the midgut and legs. This study identified CYP325G4 as a novel mosquito deltamethrin resistance factor, being involved in both metabolic and cuticular resistance mechanisms. The previously identified CYP6AA9 was investigated for its involvement in metabolic resistance and potential cuticular resistance in mosquito legs. These findings enhance our comprehension of resistance mechanisms, identifying P450s as promising targets for the future management of mosquito vector resistance, and laying a theoretical groundwork for mosquito resistance management.

Beauveria bassiana transcriptomics reveal virulence-associated shifts during insect lipid assimilation

Insect cuticular lipids, especially epicuticular hydrocarbons (CHC), have a significant role in insect ecology and interactions with other organisms, including fungi. The CHC composition of a specific insect species may influence the outcome of the interaction with a specific fungal strain. Some insects, such as Piezodorus guildinii, have low susceptibility towards fungal infections seemingly due to their CHC composition. The entomopathogenic fungus Beauveria bassiana can assimilate CHC and incorporate them as building blocks via cytochrome P450 monooxygenases (CYPs). However, little is known about other enzymes that promote the degradation/assimilation of these cuticular components. In this study, we performed a transcriptomic analysis to evaluate the in vitro response of two virulence-contrasting B. bassiana strains when grown on three different P. guildinii CHC sources. We found a different expression profile of virulence-related genes, as well as different GO and KEGG parameters enriched at 4 days post-inoculation, which could help account for the intrinsic virulence and for an alkane-priming virulence enhancement effect. The hypovirulent strain predominantly showed higher expression of cuticle penetration genes, including chitinases, proteases, and CYPs, with GO term categories of "heme binding," "monooxygenase activity," and "peroxisome" pathways enriched. The hypervirulent strain showed higher expression of cell wall remodeling and cell cycle genes, and cuticle adhesion and a distinct set of CYPs, with GO categories of "DNA-binding transcription factor activity" and KEGG pathways corresponding to "meiosis-yeast" and "cell cycle" enriched. These results suggest a delay and alternate routes in pathogenicity-related metabolism in the hypovirulent strain in comparison with the hypervirulent strain. KEY POINTS: •Transcriptomics of two B. bassiana strains grown in P. guildinii cuticular components •Virulence-related genes correlated with virulence enhancement towards P. guildinii •Differentially expressed genes, GOs and KEGGs showed different metabolic timelines associated with virulence.

The Altered Lipid Composition and Key Lipid Metabolic Enzymes in Thiacloprid-Resistant Myzus persicae, with Special Attention Paid to the Function of MpTHEM6a

Neonicotinoid resistance is increasingly prevalent in the agricultural pest Myzus persicae. Lipids play a critical role in insect defense systems, but their contribution to insect neonicotinoid resistance is disregarded. We conducted metabolomics and transcriptomics studies on M. persicae thiacloprid-resistant (THG-R) and -susceptible (FFJ-S) populations. A total of 149 lipid metabolites were identified, with 90 upregulated and 59 downregulated in THG-R compared to in FFJ-S. Metabolites in the arachidonic acid (AA) pathway substantially varied between THG-R and FFJ-S. For example, arachidonic acid, (±)11-HETE, and prostaglandin B1 were significantly upregulated, while prostaglandin A1, tetranor-PGDM, 8,15-diHETE, and (±)11(12)-EET were significantly decreased in THG-R. Transcriptomics profiles and qPCR indicated that lipid metabolic enzymes, including fatty acid synthase (FAS), the elongase of very-long-chain fatty acids (ELO), fatty acid desaturase (FAD), and phospholipase (PL) genes, were not overexpressed in THG-R. Among the twelve thioesterase genes, only MpTHEM6a was significantly upregulated in THG-R. Knocking down the expression of MpTHEM6a in THG-R significantly increased the toxicity of the three neonicotinoids, reduced the lifespan of adults, and decreased the number of nonviable nymphs produced by female adults. The metabolites AA, (±)11-HETE, and prostaglandin B1 are potential biomarkers in neonicotinoid-resistant M. persicae. MpTHEM6a may become a potential target for combating neonicotinoid-resistant M. persicae.

Cytochrome P450 monooxygenase systems: Diversity and plasticity for adaptive stress response

Superfamily of cytochromes P450 (CYPs) is composed of heme-thiolate-containing monooxygenase enzymes, which play crucial roles in the biosynthesis, bioactivation, and detoxification of a variety of organic compounds, both endogenic and exogenic. Majority of CYP monooxygenase systems are multi-component and contain various redox partners, cofactors and auxiliary proteins, which contribute to their diversity in both prokaryotes and eukaryotes. Recent progress in bioinformatics and computational biology approaches make it possible to undertake whole-genome and phylogenetic analyses of CYPomes of a variety of organisms. Considerable variations in sequences within and between CYP families and high similarity in secondary and tertiary structures between all CYPs along with dramatic conformational changes in secondary structure elements of a substrate binding site during catalysis have been reported. This provides structural plasticity and substrate promiscuity, which underlie functional diversity of CYPs. Gene duplication and mutation events underlie CYP evolutionary diversity and emergence of novel selectable functions, which provide the involvement of CYPs in high adaptability to changing environmental conditions and dietary restrictions. In our review, we discuss the recent advancements and challenges in the elucidating the evolutionary origin and mechanisms underlying the CYP monooxygenase system diversity and plasticity. Our review is in the view of hypothesis that diversity of CYP monooxygenase systems is translated into the broad metabolic profiles, and this has been acquired during the long evolutionary time to provide structural plasticity leading to high adaptative capabilities to environmental stress conditions.

The effect of next-generation, dual-active-ingredient, long-lasting insecticidal net deployment on insecticide resistance in malaria vectors in Benin: results of a 3-year, three-arm, cluster-randomised, controlled trial

BACKGROUND

Insecticide resistance among malaria vector species now occurs in 84 malaria-endemic countries and territories worldwide. Novel vector-control interventions, including long-lasting insecticidal nets (LLINs) that incorporate new active ingredients with distinct modes of action, are urgently needed to delay the evolution and spread of resistance and to alleviate reversals in malaria-control gains. We aimed to assess the longitudinal effect of two dual-active-ingredient LLINs on insecticide resistance during a cluster-randomised, controlled trial in Benin.

METHODS

This 3-year, three-arm, cluster-randomised, controlled trial was conducted between Oct 17, 2019, and Oct 24, 2022, in three districts in southern Benin, to compare the effects of LLINs containing chlorfenapyr-pyrethroid or pyriproxyfen-pyrethroid with LLINs containing pyrethroid only. In 19 292 mosquitoes (Anopheles gambiae sensu lato) collected over 36 months-3 months of baseline followed by 3 years post-intervention-we measured longitudinal phenotypic insecticide resistance profiles using bioassays and genotypic resistance profiles using quantitative, real-time, reverse transcriptase PCR of metabolic resistance genes in two clusters per trial group. The trial was registered with ClinicalTrials.gov, NCT03931473.

FINDINGS

In all three trial groups, a significant effect of LLINs on insecticide resistance selection was evident, with the median lethal dose (LD50) of α-cypermethrin approximately halving between baseline and 12 months post-LLIN distribution (pyrethroid-only LLIN cluster 21: LD50 78·78 μg/ml [95% CI 65·75-94·48] vs 35·93 [29·41-43.86] and cluster 31: 79·26 [65·40-96·44] vs 38·71 [30·88-48·53]; chlorfenapyr-pyrethroid LLIN cluster 43: 104·30 [82·97-133·58] vs 43·99 [35·30-54·86]; and pyriproxyfen-pyrethroid LLIN cluster 36: 63·76 [52·14-77·75] vs 37·96 [30·88-46·69] and cluster 53: 77·67 [57·63-104·56] vs 39·72 [29·26-53·97]). Over the subsequent 2 years, the LD50 of α-cypermethrin increased past baseline values in all three trial groups (year 3 pyrethroid-only LLIN cluster 21: 141·01 [111·70-181·90] and cluster 31: 115·15 [93·90-143·09]; chlorfenapyr-pyrethroid LLIN cluster 43: 97·00 [77·24-123·54] and cluster 55: 126·99 [102·34-161·26]; and pyriproxyfen-pyrethroid LLIN cluster 36: 142·29 [112·32-184·84] and cluster 53: 109·88 [79·31-157·70]). We observed minimal reductions in chlorfenapyr susceptibility and variable but significant reductions in fertility after pyriproxyfen exposure, with an overall trend of increasing susceptibility across trial years. Several metabolic genes were implicated in resistance selection, including CYP6P4 in the pyriproxyfen-pyrethroid LLIN group, which encodes an enzyme known to metabolise pyriproxyfen in vitro, and CYP6P3 and CYP9K1 in the chlorfenapyr-pyrethroid LLIN group, both of which encode enzymes that are involved in pro-insecticide activation.

INTERPRETATION

After 24 months of use, chlorfenapyr-pyrethroid LLINs no longer mitigated pyrethroid resistance selection in this area of southern Benin, which has high malaria transmission dominated by highly resistant A gambiae sensu lato. This finding raises issues for current net-procurement schedules, which are based on an operational net lifespan of 3 years. Knowledge of the effects of next-generation LLINs on insecticide-resistance selection is crucial for the pragmatic design of prospective resistance-management strategies.

FUNDING

UNITAID and The Global Fund to Fight AIDS, Tuberculosis and Malaria.

Lipid Metabolism as a Target Site in Pest Control

Lipid metabolism is essential to insect life as insects use lipids for their development, reproduction, flight, diapause, and a wide range of other functions. The central organ for insect lipid metabolism is the fat body, which is analogous to mammalian adipose tissue and liver, albeit less structured. Various other systems including the midgut, brain, and neural organs also contribute functionally to insect lipid metabolism. Lipid metabolism is under the control of core lipogenic [e.g. acetyl-CoA-carboxylase (ACC), fatty acid synthase (FAS), perilipin 2 (LSD2)], and lipolytic (lipases, perilipin 1) enzymes that are primarily expressed in the fat body, as well as hormones [insulin-like peptides (ILP), adipokinetic hormone (AKH)], transcription factors (SREBPs, foxO, and CREB), secondary messengers (calcium) and post-translational modifications (phosphorylation). Essential roles of the fat body, together with the fact that proper coordination of lipid metabolism is critical for insects, render lipid metabolism an attractive target site in pest control. In the current chapter, we focus on pest control tactics that target insect lipid metabolism. Various classes of traditional chemical insecticides [e.g. organophosphates, pyrethroids, neonicotinoids, and chitin synthesis inhibitors (Sects. 2.1 and 2.2)] have been shown to interfere with lipid metabolism, albeit it is not their primary site of action. However, the discovery of "lipid biosynthesis inhibitors", tetronic and tetramic acid derivatives commonly known as ketoenols (Sect. 2.3), was a milestone in applied entomology as they directly target lipid biosynthesis, particularly in sucking pests. Spirodiclofen, spiromesifen, and spirotetramat targeting ACC act against various insect and mite pests, while spiropidion and spidoxamat have been introduced to the market only recently. Efforts have concentrated on the development of chemical alternatives, such as hormone agonists and antagonists (Sect. 2.4), dsRNA-based pesticides that depend on RNA interference, which have great potential in pest control (Sect. 2.5) and other eco-friendly alternatives (Sect. 2.6).

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 investigated the effect of dietary L-DOPA on mosquito physiology and immunity to Plasmodium falciparum and Cryptococcus neoformans infection. Dietary L-DOPA was incorporated into mosquito melanin via a non-canonical pathway and had profound transcriptional effects that were associated with enhanced immunity, increased pigmentation, and reduced lifespan. Increased melanization resulted in an enhanced capacity to absorb electromagnetic radiation that affected mosquito temperatures. Bacteria in the mosquito microbiome were sources of dopamine, which is 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.

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.

No sexual pheromones in Anopheles mosquitoes?

Swarming behavior is the cornerstone of the anopheline mating system. At dusk, males congregate in monospecific swarms in which females come to find a mate once in their lives. Although many Anopheles species coexist in sympatry, hybrids are infrequent, suggesting the existence of strong premating reproductive barriers. Chemical cues, particularly pheromones, often play a crucial role in bringing sexes together in a species-specific manner among insects. While the existence of sexual pheromones in Anopheles species has been postulated, only a few studies developed experimental designs to investigate their presence. Here, we discuss the contrasting and debatable findings regarding both long-range and contact sex pheromones in the context of swarm ecology in Anopheles species.

The cytochrome P450 gene CYP4g1 driven by high temperature confers abamectin tolerance on Liriomyza trifolii through promoting cuticular hydrocarbons biosynthesis

Liriomyza trifolii, an invasive pest, poses a substantial threat to horticultural and vegetable plants. It spreads rapidly, especially in hot weather, leading to large-scale outbreaks with strong thermotolerance and insecticide resistance. In this study, mortality and LtCYP4g1 expression in L. trifolii were evaluated after thermal and insecticides exposure. Furthermore, functional verification of LtCYP4g1 was conducted through RNA interference and bacterial survival assays in Escherichia coli containing recombinant LtCYP4g1 protein. Results indicated that a short time exposure to high temperature incresed insecticide tolerance of L. trifolii, attributed to decreased mortality and induced LtCYP4g1 expression; LtCYP4g1 was involved in stimulating synthesis of cuticular hydrocarbons (CHCs) and elevating epicuticle lipid content and thickness, and E. coli cells overexpressing LtCYP4g1 exhibited significant tolerance to thermal and insecticide stress. In general, P450-mediated tolerance of L. trifolii was enhanced by high temperature, with LtCYP4g1 playing a role in promoting biosynthesis of CHCs for thickening epidermal lipid barrier and reducing cuticular penetration. This study provides a framework for delving into the function of CYP450s in insecticide detoxification and illustrates the role of global warming in driving the evolution of L. trifolii.

Genetic surveillance of insecticide resistance in African Anopheles populations to inform malaria vector control

Insecticide resistance in malaria vector populations poses a major threat to malaria control, which relies largely on insecticidal interventions. Contemporary vector-control strategies focus on combatting resistance using multiple insecticides with differing modes of action within the mosquito. However, diverse genetic resistance mechanisms are present in vector populations, and continue to evolve. Knowledge of the spatial distribution of these genetic mechanisms, and how they impact the efficacy of different insecticidal products, is critical to inform intervention deployment decisions. We developed a catalogue of genetic-resistance mechanisms in African malaria vectors that could guide molecular surveillance. We highlight situations where intervention deployment has led to resistance evolution and spread, and identify challenges in understanding and mitigating the epidemiological impacts of resistance.

Unravelling nicotinic receptor and ligand features underlying neonicotinoid knockdown actions on the malaria vector mosquito Anopheles gambiae

With the spread of resistance to long-established insecticides targeting Anopheles malaria vectors, understanding the actions of compounds newly identified for vector control is essential. With new commercial vector-control products containing neonicotinoids under development, we investigate the actions of 6 neonicotinoids (imidacloprid, thiacloprid, clothianidin, dinotefuran, nitenpyram and acetamiprid) on 13 Anopheles gambiae nicotinic acetylcholine receptor (nAChR) subtypes produced by expression of combinations of the Agα1, Agα2, Agα3, Agα8 and Agβ1 subunits in Xenopus laevis oocytes, the Drosophila melanogaster orthologues of which we have previously shown to be important in neonicotinoid actions. The presence of the Agα2 subunit reduces neonicotinoid affinity for the mosquito nAChRs, whereas the Agα3 subunit increases it. Crystal structures of the acetylcholine binding protein (AChBP), an established surrogate for the ligand-binding domain, with dinotefuran bound, shows a unique target site interaction through hydrogen bond formation and CH-N interaction at the tetrahydrofuran ring. This is of interest as dinotefuran is also under trial as the toxic element in baited traps. Multiple regression analyses show a correlation between the efficacy of neonicotinoids for the Agα1/Agα2/Agα8/Agβ1 nAChR, their hydrophobicity and their rate of knockdown of adult female An. gambiae, providing new insights into neonicotinoid features important for malaria vector control.

Association of a rapidly selected 4.3kb transposon-containing structural variation with a P450-based resistance to pyrethroids in the African malaria vector Anopheles funestus

Deciphering the evolutionary forces controlling insecticide resistance in malaria vectors remains a prerequisite to designing molecular tools to detect and assess resistance impact on control tools. Here, we demonstrate that a 4.3kb transposon-containing structural variation is associated with pyrethroid resistance in central/eastern African populations of the malaria vector Anopheles funestus. In this study, we analysed Pooled template sequencing data and direct sequencing to identify an insertion of 4.3kb containing a putative retro-transposon in the intergenic region of two P450s CYP6P5-CYP6P9b in mosquitoes of the malaria vector Anopheles funestus from Uganda. We then designed a PCR assay to track its spread temporally and regionally and decipher its role in insecticide resistance. The insertion originates in or near Uganda in East Africa, where it is fixed and has spread to high frequencies in the Central African nation of Cameroon but is still at low frequency in West Africa and absent in Southern Africa. A marked and rapid selection was observed with the 4.3kb-SV frequency increasing from 3% in 2014 to 98% in 2021 in Cameroon. A strong association was established between this SV and pyrethroid resistance in field populations and is reducing pyrethroid-only nets' efficacy. Genetic crosses and qRT-PCR revealed that this SV enhances the expression of CYP6P9a/b but not CYP6P5. Within this structural variant (SV), we identified putative binding sites for transcription factors associated with the regulation of detoxification genes. An inverse correlation was observed between the 4.3kb SV and malaria parasite infection, indicating that mosquitoes lacking the 4.3kb SV were more frequently infected compared to those possessing it. Our findings highlight the underexplored role and rapid spread of SVs in the evolution of insecticide resistance and provide additional tools for molecular surveillance of insecticide resistance.

Lipid Metabolism in Insect Vectors of Diseases

According to the World Health Organization vector-borne diseases account for more than 17% of all infectious diseases, causing more than 700,000 deaths annually. Vectors are organisms that are able to transmit infectious pathogens between humans, or from animals to humans. Many of these vectors are hematophagous insects, which ingest the pathogen from an infected host during a blood meal, and later transmit it into a new host. Malaria, dengue, African trypanosomiasis, yellow fever, leishmaniasis, Chagas disease, and many others are examples of diseases transmitted by insects.Both the diet and the infection with pathogens trigger changes in many metabolic pathways, including lipid metabolism, compared to other insects. Blood contains mostly proteins and is very poor in lipids and carbohydrates. Thus, hematophagous insects attempt to efficiently digest and absorb diet lipids and also rely on a large de novo lipid biosynthesis based on utilization of proteins and carbohydrates as carbon source. Blood meal triggers essential physiological processes as molting, excretion, and oogenesis; therefore, lipid metabolism and utilization of lipid storage should be finely synchronized and regulated regarding that, in order to provide the necessary energy source for these events. Also, pathogens have evolved mechanisms to hijack essential lipids from the insect host by interfering in the biosynthesis, catabolism, and transport of lipids, which pose challenges to reproduction, survival, fitness, and other insect traits.In this chapter, we have tried to collect and highlight the current knowledge and recent discoveries on the metabolism of lipids in insect vectors of diseases related to the hematophagous diet and pathogen infection.

Uncovering the genetic diversity in Aedes aegypti insecticide resistance genes through global comparative genomics

Aedes aegypti is vector of many arboviruses including Zika, dengue, yellow fever, West Nile, and Chikungunya. Its control efforts are hampered by widespread insecticide resistance reported in the Americas and Asia, while data from Africa is more limited. Here we use publicly available 729 Ae. aegypti whole-genome sequencing samples from 15 countries, including nine in Africa, to investigate the genetic diversity in four insecticide resistance linked genes: ace-1, GSTe2, rdl and vgsc. Apart from vgsc, the other genes have been less investigated in Ae. aegypti, and almost no genetic diversity information is available. Among the four genes, we identified 1,829 genetic variants including 474 non-synonymous substitutions, some of which have been previously documented, as well as putative copy number variations in GSTe2 and vgsc. Global insecticide resistance phenotypic data demonstrated variable resistance in geographic areas with resistant genotypes. Overall, our work provides the first global catalogue and geographic distribution of known and new amino-acid mutations and duplications that can be used to guide the identification of resistance drivers in Ae. aegypti and thereby support monitoring efforts and strategies for vector control.

Matrix metalloproteinase 2 contributes to adult eclosion and immune response in the small hive beetle, Aethina tumida

During the pupal-adult eclosion process of holometabolous insects, the old cuticle is shed and replaced by a completely different new cuticle that requires tanning and expansion, along with extensive extracellular matrix (ECM) remodeling. In vertebrates, matrix metalloproteinases (MMPs), a class of zinc-dependent endopeptidases, play key roles in regulating the ECM that surrounds cells. However, little is known about these extracellular proteinases available in insects. The small hive beetle (SHB), Aethina tumida, is a widespread invasive parasite of honey bees. In this study, 6 MMP homologs were identified in the SHB genome. RNA interference experiments showed that all 6 AtMmps are not required for the larval-pupal transition, only AtMmp2 was essential for pupal-adult eclosion in SHB. Knockdown of AtMmp2 resulted in eclosion defects and wing expansion failure, as well as mortality within 3 d of adult eclosion. Transcriptomic analysis revealed that knockdown of AtMmp2 significantly increased expression of the Toll and Imd pathways, chitin metabolism, and cross-linking (such as the pro-phenoloxidase activating cascade pathway and the tyrosine-mediated cuticle sclerotization and pigmentation pathway). These data revealed evolutionarily conserved functions of Mmp2 in controlling adult eclosion and wing expansion, also provided a preliminary exploration of the novel function of regulating Toll and Imd pathways, as well as new insights into how MMPs regulate insect development and defense barriers.

Role of CYP311A1 in wing development of Drosophila melanogaster

Lipid homeostasis is crucial for growth and development of organisms. Several cytochrome P450 monooxygenases (CYPs) are involved in lipid metabolism. The function of Cyp311a1 in the anterior midgut as a regulator of phosphatidylethanolamine (PE) metabolism in Drosophila melanogaster has been demonstrated, as depletion of Cyp311a1 caused larval growth arrest that was partially rescued by supplying PE. In this study, we investigated the role of CYP311A1 in wing morphogenesis in Drosophila. Using the GAL4-UAS system, Cyp311a1 was selectively knocked down in the wing disc. A deformed wing phenotype was observed in flies with reduced Cyp311a1 transcripts. BODIPY and oil red O staining revealed a reduction of neutral lipids in the wing disc after the depletion of Cyp311a1. In addition, we observed an enhanced sensitivity to Eosin Y penetration in the wings of Cyp311a1 knocked-down flies. Moreover, the reduction of CYP311A1 function in developing wings does not affect cell proliferation and apoptosis, but entails disordered Phalloidin or Cadherin distribution, suggesting an abnormal cell morphology and cell cortex structure in wing epithelial cells. Taken together, our results suggest that Cyp311a1 is needed for wing morphogenesis by participating in lipid assembly and cell homeostasis.

New and emerging mechanisms of insecticide resistance

The continuous use of insecticides over the last eight decades has led to the development of resistance to these insecticides. Research in the last few decades showed that the mechanisms underlying resistance are diverse but can generally be classified under several modes of resistance such as target-site resistance, metabolic resistance, and penetration resistance. In this review, we highlight new discoveries in insecticide resistance research made over the past few years, including an emerging new mode of resistance, sequestration resistance, where the overexpression of olfactory proteins binds and sequesters insecticides in resistant strains, as well as recent research on how posttranscriptional regulation can impact resistance. Future research will determine the generality of these emerging mechanisms across insect species.

Unveiling candidate genes for metabolic resistance to malathion in Aedes albopictus through RNA sequencing-based transcriptome profiling

Aedes albopictus, also known as the Asian tiger mosquito, is indigenous to the tropical forests of Southeast Asia. Ae. albopictus is expanding across the globe at alarming rates, raising concern over the transmission of mosquito-borne diseases, such as dengue, West Nile fever, yellow fever, and chikungunya fever. Since Ae. albopictus was reported in Houston (Harris County, Texas) in 1985, this species has rapidly expanded to at least 32 states across the United States. Public health efforts aimed at controlling Ae. albopictus, including surveillance and adulticide spraying operations, occur regularly in Harris County. Despite rotation of insecticides to mitigate the development of resistance, multiple mosquito species including Culex quinquefasciatus and Aedes aegypti in Harris County show organophosphate and pyrethroid resistance. Aedes albopictus shows relatively low resistance levels as compared to Ae. aegypti, but kdr-mutation and the expression of detoxification genes have been reported in Ae. albopictus populations elsewhere. To identify potential candidate detoxification genes contributing to metabolic resistance, we used RNA sequencing of field-collected malathion-resistant and malathion-susceptible, and laboratory-maintained susceptible colonies of Ae. albopictus by comparing the relative expression of transcripts from three major detoxification superfamilies involved in malathion resistance due to metabolic detoxification. Between these groups, we identified 12 candidate malathion resistance genes and among these, most genes correlated with metabolic detoxification of malathion, including four P450 and one alpha esterase. Our results reveal the metabolic detoxification and potential cuticular-based resistance mechanisms associated with malathion resistance in Ae. albopictus in Harris County, Texas.

Ivermectin resistance mechanisms in ectoparasites: a scoping review

Ivermectin mass drug administration has been used for decades to target human and veterinary ectoparasites, and is currently being considered for use against malaria vectors. Although there have been few reports of resistance to date in human ectoparasites, we must anticipate the development of resistance in mosquitoes in the future. Hence, through this review, we mapped the existing evidence on ivermectin resistance mechanisms in human ectoparasites. A search was conducted on the 8th November 2023 through databases, PubMed, Web of Science, and Google Scholar, using terms related to ivermectin, human and veterinary ectoparasites, and resistance. Abstracts (5893) were screened by JFA and CK. Data on the study organism, the type of resistance, the analysis methods, and, where applicable, the gene loci of interest were extracted from the studies. Details of the methodology and results of each study were summarised narratively and in a table. Eighteen studies were identified describing ivermectin resistance in ectoparasites. Two studies described target site resistance; and 16 studies reported metabolic resistance and/or changes in efflux pump expression. The studies investigated genetic mutations in resistant organisms, detoxification, and efflux pump expression in resistant versus susceptible organisms, and the effect of synergists on mortality or detoxification enzyme/efflux pump transcription. To date, very few studies have been conducted examining the mechanisms of ivermectin resistance in ectoparasites, with only two on Anopheles spp. Of the existing studies, most examined detoxification and efflux pump gene expression, and only two studies in lice investigated target-site resistance. Further research in this field should be encouraged, to allow for close monitoring in ivermectin MDA programmes, and the development of resistance mitigation strategies.

CYP4G subfamily genes mediate larval integument development in Spodoptera frugiperda

Cytochrome P450 (CYP) 4G subfamily is closely related to the synthesis of cuticular hydrocarbons, leading to the enhanced desiccation and insecticide resistance of pests. However, functions of CYP4Gs in larval integument development remain unknown in Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), which is a major transboundary migratory pest and become a common pest in China. On the basis of the genome and transcriptome datasets of S. frugiperda, CYP4G74, CYP4G75, CYP4G108, and CYP4G109 were identified, which contained the conserved domains of P450s and CYP4Gs. The spatial and temporal expression analysis showed that CYP4G74 and CYP4G75 were significantly highly expressed in adults and larval integuments, while CYP4G108 and CYP4G109 had low expressions in larval integuments. After silencing CYP4G74 and CYP4G75 by RNA interference, abnormal integument development occurred in larvae, some of which became smaller and dead, indicating important roles of CYP4G74 and CYP4G75 in the synthesis and development of integuments. The results clarify the functions of CYP4Gs in S. frugiperda and provide potential targets for the control of this pest.

Transcription Factors AhR and ARNT Regulate the Expression of CYP6SX1 and CYP3828A1 Involved in Insecticide Detoxification in Bradysia odoriphaga

Aryl hydrocarbon receptor (AhR) and aryl hydrocarbon receptor nuclear translocator (ARNT) mediate the responses of adaptive metabolism to various xenobiotics. Here, we found that BoAhR and BoARNT are highly expressed in the midgut of Bradysia odoriphaga larvae. The expression of BoAhR and BoARNT was significantly increased after exposure to imidacloprid and phoxim. The knockdown of BoAhR and BoARNT significantly decreased the expression of CYP6SX1 and CYP3828A1 as well as P450 enzyme activity and caused a significant increase in the sensitivity of larvae to imidacloprid and phoxim. Exposure to β-naphthoflavone (BNF) significantly increased the expression of BoAhR, BoARNT, CYP6SX1, and CYP3828A1 as well as P450 activity and decreased larval sensitivity to imidacloprid and phoxim. Furthermore, CYP6SX1 and CYP3828A1 were significantly induced by imidacloprid and phoxim, and the silencing of these two genes significantly reduced larval tolerance to imidacloprid and phoxim. Taken together, the BoAhR/BoARNT pathway plays key roles in larval tolerance to imidacloprid and phoxim by regulating the expression of CYP6SX1 and CYP3828A1.

Transcriptomic analysis of Anopheles gambiae from Benin reveals overexpression of salivary and cuticular proteins associated with cross-resistance to pyrethroids and organophosphates

BACKGROUND

Insecticide resistance (IR) is one of the major threats to malaria vector control programs in endemic countries. However, the mechanisms underlying IR are poorly understood. Thus, investigating gene expression patterns related to IR can offer important insights into the molecular basis of IR in mosquitoes. In this study, RNA-Seq was used to characterize gene expression in Anopheles gambiae surviving exposure to pyrethroids (deltamethrin, alphacypermethrin) and an organophosphate (pirimiphos-methyl).

RESULTS

Larvae of An. gambiae s.s. collected from Bassila and Djougou in Benin were reared to adulthood and phenotyped for IR using a modified CDC intensity bottle bioassay. The results showed that mosquitoes from Djougou were more resistant to pyrethroids (5X deltamethrin: 51.7% mortality; 2X alphacypermethrin: 47.4%) than Bassila (1X deltamethrin: 70.7%; 1X alphacypermethrin: 77.7%), while the latter were more resistant to pirimiphos-methyl (1.5X: 48.3% in Bassila and 1X: 21.5% in Djougou). RNA-seq was then conducted on resistant mosquitoes, non-exposed mosquitoes from the same locations and the laboratory-susceptible An. gambiae s.s. Kisumu strain. The results showed overexpression of detoxification genes, including cytochrome P450s (CYP12F2, CYP12F3, CYP4H15, CYP4H17, CYP6Z3, CYP9K1, CYP4G16, and CYP4D17), carboxylesterase genes (COEJHE5E, COE22933) and glutathione S-transferases (GSTE2 and GSTMS3) in all three resistant mosquito groups analyzed. Genes encoding cuticular proteins (CPR130, CPR10, CPR15, CPR16, CPR127, CPAP3-C, CPAP3-B, and CPR76) were also overexpressed in all the resistant groups, indicating their potential role in cross resistance in An. gambiae. Salivary gland protein genes related to 'salivary cysteine-rich peptide' and 'salivary secreted mucin 3' were also over-expressed and shared across all resistant groups.

CONCLUSION

Our results suggest that in addition to metabolic enzymes, cuticular and salivary gland proteins could play an important role in cross-resistance to multiple classes of insecticides in Benin. These genes warrant further investigation to validate their functional role in An. gambiae resistance to insecticides.

Insecticide resistance in social insects: assumptions, realities, and possibilities

Insecticide resistance is an evolved ability to survive insecticide exposure. Compared with nonsocial insects, eusocial insects have lower numbers of documented cases of resistance. Eusocial insects include beneficial and pest species that can be incidentally or purposely targeted with insecticides. The central goal of this review is to explore factors that either limit resistance or the ability to detect it in eusocial insects. We surveyed the literature and found that resistance has been documented in bees, but in other pest groups such as ants and termites, the evidence is more sparse. We suggest the path forward for better understanding eusocial resistance should include more tractable experimental models, comprehensive geographic sampling, and targeted testing of the impacts of social, symbiont, genetic, and ecological factors.

Whole transcriptomic analysis reveals overexpression of salivary gland and cuticular proteins genes in insecticide-resistant Anopheles arabiensis from Western Kenya

BACKGROUND

Effective vector control is key to malaria prevention. However, this is now compromised by increased insecticide resistance due to continued reliance on insecticide-based control interventions. In Kenya, we have observed heterogenous resistance to pyrethroids and organophosphates in Anopheles arabiensis which is one of the most widespread malaria vectors in the country. We investigated the gene expression profiles of insecticide resistant An. arabiensis populations from Migori and Siaya counties in Western Kenya using RNA-Sequencing. Centers for Disease Control and Prevention (CDC) bottle assays were conducted using deltamethrin (DELTA), alphacypermethrin (ACYP) and pirimiphos-methyl (PMM) to determine the resistance status in both sites.

RESULTS

Mosquitoes from Migori had average mortalities of 91%, 92% and 58% while those from Siaya had 85%, 86%, and 30% when exposed to DELTA, ACYP and PMM, respectively. RNA-Seq analysis was done on pools of mosquitoes which survived exposure ('resistant'), mosquitoes that were not exposed, and the insecticide-susceptible An. arabiensis Dongola strain. Gene expression profiles of resistant mosquitoes from both Migori and Siaya showed an overexpression mainly of salivary gland proteins belonging to both the short and long form D7 genes, and cuticular proteins (including CPR9, CPR10, CPR15, CPR16). Additionally, the overexpression of detoxification genes including cytochrome P450s (CYP9M1, CYP325H1, CYP4C27, CYP9L1 and CYP307A1), 2 carboxylesterases and a glutathione-S-transferase (GSTE4) were also shared between DELTA, ACYP, and PMM survivors, pointing to potential contribution to cross resistance to both pyrethroid and organophosphate insecticides.

CONCLUSION

This study provides novel insights into the molecular basis of insecticide resistance in An. arabiensis in Western Kenya and suggests that salivary gland proteins and cuticular proteins are associated with resistance to multiple classes of insecticides.

Exploring the molecular mechanisms of increased intensity of pyrethroid resistance in Central African population of a major malaria vector Anopheles coluzzii

Molecular mechanisms driving the escalation of pyrethroid resistance in the major malaria mosquitoes of Central Africa remain largely uncharacterized, hindering effective management strategies. Here, resistance intensity and the molecular mechanisms driving it were investigated in a population of Anopheles coluzzii from northern Cameroon. High levels of pyrethroid and organochloride resistance were observed in An. coluzzii population, with no mortality for 1× permethrin; only 11% and 33% mortalities for 5× and 10× permethrin diagnostic concentrations, and <2% mortalities for deltamethrin and DDT, respectively. Moderate bendiocarb resistance (88% mortality) and full susceptibility to malathion were observed. Synergist bioassays with piperonyl butoxide recovered permethrin susceptibility, with mortalities increasing to 53.39%, and 87.30% for 5× and 10× permethrin, respectively, implicating P450 monooxygenases. Synergist bioassays with diethyl maleate (DEM) recovered permethrin and DDT susceptibilities (mortalities increasing to 34.75% and 14.88%, respectively), implicating glutathione S-transferases. RNA-seq-based genome-wide transcriptional analyses supported by quantitative PCR identified glutathione S-transferase, GSTe2 (RNA-seqFC = 2.93 and qRT-PCRFC = 8.4, p < 0.0043) and CYP450, CYP6Z2 (RNA-seqFC = 2.39 and qRT-PCRFC = 11.7, p < 0.0177) as the most overexpressed detoxification genes in the pyrethroid-resistant mosquitoes, compared to mosquitoes of the susceptible Ngousso colony. Other overexpressed genes include P450s, CYP6M2 (FC = 1.68, p < 0.0114), CYP4G16 (FC = 2.02, p < 0.0005), and CYP4G17 (FC = 1.86, p < 0.0276). While high frequency of the 1014F kdr mutation (50%) and low frequencies of 1014S (6.61%) and 1575Y (10.29%) were observed, no ace-1 mutation was detected in bendiocarb-resistant populations, suggesting the preeminent role of metabolic mechanism. Overexpression of metabolic resistance genes (including GSTe2 and CYP6Z2 known to confer resistance to multiple insecticides) in An. coluzzii from the Sudan Savannah of Cameroon highlights the need for alternative management strategies to reduce malaria burden in northern Cameroon.

Comprehensive analysis of the overexpressed cytochrome P450-based insecticide resistance mechanism in Spodoptera litura

Cytochrome P450s play critical roles in the metabolic resistance of insecticides in insects. Previous findings showed that enhanced P450 activity was an important mechanism mediating indoxacarb resistance, and multiple P450 genes were upregulated in indoxacarb resistant strains of Spodoptera litura. However, the functions of these P450 genes in insecticide resistance remain unknown. Here, the P450 inhibitor PBO effectively decreased the resistance of S. litura to indoxacarb. Ten upregulated P450 genes were characterized, all of which were overexpressed in response to indoxacarb induction. Knockdown of nine P450 genes decreased cell viability against indoxacarb, and further silencing of three genes (CYP339A1, CYP340G2, CYP321A19) in larvae enhanced the sensitivity to indoxacarb. Transgenic overexpression of these three genes increased resistance to indoxacarb in Drosophila melanogaster. Moreover, molecular modeling and docking predicted that these three P450 proteins could bind tightly to indoxacarb and N-decarbomethoxylated metabolite (DCJW). Interestingly, these three P450 genes may also mediate cross-resistance to chlorantraniliprole, λ-cyhalothrin and imidacloprid. Additionally, heterologous expression and metabolic assays confirmed that three recombinant P450s could effectively metabolize indoxacarb and DCJW. This study strongly demonstrates that multiple overexpressed mitochondrial and microsomal P450 genes were involved in insecticide resistance in S. litura.

A cuticular protein, BgCPLCP1, contributes to insecticide resistance by thickening the cockroach endocuticle

Overuse of insecticides has led to severe environmental problems. Insect cuticle, which consists mainly of chitin, proteins and a thin outer lipid layer, serves multiple functions. Its prominent role is as a physical barrier that impedes the penetration of xenobiotics, including insecticides. Blattella germanica (L.) is a major worldwide indoor pest that causes allergic disease and asthma. Extensive use of pyrethroid insecticides, including β-cypermethrin, has selected for the rapid and independent evolution of resistance in cockroach populations on a global scale. We demonstrated that BgCPLCP1, the first CPLCP (cuticular proteins of low complexity with a highly repetitive proline-rich region) family cuticular protein in order Blattodea, contributes to insecticide penetration resistance. Silencing BgCPLCP1 resulted in 85.0 %-85.7 % and 81.0 %-82.0 % thinner cuticle (and especially thinner endocuticle) in the insecticide-susceptible (S) and β-cypermethrin-resistant (R) strains, respectively. The thinner and more permeable cuticles resulted in 14.4 % and 20.0 % lower survival of β-cypermethrin-treated S- and R-strain cockroaches, respectively. This study advances our understanding of cuticular penetration resistance in insects and opens opportunities for the development of new efficiently and environmentally friendly insecticides targeting the CPLCP family of cuticular proteins.

Arboviruses: Transmission and Host Resistance

In this review, there is a complete description of the classes of arboviruses, their evolutionary process, virus characterization, disease transmission methods; it also describes about the vectors involved in transmission and their mood of transmission, both biologically as well as non-biologically and, about host, the resistance mechanism in host, and artificial methods of preventing those viral transmissions. Arboviruses transmitted to hosts by some vectors such as mosquitoes, ticks, etc. The virus replicates in the host can be prevented by some host resistance mechanisms like RNA interference (RNAi), which degrade virus RNA by its antiviral activity, insect repellents, IGRs, and PI technology.

Insights into unique features of Drosophila CYP4G enzymes

The cytochrome P450 enzymes of the CYP4G subfamily are some of the most intriguing insect P450s in terms of structure and function. In Drosophila, CYP4G1 is highly expressed in the oenocytes and is the last enzyme in the biosynthesis of cuticular hydrocarbons, while CYP4G15 is expressed in the brain and is of unknown function. Both proteins have a CYP4G-specific and characteristic amino acid sequence insertion corresponding to a loop between the G and H helices whose function is unclear. Here we address these enigmatic structural and functional features of Drosophila CYP4Gs. First, we used reverse genetics to generate D. melanogaster strains in which all or part of the CYP4G-specific loop was removed from CYP4G1. We showed that the full loop was not needed for proper folding of the P450, but it is essential for function, and that just a short stretch of six amino acids is required for the enzyme's ability to make hydrocarbons. Second, we confirmed by immunocytochemistry that CYP4G15 is expressed in the brain and showed that it is specifically associated with the cortex glia cell subtype. We then expressed CYP4G15 ectopically in oenocytes, revealing that it can produce of a blend of hydrocarbons, albeit to quantitatively lower levels resulting in only a partial rescue of CYP4G1 knockdown flies. The CYP4G1 structural variants studied here should facilitate the biochemical characterization of CYP4G enzymes. Our results also raise the question of the putative role of hydrocarbons and their synthesis by cortex glial cells.

The role of P450 enzymes in malaria and other vector-borne infectious diseases

Vector-borne infectious diseases are still an important global health problem. Malaria is the most important among them, mainly pediatric, life-threatening disease. Malaria and other vector-borne disorders caused by parasites, bacteria, and viruses have a strong impact on public health and significant economic costs. Most vector-borne diseases could be prevented by vector control, with attention to the ecological and biodiversity conservation aspects. Chemical control with pesticides and insecticides is widely used as a measure of prevention although increasing resistance to insecticides is a serious issue in vector control. Metabolic resistance is the most common mechanism and poses a big challenge. Insect enzyme systems, including monooxygenase CYP P450 enzymes, are employed by vectors mainly to metabolize insecticides thus causing resistance. The discovery and application of natural specific inhibitors/blockers of vector P450 enzymes as synergists for commonly used pesticides will contribute to the "greening" of insecticides. Besides vector CYPs, host CYP enzymes could also be exploited to fight against vector-borne diseases: using mostly their detoxifying properties and involvement in the immune response. Here, we review published research data on P450 enzymes from all players in vector-borne infections, that is, pathogens, vectors, and hosts, regarding the potential role of CYPs in disease. We discuss strategies on how to exploit cytochromes P450 in vector-borne disease control.