Resistance Management Strategies Research Articles

Susceptibility to organophosphate insecticides in Aedes aegypti (Diptera: Culicidae) from northern Colombia and associated resistance mechanisms

BackgroundAedes aegypti is the primary vector of dengue, chikungunya, and Zika viruses in Colombia. Various insecticides, including pyrethroid, organophosphate, and carbamate insecticides; growth regulators; and biological insecticides, such as Bacillus thuringiensis var. israelensis, have been used to control Ae. aegypti populations. However, organophosphates such as malathion, pirimiphos-methyl, and temephos have been used over the last decade owing to the high resistance to pyrethroids.MethodsThis study assessed the susceptibility to organophosphates in 14 Ae. aegypti populations from the Córdoba department in northern Colombia. Moreover, possible resistance mechanisms were investigated by determining the activity levels of α-esterases, β-esterases, mixed function oxidases (MFOs), glutathione S-transferases (GSTs), and insensitive acetylcholinesterase (iAChE). Additionally, the Ace-1 gene was sequenced to identify mutations at the target site of action.ResultsThe populations were susceptible to temephos and malathion but resistant to fenitrothion, and in three of them, to pirimiphos-methyl. Alterations in the enzyme activity levels of α-esterases and β-esterases, GST, and iAChE were observed among the populations, with high enzyme activity levels of α and β esterases associated with resistance to fenitrothion. No mutations were identified in the Ace-1 gene.ConclusionsThese findings are highly relevant for vector control programs in the region, as they allow for adjustments in resistance management strategies and improve the effectiveness of interventions against these arboviruses.Graphical

Establishing best practices for insect resistance management: a new paradigm for genetically engineered toxins in cotton expressing Mpp51Aa2.

Debate over resistance management tactics for genetically engineered (GE) crops expressing insecticidal toxins is not new. For several decades, researchers, regulators, and agricultural industry scientists have developed strategies to limit the evolution of resistance in populations of lepidopteran and coleopteran pests. A key attribute of many of these events was insecticide resistance management (IRM) strategies designed around a presumed high-dose expression sufficient to kill 99.5% of exposed larvae for some of the main target pests in corn, Zea mays L. and cotton, Gossypium hirsutum L. In contrast, other target pests did not meet this high-dose criterion. Similarly, the recent release of ThryvOn cotton that expresses thysanopteran and hemipteran active Mpp51Aa2.834_16 toxin is not high dose, working on a combination of behavioral and sublethal effects to suppress populations. This unique mode of control has generated considerable uncertainty about what IRM strategies will be most effective to limit field-evolved resistance to this unique spectrum of pests. The goal of this manuscript is to present several knowledge gaps that exist in proposed Mpp51Aa2 IRM plans, focusing on its activity on thrips, Frankliniella spp. Addressing these gaps will be crucial to limit resistance and preserve the benefits that this technology may provide by alleviating reliance on conventional insecticides and seed treatments. Broadly, these considerations will be important for future GE events that are non-high dose but remain valuable components of a more holistic insect management programs that integrate multiple tactics to reduce conventional insecticide use for challenging pests.

Genome-wide association studies unveil major genetic loci driving insecticide resistance in Anopheles funestus in four eco-geographical settings across Cameroon

BackgroundInsecticide resistance is jeopardising malaria control efforts in Africa. Deciphering the evolutionary dynamics of mosquito populations country-wide is essential for designing effective and sustainable national and subnational tailored strategies to accelerate malaria elimination efforts. Here, we employed genome-wide association studies through pooled template sequencing to compare four eco-geographically different populations of the major vector, Anopheles funestus, across a South North transect in Cameroon, aiming to identify genomic signatures of adaptive responses to insecticides.ResultsOur analysis revealed limited population structure within Northern and Central regions (FST<0.02), suggesting extensive gene flow, while populations from the Littoral/Coastal region exhibited more distinct genetic patterns (FST>0.049). Greater genetic differentiation was observed at known resistance-associated loci, resistance-to-pyrethroids 1 (rp1) (2R chromosome) and CYP9 (X chromosome), with varying signatures of positive selection across populations. Allelic variation between variants underscores the pervasive impact of selection pressures, with rp1 variants more prevalent in Central and Northern populations (FST>0.3), and the CYP9 associated variants more pronounced in the Littoral/Coastal region (FST =0.29). Evidence of selective sweeps was supported by negative Tajima’s D and reduced genetic diversity in all populations, particularly in Central (Elende) and Northern (Tibati) regions. Genomic variant analysis identified novel missense mutations and signatures of complex genomic alterations such as duplications, deletions, transposable element (TE) insertions, and chromosomal inversions, all associated with selective sweeps. A 4.3 kb TE insertion was fixed in all populations with Njombe Littoral/Coastal population, showing higher frequency of CYP9K1 (G454A), a known resistance allele and TE upstream compared to elsewhere.ConclusionOur study uncovered regional variations in insecticide resistance candidate variants, emphasizing the need for a streamlined DNA-based diagnostic assay for genomic surveillance across Africa. These findings will contribute to the development of tailored resistance management strategies crucial for addressing the dynamic challenges of malaria control in Cameroon.

Two highly selected mutations in the tandemly duplicated CYP6P4a and CYP6P4b genes drive pyrethroid resistance in Anopheles funestus in West Africa

BackgroundGaining a comprehensive understanding of the genetic mechanisms underlying insecticide resistance in malaria vectors is crucial for optimising the effectiveness of insecticide-based vector control methods and developing diagnostic tools for resistance management. Considering the heterogeneity of metabolic resistance in major malaria vectors, the implementation of tailored resistance management strategies is essential for successful vector control. Here, we provide evidence demonstrating that two highly selected mutations in CYP6P4a and CYP6P4b are driving pyrethroid insecticide resistance in the major malaria vector Anopheles funestus, in West Africa.ResultsContinent-wide polymorphism survey revealed escalated signatures of directional selection of both genes between 2014 and 2021. In vitro insecticide metabolism assays with recombinant enzymes from both genes showed that mutant alleles under selection exhibit higher metabolic efficiency than their wild-type counterparts. Using the GAL4-UAS expression system, transgenic Drosophila flies overexpressing mutant alleles exhibited increased resistance to pyrethroids. These findings were consistent with in silico predictions which highlighted changes in enzyme active site architecture that enhance the affinity of mutant alleles for type I and II pyrethroids. Furthermore, we designed two DNA-based assays for the detection of CYP6P4a-M220I and CYP6P4b-D284E mutations, showing their current confinement to West Africa. Genotype/phenotype correlation analyses revealed that these markers are strongly associated with resistance to types I and II pyrethroids and combine to drastically reduce killing effects of pyrethroid bed nets.ConclusionsOverall, this study demonstrated that CYP6P4a and CYP6P4b contribute to pyrethroid resistance in An. funestus and provided two additional insecticide resistance molecular diagnostic tools that would contribute to monitoring and better management of resistance.

Characterization of acetolactate synthase genes and resistance mechanisms of multiple herbicide resistant Lolium multiflorum

Combining imidazolinone-tolerant wheat with imazamox presents an effective solution to combat weed resistance. However, Lolium multiflorum, a troublesome resistant weed infesting wheat fields, may have developed resistance to imazamox, and the potential resistance mechanisms are intriguing. In this study, we explored the susceptibility of L. multiflorum to imazamox and investigated the resistance mechanisms, including the contribution of the target enzyme acetolactate synthase (ALS) to resistance and the presence of non-target-site resistance (NTSR). Eight L. multiflorum populations suspected of being resistant to imazamox were collected, and six populations exhibited resistance, ranging from 2.45-fold to 16.32-fold. The LmALS1 gene from susceptible population D3 plants and multiple copies of the LmALS gene (LmALS1, LmALS2, LmALS2α, LmALS3, LmALS3α, LmALS3β) from resistant populations D5 and D8 plants were separately amplified. Two mutations (Pro/Gln197 to Thr, Trp574 to Leu) were found in LmALS1 in the resistant populations. Compared to D3, LmALS1 was overexpressed in D5 but not in D8. The presence of LmALS1 mutants (LmALS1-Thr197 and LmALS1- Leu574), along with LmALS2, LmALS3, and their subunits, contribute to the resistance phenotype by increasing bonding energies, weakening hydrogen bonds, or decreasing protein binding pocket volumes and surface area. Additionally, D5 and D8 populations exhibited multiple resistance (>40-fold) to three other ALS inhibitors: pyroxsulam, flucarbazone-sodium, and mesosulfuron-methyl. Pre-treatment with malathion and 4-chloro-7-nitrobenzoxadiazole (cytochrome P450 monooxygenase and glutathione S-transferase inhibitors respectively) reversed the resistance of the D8 population and partially reversed the resistance of the D5 population to imazamox. This study characterizes ALS genes and extends our knowledge into the ALS resistance mechanisms involved in L. multiflorum. It also deepens our understanding of the complex diversification resistance mechanisms, thereby facilitating advances in weed resistance management strategies in wheat fields.

The Evolution and Mechanisms of Multiple-Insecticide Resistance in Rice Stem Borer, Chilo suppressalis Walker (Lepidoptera: Crambidae).

The emergence of insecticide resistance in the rice stem borer, Chilo suppressalis, is a growing threat to the sustainable control of this important insect crop pest. Thus, monitoring of C. suppressalis populations for insecticide resistance and characterization of the underlying genetic mechanisms is essential to inform rational control decisions and the development of resistance management strategies. Here, we monitored 126 C. suppressalis field populations from China for resistance evolution to four major insecticides: 53 for chlorantraniliprole, 50 for abamectin, 74 for triazophos, and 76 for spinetoram. Moderate to high levels of resistance were observed to all four insecticides. Investigation of the underlying resistance mechanisms revealed multiple mutations in the ryanodine receptor (RyR) and acetylcholinesterase 1 (AChE1), leading to target-site resistance to chlorantraniliprole and triazophos, respectively. In contrast, the absence of mutations in the glutamate-gated chloride channel (GluCl) and α6 nicotinic acetylcholine receptor (nAChR α6) subunit suggested that nontarget site mechanisms contribute to the multiple-insecticide resistance phenotypes observed in C. suppressalis. In this regard, we revealed overexpression of the uridine 5'-diphospho-glycosyltransferase UGT33AF1 and cytochrome P450 CYP6AB45 in C. suppressalis field populations. Functional characterization using transgenic Drosophila demonstrated that UGT33AF1 confers resistance against multiple insecticides in vivo, whereas CYP6AB45 does not appear to contribute to resistance. Collectively, our findings reveal the current status of resistance of C. suppressalis to insecticides in China and uncover a diverse profile of resistance mechanisms in this species. These findings provide a foundation for the development of sustainable strategies to effectively manage and control this pest.

Organophosphate and carbamate susceptibility profiling of Anopheles gambiae sl. across different ecosystems in southern Benin.

To overcome the spread of high pyrethroid resistance in the main malaria vectors and malaria disease persistence, it is crucial to look for effective and better resistance management strategies. Understanding the phenotypic profile of Anopheles gambiae sl. against alternatives insecticides like organophosphates and carbamates is crucial. Anopheles larvae and pupae were collected from the breeding sites in rice fields, pineapple crop areas, and peri-urban areas. WHO susceptibility tests were conducted on unfed female mosquitoes aged 3-5 days old. Mosquitoes were exposed to malathion 5%, pirimiphos-methyl 0.25%, and bendiocarb 0.1% using the standard WHO protocol. Polymerase chain reaction (PCR) techniques were used to detect species, kdr and Ace-1 mutations. Anopheles gambiae sl. from Sèdjè-Dénou rice field population was resistant to bendiocarb (0.1%) with a mortality rate of 72.2% whereas Anopheles gambiae sl. populations from Zinvié-Dokomey (rice field), Zè-Tozounmè (pineapple field), and Adjagbo (peri-urban area) were suspected to be resistant with mortality rates of 90%, 93.5%, 95.4% respectively. However, all of them were susceptible to organophosphates (malathion and pirimiphos-methyl) with a mortality rate of 100%. PCR assay revealed that 100% of the mosquitoes tested were Anopheles coluzzii. The frequencies of Ace-1R mutation in all Anopheles coluzzii populations tested were low (3-27%). Organophosphates (malathion and pirimiphos-methyl) have maintained their efficacy against Anopheles coluzzii populations from Sèdjè-Dénou (rice field), Zè Tozounmè (pineapple field), Zinvié Dokomey (rice field), or Adjagbo (peri-urban area). The good efficacy of these organophosphates against Anopheles coluzzii populations from the southern part of Benin are observed in the current study. The use of pirimiphos-methyl for IRS in this part of the country would be a successful alternative for malaria control in this area.

Droplet Digital PCR: A New Molecular Method to Detect G1105S/V Mutations in Plasmopara viticola CesA3 Gene.

Plasmopara viticola is the causal agent of Grapevine Downy Mildew (GDM), which is a devastating disease of grapevines in humid temperate regions. The most employed method for protecting grapevines against GDM is the application of chemical fungicides. In Spain, Carboxylic Acid Amides (CAAs) are a fungicide group currently utilized in GDM control. In P. viticola, resistance to CAAs is conferred by G1105S and G1105V mutations in the CesA3 gene. Droplet digital polymerase chain reaction (ddPCR) is an innovative technique that combines PCR and droplet microfluidics to disperse the sample into thousands of water-in-oil droplets in which an amplification reaction is individually performed. In this study, we set up a ddPCR protocol to quantify S1105 and V1105 mutations conferring resistance to CAAs in P. viticola. The optimal PCR conditions were established, and the sensitivity and precision of the protocol were assessed. Four P. viticola populations coming from commercial vineyards in northern Spain were analyzed, and different allele frequencies were found in the analyzed samples corresponding to the different fungicide management strategies, ranging from 7.72% to 100%. Knowing the level of mutated alleles allows for designing resistance management strategies suited for each location. This suggests that similar ddPCR assays could be developed for studying mutations implicated in fungicide resistance in other fungicide groups and plant pathogens.

Is It Time to Start Worrying? A Comprehensive Report on the Three-Year Prevalence of ESBL-Producing Bacteria and Their Trends in Antibiotic Resistance from the Largest University Hospital in Slovakia.

Over the past few decades, extended-spectrum β-lactamase (ESBL)-producing bacteria have become a great concern in healthcare systems worldwide, imposing large burdens by increasing antimicrobial resistance and patient morbidity. Given the high mortality rates and emergence of multidrug-resistant (MDR) strains, monitoring ESBL prevalence and resistance patterns is crucial. This study aimed to evaluate ESBL-producing Escherichia coli, Proteus mirabilis, and Klebsiella pneumoniae over three years, focusing on phenotypic distribution and resistance profiles. A total of 1599 ESBL-producing bacterial samples were collected and analysed. A panel of 20 antibiotics was tested to determine resistance traits. Data were recorded on phenotypical distribution, isolation types, changes in antibiotic resistance, and the relation of such changes to antibiotic consumption (defined daily dose) from clinical isolates. Phenotypical analysis revealed the minimal presence of the Cefotaximase from Munich (CTX-M) phenotype in E. coli and K. pneumoniae, creating a distinct epidemiological profile compared to global patterns. Shifts in isolation trends, particularly in P. mirabilis, suggest an expected increase in associated-mortality-rate in the coming years. While resistance trends were not statistically significant, MDR and extensively drug-resistant (XDR) strains were identified across all three bacteria. Only meropenem showed consistent 100% efficacy against E. coli, with other antibiotics displaying only partial effectiveness. These findings highlight the need for ongoing surveillance of ESBL-producing bacteria and underscore challenges in managing antibiotic resistance due to limited efficacy of last-resort treatments. The unique phenotypical distribution observed could impact local resistance management strategies in hospital settings in the coming years.

Monitoring of pyrethroid resistance in Aedes aegypti: first report of double and triple kdr mutations in Buenos Aires Province

BackgroundDengue is an emerging disease in Argentina due to the colonization of Aedes aegypti, the mosquito vector. Buenos Aires Province is the biggest and most populated district in Argentina, suffering dengue outbreaks of growing magnitude. During epidemic periods, pyrethroid insecticides are used in this country to control adult mosquitoes. Pyrethroid resistance in dengue vectors has been reported worldwide, making it necessary to implement resistance management strategies. The voltage-gated sodium channel is the target site of pyrethroids. Mutations in the gene encoding this protein, called kdr mutations, are usually the molecular cause of pyrethroid resistance in insects. In Ae. aegypti from the Americas, three kdr substitutions were described: V410L, V1016I, and F1534C. The diagnostic of kdr mutations is recommended for the early detection of pyrethroid resistance as well as the consequent planning of evidence-based control policies.MethodsWe distributed ovitraps across 16 localities in Buenos Aires Province, collecting 22,123 eggs. A total of 522 mosquitoes were genotyped in positions 1016 and 1534 of voltage-gated channel using multiplex high-resolution melting and/or TaqMan probe methods. A subset of 449 samples was also genotyped by a singleplex high-resolution melting method developed ad hoc and/or Sanger sequencing.ResultsWe have documented, for the first time to our knowledge in the central region of Argentina, the presence of the 1016Ikdr + 1534Ckdr allele. Additionally, our study reports the first identification of the V410L mutation in central Argentina. These results underscore a growing trend of pyrethroid resistance in Ae. aegypti, fueled by the widespread use of these insecticides.ConclusionsWe detected 1016Ikdr + 1534Ckdr and 410Lkdr mutations in central Argentina for the first time and improved the processivity and accuracy of kdr genotyping methods. The results are both a tool for resistance monitoring and a sign of alarm to direct efforts towards finding sustainable methods for vector control to complement or replace pyrethroids. Joint efforts between academia and authorities to develop and implement public policies for vector control are a productive way to transfer scientific results for their application in public health.Graphical

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

Insecticide resistance among malaria vector species now occurs in 84 malaria-endemic countries and territories worldwide. Novel vector-control interventions, including long-lasting insecticidal nets (LLINs) that incorporate new active ingredients with distinct modes of action, are urgently needed to delay the evolution and spread of resistance and to alleviate reversals in malaria-control gains. We aimed to assess the longitudinal effect of two dual-active-ingredient LLINs on insecticide resistance during a cluster-randomised, controlled trial in Benin. This 3-year, three-arm, cluster-randomised, controlled trial was conducted between Oct 17, 2019, and Oct 24, 2022, in three districts in southern Benin, to compare the effects of LLINs containing chlorfenapyr-pyrethroid or pyriproxyfen-pyrethroid with LLINs containing pyrethroid only. In 19 292 mosquitoes (Anopheles gambiae sensu lato) collected over 36 months-3 months of baseline followed by 3 years post-intervention-we measured longitudinal phenotypic insecticide resistance profiles using bioassays and genotypic resistance profiles using quantitative, real-time, reverse transcriptase PCR of metabolic resistance genes in two clusters per trial group. The trial was registered with ClinicalTrials.gov, NCT03931473. In all three trial groups, a significant effect of LLINs on insecticide resistance selection was evident, with the median lethal dose (LD50) of α-cypermethrin approximately halving between baseline and 12 months post-LLIN distribution (pyrethroid-only LLIN cluster 21: LD50 78·78 μg/ml [95% CI 65·75-94·48] vs 35·93 [29·41-43.86] and cluster 31: 79·26 [65·40-96·44] vs 38·71 [30·88-48·53]; chlorfenapyr-pyrethroid LLIN cluster 43: 104·30 [82·97-133·58] vs 43·99 [35·30-54·86]; and pyriproxyfen-pyrethroid LLIN cluster 36: 63·76 [52·14-77·75] vs 37·96 [30·88-46·69] and cluster 53: 77·67 [57·63-104·56] vs 39·72 [29·26-53·97]). Over the subsequent 2 years, the LD50 of α-cypermethrin increased past baseline values in all three trial groups (year 3 pyrethroid-only LLIN cluster 21: 141·01 [111·70-181·90] and cluster 31: 115·15 [93·90-143·09]; chlorfenapyr-pyrethroid LLIN cluster 43: 97·00 [77·24-123·54] and cluster 55: 126·99 [102·34-161·26]; and pyriproxyfen-pyrethroid LLIN cluster 36: 142·29 [112·32-184·84] and cluster 53: 109·88 [79·31-157·70]). We observed minimal reductions in chlorfenapyr susceptibility and variable but significant reductions in fertility after pyriproxyfen exposure, with an overall trend of increasing susceptibility across trial years. Several metabolic genes were implicated in resistance selection, including CYP6P4 in the pyriproxyfen-pyrethroid LLIN group, which encodes an enzyme known to metabolise pyriproxyfen in vitro, and CYP6P3 and CYP9K1 in the chlorfenapyr-pyrethroid LLIN group, both of which encode enzymes that are involved in pro-insecticide activation. After 24 months of use, chlorfenapyr-pyrethroid LLINs no longer mitigated pyrethroid resistance selection in this area of southern Benin, which has high malaria transmission dominated by highly resistant A gambiae sensu lato. This finding raises issues for current net-procurement schedules, which are based on an operational net lifespan of 3 years. Knowledge of the effects of next-generation LLINs on insecticide-resistance selection is crucial for the pragmatic design of prospective resistance-management strategies. UNITAID and The Global Fund to Fight AIDS, Tuberculosis and Malaria.

Resistance of Anopheles gambiae s.s. against commonly used insecticides and implication of cytochrome P450 monooxygenase in resistance to pyrethroids in Lambaréné (Gabon)

BackgroundInsecticides are a crucial component of vector control. However, resistance constitute a threat on their efficacy and the gains obtained over the years through malaria vector control. In Gabon, little data on phenotypic insecticide resistance in Anopheles vectors are published, compromising the rational implementation of resistance management strategies. We assessed the susceptibility to pyrethroids, carbamates and organophosphates of Anopheles gambiae sensu lato (s.l.) and discuss the mechanisms involved in the pyrethroid resistance-phenotype.MethodsA. gambiae s.l. larvae were collected from breeding sites in Lambaréné. Emerging adults were used in WHO tube assays at an insecticide concentration that defines resistance (diagnostic concentration). Subsequently, deltamethrin and permethrin were used at 5x and 10x diagnostic concentrations and after preexposure with the cytochrome p450 (and glutathione S-transferase) inhibitor piperonyl butoxide (PBO). A subset of mosquitoes was typed by molecular methods and screened using Taqman assays for mutations conferring target site resistance at the Voltage-gated sodium channel 1014 (Vgsc-1014) locus and the acetylcholinesterase (Ace-1) gene.ResultsAll mosquitoes were A. gambiae sensu stricto (s.s.) and resistant to permethrin, deltamethrin and alphacypermethrin (mortality less than 98%). However, mosquitoes were susceptible to malathion but resistant to bendiocarb. The level of resistance was high for permethrin and at least moderate for deltamethrin. Pre-exposure to PBO significantly increased the mortality of resistant mosquitoes (P < 0.0001). They became fully susceptible to deltamethrin and permethrin-induced mortality increased 4-fold. The G119S Ace-1 resistance allele, which confers resistance to both organophosphates and carbamates, was not present. All sampled mosquitoes were either homozygous for the Vgsc-L1014F or heterozygous for Vgsc-L1014F/L1014S, a marker for resistance to pyrethroids and organochlorides.ConclusionThese findings demonstrate a role of cytochrome P450 monooxygenases in the pyrethroid-resistance of A. gambiae s.s. from Lambaréné. Combining PBO with pyrethroids, as done in second generation bednets, may be used to revert resistance. In addition, malathion could also be used in combination with pyrethroids-based methods for resistance management.

Numerical Modeling Reveals That Resistant Western Corn Rootworm Are Stronger Fliers than Their Susceptible Conspecifics.

The hindwing geometry, aspect ratio, and numerical modeling of susceptible, Bt-Corn- and rotation-resistant western corn rootworm (WCR) wings was investigated. All variants had similar hindwing geometries and aspect ratio (AR: 6-7). These AR values correspond to wings suited to lower altitude flights of a shorter distance. These AR values are characteristic of wings that can carry heavier loads and are capable of precision flying. Numerical modeling using the finite element method (FEM) showed that the Bt-Corn-resistant and rotation-resistant WCR hindwings could potentially resist higher wind speeds with minimal deformations compared to conspecific susceptible WCR. Understanding the physiology and dispersal of resistant WCR enables a better understanding of how these variants spread their alleles across large scale agricultural landscapes. This may have important implications for integrated resistant management strategies for WCR.

Resistance risk assessment of Rhizoctonia solani to four fungicides.

Hexaconazole, thifluzamide, difenoconazole and azoxystrobin are widely used fungicides for the control of Rhizoctonia solani in China. However, few studies have assessed the sensitivity and resistance risk of R. solani to these four fungicides. The sensitivities of 126 R. solani isolates to hexaconazole, thifluzamide, difenoconazole and azoxystrobin were determined, with average half maximal effective concentration (EC50) values of 0.0386, 0.0659, 0.663 and 1.508 μg mL-1, respectively. Field resistance monitoring of the four fungicides showed that the three isolates had moderate resistance to difenoconazole. Resistant mutants to the four fungicides were obtained by fungicide adaptation, and resistance could be stably inherited by most mutants. Compared with those of the parent isolates, the biological characteristics of hexaconazole-resistant mutants exhibited enhanced or similar compound fitness index (CFI), whereas most of the other mutants displayed reduced or comparable CFI. There was evidence of positive cross-resistance between hexaconazole and difenoconazole. In the presence of fungicides, the expression of the CYP51 genes in hexaconazole- and difenoconazole-resistant mutants significantly increased, the expression of SDH genes in thifluzamide-resistant mutants significantly decreased, and the expression of the Cyt b gene in azoxystrobin-resistant mutants did not significantly change. Based on these data, we speculated that R. solani had a low-to-medium resistance risk to four fungicides. The change of target gene expression may be one of the reasons for fungicide resistance in R. solani. This study provides a theoretical basis for monitoring resistance emergence and developing resistance management strategies to control R. solani. © 2024 Society of Chemical Industry.

Area-wide survey and monitoring of insecticide resistance in the brown planthopper, Nilaparvata lugens (Stål), from 2020 to 2023 in China

The brown planthopper (BPH), Nilaparvata lugens (Stål), is a notorious pest affecting Asian rice crops. The evolution of insecticide resistance in BPH has emerged as a significant challenge in effectively managing this pest. This study revealed the resistance status of BPH to nine insecticides in ten provinces and Shanghai City in China from 2020 to 2023. Monitoring results showed that the resistance of BPH to triflumezopyrim, nitenpyram, and dinotefuran increased rapidly. The average resistance ratio of BPH to triflumezopyrim increased from 2.5 to 7.1 fold, nitenpyram from 18.3 to 37.7 fold, and dinotefuran from 119.5 to 268.1 fold. All populations remained extremely high resistance to imidacloprid, thiamethoxam, and buprofezin. Most field populations of BPH maintained moderate resistance to chlorpyrifos and sulfoxaflor, and high resistance to pymetrozine by rice stem dipping method. However, considering the reproduction-inhibiting character of pymetrozine, susceptible to low resistance levels to pymetrozine were monitored by Insecticide Resistance Action Committee (IRAC) NO.005 method. This result indicated that pymetrozine might lose efficacy in the control of application generation, but it could significantly inhibit the reproduction of field populations of BPH. Additionally, we compared the expression levels of 11 nicotinic acetylcholine receptor (nAChR) genes, the targets of nAChR competitive modulators, in four field populations (FY23, YH23, LJ23, LP23) and susceptible strain. The expression level of nAChR α4 was significantly reduced in all field populations, while α1, α2, α6, and α7 were significantly reduced in some field populations. Our findings provide valuable information for resistance management strategies in N. lugens and offer new insights into the resistance mechanisms of nAChR competitive modulators.

Stability, Inheritance, Cross-Resistance, and Fitness Cost of Resistance to λ-Cyhalothrin in Cydia pomonella.

Insecticides are commonly utilized in agriculture and forestry for pest control, but their dispersal can pose hazards to humans and environment. Understanding resistance, inheritance patterns, and fitness costs can help manage resistance. A λ-cyhalothrin-resistant population (LCR) of Cydia pomonella, a global pest of pome fruits and walnuts, was obtained through selective insecticide breeding for 15 generations, showing stable moderate resistance (23.85-fold). This population was cross-resistant to deltamethrin (4.26-fold) but not to β-cypermethrin, chlorantraniliprole, chlorpyrifos, and avermectin. Genetic analysis revealed the resistance was autosomal, incompletely dominant, and controlled by multiple genes. Increased activity of glutathione S-transferases and cytochrome P450 monooxygenases (P450s) played a primary role in resistance, with specific genes up-regulated in LCR, and exhibited significant expression in midgut. LCR also exhibited fitness costs, including delays in development, reduced fecundity, and slower population growth. These findings contribute to understanding λ-cyhalothrin resistance in C. pomonella and can guide resistance management strategies.

Revealing antibiotic resistance's ancient roots: insights from pristine ecosystems.

The prevailing belief that antibiotic resistance mechanisms emerged with human antibiotic use has been challenged. Evidence indicates that some antibiotic resistance genes (ARGs) have a long evolutionary history, predating the advent of antibiotics in human medicine, thereby demonstrating that resistance is an ancient phenomenon. Despite extensive surveys of resistance elements in environments impacted by human activity, limited data are available from remote and pristine habitats. This minireview aims to compile the most relevant research on the origins and evolution of ARGs in these habitats, which function as reservoirs for ancient resistance mechanisms. These studies indicate that ancient ARGs functionally similar to modern resistance genes, highlighting the general role of natural antimicrobial substances in fostering the evolution and exchange of diverse resistance mechanisms through horizontal gene transfer over time. This minireview underscores that antibiotic resistance was present in ancestral microbial communities and emphasizes the ecological role of antibiotics and resistance determinants. Understanding ancient ARGs is crucial for predicting and managing the evolution of antibiotic resistance. Thus, these insights provide a foundational basis for developing new antibiotics and strategies for microbial resistance management.

V1848I Mutation in the Voltage-Gated Sodium Channel Confers High-Level Resistance to Indoxacarb and Metaflumizone in Spodoptera exigua.

Spodoptera exigua is one of the most serious lepidopteran pests of global importance. With the intensive use of insecticides, S. exigua has evolved resistance to many insecticides, including the sodium channel blocker insecticides (SCBIs) indoxacarb and metaflumizone. In this study, we investigated the role of the V1848I mutation in the voltage-gated sodium channel (VGSC) in SCBI resistance and its inheritance patterns in S. exigua through the development and characterization of a near-isogenic resistant strain. The AQ-23 strain of S. exigua, collected in 2023 from Anqing, Anhui province of China, shows 165-fold resistance to indoxacarb compared with the susceptible WH-S strain. A frequency of 44.6% for the V1848I mutation was detected in the SeVGSC of the AQ-23 strain, while no F1845Y mutation was found. Through repeated backcrossing and marker-assisted selection, the V1848I mutation in the AQ-23 strain was introgressed into the susceptible WH-S strain, creating a near-isogenic strain named WH-1848I. This WH-1848I strain exhibits high levels of resistance to indoxacarb (146-fold) and metaflumizone (431-fold) but remains susceptible to broflanilide and spinosad compared with the WH-S strain. Inheritance analysis revealed that SCBI resistance in the WH-1848I strain is autosomal, nonrecessive, and genetically linked to the V1848I mutation. These findings establish a clear link between the V1848I mutation and SCBI resistance in S. exigua, offering valuable insights for developing molecular detection tools and resistance management strategies.

Screening of rice cultivars against Scirpophaga incertulas Walker : utilising cluster analysis as a tool to identify resistant cultivars

The field experiment was conducted in the Boro season from December 2022 to April 2023 at the Institutional research farm, Institute of Agriculture, Palli Siksha Bhavana, Visva-Bharati, Sriniketan, Birbhum, West Bengal, for the screening of thirty-three rice cultivars for their resistance to yellow stem borer, Scirpophaga incertulas Walker. The experiment utilized modified percent damage values to grade these cultivars during both vegetative and reproductive stages. Early-duration cultivars displayed varied reactions, with Jaldi 13 (2) exhibiting consistent resistance (2.53% DH, 12.65% D), while others showed moderate resistance or susceptibility with deadheart percentages ranging from 4.73% to 8.51% and corresponding damage percentages between 23.65% and 42.55%. This trend extended to reproductive stages, where all early-duration cultivars demonstrated moderate to high susceptibility, with damage percentages between 30.8% and 54.5%. The mid-early duration cultivars displayed mixed responses, with Sahabhagi (4) demonstrating moderate resistance (4.92% DH) and Sukumar (3) exhibiting moderate susceptibility (8.21% DH) during the vegetative stage. These diverse reactions continued into the reproductive stage, providing a comprehensive understanding of their responses to the pest. Additionally, in medium and late-duration cultivars, a range of reactions persisted, with cultivars like Pratiksha (20) showing moderate resistance (6.63% DH) in the mid-duration category and Ajith (25) displaying moderate resistance (6.33% DH) in the late-duration category. Cluster analysis categorized the cultivars into distinct groups, showcasing a mix of resistant, moderately resistant, and susceptible types across all growth durations. Notably, cultivars like Gotra 1 (10), Parijat (14), Pushpa (17), PNR 546 (19), Pravat (23) and Gotra 2 (31) consistently demonstrated resistance or moderate resistance across different growth stages, suggesting their potential suitability in tailoring resistant breeding programs and pest management strategies against the stem borer in rice cultivation.

Insect pest Spodoptera litura (Fabricius) and its resistance against the chemical insecticides: A review

A polyphagous nocturnal pest Spodoptera litura (Fabr.) commonly called armyworm, infests about 150 plant species across 44 families worldwide, with nearly 60 plant species affected just in India. The majority of leaf tissues are consumed by the larvae and only the stem and side shoots will remain in the field. They entirely consume the interior content by boring into them, causing squares and young bolls to shed. This insect can badly affect crops and has a wide range of potential hosts, which can lead to financial losses for farmers and food shortages for consumers. The worldwide distribution of S. litura as a pest results in significant impact on productivity of many crops. They have the capability to invade new places as a wide-ranging species. Armyworm frequently reappears in India every year and causes evident destruction. Different records on the insect population outbreak have been reported from many countries all around the world. The larvae of insect pests enter the fruits and even contaminate it and this causes yield and economic losses. The low temperatures of winter season are the limiting factors that affect species. It migrates mainly to breed during the summer season but is unable to survive in winters. S. litura acquired resistance to several synthetic insecticides, which led to pest outbreaks that were irregular and caused failure of different crops. The resistance and cross-resistance of this pest against insecticide toxin make it more difficult to reduce its population below threshold level. Understanding the mechanisms of resistance is crucial for developing effective resistance management strategies that can restrict or halt the spread of resistance in these pest populations.