Genomic analysis of detoxification genes in the mosquito Aedes aegypti

Exploring the Wilderness within: An Integrative Metabolomics and Transcriptomics Study on Near-Wild and Colonized Aedes aegypti

This study examines the phenotypic differences between wild-derived F2 Central Valley mosquitoes and the insecticide-susceptible Rockefeller (Rock) lab strain of Ae. aegypti. Given the rarity of wild pyrethroid-susceptible populations, the focus of this work is to develop an understanding of the resistance physiology in this invasive mosquito population and explore the potential of metabolites as diagnostic biomarkers for metabolic resistance. This study utilizes metabolomic, gene expression, and lifespan data for a comparison between strains. The findings indicate that wild-derived mosquitoes with greater metabolic resistance have a lifespan sensitivity to restricted larval nutrition. In terms of metabolism and gene expression, Central Valley mosquitoes show increased activity in oxidoreductase, glutathione metabolism, and the pentose phosphate pathway. Conversely, Rock mosquitoes display signs of metabolic inefficiency and mitochondrial dysregulation, likely tolerated due to the consistency and nutritional abundance of a controlled lab environment. The study also examines Ae. aegypti P450 and GSTE profiles in relation to other insecticide-resistant groups. While metabolomic data can differentiate our study groups, the challenges in biomarker development arise from few detected markers meeting high fold change thresholds.

Parallel Evolution in Mosquito Vectors-A Duplicated Esterase Locus is Associated With Resistance to Pirimiphos-methyl in Anopheles gambiae

The primary control methods for the African malaria mosquito, Anopheles gambiae, are based on insecticidal interventions. Emerging resistance to these compounds is therefore of major concern to malaria control programs. The organophosphate (OP), pirimiphos-methyl, is a relatively new chemical in the vector control armory but is now widely used in indoor-residual spray campaigns. While generally effective, phenotypic resistance has developed in some areas in malaria vectors. Here, we used a population genomic approach to identify novel mechanisms of resistance to pirimiphos-methyl in A. gambiae s.l mosquitoes. In multiple populations, we found large and repeated signals of selection at a locus containing a cluster of detoxification enzymes, some of whose orthologs are known to confer resistance to OPs in Culex pipiens. Close examination revealed a pair of alpha-esterases, Coeae1f and Coeae2f, and a complex and diverse pattern of haplotypes under selection in A. gambiae, A. coluzzii and A. arabiensis. As in C. pipiens, copy number variants have arisen at this locus. We used diplotype clustering to examine whether these signals arise from parallel evolution or adaptive introgression. Using whole-genome sequenced phenotyped samples, we found that in West Africa, a copy number variant in A. gambiae is associated with resistance to pirimiphos-methyl. Overall, we demonstrate a striking example of contemporary parallel evolution which has important implications for malaria control programs.

The impact of agrochemical pollutant mixtures on the selection of insecticide resistance in the malaria vector Anopheles gambiae: insights from experimental evolution and transcriptomics

BACKGROUND

There are several indications that pesticides used in agriculture contribute to the emergence and spread of resistance of mosquitoes to vector control insecticides. However, the impact of such an indirect selection pressure has rarely been quantified and the molecular mechanisms involved are still poorly characterized. In this context, experimental selection with different agrochemical mixtures was conducted in Anopheles gambiae. The multi-generational impact of agrochemicals on insecticide resistance was evaluated by phenotypic and molecular approaches.

METHODS

Mosquito larvae were selected for 30 generations with three different agrochemical mixtures containing (i) insecticides, (ii) non-insecticides compounds, and (iii) both insecticide and non-insecticide compounds. Every five generations, the resistance of adults to deltamethrin and bendiocarb was monitored using bioassays. The frequencies of the kdr (L995F) and ace1 (G119S) target-site mutations were monitored every 10 generations. RNAseq was performed on all lines at generation 30 in order to identify gene transcription level variations and polymorphisms associated with each selection regime.

RESULTS

Larval selection with agrochemical mixtures did not affect bendiocarb resistance and did not select for ace1 mutation. Contrastingly, an increased deltamethrin resistance was observed in the three selected lines. Such increased resistance was not majorly associated with the presence of kdr L995F mutation in selected lines. RNA-seq identified 63 candidate resistance genes over-transcribed in at least one selected line. These include genes coding for detoxification enzymes or cuticular proteins previously associated with insecticide resistance, and other genes potentially associated with chemical stress response. Combining an allele frequency filtering with a Bayesian FST-based genome scan allowed to identify genes under selection across multiple genomic loci, supporting a multigenic adaptive response to agrochemical mixtures.

CONCLUSION

This study supports the role of agrochemical contaminants as a significant larval selection pressure favouring insecticide resistance in malaria vectors. Such selection pressures likely impact kdr mutations and detoxification enzymes, but also more generalist mechanisms such as cuticle resistance, which could potentially lead to cross-tolerance to unrelated insecticide compounds. Such indirect effect of global landscape pollution on mosquito resistance to public health insecticides deserves further attention since it can affect the nature and dynamics of resistance alleles circulating in malaria vectors and impact the efficacy of control vector strategies.

Pyrethroid susceptibility reversal in Aedes aegypti: A longitudinal study in Tapachula, Mexico

Pyrethroid resistance in Aedes aegypti has become widespread after almost two decades of frequent applications to reduce the transmission of mosquito-borne diseases. Because few insecticide classes are available for public health use, insecticide resistance management (IRM) is proposed as a strategy to retain their use. A key hypothesis of IRM assumes that negative fitness is associated with resistance, and when insecticides are removed from use, susceptibility is restored. In Tapachula, Mexico, pyrethroids (PYRs) were used exclusively by dengue control programs for 15 years, thereby contributing to selection for high PYR resistance in mosquitoes and failure in dengue control. In 2013, PYRs were replaced by organophosphates-insecticides from a class with a different mode of action. To test the hypothesis that PYR resistance is reversed in the absence of PYRs, we monitored Ae. aegypti's PYR resistance from 2016 to 2021 in Tapachula. We observed significant declining rates in the lethal concentration 50 (LC50), for permethrin and deltamethrin. For each month following the discontinuation of PYR use by vector control programs, we observed increases in the odds of mosquitoes dying by 1.5% and 8.4% for permethrin and deltamethrin, respectively. Also, knockdown-resistance mutations (kdr) in the voltage-gated sodium channel explained the variation in the permethrin LC50s, whereas variation in the deltamethrin LC50s was only explained by time. This trend was rapidly offset by application of a mixture of neonicotinoid and PYRs by vector control programs. Our results suggest that IRM strategies can be used to reverse PYR resistance in Ae. aegypti; however, long-term commitment by operational and community programs will be required for success.

Tarsal exposure to atovaquone inhibits chikungunya virus transmission by Aedes aegypti mosquitoes, but not the transmission of Zika virus

The antimalarial drug atovaquone was recently reported to inhibit the in vitro replication of different arboviruses, including chikungunya virus (CHIKV) and Zika virus (ZIKV). Furthermore, atovaquone was shown to block Plasmodium parasite transmission by Anopheles mosquitoes when the mosquitoes were exposed to low concentrations on treated surfaces (i.e. tarsal exposure). Therefore, we evaluated the anti-CHIKV and -ZIKV effects of atovaquone via tarsal exposure in Aedes aegypti mosquitoes. We first confirmed that atovaquone exerted a dose-dependent antiviral effect on CHIKV and ZIKV replication in mosquito-derived cells. The modest antiviral effect could be rescued by adding exogenous uridine. Next, we assessed the effect of tarsal exposure to atovaquone on the fitness of Ae. aegypti. Concentrations up to 100 μmol/m2 did not affect the fecundity and egg-hatching rate. No significant effect on mosquito survival was observed when mosquitoes were exposed to concentrations up to 25 μmol/m2. To evaluate the antiviral effect of atovaquone against CHIKV, we exposed female mosquitoes to 100 μmol/m2 atovaquone for 1h, after which the mosquitoes were immediately infected with CHIKV or ZIKV via bloodmeal. Atovaquone did not significantly reduce ZIKV or CHIKV infection in Ae. aegypti, but successfully blocked the transmission of CHIKV in saliva. Tarsal exposure to antiviral drugs could therefore be a potential new strategy to reduce virus transmission by mosquitoes.

Quantitative proteomics analysis of permethrin and temephos-resistant Ae. aegypti revealed diverse differentially expressed proteins associated with insecticide resistance from Penang Island, Malaysia

Synthetic insecticides are the primary vector control method used globally. However, the widespread use of insecticides is a major cause of insecticide-resistance in mosquitoes. Hence, this study aimed at elucidating permethrin and temephos-resistant protein expression profiles in Ae. aegypti using quantitative proteomics. In this study, we evaluated the susceptibility of Ae. aegypti from Penang Island dengue hotspot and non-hotspot against 0.75% permethrin and 31.25 mg/l temephos using WHO bioassay method. Protein extracts from the mosquitoes were then analysed using LC-ESI-MS/MS for protein identification and quantification via label-free quantitative proteomics (LFQ). Next, Perseus 1.6.14.0 statistical software was used to perform differential protein expression analysis using ANOVA and Student's t-test. The t-test selected proteins with≥2.0-fold change (FC) and ≥2 unique peptides for gene expression validation via qPCR. Finally, STRING software was used for functional ontology enrichment and protein-protein interactions (PPI). The WHO bioassay showed resistance with 28% and 53% mortalities in adult mosquitoes exposed to permethrin from the hotspot and non-hotspot areas. Meanwhile, the susceptibility of Ae. aegypti larvae revealed high resistance to temephos in hotspot and non-hotspot regions with 80% and 91% mortalities. The LFQ analyses revealed 501 and 557 (q-value <0.05) differentially expressed proteins in adults and larvae Ae. aegypti. The t-test showed 114 upregulated and 74 downregulated proteins in adult resistant versus laboratory strains exposed to permethrin. Meanwhile, 13 upregulated and 105 downregulated proteins were observed in larvae resistant versus laboratory strains exposed to temephos. The t-test revealed the upregulation of sodium/potassium-dependent ATPase β2 in adult permethrin resistant strain, H15 domain-containing protein, 60S ribosomal protein, and PB protein in larvae temephos resistant strain. The downregulation of troponin I, enolase phosphatase E1, glucosidase 2β was observed in adult permethrin resistant strain and tubulin β chain in larvae temephos resistant strain. Furthermore, the gene expression by qPCR revealed similar gene expression patterns in the above eight differentially expressed proteins. The PPI of differentially expressed proteins showed a p-value at <1.0 x 10-16 in permethrin and temephos resistant Ae. aegypti. Significantly enriched pathways in differentially expressed proteins revealed metabolic pathways, oxidative phosphorylation, carbon metabolism, biosynthesis of amino acids, glycolysis, and citrate cycle. In conclusion, this study has shown differentially expressed proteins and highlighted upregulated and downregulated proteins associated with insecticide resistance in Ae. aegypti. The validated differentially expressed proteins merit further investigation as a potential protein marker to monitor and predict insecticide resistance in field Ae. aegypti. The LC-MS/MS data were submitted into the MASSIVE database with identifier no: MSV000089259.

A detoxification pathway initiated by a nuclear receptor TcHR96h in Tetranychus cinnabarinus (Boisduval)

Understanding the mechanism of detoxification initiation in arthropods after pesticide exposure is crucial. Although the identity of transcription factors that induce and regulate the expression of detoxification genes in response to pesticides is beginning to emerge, whether transcription factors directly interact with xenobiotics is unclear. The findings of this study revealed that a nuclear hormone receptor, Tetranychus cinnabarinus hormone receptor (HR) TcHR96h, regulates the overexpression of the detoxification gene TcGSTm02, which is involved in cyflumetofen resistance. The nuclear translocation of TcHR96h increased after cyflumetofen exposure, suggesting direct binding with cyflumetofen. The direct binding of TcHR96h and cyflumetofen was supported by several independent proteomic assays that quantify interactions with small molecules. Together, this study proposes a model for the initiation of xenobiotic detoxification in a polyphagous agricultural pest. These insights not only provide a better understanding of the mechanisms of xenobiotic detoxification and metabolism in arthropods, but also are crucial in understanding adaptation in polyphagous herbivores.

Can the use of larviciding with biological compounds contribute in increasing Anopheles gambiae s.l. susceptibility to pyrethroid in a population expressing high resistance intensity?

BACKGROUND

Larviciding using non-insecticide compounds is considered appropriate for controlling outdoor biting mosquitoes and for managing insecticide resistance. However, there is still not enough information on the influence of larviciding in managing pyrethroid resistance. In the present study, we checked whether the introduction of larviciding using the biolarvicide VectoMax G in the city of Yaoundé is contributing in restoring the susceptibility of An. coluzzii populations to pyrethroids.

METHODOLOGY

The susceptibility status of field An. coluzzii population was evaluated at different time points before and during larviciding treatments. In addition, An. coluzzii larvae collected in the city of Yaoundé, were split into four groups and exposed to different selection regimes for many generations as follow; (i): deltamethrin 0.05%_only, (ii): Vectomax_only, (iii): Vectomax+deltamethrin 0.05%, (iv): VectoMax+deltamethrin 0.05% + susceptible. Life traits parameters were measured in the progeny and compared between colonies. The control was the susceptible laboratory strain "Ngousso". Kdr allele frequency and the profile of expression of different detoxification genes and oxidative stress genes was checked using qPCR analysis. Gene's expression was compared between the first and the last generation of each colony and in field populations collected before and during larviciding.

RESULTS

An increase in mosquito susceptibility to deltamethrin and permethrin was recorded for the field populations after larviciding implementation. Resistance intensity to deltamethrin was found to decrease from high to low in field populations. Only the colony vectomax+deltamethrin+susceptible presented a high susceptibility to deltamethrin after 21 generations. The kdr gene frequency was found to be unchanged in the field population and laboratory colonies. A significant decrease in the overexpression profile of Gste2 was detected in field population after larviciding implementation. Other genes showing a similar pattern though not significant were Cyp6z1, Cyp6p1 and Cyp6g16. Concerning fitness only the colony vectomax+deltamethrin+susceptible was found to display a fitness profile similar to the susceptible colony with high fecundity, high hatching rate, short development time and long adult survival rate.

CONCLUSION

The profile of the field population supported reversal of phenotypic resistance to pyrethroids however no reduction in the frequency of the kdr allele was recorded. Some detoxification genes were detected less overexpressed. The study suggest that reversal may take longer to achieve in a population expressing a very high resistance profile and under continuous insecticide selection pressure.

Chlorfenapyr metabolism by mosquito P450s associated with pyrethroid resistance identifies potential activation markers

Chlorfenapyr is a pro-insecticide increasingly used in combination with pyrethroids such as a-cypermethrin or deltamethrin in insecticide treated bednets (ITNs) to control malaria transmitted by pyrethroid-resistant mosquito populations. Chlorfenapyr requires P450 activation to produce tralopyril and other bioactive metabolites. Pyrethroid resistance is often associated with elevated levels of chemoprotective P450s with broad substrate specificity, which could influence chlorfenapyr activity. Here, we have investigated chlorfenapyr metabolism by a panel of eight P450s commonly associated with pyrethroid resistance in An. gambiae and Ae. aegypti, the major vectors of malaria and arboviruses. Chlorfenapyr was activated to tralopyril by An. gambiae CYP6P3, CYP9J5, CYP9K1 and Ae. aegypti, CYP9J32. The Kcat/KM value of 0.66 μM-1 min-1 for CYP9K1 was, 6.7 fold higher than CYP6P3 and CYP9J32 (both 0.1 μM-1 min-1) and 22-fold higher than CYP9J5 (0.03 μM-1 min-1). Further investigation of the effect of -cypermethrin equivalent to the ratios used with chlorfenapyr in bed nets (~ 1:2 molar ratio) resulted in a reduction in chlorfenapyr metabolism by CYP6P3 and CYP6K1 of 76.8% and 56.8% respectively. This research provides valuable insights into the metabolism of chlorfenapyr by mosquito P450s and highlights the need for continued investigation into effective vector control strategies.

Comparative Transcriptomic Analysis of Insecticide-Resistant Aedes aegypti from Puerto Rico Reveals Insecticide-Specific Patterns of Gene Expression

Aedes aegypti transmits major arboviruses of public health importance, including dengue, chikungunya, Zika, and yellow fever. The use of insecticides represents the cornerstone of vector control; however, insecticide resistance in Ae. aegypti has become widespread. Understanding the molecular basis of insecticide resistance in this species is crucial to design effective resistance management strategies. Here, we applied Illumina RNA-Seq to study the gene expression patterns associated with resistance to three widely used insecticides (malathion, alphacypermethrin, and lambda-cyhalothrin) in Ae. aegypti populations from two sites (Manatí and Isabela) in Puerto Rico (PR). Cytochrome P450s were the most overexpressed detoxification genes across all resistant phenotypes. Some detoxification genes (CYP6Z7, CYP28A5, CYP9J2, CYP6Z6, CYP6BB2, CYP6M9, and two CYP9F2 orthologs) were commonly overexpressed in mosquitoes that survived exposure to all three insecticides (independent of geographical origin) while others including CYP6BY1 (malathion), GSTD1 (alpha-cypermethrin), CYP4H29 and GSTE6 (lambda-cyhalothrin) were uniquely overexpressed in mosquitoes that survived exposure to specific insecticides. The gene ontology (GO) terms associated with monooxygenase, iron binding, and passive transmembrane transporter activities were significantly enriched in four out of six resistant vs. susceptible comparisons while serine protease activity was elevated in all insecticide-resistant groups relative to the susceptible strain. Interestingly, cuticular-related protein genes (chinase and chitin) were predominantly downregulated, which was also confirmed in the functional enrichment analysis. This RNA-Seq analysis presents a detailed picture of the candidate detoxification genes and other pathways that are potentially associated with pyrethroid and organophosphate resistance in Ae. aegypti populations from PR. These results could inform development of novel molecular tools for detection of resistance-associated gene expression in this important arbovirus vector and guide the design and implementation of resistance management strategies.

High-quality chromosome-level scaffolds of the plant bug Pachypeltis micranthus provide insights into the availability of Mikania micrantha control

BACKGROUND

The plant bug, Pachypeltis micranthus Mu et Liu (Hemiptera: Miridae), is an effective potential biological control agent for Mikania micrantha H.B.K. (Asteraceae; one of the most notorious invasive weeds worldwide). However, limited knowledge about this species hindered its practical application and research. Accordingly, sequencing the genome of this mirid bug holds great significance in controlling M. micrantha.

RESULTS

Here, 712.72 Mb high-quality chromosome-level scaffolds of P. micranthus were generated, of which 707.51 Mb (99.27%) of assembled sequences were anchored onto 15 chromosome-level scaffolds with contig N50 of 16.84 Mb. The P. micranthus genome had the highest GC content (42.43%) and the second highest proportion of repetitive sequences (375.82 Mb, 52.73%) than the three other mirid bugs (i.e., Apolygus lucorum, Cyrtorhinus lividipennis, and Nesidiocoris tenuis). Phylogenetic analysis showed that P. micranthus clustered with other mirid bugs and diverged from the common ancestor approximately 200 million years ago. Gene family expansion and/or contraction were analyzed, and significantly expanded gene families associated with P. micranthus feeding and adaptation to M. micrantha were manually identified. Compared with the whole body, transcriptome analysis of the salivary gland revealed that most of the upregulated genes were significantly associated with metabolism pathways and peptidase activity, particularly among cysteine peptidase, serine peptidase, and polygalacturonase; this could be one of the reasons for precisely and highly efficient feeding by the oligophagous bug P. micranthus on M. micrantha.

CONCLUSION

Collectively, this work provides a crucial chromosome-level scaffolds resource to study the evolutionary adaptation between mirid bug and their host. It is also helpful in searching for novel environment-friendly biological strategies to control M. micrantha.

Identification, expression profiles and involvement in insecticides tolerance and detoxification of carboxylesterase genes in Bactrocera dorsalis

Carboxylesterases (CarEs) are a multifunctional superfamily of enzymes and play an important role in detoxification of various insecticides in insects. The oriental fruit fly, Bactrocera dorsalis, is one of the most destructive agricultural pests and has developed different degrees of resistance to organophosphates in field. However, the involvement of BdCarEs in tolerance or resistance to other alternative insecticides are still unclear. In the present study, 33 BdCarEs genes were identified based on the genome database of B. dorsalis. Phylogenetic analysis demonstrated that they were classified into nine clades, with abundance of α-esterases. Meanwhile, the sequence characterization and the chromosome distribution were also analyzed. The spatiotemporal expression analysis of BdCarEs genes suggested that the diversity of potential function in different physiological processes. With the exception of BdCarE21, all BdCarEs genes responded to at least one insecticide exposure, and BdCarE20 was found to be up-regulated after exposure to all five tested insecticides individually. Eight BdCarEs genes were overexpressed in MR strain when compared to that in SS strain. Subsequently, knockdown the expression of representative BdCarEs genes significantly increased the susceptibility of the oriental fruit fly to corresponding insecticides, which indicated that the tested BdCarEs genes contributed to one or multiple insecticide detoxification. These findings provide valuable insights into the potential role in respond to tolerance or resistance to insecticides with different mode of action, and will facilitate development of efficiency management strategy for B. dorsalis.

Recombinant expression and characterization of GSTd3 from a resistant population of Anopheles arabiensis and comparison of DDTase activity with GSTe2

The development of insecticide resistance in malaria vectors is a challenge for the global effort to control and eradicate malaria. Glutathione S-transferases (GSTs) are multifunctional enzymes involved in the detoxification of many classes of insecticides. For mosquitoes, it is known that overexpression of an epsilon GST, GSTe2, confers resistance towards DDT and pyrethroids. In addition to GSTe2, consistent overexpression of a delta class GST, GSTd3, has been observed in insecticide resistant populations of different malaria vector species. However, the functional role of GSTd3 towards DDT resistance has not yet been investigated. Here, we recombinantly expressed both GSTe2 and GSTd3 from Anopheles arabiensis and compared their metabolic activities against DDT. Both AaGSTd3 and AaGSTe2 exhibited CDNB-conjugating and glutathione peroxidase activity and DDT metabolism was observed for both GSTs. However, the DDT dehydrochlorinase activity exhibited by AaGSTe2 was much higher than for AaGSTd3, and AaGSTe2 was also able to eliminate DDE although the metabolite could not be identified. Molecular modeling revealed subtle differences in the binding pocket of both enzymes and a better fit of DDT within the H-site of AaGSTe2. The overexpression but much lower DDT metabolic activity of AaGSTd3, might suggest that AaGSTd3 sequesters DDT. These findings highlight the complexity of insecticide resistance in the major malaria vectors and the difficulties associated with control of the vectors using DDT, which is still used for indoor residual spraying.

The buzz in the field: the interaction between viruses, mosquitoes, and metabolism

Among many medically important pathogens, arboviruses like dengue, Zika and chikungunya cause severe health and economic burdens especially in developing countries. These viruses are primarily vectored by mosquitoes. Having surmounted geographical barriers and threat of control strategies, these vectors continue to conquer many areas of the globe exposing more than half of the world's population to these viruses. Unfortunately, no medical interventions have been capable so far to produce successful vaccines or antivirals against many of these viruses. Thus, vector control remains the fundamental strategy to prevent disease transmission. The long-established understanding regarding the replication of these viruses is that they reshape both human and mosquito host cellular membranes upon infection for their replicative benefit. This leads to or is a result of significant alterations in lipid metabolism. Metabolism involves complex chemical reactions in the body that are essential for general physiological functions and survival of an organism. Finely tuned metabolic homeostases are maintained in healthy organisms. However, a simple stimulus like a viral infection can alter this homeostatic landscape driving considerable phenotypic change. Better comprehension of these mechanisms can serve as innovative control strategies against these vectors and viruses. Here, we review the metabolic basis of fundamental mosquito biology and virus-vector interactions. The cited work provides compelling evidence that targeting metabolism can be a paradigm shift and provide potent tools for vector control as well as tools to answer many unresolved questions and gaps in the field of arbovirology.

Cardinium infection alters cotton defense and detoxification metabolism of its whitefly host

Field monitoring revealed that the infection ratio of the bacterial symbiont Cardinium in the whitefly (Bemisia tabaci MED) was relatively low in northern China. However, the role of this symbiont and the symbiont-whitefly-host plant interaction mechanism are poorly understood. We investigated the influence of Cardinium on the competitiveness of the host whitefly and the physiological interaction between the host plants and host whiteflies. Cardinium-infected whiteflies were displaced by uninfected whiteflies after 5 generations, which showed that Cardinium infection reduced whitefly competitiveness. The defense response genes of cotton significantly decreased under infestation by infected whiteflies compared to uninfected whiteflies. The expression of detoxification metabolism genes, especially the uridine 5'-diphospho-glucuronyltransferase and P450 genes, in infected whiteflies significantly decreased. These results demonstrated that Cardinium could inhibit the defense response of the host plant and decrease the detoxification metabolism ability of the host whitefly. The reduced competitiveness of infected whiteflies may be associated with the inhibition of the whitefly detoxification metabolism by Cardinium, resulting in the reduced performance of infected whiteflies. However, Cardinium infection can suppress plant defenses, which may benefit both infected and uninfected whiteflies when they coexist. This research illustrates the symbiont-whitefly-host plant interaction mechanism and the population dynamics of the whitefly.

Dynamic Roles of Insect Carboxyl/Cholinesterases in Chemical Adaptation

Insects have evolved several intricate defense mechanisms to adapt to their chemical environment. Due to their versatile capabilities in hydrolytic biotransformation, insect carboxyl/cholinesterases (CCEs) play vital roles in the development of pesticide resistance, facilitating the adaptation of insects to their host plants, and manipulating insect behaviors through the olfaction system. CCEs confer insecticide resistance through the mechanisms of qualitative or quantitative changes of CCE-mediated enhanced metabolism or target-site insensitivity, and may contribute to the host plant adaptation. CCEs represent the first odorant-degrading enzymes (ODEs) discovered to degrade insect pheromones and plant odors and remain the most promising ODE candidates. Here, we summarize insect CCE classification, currently characterized insect CCE protein structure characteristics, and the dynamic roles of insect CCEs in chemical adaptation.

Role of Insect and Mammal Glutathione Transferases in Chemoperception

Glutathione transferases (GSTs) are ubiquitous key enzymes with different activities as transferases or isomerases. As key detoxifying enzymes, GSTs are expressed in the chemosensory organs. They fulfill an essential protective role because the chemosensory organs are located in the main entry paths of exogenous compounds within the body. In addition to this protective function, they modulate the perception process by metabolizing exogenous molecules, including tastants and odorants. Chemosensory detection involves the interaction of chemosensory molecules with receptors. GST contributes to signal termination by metabolizing these molecules. By reducing the concentration of chemosensory molecules before receptor binding, GST modulates receptor activation and, therefore, the perception of these molecules. The balance of chemoperception by GSTs has been shown in insects as well as in mammals, although their chemosensory systems are not evolutionarily connected. This review will provide knowledge supporting the involvement of GSTs in chemoperception, describing their localization in these systems as well as their enzymatic capacity toward odorants, sapid molecules, and pheromones in insects and mammals. Their different roles in chemosensory organs will be discussed in light of the evolutionary advantage of the coupling of the detoxification system and chemosensory system through GSTs.

Genome-wide and expression-profiling analyses of the cytochrome P450 genes in Tenebrionidea

Cytochrome P450 monooxygenases (CYPs) are present in almost all areas of the tree of life. As one of the largest and most diverse superfamilies of multifunctional enzymes, they play important roles in the metabolism of xenobiotics and biosynthesis of endogenous compounds, shaping the success of insects. In this study, the CYPome (an omics term for all the CYP genes in a genome) diversification was examined in the four Tenebrionidea species through genome-wide analysis. A total of 483 CYP genes were identified, of which 103, 157, 122, and 101 were respectively deciphered from the genomes of Tebebrio molitor, Asbolus verucosus, Hycleus cichorii and Hycleus phaleratus. These CYPs were classified into four major clans (mitochondrial, CYP2, CYP3, and CYP4), and clans CYP3 and CYP4 are most diverse. Phylogenetic analysis showed that most CYPs of these Tenebrionidea beetles from each clan had a very close 1:1 orthology to each other, suggesting that they originate closely and have evolutionally conserved function. Expression analysis at different developmental stages and in various tissues showed the life stage-, gut-, salivary gland-, fat body-, Malpighian tubule-, antennae-, ovary- and testis-specific expression patterns of T. molitor CYP genes, implying their various potential roles in development, detoxification, immune response, digestion, olfaction, and reproduction. Our studies provide a platform to understand the evolution of Tenebrionidea CYP gene superfamily, and a basis for further functional investigation of the T. molitor CYPs involved in various biological processes.

Comparative genomic analysis of carboxylesterase genes in Tenebrio molitor and other four tenebrionids

Carboxylesterases (COEs) have various functions in wide taxons of organisms. In insects, COEs are important enzymes involved in the hydrolysis of a variety of ester-containing xenobiotics, neural signal transmission, pheromone degradation, and reproductive development. Understanding the diversity of COEs is basic to illustrate their functions. In this study, we identified 53, 105, 37, and 39 COEs from the genomes of Tenebrio molitor, Asbolus verucosus, Hycleus cichorii, and H. phaleratus in the superfamily of Tenebrionidea, respectively. Phylogenetic analysis showed that 234 COEs from these four species and those reported in Tribolium castaneum (63) could be divided into 12 clades and three major classes. The α-esterases significantly expanded in T. molitor, A. verucosus, and T. castaneum compared to dipteran and hymenopteran insects. In T. molitor, most COEs showed tissue and stage-specific but not a sex-biased expression. Our results provide insights into the diversity and evolutionary characteristics of COEs in tenebrionids, and lay a foundation for the functional characterization of COEs in the yellow mealworm.

Cytochrome P450 Genes Expressed in Phasmatodea Midguts

Cytochrome P450s (CYPs) are xenobiotic detoxification genes found in most eukaryotes, and linked in insects to the tolerance of plant secondary chemicals and insecticide resistance. The number and diversity of CYP clans, families, and subfamilies that an organism produces could correlate with its dietary breadth or specialization. This study examined the CYP diversity expressed in the midguts of six species of folivorous stick insects (Phasmatodea), to identify their CYP complement and see if any CYPs correlate with diet toxicity or specialization, and see what factors influenced their evolution in this insect order. CYP genes were mined from six published Phasmatodea transcriptomes and analyzed phylogenetically. The Phasmatodea CYP complement resembles that of other insects, though with relatively low numbers, and with significant expansions in the CYP clades 6J1, 6A13/14, 4C1, and 15A1. The CYP6 group is known to be the dominant CYP family in insects, but most insects have no more than one CYP15 gene, so the function of the multiple CYP15A1 genes in Phasmatodea is unknown, with neofunctionalization following gene duplication hypothesized. No correlation was found between CYPs and diet specialization or toxicity, with some CYP clades expanding within the Phasmatodea and others likely inherited from a common ancestor.

De novo genome assembly of Bradysia cellarum (Diptera: Sciaridae), a notorious pest in traditional special vegetables in China

Bradysia cellarum (Diptera: Sciaridae) is a destructive vegetable insect pest infesting more than 30 species of host plants from seven families in Asia and Europe. B. cellarum causes grave problems in Chinese chive, which originated in China and is cultivated widely in East Asia. The B. cellarum infestation results in economic losses and subsequent severe food safety problems in farm productions, insecticide resistance and environmental pollution. The genomic and molecular information of B. cellarum to delineate the biological features, insecticide resistance, evolution remains poorly understood. Herein, we decode the whole genome of B. cellarum to delineate the underlying molecular mechanisms causing insecticide resistance. We constructed a highly reliable genome for B. cellarum using PacBio, Illumina and 10X Genomics sequencing platforms. The genome size of B. cellarum was 375.91 Mb with a contig N50 of 1.57 Mb. A total of 16,231 genes were identified, among which 93.8% were functionally annotated, and 42.06% were repeat sequences. According to phylogenetic analysis, B. cellarum diverged from the common ancestor of Drosophila melanogaster and Musca domestica ~139.3-191.0 million years ago. Moreover, some important genes responsible for significant insecticide resistance, such as cytochrome P450s, ABC transporters and those involved in glutathione metabolism, were expanded in B. cellarum. We assembled a high-quality B. cellarum genome to provide valuable insights into their life history strategies, insecticide resistance and biological behaviours. It also lays the foundation for exploring gene structure and functional evolution, as well as comparative genomics of B. cellarum and other model insect species.

Defining the mechanisms of action and mosquito larva midgut response to a yeast-encapsulated orange oil larvicide

BACKGROUND

Yeast-encapsulated orange oil (YEOO) is a novel, ingestible larvicide that combines the benefits of a low-cost essential oil with yeast, an attractive food source for mosquito larvae. In this work, we investigated the underlying mechanisms of action associated with YEOO ingestion by Aedes aegypti larvae.

METHODS

Aedes aegypti third-stage larvae (L3) were treated with sublethal or lethal concentrations of YEOO. Genes associated with apoptosis, autophagy and innate immune responses were investigated by RT-qPCR in guts and carcasses dissected from treated and control larvae. Differential expression of cytochrome P450 genes in the CYP6 and CYP9 families were also investigated. Confocal and transmission electron microscopy were used to assess damage caused by YEOO throughout the larval alimentary canal. TUNEL was used to assess apoptosis via DNA fragmentation.

RESULTS

The apoptosis genes IAP1 and IAP2 in larvae displayed opposing effects following exposure to lethal doses of YEOO, with a 26-fold induction of IAP1 at 8 h post YEOO ingestion. The effector caspase CASPS8 displayed a 6.7-fold induction in the gut and concomitant 70-fold induction in the carcass at 8 h post YEOO ingestion. The midgut epithelia regenerator, Vein, had an 11-fold induction in the gut after 4 h and was repressed 7.6-fold in the carcass at 24 h. Sublethal concentrations (< LC₅₀) led to significant differential expression of CYP6 and CYP9 genes. Midgut epithelial damage was highlighted by the destruction of microvilli, vacuolization of midgut cells and damage to cell junctions and basal lamina as early as 30 min. Larval type 2 peritrophic matrix structural integrity and porosity remain unchanged.

CONCLUSION

Our results strongly suggest that the robust larvicidal activity of YEOO is due to a generalized broad-acting mechanism combining epithelial damage and apoptosis, with concomitant expression of multiple innate response genes involved in epithelial regeneration and detoxification. YEOO's amenability for use as part of an integrated vector management program makes this novel larvicide a practical approach for mosquito larval control in the future.

Comparative transcriptome and RNA interference reveal CYP6DC1 and CYP380C47 related to lambda-cyhalothrin resistance in Rhopalosiphum padi

The bird-cherry-oat aphid, Rhopalosiphum padi, is a serious agricultural pest of Triticeae crops, and pyrethroids are the most widely used chemical pesticides for the control of the aphid. Our previous studies found that some R. padi field populations have developed resistance against pyrethroids; an M918L target-site mutation of the voltage gated sodium channel was present in the pyrethroid resistant individuals, while the high-level resistance to lambda-cyhalothrin revealed the presence of other mechanisms in the pest. Here, we conducted genome-wide transcriptional analysis for the lambda-cyhalothrin susceptible (SS) and resistant (LC-RR) strains of R. padi. Results indicated that 2457 genes were differently expressed between the SS and LC-RR strains. In the LC-RR, a total of 1265 and 1192 genes were up- and down-regulated, respectively. KEGG analysis implicated enrichment of P450 involved in insecticide metabolic pathways in the resistant transcriptome. qRT-PCR results confirmed that two P450 genes (CYP6DC1 and CYP380C47) were significantly overexpressed in the LC-RR individuals. Furthermore, RNA interference (RNAi) of CYP6DC1 or CYP380C47 significantly increased mortality of R. padi exposure to lambda-cyhalothrin. These results suggest that the overexpression of CYP6DC1 and CYP380C47 contributed to the lambda-cyhalothrin resistance in the pest. This study provides knowledge for further analyzing the molecular mechanism of resistance to pyrethroids in R. padi.

Identification and Characterization of CYP6 Family Genes from the Oriental Fruit Moth (Grapholita molesta) and Their Responses to Insecticides

Simple Summary

Eight CYP6 family genes were identified in Grapholita molesta (Busck). The expression of individual gene members differed between the developmental stages and insect tissues. High expression was found in third/fourth-instar larvae and in the midgut and Malpighian tubules. The response patterns of the genes exhibited diverse response patterns to the three representative insecticides were diverse.

Abstract

Cytochrome P450 (CYP) monooxygenases comprise a superfamily of proteins that detoxify xenobiotics and plant secondary metabolites in insects. The CYP6 family is unique to the class Insecta, and its members participate in the metabolism of exogenous substances. In this study, we sequenced and characterized the full-length cDNAs of eight CYP6 family genes from Grapholita molesta (Busck), a global pest of pome fruits. P450 genes with the exception of CYP6AN35, which was most highly expressed in adults, consistently showed high expression in third- or fourth-instar larvae. The analysis of different tissues of adults showed that most of these genes were predominantly expressed in the midgut, Malpighian tubules, and/or fat body. The expression of these eight CYP6 genes was differentially affected by three representative insecticides: malathion (organophosphate), deltamethrin (pyrethroid), and chlorantraniliprole (carbamate). All eight CYP6 genes responded to malathion treatment. Only three CYP6 genes were highly expressed in deltamethrin-treated individuals. Chlorantraniliprole treatment exerted weak effects on gene expression. Interestingly, CYP6AN35 was a highly expression level in the adult head and its expression was induced by all three insecticides. CYP6AN35 may be a key gene in the metabolism of insecticides. This study provides a fundamental understanding of the functions of the CYP6 gene family in insecticide metabolism in G. molesta.

Molecular and functional characterization of three novel carboxylesterases in the detoxification of permethrin in the mosquito, Culex quinquefasciatus

Carboxylesterases (CarEs) belong to a super family of multifunctional enzymes associated with the degradation of endogenous and exogenous compounds. Many insect CarEs are known to play important roles in catalyzing the hydrolysis of organophosphates (OPs), carbamates, and synthetic pyrethroids (SPs). The elevation of esterase activity through gene amplification and overexpression of estα2 and estβ2 genes contributes to the development of resistance to OP insecticides in the mosquito Culex quinquefasciatus. Three additional CarE genes are upregulated in permethrin-resistant Cx. quinquefasciatus according to an RNA-seq analysis, but their function remains unknown. In this study, we, for the first time, characterized the function of these three novel genes using in vitro protein expression, an insecticide metabolism study and molecular docking analysis. All three CarE genes were significantly overexpressed in resistant mosquito larvae, but not adults, compared to susceptible strain. No gene copy differences in these three genes were found in the mosquitoes tested. In vitro high-performance liquid chromatography (HPLC) revealed that CPIJ018231, CPIJ018232, and CPIJ018233 metabolized 30.4% ± 2.9%, 34.7% ± 6.8%, and 23.2% ± 2.2% of the permethrin, respectively. No mutations in resistant strains might significantly affect their CarE hydrolysis ability. A docking analysis further confirmed that these three CarEs from resistant strain all potentially metabolize permethrin. Taken together, these three carboxylesterase genes could play important roles in the development of permethrin resistance in Cx. quinquefasciatus larvae through transcriptional overexpression, metabolism, and detoxification.

The Central Role of Multiple P450 Genes and Their Co-factor CPR in the Development of Permethrin Resistance in the Mosquito Culex quinquefasciatus

Mosquitoes’ increasing resistance to insecticides is becoming a major threat for control efforts worldwide. Multiple P450 genes that are up-regulated in permethrin resistant strains of Culex quinquefasciatus have been linked to the development of resistance. In the current study, we characterized the function of six P450 genes, CYP6P14, CYP6BZ2, CYP9J33, CYP9J34, CYP9J40, and CYP9J45, that are overexpressed in the permethrin resistant Culex mosquitoes and showed their capability in metabolism of permethrin. These six P450 genes can convert 3-phenoxybenzoic alcohol (PBCHO) to a less toxic product, 3-phenoxybenzoic acid (PBCOOH), indicating that these P450s play an important role in permethrin degradation pathways. Although we know multiple P450 genes are over-expressed in permethrin resistant Culex mosquitoes, it remains to be seen whether cytochrome P450-reductase (CPR) gene that are co-overexpressed with P450 genes in permethrin resistant mosquitoes do indeed serve as a resistance mechanism. An in-depth investigation of the expression of CPR gene in resistant mosquitoes was conducted in permethrin resistant mosquitoes. The finding of CPR gene overexpression in permethrin resistant mosquitoes suggested the importance of co-overexpression of multiple P450 genes with their obligatory electron donor CPR in the complex detoxification system, boosting the metabolism of permethrin and hence the development of permethrin resistance in Cx. quinquefasciatus.

Expansive and Diverse Phenotypic Landscape of Field Aedes aegypti (Diptera: Culicidae) Larvae with Differential Susceptibility to Temephos: Beyond Metabolic Detoxification

Arboviruses including dengue, Zika, and chikungunya are amongst the most significant public health concerns worldwide. Arbovirus control relies on the use of insecticides to control the vector mosquito Aedes aegypti (Linnaeus), the success of which is threatened by widespread insecticide resistance. The work presented here profiled the gene expression of Ae. aegypti larvae from field populations of Ae. aegypti with differential susceptibility to temephos originating from two Colombian urban locations, Bello and Cúcuta, previously reported to have distinctive disease incidence, socioeconomics, and climate. We demonstrated that an exclusive field-to-lab (Ae. aegypti strain New Orleans) comparison generates an over estimation of differential gene expression (DGE) and that the inclusion of a geographically relevant field control yields a more discrete, and likely, more specific set of genes. The composition of the obtained DGE profiles is varied, with commonly reported resistance associated genes including detoxifying enzymes having only a small representation. We identify cuticle biosynthesis, ion exchange homeostasis, an extensive number of long noncoding RNAs, and chromatin modelling among the differentially expressed genes in field resistant Ae. aegypti larvae. It was also shown that temephos resistant larvae undertake further gene expression responses when temporarily exposed to temephos. The results from the sampling triangulation approach here contribute a discrete DGE profiling with reduced noise that permitted the observation of a greater gene diversity, increasing the number of potential targets for the control of insecticide resistant mosquitoes and widening our knowledge base on the complex phenotypic network of the Ae. aegypti response to insecticides.

Impact of selection regime and introgression on deltamethrin resistance in the arbovirus vector Aedes aegypti - a comparative study between contrasted situations in New Caledonia and French Guiana

BACKGROUND

Pyrethroid insecticides such as deltamethrin have been massively used against Aedes aegypti leading to the spread of resistance alleles worldwide. In an insecticide resistance management context, we evaluated the temporal dynamics of deltamethrin resistance using two distinct populations carrying resistant alleles at different frequencies. Three different scenarios were followed: a continuous selection, a full release of selection, or a repeated introgression with susceptible individuals. The responses of each population to these selection regimes were measured across five generations by bioassays and by monitoring the frequency of knockdown resistance (kdr) mutations and the transcription levels and copy number variations of key detoxification enzymes.

RESULTS

Knockdown resistance mutations, overexpression and copy number variations of detoxification enzymes as a mechanism of metabolic resistance to deltamethrin was found and maintained under selection across generations. On comparison, the release of insecticide pressure for five generations did not affect resistance levels and resistance marker frequencies. However, introgressing susceptible alleles drastically reduced deltamethrin resistance in only three generations.

CONCLUSION

The present study confirmed that strategies consisting to stop deltamethrin spraying are likely to fail when the frequencies of resistant alleles are too high and the fitness cost associated to resistance is low. In dead-end situations like in French Guiana where alternative insecticides are not available, alternative control strategies may provide a high benefit for vector control, particularly if they favor the introgression of susceptible alleles in natural populations. © 2021 Society of Chemical Industry.

Current Status of Pyrethroids Resistance in Aedes aegypti (Culicidae: Diptera) in Lahore District, Pakistan: A Novel Mechanistic Insight

Aedes aegypti (Linnaeus, 1762) is a major vector responsible for dengue transmission. Insecticides are being used as the most effective tool to control vector populations in Lahore, Pakistan. Control of Ae. aegypti is threatened by the development of resistance against insecticides. The current status of insecticide resistance was evaluated against pyrethroids (deltamethrin, cypermethrin, and lambda-cyhalothrin) in different populations of Lahore (Model Town, Mishri Shah, Sadar Cantt, Walton, and Valencia). The susceptibility of the larval and adult populations was tested following the standard WHO guidelines. Moderate to high levels of resistance were found against pyrethroids in the larval (RR50: 3.6-27.2 and RR90: 5-90) and adult populations (percentage mortality < 98%). Biochemical assays revealed a statistically significant increase in the enzyme level in all field populations compared to the laboratory strain. The value of esterase was one-fold higher, monooxygenase was 3.9- to 4.7-fold higher, and glutathione S-transferases was 1.9- to 2.6-fold higher in field populations compared to the laboratory strain. These results depict the presence of resistance against deltamethrin, cypermethrin, and lambda-cyhalothrin in field populations of Lahore mediated by metabolic enzymes i.e. esterases, monooxygenases, and glutathione S-transferase.

Transcriptomic and proteomic analysis of pyrethroid resistance in the CKR strain of Aedes aegypti

Aedes aegypti is an important vector of human viral diseases. This mosquito is distributed globally and thrives in urban environments, making it a serious risk to human health. Pyrethroid insecticides have been the mainstay for control of adult A. aegypti for decades, but resistance has evolved, making control problematic in some areas. One major mechanism of pyrethroid resistance is detoxification by cytochrome P450 monooxygenases (CYPs), commonly associated with the overexpression of one or more CYPs. Unfortunately, the molecular basis underlying this mechanism remains unknown. We used a combination of RNA-seq and proteomic analysis to evaluate the molecular basis of pyrethroid resistance in the highly resistant CKR strain of A. aegypti. The CKR strain has the resistance mechanisms from the well-studied Singapore (SP) strain introgressed into the susceptible Rockefeller (ROCK) strain genome. The RNA-seq and proteomics data were complimentary; each offering insights that the other technique did not provide. However, transcriptomic results did not quantitatively mirror results of the proteomics. There were 10 CYPs which had increased expression of both transcripts and proteins. These CYPs appeared to be largely trans-regulated, except for some CYPs for which we could not rule out gene duplication. We identified 65 genes and lncRNAs as potentially being responsible for elevating the expression of CYPs in CKR. Resistance was associated with multiple loci on chromosome 1 and at least one locus on chromosome 3. We also identified five CYPs that were overexpressed only as proteins, suggesting that stabilization of CYP proteins could be a mechanism of resistance. Future studies to increase the resolution of the resistance loci, and to examine the candidate genes and lncRNAs identified here will greatly enhance our understanding of CYP-mediated resistance in A. aegypti.

Genomic analysis of the carboxylesterase family in the salmon louse (Lepeophtheirus salmonis)

The pyrethroid deltamethrin and the macrocyclic lactone emamectin benzoate (EMB) are used to treat infestations of farmed salmon by parasitic salmon lice, Lepeophtheirus salmonis. While the efficacy of both compounds against Atlantic populations of the parasite has decreased as a result of the evolution of resistance, the molecular mechanisms of drug resistance in L. salmonis are currently not fully understood. The functionally diverse carboxylesterases (CaE) family includes members involved in pesticide resistance phenotypes of terrestrial arthropods. The present study had the objective to characterize the CaE family in L. salmonis and assess its role in drug resistance. L. salmonis CaE homologues were identified by homology searches in the parasite's transcriptome and genome. The transcript expression of CaEs predicted to be catalytically competent was studied using quantitative reverse-transcription PCR in drug susceptible and multi-resistant L. salmonis. The above strategy led to the identification of 21 CaEs genes/pseudogenes. Phylogenetic analyses assigned 13 CaEs to clades involved in neurodevelopmental signaling and cell adhesion, while three sequences were predicted to encode secreted enzymes. Ten CaEs were identified as being potentially catalytically competent. Transcript expression of acetylcholinesterase (ace1b) was significantly increased in multi-resistant lice compared to drug-susceptible L. salmonis, with transcript abundance further increased in preadult-II females following EMB exposure. In summary, results from the present study demonstrate that L. salmonis possesses fewer CaE gene family members than most arthropods characterized so far. Drug resistance in L. salmonis was associated with overexpression of ace1b.

Dengue fever and insecticide resistance in Aedes mosquitoes in Southeast Asia: a review

Dengue fever is the most important mosquito-borne viral disease in Southeast Asia. Insecticides remain the most effective vector control approach for Aedes mosquitoes. Four main classes of insecticides are widely used for mosquito control: organochlorines, organophosphates, pyrethroids and carbamates. Here, we review the distribution of dengue fever from 2000 to 2020 and its associated mortality in Southeast Asian countries, and we gather evidence on the trend of insecticide resistance and its distribution in these countries since 2000, summarising the mechanisms involved. The prevalence of resistance to these insecticides is increasing in Southeast Asia, and the mechanisms of resistance are reported to be associated with target site mutations, metabolic detoxification, reduced penetration of insecticides via the mosquito cuticle and behavioural changes of mosquitoes. Continuous monitoring of the status of resistance and searching for alternative control measures will be critical for minimising any unpredicted outbreaks and improving public health. This review also provides improved insights into the specific use of insecticides for effective control of mosquitoes in these dengue endemic countries.

Permethrin resistance in Aedes aegypti: Genomic variants that confer knockdown resistance, recovery, and death

Pyrethroids are one of the few classes of insecticides available to control Aedes aegypti, the major vector of dengue, chikungunya, and Zika viruses. Unfortunately, evolving mechanisms of pyrethroid resistance in mosquito populations threaten our ability to control disease outbreaks. Two common pyrethroid resistance mechanisms occur in Ae. aegypti: 1) knockdown resistance, which involves amino acid substitutions at the pyrethroid target site-the voltage-gated sodium channel (VGSC)-and 2) enhanced metabolism by detoxification enzymes. When a heterogeneous population of mosquitoes is exposed to pyrethroids, different responses occur. During exposure, a proportion of mosquitoes exhibit immediate knockdown, whereas others are not knocked-down and are designated knockdown resistant (kdr). When these individuals are removed from the source of insecticide, the knocked-down mosquitoes can either remain in this status and lead to dead or recover within a few hours. The proportion of these phenotypic responses is dependent on the pyrethroid concentration and the genetic background of the population tested. In this study, we sequenced and performed pairwise genome comparisons between kdr, recovered, and dead phenotypes in a pyrethroid-resistant colony from Tapachula, Mexico. We identified single-nucleotide polymorphisms (SNPs) associated with each phenotype and identified genes that are likely associated with the mechanisms of pyrethroid resistance, including detoxification, the cuticle, and insecticide target sites. We identified high association between kdr and mutations at VGSC and moderate association with additional insecticide target site, detoxification, and cuticle protein coding genes. Recovery was associated with cuticle proteins, the voltage-dependent calcium channel, and a different group of detoxification genes. We provide a list of detoxification genes under directional selection in this field-resistant population. Their functional roles in pyrethroid metabolism and their potential uses as genomic markers of resistance require validation.

From Global to Local-New Insights into Features of Pyrethroid Detoxification in Vector Mosquitoes

The threat of mosquito-borne diseases continues to be a problem for public health in subtropical and tropical regions of the world; in response, there has been increased use of adulticidal insecticides, such as pyrethroids, in human habitation areas over the last thirty years. As a result, the prevalence of pyrethroid-resistant genetic markers in natural mosquito populations has increased at an alarming rate. This review details recent advances in the understanding of specific mechanisms associated with pyrethroid resistance, with emphasis on features of insecticide detoxification and the interdependence of multiple cellular pathways. Together, these advances add important context to the understanding of the processes that are selected in resistant mosquitoes. Specifically, before pyrethroids bind to their targets on motoneurons, they must first permeate the outer cuticle and diffuse to inner tissues. Resistant mosquitoes have evolved detoxification mechanisms that rely on cytochrome P450s (CYP), esterases, carboxyesterases, and other oxidation/reduction (redox) components to effectively detoxify pyrethroids to nontoxic breakdown products that are then excreted. Enhanced resistance mechanisms have evolved to include alteration of gene copy number, transcriptional and post-transcriptional regulation of gene expression, as well as changes to cellular signaling mechanisms. Here, we outline the variety of ways in which detoxification has been selected in various mosquito populations, as well as key gene categories involved. Pathways associated with potential new genes of interest are proposed. Consideration of multiple cellular pathways could provide opportunities for development of new insecticides.

The pharmacokinetics and drug-drug interactions of ivermectin in Aedes aegypti mosquitoes

Mosquitoes are vectors of major diseases such as dengue fever and malaria. Mass drug administration of endectocides to humans and livestock is a promising complementary approach to current insecticide-based vector control measures. The aim of this study was to establish an insect model for pharmacokinetic and drug-drug interaction studies to develop sustainable endectocides for vector control. Female Aedes aegypti mosquitoes were fed with human blood containing either ivermectin alone or ivermectin in combination with ketoconazole, rifampicin, ritonavir, or piperonyl butoxide. Drug concentrations were quantified by LC-MS/MS at selected time points post-feeding. Primary pharmacokinetic parameters and extent of drug-drug interactions were calculated by pharmacometric modelling. Lastly, the drug effect of the treatments was examined. The mosquitoes could be dosed with a high precision (%CV: ≤13.4%) over a range of 0.01–1 μg/ml ivermectin without showing saturation (R²: 0.99). The kinetics of ivermectin were characterised by an initial lag phase of 18.5 h (CI_90%: 17.0–19.8 h) followed by a slow zero-order elimination rate of 5.5 pg/h (CI_90%: 5.1–5.9 pg/h). By contrast, ketoconazole, ritonavir, and piperonyl butoxide were immediately excreted following first order elimination, whereas rifampicin accumulated over days in the mosquitoes. Ritonavir increased the lag phase of ivermectin by 11.4 h (CI_90%: 8.7–14.2 h) resulting in an increased exposure (+29%) and an enhanced mosquitocidal effect. In summary, this study shows that the pharmacokinetics of drugs can be investigated and modulated in an Ae. aegypti animal model. This may help in the development of novel vector-control interventions and further our understanding of toxicology in arthropods.

Mosquitoes are responsible for the transmission of pathogens, which cause diseases that are of major health significance such as dengue fever and malaria. Preventive strategies involving the use of insecticides, however, have led to the emergence of resistant mosquitoes. Consequently, development of complementary approaches is urgently needed to stop the spread of these pathogens. Our study reports on a pioneering approach to investigate how well drugs are taken up by the mosquitoes and how long they reside in their body. We focused on ivermectin, which is toxic for mosquitoes, and several drugs that interfere with drug metabolising enzymes. We demonstrated that the exposure of drugs can be precisely determined in individual mosquitoes and that drugs interact with each other in the same way as observed in vertebrates. In this regard, we were able to increase the exposure and mosquito toxicity of ivermectin by co-administering ritonavir, a broad-spectrum inhibitor of drug metabolising enzymes. This study establishes Aedes mosquitoes as a new model organism for pharmacokinetic studies. It opens the door for the investigation of novel insecticide strategies and optimisation of lead compounds against mosquitoes.

The genome of the stable fly, Stomoxys calcitrans, reveals potential mechanisms underlying reproduction, host interactions, and novel targets for pest control

Background

The stable fly, Stomoxys calcitrans, is a major blood-feeding pest of livestock that has near worldwide distribution, causing an annual cost of over $2 billion for control and product loss in the USA alone. Control of these flies has been limited to increased sanitary management practices and insecticide application for suppressing larval stages. Few genetic and molecular resources are available to help in developing novel methods for controlling stable flies.

Results

This study examines stable fly biology by utilizing a combination of high-quality genome sequencing and RNA-Seq analyses targeting multiple developmental stages and tissues. In conjunction, 1600 genes were manually curated to characterize genetic features related to stable fly reproduction, vector host interactions, host-microbe dynamics, and putative targets for control. Most notable was characterization of genes associated with reproduction and identification of expanded gene families with functional associations to vision, chemosensation, immunity, and metabolic detoxification pathways.

Conclusions

The combined sequencing, assembly, and curation of the male stable fly genome followed by RNA-Seq and downstream analyses provide insights necessary to understand the biology of this important pest. These resources and new data will provide the groundwork for expanding the tools available to control stable fly infestations. The close relationship of Stomoxys to other blood-feeding (horn flies and Glossina) and non-blood-feeding flies (house flies, medflies, Drosophila) will facilitate understanding of the evolutionary processes associated with development of blood feeding among the Cyclorrhapha.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-021-00975-9.

Life as a Vector of Dengue Virus: The Antioxidant Strategy of Mosquito Cells to Survive Viral Infection

Dengue fever is a mosquito-borne viral disease of increasing global importance. The disease has caused heavy burdens due to frequent outbreaks in tropical and subtropical areas of the world. The dengue virus (DENV) is generally transmitted between human hosts via the bite of a mosquito vector, primarily Aedes aegypti and Ae. albopictus as a minor species. It is known that the virus needs to alternately infect mosquito and human cells. DENV-induced cell death is relevant to the pathogenesis in humans as infected cells undergo apoptosis. In contrast, mosquito cells mostly survive the infection; this allows infected mosquitoes to remain healthy enough to serve as an efficient vector in nature. Overexpression of antioxidant genes such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione S-transferase (GST), glutaredoxin (Grx), thioredoxin (Trx), and protein disulfide isomerase (PDI) have been detected in DENV2-infected mosquito cells. Additional antioxidants, including GST, eukaryotic translation initiation factor 5A (eIF5a), and p53 isoform 2 (p53-2), and perhaps some others, are also involved in creating an intracellular environment suitable for cell replication and viral infection. Antiapoptotic effects involving inhibitor of apoptosis (IAP) upregulation and subsequent elevation of caspase-9 and caspase-3 activities also play crucial roles in the ability of mosquito cells to survive DENV infection. This article focused on the effects of intracellular responses in mosquito cells to infection primarily by DENVs. It may provide more information to better understand virus/cell interactions that can possibly elucidate the evolutionary pathway that led to the mosquito becoming a vector.

Insecticide resistance and underlying targets-site and metabolic mechanisms in Aedes aegypti and Aedes albopictus from Lahore, Pakistan

Insecticide resistant Aedes populations have recently been reported in Pakistan, imposing a threat to their control. We aimed to evaluate the susceptibility of Aedes aegypti and Aedes albopictus populations from Lahore to WHO-recommended insecticides and to investigate metabolic and target-site resistance mechanisms. For this purpose, we first carried out bioassays with the larvicides temephos and pyriproxyfen, and the adulticides malathion, permethrin, deltamethrin, alpha-cypermethrin, and etofenprox. We looked for Knockdown resistance mutations (kdr) by qPCR, High-Resolution Melt (HRM), and sequencing. In order to explore the role of detoxifying enzymes in resistance, we carried out synergist bioassay with both species and then checked the expression of CYP9M6, CYP9J10, CYP9J28, CYP6BB2, CCAe3a, and SAP2 genes in Ae. aegypti. Both species were susceptible to organophosphates and the insect growth regulator, however resistant to all pyrethroids. We are reporting the kdr haplotypes 1520Ile + 1534Cys and T1520 + 1534Cys in high frequencies in Ae. aegypti while Ae. albopictus only exhibited the alteration L882M. PBO increased the sensitivity to permethrin in Ae. aegypti, suggesting the participation of P450 genes in conferring resistance, and indeed, CYP928 was highly expressed. We presume that dengue vectors in Lahore city are resistant to pyrethroids, probably due to multiple mechanisms, such as kdr mutations and P450 overexpression.

Assessing cross-resistance within the pyrethroids in terms of their interactions with key cytochrome P450 enzymes and resistance in vector populations

Background

It is important to understand whether the potential impact of pyrethroid resistance on malaria control can be mitigated by switching between different pyrethroids or whether cross-resistance within this insecticide class precludes this approach.

Methods

Here we assess the relationships among pyrethroids in terms of their binding affinity to, and depletion by, key cytochrome P450 enzymes (hereafter P450s) that are known to confer metabolic pyrethroid resistance in Anopheles gambiae (s.l.) and An. funestus, in order to identify which pyrethroids may diverge from the others in their vulnerability to resistance. We then investigate whether these same pyrethroids also diverge from the others in terms of resistance in vector populations.

Results

We found that the type I and II pyrethroids permethrin and deltamethrin, respectively, are closely related in terms of binding affinity to key P450s, depletion by P450s and resistance within vector populations. Bifenthrin, which lacks the common structural moiety of most pyrethroids, diverged from the other pyrethroids tested in terms of both binding affinity to key P450s and depletion by P450s, but resistance to bifenthrin has rarely been tested in vector populations and was not analysed here. Etofenprox, which also lacks the common structural moiety of most pyrethroids, diverged from the more commonly deployed pyrethroids in terms of binding affinity to key P450s and resistance in vector populations, but did not diverge from these pyrethroids in terms of depletion by the P450s. The analysis of depletion by the P450s indicated that etofenprox may be more vulnerable to metabolic resistance mechanisms in vector populations. In addition, greater resistance to etofenprox was found across Aedes aegypti populations, but greater resistance to this compound was not found in any of the malaria vector species analysed. The results for pyrethroid depletion by anopheline P450s in the laboratory were largely not repeated in the findings for resistance in malaria vector populations.

Conclusion

Importantly, the prevalence of resistance to the pyrethroids α-cypermethrin, cyfluthrin, deltamethrin, λ-cyhalothrin and permethrin was correlated across malaria vector populations, and switching between these compounds as a tool to mitigate against pyrethroid resistance is not advised without strong evidence supporting a true difference in resistance.

The Potential of Biologically Active Brazilian Plant Species as a Strategy to Search for Molecular Models for Mosquito Control

Natural products are a valuable source of biologically active compounds and continue to play an important role in modern drug discovery due to their great structural diversity and unique biological properties. Brazilian biodiversity is one of the most extensive in the world and could be an effective source of new chemical entities for drug discovery. Mosquitoes are vectors for the transmission of dengue, Zika, chikungunya, yellow fever, and many other diseases of public health importance. These diseases have a major impact on tropical and subtropical countries, and their incidence has increased dramatically in recent decades, reaching billions of people at risk worldwide. The prevention of these diseases is mainly through vector control, which is becoming more difficult because of the emergence of resistant mosquito populations to the chemical insecticides. Strategies to provide efficient and safe vector control are needed, and secondary metabolites from plant species from the Brazilian biodiversity, especially Cerrado, that are biologically active for mosquito control are herein highlighted. Also, this is a literature revision of targets as insights to promote advances in the task of developing active compounds for vector control. In view of the expansion and occurrence of arboviruses diseases worldwide, scientific reviews on bioactive natural products are important to provide molecular models for vector control and contribute with effective measures to reduce their incidence.

Permethrin Resistance in Aedes aegypti Affects Aspects of Vectorial Capacity

Aedes aegypti, as one of the vectors transmitting several arboviruses, is the main target in mosquito control programs. Permethrin is used to control mosquitoes and Aedes aegypti get exposed due to its overuse and are now resistant. The increasing percentage of permethrin resistant Aedes aegypti has become an important issue around the world and the potential influence on vectorial capacity needs to be studied. Here we selected a permethrin resistant (p-s) Aedes aegypti population from a wild Florida population and confirmed the resistance ratio to its parental population. We used allele-specific PCR genotyping of the V1016I and F1534C sites in the sodium channel gene to map mutations responsible for the resistance. Two important factors, survival rate and vector competence, that impact vectorial capacity were checked. Results indicated the p-s population had 20 times more resistance to permethrin based on LD50 compared to the parental population. In the genotyping study, the p-s population had more homozygous mutations in both mutant sites of the sodium channel gene. The p-s adults survived longer and had a higher dissemination rate for dengue virus than the parental population. These results suggest that highly permethrin resistant Aedes aegypti populations might affect the vectorial capacity, moreover, resistance increased the survival time and vector competence, which should be of concern in areas where permethrin is applied.

CYP450 core involvement in multiple resistance strains of Aedes aegypti from French Guiana highlighted by proteomics, molecular and biochemical studies

Insecticide resistance is a worldwide threat for vector control around the world, and Aedes aegypti, the main vector of several arboviruses, is a particular concern. To better understand the mechanisms of resistance, four isofemale strains originally from French Guiana were isolated and analysed using combined approaches. The activity of detoxification enzymes involved in insecticide resistance was assayed, and mutations located at positions 1016 and 1534 of the sodium voltage-gated channel gene, which have been associated with pyrethroid resistance in Aedes aegypti populations in Latin America, were monitored. Resistance to other insecticide families (organophosphates and carbamates) was evaluated. A large-scale proteomic analysis was performed to identify proteins involved in insecticide resistance. Our results revealed a metabolic resistance and resistance associated with a mutation of the sodium voltage-gated channel gene at position 1016. Metabolic resistance was mediated through an increase of esterase activity in most strains but also through the shifts in the abundance of several cytochrome P450 (CYP450s). Overall, resistance to deltamethrin was linked in the isofemale strains to resistance to other class of insecticides, suggesting that cross- and multiple resistance occur through selection of mechanisms of metabolic resistance. These results give some insights into resistance to deltamethrin and into multiple resistance phenomena in populations of Ae. aegypti.

Tissue-specific responses of Lymantria dispar L. (Lepidoptera: Erebidae) larvae from unpolluted and polluted forests to thermal stress

In this paper the effects of increased environmental temperature on the relative growth rate (RGR) and developmental time in 5th instar L. dispar larvae originating from unpolluted and polluted forests were analyzed. As indicators of the level of generated reactive oxygen species in thermal stress, we estimated midgut and hemolymph activity of the antioxidative enzymes, superoxide dismutase (SOD) and catalase (CAT), as well as the detoxifying enzymes glutathione S-transferase (GST), carboxylesterase (CaE) and acetylcholinesterase (AChE) from the midgut and brain tissue. We also examined the influence of induced thermotolerance as a species' ability to overcome the negative effects of this stressor. In larvae originating from the unpolluted forest, the midgut is the primary location of increased SOD and CAT activity and induced thermotolerance did not modified their activity in either tissue. In larvae from the polluted forest, in both tissues SOD activity was more sensitive to an increased temperature and induced thermotolerance than CAT. Carboxylesterase responded diversely to thermal stress depending on the analyzed tissue regardless the origin of larvae, while the activity of GST and AChE in tissue depended on the origin of larvae. Induced thermotolerance modified the activity of detoxifying enzymes in larvae originating from the polluted forest. Combining the selected parameters into an integrated biomarker response (IBR) the GST, CaE and AChE battery emerged as a potential biomarker for thermal stress in L. dispar larvae.

Glucose transporter GLUT1 influences Plasmodium berghei infection in Anopheles stephensi

Background

Sugar-feeding provides energy for mosquitoes. Facilitated glucose transporters (GLUTs) are responsible for the uptake of glucose in animals. However, knowledge of GLUTs function in Anopheles spp. is limited.

Methods

Phylogenetic analysis of GLUTs in Anopheles stephensi was performed by the maximum likelihood and Bayesian inference methods. The spatial and temporal expression patterns of four Asteglut genes were analyzed by qPCR. The function of Asteglut1 was examined using a dsRNA-mediated RNA interference method. Transcriptome analysis was used to investigate the global influence of Asteglut1 on mosquito physiology.

Results

We identified 4 glut genes, Asteglut1, Asteglutx, Asteglut3 and Asteglut4 in An. stephensi. Asteglut1, Asteglut3 and Asteglut4 were mainly expressed in the midgut. Plasmodium berghei infection differentially regulated the expression of Asteglut genes with significant downregulation of Asteglut1 and Asteglut4, while upregulation of Asteglutx. Only knocking-down Asteglut1 facilitated Plasmodium berghei infection in An. stephensi. This might be due to the accumulation of glucose prior to blood-feeding in dsAsteglut1-treated mosquitoes. Our transcriptome analysis revealed that knockdown of Asteglut1 differentially regulated expression of genes associated with multiple functional clusters, especially those related to detoxification and immunity. The dysregulation of multiple pathways might contribute to the increased P. berghei infection.

Conclusions

Our study shows that Asteglut1 participates in defense against P. berghei in An. stephensi. The regulation of Asteglut1 on vector competence might through modulating multiple biological processes, such as detoxification and immunity.

Knockdown of LmCYP303A1 alters cuticular hydrocarbon profiles and increases the susceptibility to desiccation and insecticides in Locusta migratoria

Cytochrome P450 monooxygenases (CYPs) serve many functions in insects, from the regulation of development to xenobiotic detoxification. Several conserved CYPs have been shown to play a role in insect growth and development. CYP303A1 is a highly conserved CYP with a single ortholog in most insects, but its underlying molecular characteristics and specific physiological functions remain poorly understood. In Drosophila melanogaster and Locusta migratoria, CYP303A1 is indispensable for eclosion to adult. Here, we report additional functions of the locust gene LmCYP303A1 in nymphal molts, cuticular lipid deposition and insecticide penetration. RT-qPCR revealed that LmCYP303A1 had a high expression level before ecdysis and was highly expressed in integument, wing pads, foregut and hindgut. Suppression of LmCYP303A1 expression by RNA interference (RNAi) caused a lethal phenotype with molting defect from nymph to nymph. In addition, LmCYP303A1 RNAi resulted in locusts being more susceptible to desiccation and to insecticide toxicity. Furthermore, knockdown of LmCYP303A1 efficiently suppressed the transcript level of key genes (ELO7, FAR15 and CYP4G102) responsible for cuticular hydrocarbon (CHC) synthesis, which led to a decrease in some CHC levels. Taken together, our results suggest that one of the functions of LmCYP303A1 is to regulate the biosynthesis of CHC, which plays critical roles in protecting locusts from water loss and insecticide penetration.

Insecticide Resistance Status of Aedes aegypti (Diptera: Culicidae) in California by Biochemical Assays

Insecticide resistance in Aedes aegypti mosquitoes poses a major threat to public health worldwide. There are two primary biological mechanisms that can lead to insecticide resistance, target site and metabolic resistance, both of which confer resistance to specific classes of insecticides. Due to the limited number of chemical compounds available for mosquito control, it is important to determine current enzymatic profiles among mosquito populations. This study assessed resistance profiles for three metabolic pathways, α-esterases, β-esterases, and mixed-function oxidases (MFOs), as well as insensitivity of the acetylcholinesterase (iAChE) enzyme in the presence of propoxur, among Ae. aegypti from the Central Valley and southern California. All field-collected Ae. aegypti demonstrated elevated MFOs and iAChE activity, indicating potential development of pyrethroid and organophosphate resistance, respectively. Although regional variations were found among α-esterase and β-esterase activity, levels were generally elevated, further suggesting additional mechanisms for developing organophosphate resistance. Furthermore, mosquito samples from southern California exhibited a higher expression level to all three metabolic enzymes and iAChE activity in comparison to mosquitoes from the central region. These results could help guide future mosquito control efforts, directing the effective use of insecticides while limiting the spread of resistance.

Insecticide resistance, fitness and susceptibility to Zika infection of an interbred Aedes aegypti population from Rio de Janeiro, Brazil

Background

Aedes aegypti is a vector of high relevance, since it transmits several arboviruses, including dengue, chikungunya and Zika. Studies on vector biology are usually conducted with laboratory strains presenting a divergent genetic composition from field populations. This may impair vector control policies that were based on laboratory observations employing only long maintained laboratory strains. In the present study we characterized a laboratory strain interbreed with Ae. aegypti collected from five different localities in Rio de Janeiro (Aedes Rio), for insecticide resistance (IR), IR mechanisms, fitness and Zika virus infection.

Methods

We compared the recently established Aedes Rio with the laboratory reference strain Rockefeller. Insecticide resistance (deltamethrin, malathion and temephos), activity of metabolic resistance enzymes and kdr mutation frequency were determined. Some life table parameters (longevity, blood-feeding, number and egg viability) and Zika virus susceptibility was also determined.

Results

Aedes Rio showed resistance to deltamethrin (resistance ratio, RR₅₀ = 32.6) and temephos (RR₅₀ = 7.0) and elevated activity of glutathione S-transferase (GST) and esterases (α-EST and pNPA-EST), but not acetylcholinesterase (AChE). In total, 92.1% of males genotyped for kdr presented a “resistant” genotype. Weekly blood-fed females from both strains, presented reduced mortality compared to sucrose-fed mosquitoes; however, Aedes Rio blood-fed females did not live as long (mean lifespan: Rockefeller = 70 ± 3.07; Aedes Rio = 53.5 ± 2.16 days). There were no differences between strains in relation to blood-feeding and number of eggs, but Aedes Rio eggs presented reduced viability (mean hatch: Rockefeller = 77.79 ± 1.4%; Aedes Rio = 58.57 ± 1.77%). Zika virus infection (plaque-forming unit, PFU) was similar in both strains (mean PFU ± SE: Aedes Rio: 4.53 × 10⁴ ± 1.14 × 10⁴ PFU; Rockefeller: 2.02 × 10⁴ ± 0.71 × 10⁴ PFU).

Conclusion

Selected conditions in the field, such as IR mechanisms, may result in pleiotropic effects that interfere in general physiology of the insect. Therefore, it is important to well characterize field populations to be tested in parallel with laboratory reference strains. This practice would improve the significance of laboratory tests for vector control methods.

Polymorphisms in GSTE2 is associated with temephos resistance in Aedes aegypti

The glutathione S-transferases (GSTs) are enzymes involved in several distinct biological processes. In insects, the GSTs, especially delta and epsilon classes, play a key role in the metabolism of xenobiotics used to control insect populations. Here, we investigated its potential role in temephos resistance, examining the GSTE2 gene from susceptible (RecL) and resistant (RecR) strains of the mosquito Aedes aegypti, vector for several pathogenic arboviruses. Total GST enzymatic activity and the GSTE2 gene expression profile were evaluated, with the GSTE2 cDNA and genomic loci sequenced from both strains. Recombinant GSTE2 and mutants were produced in a heterologous expression system and assayed for enzyme kinetic parameters. These proteins also had their 3D structure predicted through molecular modeling. Our results showed that RecR has a profile of total GST enzymatic activity higher than RecL, with the expression of the GSTE2 gene in resistant larvae increasing six folds. Four exclusive RecR mutations were observed (L111S, I150V, E178A and A198E), which were absent in the laboratory susceptible strains. The enzymatic activity of the recombinant GSTE2 showed different kinetic parameters, with the GSTE2 RecR showing an enhanced ability to metabolize its substrate. The I150V mutation was shown to induce significant changes in catalytic parameters and a 3D modeling of GSTE2 mapped two of the RecR changes (L111S and I150V) near the enzyme's catalytic pocket, also implying an impact on its catalytic activity. Our results reinforce a potential role for GSTE2 in the metabolic resistance phenotype while contributing to the understanding of the molecular basis for the resistance mechanism.