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.

Impact of the exposure of sublethal dose of mosquito coil on the development of insecticide resistance in Aedes aegypti (L.) (Diptera: Culicidae).

Mosquito coil is commonly used in many African households for protection against mosquito bites. The coil usually has semi-volatile pyrethroids as an active ingredient, which usually diffuse across open space, and the cloud either kills mosquitoes that are exposed, or mosquitoes can be exposed to sublethal doses of the insecticides. This study was conducted to assess the impact of sublethal doses of mosquito coil on the development of insecticide resistance in Aedes aegypti, a major vector for dengue fever and several other arboviral diseases. A laboratory colony of Ae. aegypti was exposed to sublethal doses of a meperfluthrin-based mosquito coil in a Peet-Grady chamber once per generation for 16 generations. The susceptibility of the exposed colony to a diagnostic dose of the mosquito coil as well as to three other insecticides was determined. Three different kdr mutations and five enzyme activities were evaluated in both the exposed and control colonies. After 16 generations of sublethal exposure to mosquito coils, the full diagnostic dose of the coil caused 68% mortality to the exposed colony compared to 100% mortality in the control colony. Mortality caused by deltamethrin (0.05%) was also significantly lower in the exposed colony. The frequency of 1016I kdr mutation as well as MFO and alpha esterase activities were higher in the exposed colony compared to the control colony. This study provides evidence of the development of pyrethroid resistance in an Ae. aegypti population due to sublethal exposure to mosquito coil for 16 generations. Given the large-scale use of mosquito coils in many African households, its role as a pyrethroid resistance selection source should be taken into consideration when designing resistance management strategies.

Diverse mechanisms confer bensulfuron-methyl resistance in Schoenoplectiella juncoides (Roxb.) lye.

The effectiveness of bensulfuron-methyl in controlling Schoenoplectiella juncoides (Roxb.) Lye has significantly decreased in rice fields in China. Hence, a bensulfuron-methyl-resistant S. juncoides population (W15) was collected from Dandong City, Liaoning Province, China, to investigate the underlying resistance mechanisms. Whole-plant dose-response experiments and ALS activity assay confirmed that W15 has evolved high-level resistance to bensulfuron-methyl compared with the susceptible S. juncoides population (W4). Molecular analysis revealed a Pro-197-Ser mutation in ALS1, while there was no significant difference in the relative ALS gene expression between W15 and W4. LC-MS/MS analysis showed W15 metabolized bensulfuron-methyl more rapidly than W4. Furthermore, bensulfuron-methyl resistance in W15 was significantly alleviated by malathion and 4-chloro-7-nitrobenzoxadiazole (NBD-Cl). Glutathione S-transferase activity was higher in W15 than in W4. Meanwhile, W15 displayed cross-resistance to halosulfuron-methyl and multi-resistance to MCPA-Na. In summary, these findings demonstrated for the first time that both target- and non-target-site resistance are relevant in the resistance of S. juncoides to bensulfuron-methyl.

Target gene overexpression and enhanced metabolism confer resistance to nicosulfuron in Eriochloa villosa (Thunb.).

Eriochloa villosa (Thunb.) Kunth is a troublesome weed widely distributed in maize (Zea mays L.) fields in Northeast China. Many populations of E. villosa have evolved resistance to nicosulfuron herbicides, which inhibit acetolactate synthase (ALS). The objectives of this research were to confirm that E. villosa is resistant to nicosulfuron and to investigate the basis of nicosulfuron resistance. Whole-plant dose-response studies revealed that the R population had not developed a high level of cross-resistance and exhibited greater resistant (25.62-fold) to nicosulfuron than that of the S population and had not yet developed a high level of cross-resistance. An in vitro ALS activity assay demonstrated that the I50 of nicosulfuron was 6.87-fold greater in the R population than the S population. However, based on ALS gene sequencing, the target ALS gene in the R population did not contain mutations. Quantitative real-time polymerase chain reaction (qRT-PCR) revealed that ALS gene expression between the R and S populations was significantly different after nicosulfuron application, but no differences were observed in the gene copy number. After the cytochrome P450 inhibitor malathion or the GST inhibitor NBD-Cl was applied, the resistant E. villosa population exhibited increased sensitivity to nicosulfuron. Based on the activities of GSTs and P450s, the activities of the R population were greater than those of the S population after nicosulfuron application. This is the first report that the resistance of E. villosa to ALS inhibitors results from increased target gene expression and increased metabolism. These findings provide a theoretical foundation for the effective control of herbicide-resistant E. villosa.

Identification and transcriptional response of ATP-binding cassette transporters to beta-cypermethrin in the poultry red mite, Dermanyssus gallinae.

Dermanyssus gallinae, a worldwide pest in birds, has developed varying degrees of resistance to insecticides. The ATP-binding cassette (ABC) transporters are essential for the removal of xenobiotics from arthropods. However, our knowledge about ABC transporter proteins in D. gallinae is limited. Forty ABC transporters were identified in the transcriptome and genome of D. gallinae. The resistant population displayed an augmented metabolic rate for beta-cypermethrin compared to the susceptible group, with a remarkable increase in the content of ABC transporters. Verapamil was found able to increase the toxicity of beta-cypermethrin in the resistant population. Results from qRT-PCR analysis showed that eleven ABC transcripts were more highly expressed in the resistant population than the susceptible group at all stages of development, and beta-cypermethrin was observed to be able to induce the expression of DgABCA5, DgABCB4, DgABCD3, DgABCE1 and DgABCG5 in D. gallinae. RNAi-mediated knockdown of the five genes was observed to increase the susceptibility of resistant mites to beta-cypermethrin. These results suggest that ABC transporters, DgABCA5, DgABCB4, DgABCD3, DgABCE1 and DgABCG5 genes, may be related to beta-cypermethrin resistance in D. gallinae. This research will serve as a foundation for further studies on mechanism of insecticide resistance, which could be beneficial for controlling D. gallinae.

Trp-574-Leu mutation and metabolic resistance by cytochrome P450 gene conferred high resistance to ALS-inhibiting herbicides in Descurainia sophia.

Descurainia sophia (flixweed) is a troublesome weed in winter wheat fields in North China. Resistant D. sophia populations with different acetolactate synthetase (ALS) mutations have been reported in recent years. In addition, metabolic resistance to ALS-inhibiting herbicides has also been identified. In this study, we collected and purified two resistant D. sophia populations (R1 and R2), which were collected from winter wheat fields where tribenuron-methyl provided no control of D. sophia at 30 g a.i. ha-1. Whole plant bioassay and ALS activity assay results showed the R1 and R2 populations had evolved high-level resistance to tribenuron-methyl and florasulam and cross-resistance to imazethapyr and pyrithiobac­sodium. The two ALS genes were cloned from the leaves of R1 and R2 populations, ALS1 (2004 bp) and ALS2 (1998 bp). A mutation of Trp 574 to Leu in ALS1 was present in both R1 and R2. ALS1 and ALS2 were cloned from R1 and R2 populations respectively and transferred into Arabidopsis thaliana. Homozygous T3 transgenic seedlings with ALS1 of R1 or R2 were resistant to ALS-inhibiting herbicides and the resistant levels were the same. Transgenic seedlings with ALS2 from R1 or R2 were susceptible to ALS-inhibiting herbicides. Treatment with cytochrome P450 inhibitor malathion decreased the resistant levels to tribenuron-methyl in R1 and R2. RNA-Seq was used to identify target cytochrome P450 genes possibly involved in resistance to ALS-inhibiting herbicides. There were five up-regulated differentially expressed cytochrome P450 genes: CYP72A15, CYP83B1, CYP81D8, CYP72A13 and CYP71A12. Among of them, CYP72A15 had the highest expression level in R1 and R2 populations. The R1 and R2 populations of D. sophia have evolved resistance to ALS-inhibiting herbicides due to Trp 574 Leu mutation in ALS1 and possibly other mechanisms. The resistant function of CYP72A15 needs further research.

The dynamics of deltamethrin resistance evolution in Aedes albopictus has an impact on fitness and dengue virus type-2 vectorial capacity.

BACKGROUND: Worldwide invasion and expansion of Aedes albopictus, an important vector of dengue, chikungunya, and Zika viruses, has become a serious concern in global public health. Chemical insecticides are the primary means currently available to control the mosquito populations. However, long-term and large-scale use of insecticides has selected for resistance in the mosquito that is accompanied by a genetic load that impacts fitness. RESULTS: A number of laboratory strains representing different resistance mechanisms were isolated and identified from laboratory-derived, deltamethrin-resistant Ae. albopictus recovered in previous work. Resistance levels and fitness costs of the strains were evaluated and compared to characterize the evolution of the resistance genotypes and phenotypes. The heterozygous F1534S mutation (1534F/S) in the voltage gated sodium channel (vgsc) gene product (VGSC), first detected in early stages of resistance evolution, not only confers high-level resistance, but also produces no significant fitness costs, leading to the rapid spread of resistance in the population. This is followed by the increase in frequency of homozygous F1534S (1534S/S) mosquitoes that have significant fitness disadvantages, prompting the emergence of an unlinked I1532T mutation with fewer side effects and a mating advantage better adapted to the selection and reproductive pressures imposed in the experiments. Metabolic resistance with no significant fitness cost and mediating a high-tolerance resistance phenotype may play a dominant role in the subsequent evolution of resistance. The different resistant strains had similar vector competence for dengue virus type-2 (DENV-2). Furthermore, a comparative analysis of vectorial capacity revealed that increased survival due to deltamethrin resistance balanced the negative fitness cost effects and contributed to the risk of dengue virus (DENV) transmission by resistant populations. The progressive evolution of resistance results in mosquitoes with both target-site insensitivity and metabolic resistance with lower fitness costs, which further leads to resistant populations with both high resistance levels and vectorial capacity. CONCLUSIONS: This study reveals a possible mechanism for the evolution of deltamethrin resistance in Aedes albopictus. These findings will help guide practical strategies for insecticide use, resistance management and the prevention and control of mosquito-borne disease.

Monitoring detoxification enzyme levels and resistance of Tetranychus urticae against some METI-group chemicals in Türkiye cotton fields.

Acaricides used against Tetranychus urticae Koch, 1836 (Acari: Tetranychidae) in cotton fields cause control failure over time. To determine the resistance status of T. urticae populations to tebufenpyrad and bifenazate, different populations collected from Aydin (AYD), Adana (ADA), Sanliurfa (SAN), and Diyarbakir (DIY) provinces of Türkiye, between 2019 and 2020, were subjected to diagnostic dose bioassays. Firstly, the spider mites were eliminated with a discriminating dose. Afterwards, LC50 and LC90 of the remaining populations were determined and the ten highest resistant populations were selected. The highest phenotypic resistance to bifenazate was observed in AYD4 and DIY2 (LC50 57.14 mg L- 1 with 85.01-fold and LC50 30.15 mg L- 1with 44.86-fold, respectively), while the lowest phenotypic resistance was found in SAN6 (LC50 1.5 mg L- 1; 2.28-fold). Considering the phenotypic resistance to tebufenpyrad, the highest resistance was found in AYD4 population (LC50 96.81 mg L- 1; 12.92-fold), while the lowest - in DIY28 population (LC50 21.23 mg L- 1; 2.83-fold). In pharmacokinetic studies, the ADA16 population was compared with the sensitive German Susceptible Strain population and it was determined that carboxylesterase activity was statistically higher (1.46 ± 0.04 nmol/min/mg protein enzyme activation 2.70-fold). The highest activation of glutathione S-transferase was detected in ADA16 (1.49 ± 0.01 nmol/min/mg protein; 2.32-fold). No mutations were found in PSST (METI 1), the point mutation site for tebufenpyrad, and Cytb (METI 3), the point mutation site for bifenazate. In terms of phenotypic resistance, bifenazate was found to be moderately resistant in two populations (85.01 and 44.86-fold), while tebufenpyrad was moderately resistant in one population (12.92-fold). This study showed that both acaricides are still effective against T. urticae populations.

Potential key genes involved in metabolic resistance to malathion in the southern house mosquito, Culex quinquefasciatus, and functional validation of CYP325BC1 and CYP9M12 as candidate genes using RNA interference.

BACKGROUND: Metabolic detoxification is one of the major mechanisms contributing to the development of resistance in mosquitoes, including the southern house mosquito, Culex quinquefasciatus. The three major detoxification supergene families, cytochrome P450s, glutathione S-transferases and general esterases, have been demonstrated to play an important role in metabolic resistance. In this study, we performed differential gene expression analysis based on high-throughput transcriptome sequencing on samples from four experimental groups to give insight into key genes involved in metabolic resistance to malathion in Cx. quinquefasciatus. We conducted a whole transcriptome analysis of field captured wild Cx. quinquefasciatus from Harris County (WI), Texas and a malathion susceptible laboratory-maintained Sebring colony (CO) to investigate metabolic insecticide resistance. Field captured mosquitoes were also phenotypically classified into the malathion resistant and malathion susceptible groups following a mortality response measure conducted using a Centers for Disease Control and Prevention (CDC) bottle assay. The live (MR) and dead (MS) specimens from the bottle assay, along with an unselected WI sample and a CO sample were processed for total RNA extraction and subjected to whole-transcriptome sequencing. RESULTS: We demonstrated that the genes coding for detoxification enzymes, particularly cytochrome P450s, were highly up-regulated in the MR group compared to the MS group with similar up-regulation observed in the WI group compared to the CO group. A total of 1,438 genes were differentially expressed in comparison between MR and MS group, including 614 up-regulated genes and 824 down-regulated genes. Additionally, 1,871 genes were differentially expressed in comparison between WI and CO group, including 1,083 up-regulated genes and 788 down-regulated genes. Further analysis on differentially expressed genes from three major detoxification supergene families in both comparisons resulted in 16 detoxification genes as candidates potentially associated with metabolic resistance to malathion. Knockdown of CYP325BC1 and CYP9M12 using RNA interference on the laboratory-maintained Sebring strain significantly increased the mortality of Cx. quinquefasciatus after exposure to malathion. CONCLUSION: We generated substantial transcriptomic evidence on metabolic detoxification of malathion in Cx. quinquefasciatus. We also validated the functional roles of two candidate P450 genes identified through DGE analysis. Our results are the first to demonstrate that knockdown of CYP325BC1 and CYP9M12 both significantly increased malathion susceptibility in Cx. quinquefasciatus, indicating involvement of these two genes in metabolic resistance to malathion.

Deltamethrin and transfluthrin select for distinct transcriptomic responses in the malaria vector Anopheles gambiae.

BACKGROUND: The widespread use of pyrethroid insecticides in Africa has led to the development of strong resistance in Anopheles mosquitoes. Introducing new active ingredients can contribute to overcome this phenomenon and ensure the effectiveness of vector control strategies. Transfluthrin is a polyfluorinated pyrethroid whose structural conformation was thought to prevent its metabolism by cytochrome P450 monooxygenases in malaria vectors, thus representing a potential alternative for managing P450-mediated resistance occurring in the field. In this study, a controlled selection was used to compare the dynamics of resistance between transfluthrin and the widely used pyrethroid deltamethrin in the mosquito Anopheles gambiae. Then, the associated molecular mechanisms were investigated using target-site mutation genotyping and RNA-seq. METHODS: A field-derived line of An. gambiae carrying resistance alleles at low frequencies was used as starting material for a controlled selection experiment. Adult females were selected across 33 generations with deltamethrin or transfluthrin, resulting in three distinct lines: the Delta-R line (selected with deltamethrin), the Transflu-R line (selected with transfluthrin) and the Tiassale-S line (maintained without selection). Deltamethrin and transfluthrin resistance levels were monitored in each selected line throughout the selection process, as well as the frequency of the L1014F kdr mutation. At generation 17, cross-resistance to other public health insecticides was investigated and transcriptomes were sequenced to compare gene transcription variations and polymorphisms associated with adaptation to each insecticide. RESULTS: A rapid increase in resistance to deltamethrin and transfluthrin was observed throughout the selection process in each selected line in association with an increased frequency of the L1014F kdr mutation. Transcriptomic data support a broader response to transfluthrin selection as compared to deltamethrin selection. For instance, multiple detoxification enzymes and cuticle proteins were specifically over-transcribed in the Transflu-R line including the known pyrethroid metabolizers CYP6M2, CYP9K1 and CYP6AA1 together with other genes previously associated with resistance in An. gambiae. CONCLUSION: This study confirms that recurrent exposure of adult mosquitoes to pyrethroids in a public health context can rapidly select for various resistance mechanisms. In particular, it indicates that in addition to target site mutations, the polyfluorinated pyrethroid transfluthrin can select for a broad metabolic response, which includes some P450s previously associated to resistance to classical pyrethroids. This unexpected finding highlights the need for an in-depth study on the adaptive response of mosquitoes to newly introduced active ingredients in order to effectively guide and support decision-making programmes in malaria control.

Species composition and insecticide resistance in malaria vectors in Ellibou, southern Côte d'Ivoire and first finding of Anopheles arabiensis in Côte d'Ivoire.

BACKGROUND: Knowing the species composition and insecticide resistance status of the target vector population is important to guide malaria vector control. The aim of this study was to characterize the malaria vector population in terms of species composition, insecticide susceptibility status and potential underlying resistance mechanisms in Ellibou, southern Côte d'Ivoire. METHODS: A 1-year longitudinal entomological survey was conducted using light traps and pyrethroid spray catches to sample adult mosquitoes in combination with larval sampling. The susceptibility status of Anopheles gambiae sensu lato (s.l.) to bendiocarb, deltamethrin, DDT and malathion was assessed using the World Health Organization insecticide susceptibility test. Additionally, An. gambiae specimens were screened for knockdown (kdr) and acetylcholineesterase (ace1) target site resistance alleles, and the expression levels of eight metabolic resistance genes, including seven cytochrome P450 monooxygenases (P450s) and one glutathione S-transferase (GST), measured with reverse transcription quantitative real-time polymerase chain reaction (qPCR). RESULTS: Overall, 2383 adult mosquitoes from 12 different taxa were collected with Culex quinquefasciatus and An. gambiae being the predominant taxa. Molecular identification of An. gambiae s.l. revealed the presence of Anopheles arabiensis, Anopheles coluzzii, An. gambiae sensu stricto (s.s.) and Anopheles coluzzii/An. gambiae s.s. hybrids. Anopheles gambiae mosquitoes were resistant to all insecticides except malathion. PCR diagnostics revealed the presence of ace1-G280S and the kdr L995F, L995S and N1570Y target-site mutations. Additionally, several genes were upregulated, including five P450s (i.e., CYP6P3, CYP6M2, CYP9K1, CYP6Z1, CYP6P1) and GSTE2. CONCLUSION: This is the first documented presence of An. arabiensis in Côte d'Ivoire. Its detection - together with a recent finding further north of the country - confirms its existence in the country, which is an early warning sign, as An. arabiensis shows a different biology than the currently documented malaria vectors. Because the local An. gambiae population was still susceptible to malathion, upregulation of P450s, conferring insecticide resistance to pyrethroids, together with the presence of ace1, suggest negative cross-resistance. Therefore, organophosphates could be an alternative insecticide class for indoor residual spraying in the Ellibou area, while additional tools against the outdoor biting An. arabiensis will have to be considered.

Evaluating insecticide resistance across African districts to aid malaria control decisions.

Malaria vector control may be compromised by resistance to insecticides in vector populations. Actions to mitigate against resistance rely on surveillance using standard susceptibility tests, but there are large gaps in the monitoring data across Africa. Using a published geostatistical ensemble model, we have generated maps that bridge these gaps and consider the likelihood that resistance exceeds recommended thresholds. Our results show that this model provides more accurate next-year predictions than two simpler approaches. We have used the model to generate district-level maps for the probability that pyrethroid resistance in Anopheles gambiae s.l. exceeds the World Health Organization thresholds for susceptibility and confirmed resistance. In addition, we have mapped the three criteria for the deployment of piperonyl butoxide-treated nets that mitigate against the effects of metabolic resistance to pyrethroids. This includes a critical review of the evidence for presence of cytochrome P450-mediated metabolic resistance mechanisms across Africa. The maps for pyrethroid resistance are available on the IR Mapper website, where they can be viewed alongside the latest survey data.

Contribution of UDP-glycosyltransferases to chlorpyrifos resistance in Nilaparvata lugens.

As a multigene superfamily of Phase II detoxification enzymes, uridine diphosphate (UDP)-glycosyltransferases (UGTs) play important roles in the metabolism of xenobiotics including insecticides. In this study, 5-nitrouracil, an inhibitor of UGT enzyme activity, effectively increased the toxicity of chlorpyrifos to the chlorpyrifos-resistant strain of Nilaparvata lugens, one of the most resistant rice pests. The enzyme content of UGT in the resistant strain was significantly higher than that in the susceptible strain. Among 20 identified UGT genes, UGT386H2, UGT386J2, UGT386N2 and UGT386P1 were found significantly overexpressed in the resistant strain and can be effectively induced by chlorpyrifos. These four UGT genes were most highly expressed in the midgut and/or fat body, two main insect detoxification tissues. Amino acid sequence alignments revealed that these four UGTs contained a variable N-terminal substrate-binding domain and a conserved C-terminal sugar donor-binding domain. Furthermore, homology modeling and molecular docking analyses showed that these UGTs could stably bind to chlorpyrifos and chlorpyrifos oxon, with the binding free energies from -19.4 to -110.62 kcal mol-1. Knockdown of UGT386H2 or UGT386P1 by RNA interference dramatically increased the susceptibility of the resistant strain to chlorpyrifos. These findings suggest that overexpression of these two UGT genes contributes to chlorpyrifos resistance in N. lugens.

ACCase gene mutations and P450-mediated metabolism contribute to cyhalofop-butyl resistance in Eleusine indica biotypes from direct-seeding paddy fields.

Eleusine indica causes problems in direct-seeding rice fields across Jiangsu Province in China. Long-term application of chemical herbicides has led to the widespread evolution of resistance in E. indica. In this study, we surveyed the resistance level of cyhalofop-butyl (CyB) in 19 field-collected E. indica biotypes, and characterized its underlying resistance mechanisms. All 19 biotypes evolved moderate- to high-level resistance to CyB (from 5.8- to 171.1-fold). 18 biotypes had a target-site mechanism with Trp-1999-Ser, Trp-2027-Cys, or Asp-2078-Gly mutations, respectively. One biotype (JSSQ-1) was identified to have metabolic resistance, in which malathion pretreatment significantly reduced the CyB resistance, and cyhalofop acid was degraded 1.7- to 2.5-times faster in this biotype compared with a susceptible control. Furthermore, the JSSQ-1 biotype showed multiple resistance to acetyl-CoA carboxylase (ACCase) inhibitor metamifop (RI = 4.6) and fenoxaprop-p-ethyl (RI = 5.1), acetolactate synthase (ALS) inhibitor imazethapyr (RI = 4.1), and hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor mesotrione (RI = 3.5). In addition, 11 out of 19 E. indica biotypes exhibited multiple resistance to glyphosate. This research has identified the widespread occurrence of CyB resistance in E. indica, attributed to target-site mutations or enhanced metabolism. Moreover, certain biotypes have exhibited resistance to multiple herbicides or even cross-resistance. Consequently, there is an urgent need to implement diverse weed management practices to effectively combat the proliferation of this weed in rice fields.

Investigation of resistance mechanisms to fomesafen in Ipomoea nil from China.

Recently, the herbicide fomesafen has frequently failed to control the troublesome weed Ipomoea nil in soybean fields in Liaoning Province, China. Hence, we collected 10 suspected resistant populations and evaluated their sensitivity to fomesafen. The results revealed various degrees of Ipomoea nil resistance to fomesafen, with a resistance index of 2.88 to 22.43; the highest value occurred in the LN3 population. Therefore, the mechanisms of the resistance in LN3 to fomesafen were explored. After fomesafen treatment, the expression levels of InPPX1 and InPPX2 genes were 4.19- and 9.29-fold higher, respectively, in LN3 than those in the susceptible (LN1) population. However, mutations and copy number variations were not detected between the two populations. Additionally, malathion pretreatment reduced the dose necessary to halve the growth rate of LN3 by 58%. Liquid chromatography with tandem mass spectrometry demonstrated that metabolism of fomesafen was significantly suppressed by malathion. Moreover, LN3 displayed increased reactive oxygen species scavenging capacity, which was represented by higher superoxide dismutase and peroxidase activities after fomesafen application than those in LN1. An orthogonal partial least squares-discriminant analysis revealed that the high resistance in LN3 could be attributed mainly to enhanced metabolism. Fortunately, the fomesafen-resistant I. nil remained sensitive to 2,4-D-ethylhexylester and bentazon, providing methods for its control.

Target-site and non-target-site based resistance to clodinafop-propargyl in wild oats (Avena fatua L.).

Wild oat (Avena fatua L.) is a common and problematic weed in wheat fields in China. In recent years, farmers found it increasingly difficult to control A. fatua using acetyl-CoA carboxylase (ACCase)-inhibiting herbicides. The purpose of this study was to identify the molecular basis of clodinafop-propargyl resistance in A. fatua. In comparison to the S1496 population, whole dose response studies revealed that the R1623 and R1625 populations were 71.71- and 67.76-fold resistant to clodinafop-propargyl, respectively. The two resistant A. fatua populations displayed high resistance to fenoxaprop-p-ethyl (APP) and low resistance to clethodim (CHD) and pinoxaden (PPZ), but they were still sensitive to the ALS inhibitors mesosulfuron-methyl and pyroxsulam. An Ile-2041-Asn mutation was identified in both resistant individual plants. The copy number and relative expression of the ACCase gene in the resistant population were not significantly different from those in the S1496 population. Under the application of 2160 g ai ha -1 of clodinafop-propargyl, the fresh weight of the R1623 population was reduced to 74.9%; however, pretreatment with the application of the cytochrome P450 inhibitor malathion and the GST inhibitor NBD-Cl reduced the fresh weight to 50.91% and 47.16%, respectively, which proved the presence of metabolic resistance. This is the first report of an Ile-2041-Asn mutation and probable metabolic resistance in A. fatua, resulting in resistance to clodinafop-propargyl.

Enhanced metabolic resistance mechanism endows resistance to metamifop in Echinochloa crus-galli (L.) P. Beauv.

Barnyardgrass (Echinochloa crus-galli (L.) P. Beauv.), one of the worst weeds in paddy fields in China, has been frequently reported evolving resistance to acetyl-CoA carboxylase (ACCase) inhibiting herbicides. However, in the previous research, more attention was paid to target-site resistance (TSR) mechanisms, the non-target-site resistance (NTSR) mechanisms have not been well-established. In this study, the potential mechanism of resistance in a metamifop-resistant E. crus-galli collected from Kunshan city, Jiangsu Province, China was investigated. Dose-response assays showed that the phenotypic resistant population (JS-R) has evolved 4.3-fold resistance to metamifop compared with the phenotypic susceptible population (YN-S). The ACCase CT gene sequencing and relative ACCase gene expression levels studies showed that no mutations were detected in the ACCase CT gene in both YN-S and JS-R, and there was no significant difference in the relative ACCase gene expression between YN-S and JS-R. After the pre-processing of glutathione-S-transferase (GSTs) inhibitor NBD-Cl, the resistance level of JS-R to metamifop was reversed 18.73%. Furthermore, the GSTs activity of JS-R plants was significantly enhanced compared to that of YN-S plants. UPLC-MS/MS revealed that JS-R plants had faster metabolic rates to metamifop than YN-S plants. Meanwhile, the JS-R popultion exhibited resistant to cyhalofop-butyl and penoxsulam. In summary, this study presented a novel discovery regarding the global emergence of metabolic resistance to metamifop in E. crus-galli. The low-level resistance observed in the JS-R population was not found to be related to TSR but rather appeared to be primarily associated with the overexpression of genes in the GSTs metabolic enzyme superfamily.

Molecular Characterization of Resistance to Nicosulfuron in Setaria viridis.

The green foxtail, Setaria viridis (L.) P. Beauv. (Poales: Poaceae), is a troublesome and widespread grass weed in China. The acetolactate synthase (ALS)-inhibiting herbicide nicosulfuron has been intensively used to manage S. viridis, and this has substantially increased the selection pressure. Here we confirmed a 35.8-fold resistance to nicosulfuron in an S. viridis population (R376 population) from China and characterized the resistance mechanism. Molecular analyses revealed an Asp-376-Glu mutation of the ALS gene in the R376 population. The participation of metabolic resistance in the R376 population was proved by cytochrome P450 monooxygenases (P450) inhibitor pre-treatment and metabolism experiments. To further elucidate the mechanism of metabolic resistance, eighteen genes that could be related to the metabolism of nicosulfuron were obtained bythe RNA sequencing. The results of quantitative real-time PCR validation indicated that three ATP-binding cassette (ABC) transporters (ABE2, ABC15, and ABC15-2), four P450 (C76C2, CYOS, C78A5, and C81Q32), and two UDP-glucosyltransferase (UGT) (UGT13248 and UGT73C3), and one glutathione S-transferases (GST) (GST3) were the major candidates that contributed to metabolic nicosulfuron resistance in S. viridis. However, the specific role of these ten genes in metabolic resistance requires more research. Collectively, ALS gene mutations and enhanced metabolism may be responsible for the resistance of R376 to nicosulfuron.

Current status of insecticide resistance and its underlying mechanisms in Aedes aegypti (L.) in Punjab, Pakistan.

Aedes aegypti (Linnaeus) plays an important role as a vector of different deadly diseases particularly dengue fever. Insecticides are used as a primary tool to control Ae. aegypti. However, due to the excessive use of insecticides on agricultural, public health, and industrial levels, mosquitoes have developed resistance. In this study, the current susceptibility status of Ae. aegypti mosquitoes against different insecticides (Temephos, DDT, dieldrin, Malathion, Bendiocarb, Permethrin, Cypermethrin, and Lambda-cyhalothrin) was evaluated in district Lahore and district Muzaffargarh of Punjab, Pakistan. For this purpose, WHO bioassays and biochemical assays were performed on Ae. aegypti population from Lahore (APLa) and Aedes population from Muzaffargarh (APMg). Results of APLa and APMg showed high levels of resistance against the larvicide Temephos. Resistance against all adulticides was also observed in APLa and APMg (% mortality < 98%). The biochemical assays indicated statistically significant elevated levels of detoxification enzymes in APLa and APMg. APLa showed slightly higher levels as compared to APMg. Mosquitoes were also screened for the presence of kdr mutations. The results revealed no mutation in domain II while the presence of mutation F1534C in domain III was found in both field populations. The results showed the presence of moderate to high grade resistance against all insecticides in Ae. aegypti in district Lahore and district Muzaffargarh of Punjab, Pakistan.

Characterization of the glutathione S-transferase genes in the sand flies Phlebotomus papatasi and Lutzomyia longipalpis shows expansion of the novel glutathione S-transferase xi (X) class.

Leishmaniasis control often relies upon insecticidal control of phlebotomine sandfly vector populations. Such methods are vulnerable to the evolution of insecticide resistance via a range of molecular mechanisms. There is evidence that two major resistance mechanisms, target site insensitivity and metabolic resistance, have evolved in some sandfly populations and further genetic characterization of resistance would be useful to understand and combat it. To facilitate the study of the mechanisms of metabolic resistance, here we improved the annotation and characterized a major detoxification gene family, the glutathione-s-transferases (GST), in the genomes of two sand fly species: Phlebotomus papatasi and Lutzomyia longipalpis. The compositions of the GST gene family differ markedly from those of Aedes and Anopheles mosquitoes. Most strikingly, the xi (X) class of GSTs appears to have expanded in both sand fly genomes. Our results provide a basis for further studies of metabolic resistance mechanisms in these important disease vector species.