Multiple origins of kdr-type resistance in the house fly, Musca domestica

Organochlorine knockdown-resistance (kdr) association in housefly (Musca domestica): A systematic review and meta-analysis

Introduction

Although house flies (Musca domestica) do not directly cause disease in humans, they transmit pathogens to them, which provide the basis for many diseases. The main way to deal with this insect is to use insecticides. Due to the resistance from insecticides, the fight against house flies has been hampered. This study aimed to determine the prevalence of knockdown resistance against organochlorine insecticides in house flies worldwide.

Methods

This study was conducted via a systematic review and meta-analysis to investigate the prevalence of knockdown resistance against organochlorine insecticides in house flies. Accordingly, by searching the databases of Web of Science, PubMed, Scopus, Proquest, Bioone, and Embase, all published articles were extracted, and reviewed until the end of May 2022. Statistical data analysis was performed using the random-effects model in the meta-analysis, meta-regression, and I2 index.

Results

Nine studies entered the meta-analysis process. Based on this, the prevalence of knockdown resistance against organochlorine insecticide in house flies was estimated to be 49.1%. Meta-regression showed that the prevalence of knockdown resistance increased with increasing years of study but decreased with increasing sample size.

Conclusion

According to the findings, about 50% of house flies have knockdown resistance against organochlorine insecticide. As a result, it is necessary to adopt effective and combined methods to combat this insect to control it and prevent the transmission of diseases caused by it.

Frequencies and distribution of kdr and Ace alleles that cause insecticide resistance in house flies in the United States

House flies (Musca domestica L) are nuisances and vectors of pathogens between and among humans and livestock. Population suppression has been accomplished for decades with pyrethroids and acetylcholinesterase (AChE) inhibitors, but recurrent selection has led to increased frequency of alleles conferring resistance to those two classes of active ingredients (Geden et al., 2021). A common mechanism of resistance to both classes involves an altered target site (mutations in Voltage gated sodium channel (Vgsc) for pyrethroids or in Ace for AChE inhibitors). As part of ongoing efforts to understand the origin, spread and evolution of insecticide resistance alleles in house fly populations, we sampled flies in 11 different US states, sequenced, and then estimated frequencies of the Vgsc and Ace alleles. There was substantial variation in frequencies of the four common knockdown resistance alleles (kdr (L1014F), kdr-his (L1014H), super-kdr (M918T + L10414F) and 1B (T929I + L1014F) across the sampled states. The kdr allele was found in all 11 states and was the most common allele in four of them. The super-kdr allele was detected in only six collections, with the highest frequencies found in the north, northeast and central United States. The kdr-his allele was the most common allele in PA, NC, TN and TX. In addition, a novel super-kdr-like mutation in mutually exclusive exon 17a was found. The overall frequencies of the different Ace alleles, which we name based on the amino acid present at the mutation sites (V260L, A316S, G342A/V and F407Y), varied considerably between states. Five Ace alleles were identified: VAGF, VAVY, VAGY, VAAY and VSAY. Generally, the VSAY allele was the most common in the populations sampled. The susceptible allele (VAGF) was found in all populations, ranging in frequency from 3% (KS) to 41% (GA). Comparisons of these resistance allele frequencies with those previously found suggests a dynamic interaction between the different alleles, in terms of levels of resistance they confer and likely fitness costs they impose in the absence of insecticides.

Evaluation of resistance of human head lice to pyrethroid insecticides: A meta-analysis study

Introduction

Pediculosis is one of the most common annoying infections caused by parasitic lice in humans. Pyrethroids are one of the main insecticides used to treat this infection. But recently, due to the Resistance of lice to this group of insecticides, its insecticidal effects have been affected. The present study was conducted through a meta-analysis to investigate the prevalence of pyrethroid resistance against these insecticides worldwide.

Methods

This study was conducted as a meta-analysis of the prevalence of treatment resistance in human head lice against pyrethroid insecticides worldwide. Based on this, all articles published without a time limit until the end of June 2022 in PubMed/MEDLINE, Web of Science (ISI), Scopus, and Google Scholar databases were extracted and using random-effects meta-analysis model statistical methods in the meta-analysis, Cochrane, Index I^2, and funnel plot were analyzed by STATA software.

Results

Twenty studies were included in the meta-analysis process. According to this, the prevalence of pyrethroid resistance insecticides in human head lice was estimated at 59% (CI95%: 50%-68%). Among pyrethroid insecticides, the highest prevalence of pyrethroid resistance against permethrin insecticide was 65%. Regarding the prevalence of Resistance by year, the prevalence before 2004 was estimated at 33%, but after 2015, this rate reached 82%. Also, the majority of pyrethroid resistance was estimated at 68% using genetic diagnosis methods and 43% using clinical diagnosis methods.

Conclusion

More than half of human head lice pyrethroid resistance insecticides. Based on this, it is recommended that before using this treatment method to treat human head lice Infestation, it should investigate the prevalence of pyrethroid resistance in that area, and if the majority of Resistance is high, alternative or combined treatment methods should be used.

Evaluation of the evolutionary genetics and population structure of Culex pipiens pallens in Shandong province, China based on knockdown resistance (kdr) mutations and the mtDNA-COI gene

BACKGROUND

Mosquitoes are important vectors for a range of diseases, contributing to high rates of morbidity and mortality in the human population. Culex pipiens pallens is dominant species of Culex mosquito in northern China and a major vector for both West Nile virus and Bancroftian filariasis. Insecticide application were largely applied to control the mosquito-mediated spread of these diseases, contributing to increasing rates of resistance in the mosquito population. The voltage-gated sodium channel (Vgsc) gene is the target site of pyrethroids, and mutations in this gene cause knockdown resistance (kdr). While these kdr mutations are known to be critical to pyrethroid resistance, their evolutionary origins remain poorly understood. Clarifying the origins of these mutations is potential to guide further vector control and disease prevention efforts. Accordingly, the present study was designed to study the evolutionary genetics of kdr mutations and their association with the population structure of Cx. p. pallens in Shandong province, China.

METHODS

Adult Culex females were collected from Shandong province and subjected to morphological identification under a dissection microscope. Genomic DNA were extracted from the collected mosquitoes, the Vgsc gene were amplified via PCR and sequenced to assess kdr allele frequencies, intron polymorphisms, and kdr codon evolution. In addition, population genetic diversity and related population characteristics were assessed by amplifying and sequencing the mitochondrial cytochrome C oxidase I (COI) gene.

RESULTS

Totally, 263 Cx. p. pallens specimens were used for DNA barcoding and sequencing analyses to assess kdr allele frequencies in nine Culex populations. The kdr codon L1014 in the Vgsc gene identified two non-synonymous mutations (L1014F and L1014S) in the analyzed population. These mutations were present in the eastern hilly area and west plain region of Shandong Province. However, only L1014F mutation was detected in the southern mountainous area and Dongying city of Shandong Province, where the mutation frequency was low. Compared to other cities, population in Qingdao revealed significant genetic differentiation. Spatial kdr mutation patterns are likely attributable to some combination of prolonged insecticide-mediated selection coupled with the genetic isolation of these mosquito populations.

CONCLUSIONS

These data suggest that multiple kdr alleles associated with insecticide resistance are present within the Cx. p. pallens populations of Shandong Province, China. The geographical distributions of kdr mutations in this province are likely that the result of prolonged and extensive insecticide application in agricultural contexts together with frequent mosquito population migrations. In contrast, the low-frequency kdr mutation detected in central Shandong Province populations may originate from the limited selection pressure in this area and the relative genetic isolation. Overall, the study compares the genetic patterns revealed by a functional gene with a neutral marker and demonstrates the combined impact of demographic and selection factors on population structure.

Global Pattern of kdr-Type Alleles in Musca domestica (L.)

Purpose of Review

Houseflies, Musca domestica L., are an important sanitary pest that affects human and domesticated animals. They are mechanical carriers of more than 100 human and animal diseases including protozoan, bacterial, helminthic, and viral infections. Recently, it was demonstrated that houseflies acquired, harbored, and transmitted SARS-CoV-2 (COVID-19) for up to 1 day post-exposure. The most widely used control strategy relays on the application of pyrethroid insecticides due to their effectiveness, low mammalian toxicity, low cost, and environmental safety. The main mechanism of action of pyrethroids is to exert their toxic effects through affecting the voltage-sensitive sodium channel (VSSC) modifying the transmission of the nerve impulse and leading to the death of the insects. Target site insensitivity of the VSSC is due to the presence of single nuclear polymorphisms (SNPs) named knockdown mutations (kdr). In this review, we synthetize recent data on the type and distribution of these mutations globally.

Recent Findings

Housefly resistance is reported in several countries. Increased applications of pyrethroids to control housefly populations led to the emergence of multiple evolutionary origins of resistance determined by five amino acid substitutions or specific mutations in the VSSC: kdr (L1014F), kdr-his (L1014H), super-kdr (M918T + L1014F), type N (D600N + M918T + L1014F), and 1B (T929I + L1014F). According to the global map obtained, high levels of resistance to pyrethroids are associated with the L1014F mutation found mostly in North America, Europe, and Asia, while the super-kdr mutation was mostly found in the American continent. The level of protection conferred by these alleles against pyrethroids was generally kdr-his < kdr < Type N ≤ super-kdr ≤ 1B. The relative fitness of the alleles under laboratory conditions was susceptible ≅ kdr-his > kdr > super-kdr suggesting that the fitness cost of an allele was relative to the presence of other alleles in a population and that the reversion of resistance in a free insecticide environment might be quite variable from one region to another.

Summary

An adequate integrated pest management program should consider monitoring susceptibility to pyrethroids to detect early levels of resistance and predict the spread and evolution of resistant phenotypes and genotypes. From this review, the pyrethroid resistance status of housefly population was determined in very few countries and has evolved independently in different areas of the world affecting chemical control programs.

Differential role of chronic liver diseases on the incidence of cancer: a longitudinal analysis among 248,224 outpatients in Germany

BACKGROUND

Chronic liver diseases, especially chronic hepatitis, are a known risk factor for the development of liver cancer. However, the risk of total cancer development and malignant potential from these diseases is largely unknown. Systematic data on the risk of cancer development from these diseases are missing. Therefore, the goal of this study is to analyze the risk of total cancer development in chronic liver diseases.

METHODS

A cohort of 15,706 patients with chronic hepatitis and 15,706 patients without hepatitis were matched by propensity scoring from outpatient practices in Germany over a period of 15 years. Cox regression models were conducted to study the association between alcoholic hepatitis, autoimmune hepatitis, hepatitis B, hepatitis C and cancer incidence, including liver, other digestive organs, skin, prostate, breast and lymphoid and hematopoietic tissue cancer.

RESULTS

Within 10 years of the index date, 19.3% of patients with alcoholic hepatitis and 13.4% of non-hepatitis individuals were diagnosed with cancer (log-rank p = 0.035). These proportions were 15.0 vs. 9.9% (p = 0.078) for autoimmune hepatitis, 8.7 vs. 7.1% (p = 0.015) for hepatitis B, and 12.7 vs. 7.6% (p < 0.001) for hepatitis C. In regression analyses, only alcoholic hepatitis (HR: 1.84, 95% CI 1.32-2.54) and hepatitis C (HR: 2.10, 95% CI 1.77-2.50) were significantly associated with increased risk of cancer. There was a very strong positive association between hepatitis C and liver cancer (HR: 78.2 (95% CI 10.9-560.7). Furthermore, hepatitis C was associated with an increased risk of respiratory organ cancer (HR: 2.59, 95% CI 1.42-4.73).

CONCLUSION

This study confirms the strong association between chronic hepatitis and liver cancer, but also with an overall elevated cancer risk, and especially of cancer in the respiratory tract in patients with chronic hepatitis C.

Frequency of pyrethroid resistance in human head louse treatment: systematic review and meta-analysis

Head lice (Pediculus humanus capitis) are one of the most common insects causing infestations in humans worldwide, and infestation is associated with adverse socio-economic and public health effects. The development of genetic insensitivity (e.g., target site insensitivity = knockdown resistance or kdr) to topical insecticides has impaired effective treatment. Therefore, this study was undertaken to review and meta-analyze the frequency of pyrethroid resistance in treated head louse populations from the beginning of 2000 to the end of June 2021 worldwide. In order to accomplish this, all English language articles published over this period were extracted and reviewed. Statistical analyses of data were performed using fixed and random effect model tests in meta-analysis, Cochrane, meta-regression and I2 index. A total of 24 articles from an initial sample size of 5033 were accepted into this systematic review. The mean frequency of pyrethroid resistance was estimated to be 76.9%. In collected resistant lice, 64.4% were homozygote and 30.3% were heterozygote resistant. Globally, four countries (Australia, England, Israel, and Turkey) have 100% kdr gene frequencies, likely resulting in the ineffectiveness of pyrethrin- and pyrethroid-based pediculicides. The highest resistance recorded in these studies was against permethrin. This study shows that pyrethroid resistance is found at relatively high frequencies in many countries. As a result, treatment with current insecticides may not be effective and is likely the cause of increased levels of infestations. It is recommended that resistance status be evaluated prior to insecticide treatment, to increase efficacy.

Multiple Genetic Mutations Related to Insecticide Resistance are Detected in Field Kazakhstani House Flies (Muscidae: Diptera)

The house fly (Musca domestica Linnaeus) is an important disease vector. Insecticide resistance is an obstacle to effective house fly control. Previous studies have demonstrated that point mutations in acetylcholinesterase (Ace), carboxylesterase (MdαE7) and voltage-sensitive sodium channel (Vssc), and over-expression of CYP6D1v1 confer insecticide resistance in the house fly. However, information about the status and underlying mechanisms of insecticide resistance in Kazakhstani house flies is lacking. In this study, we investigated the occurrence of genetic mutations associated with insecticide resistance in field house flies collected at six different locations in southern Kazakhstan. Four mutations (V260L, G342A/V, and F407Y) in Ace and three mutations (G137D and W251L/S) in MdαE7 were detected with appreciable frequencies. Notably, haplotypes carrying triple-loci mutations in Ace and double mutations in MdαE7 were found in Kazakhstan. The L1014H and L1014F mutations in Vssc, and CYP6D1v1 resistance allele were detected at a low frequency in some of the six investigated house fly populations. Phylogenetic analyses of haplotypes supported multiple origins of resistance mutations in Ace and MdαE7. These observations suggest that house flies in southern Kazakhstan may exhibit significant resistance to organophosphates and carbamates. Regular monitoring of insecticide resistance is recommended to achieve effective house fly control by chemical agents in southern Kazakhstan.

Identification and phylogenetic analysis of voltage-gated sodium channel haplotypes in the malaria vector Anopheles sinensis using a high-throughput amplicon sequencing approach

Background

Anopheles sinensis is a dominant vector for malaria transmission in Asian countries. Voltage-gated sodium channel (VGSC) mutation-mediated knock-down resistance (kdr) has developed in many A. sinensis populations because of intensive and long-term use of pyrethroids. Our previous study showed that multiple mutations at position 1014 of the VGSC were heterogeneously distributed in A. sinensis populations across Sichuan, China.

Methods

To understand resistance genotypes at the haplotype level and reconstruct the phylogenetic relationship of VGSC haplotypes, a cost-effective next-generation sequencing (NGS)-based amplicon sequencing approach was established to clarify haplotypes containing codon 1014 of the VGSC gene from a total of 446 adults collected in 12 locations of Sichuan, China.

Results

Nineteen (19) haplotypes were identified, including 11 wild 1014L, 6 resistance 1014F, and 2 resistance 1014C haplotypes. We found that resistance haplotypes of A. sinensis VGSC were widely distributed at frequencies ranging from 3.67 to 92.61%. The frequencies of the 1014C haplotype in the southeast of Sichuan (Luzhou, Guangan, and Suining) were relatively higher than those in other sampling locations. Phylogenetic analyses support that kdr-type mutation at position 1014 is not singly originated and resistance 1014C haplotypes evolve from TTT-encoding 1014F.

Conclusions

A cost-effective next-generation sequencing (NGS)-based amplicon sequencing approach has been established in this study. The data revealed the patchy distribution of VGSC resistance haplotypes with overall high frequencies in Sichuan, China. Phylogenetic analyses support multiple origins and sequential evolution (1014L → 1014F → 1014C) for kdr-type mutations in A. sinensis.

Graphical abstract

Analysis of the insecticide resistance mechanism in Anopheles culicifacies sensu lato from a malaria-endemic state in India

BACKGROUND

Understanding the dynamics and mechanisms of insecticide resistance in malaria vectors is crucial for vector control activities. The present study investigates the level of insecticide resistance in Anopheles culicifacies and explores the role of two main mechanisms in conferring resistance target site insensitivity and metabolic resistance.

METHODS

A. culicifacies mosquitoes were collected and the voltage-gated sodium channel (VGSC) gene was amplified and sequenced to analyse the knockdown resistance (kdr) mutations. Further, a non-experimental homology model was generated to investigate the effect of kdr mutations on the conformation of protein. Metabolic resistance was determined using bioassay-based resistant and susceptible mosquitoes and the expression levels of the genes CYP6Z1 and GSTe2 were compared between the two groups.

RESULTS

Sequence analysis of the VGSC gene revealed the presence of L1014F (n=48 [17%]), L1014S and V1010L (n=5 [1.7%]) mutations in the study area. In gene expression studies, a significant upregulation of CYP6Z1 in deltamethrin-resistant (fold change 243.62; p=0.02) mosquitoes and that of GSTe2 in dichlorodiphenyltrichloroethane (fold change 403.45; p=0.01) and alpha-cypemethrin resistant (fold change 217.51; p=0.0005) mosquitoes was observed.

CONCLUSIONS

The study revealed that expression of the genes (CYP6Z1 and GSTe2) conferring metabolic resistance play a key role in insecticide resistance in A. culicifacies populations in central India. However, mutations L101F, L10104S and V10101L also have a role to some extent in spreading resistance. GeneBank accession numbers: MW559058, MW559059 and MW559060 Cover Image: Workflow of Chimera-Modeller interface. In the top window of Chimera's multi-align viewer the sequence alignment of VGSC proteins of human (pdb id_6AGF), cockroach (pdb id 5XOM) and A. culicifacies (ACT176122.1) is shown. The dialog box in the middle is of the comparative modelling tool of Modeller. The A. culicifacies sequence is designated as the target while human and cockroach sequences are templates. Upon selection of the template sequences in the dialog box, the structures of the respective proteins are displayed in the Chimera window. As the run is completed, the results are displayed in the form of a list of models with their scores in a table.

All resistance alleles are not equal: the high fitness cost of super-kdr in the absence of insecticide

BACKGROUND

Mutations in the voltage-sensitive sodium channel are an important mechanism of resistance to pyrethroid insecticides. In Musca domestica, common resistance alleles are kdr, super-kdr and kdr-his. The levels of resistance that these alleles confer is known, but the fitness of these alleles relative to each other and to susceptible alleles is unknown. We used crosses from congenic strains of M. domestica to establish populations with known allele frequencies and then examined the changes in allele and genotype frequencies over 25 generations under laboratory conditions.

RESULTS

There was a significant fitness cost for the super-kdr allele, which decreased from the starting frequency of 0.25 to 0.05 after 25 generations. The fitness of the kdr, kdr-his and susceptible alleles were similar. The greatest change in genotype frequency was seen for the super-kdr/super-kdr genotype, which was no longer detected after 25 generations.

CONCLUSION

The fitness cost associated with the super-kdr allele is consistent with previous reports and appears to be a factor in helping to restrain high levels of resistance in field populations (the super-kdr allele confers higher levels of resistance than kdr or kdr-his). It is known that the relative costs of different alleles are environmentally dependent, but our results also demonstrate that the relative fitness of given alleles depends on which alleles are present in a given population, as previous pairwise comparisons of allele fitness do not exactly match (except for super-kdr) the results obtained using this four allele study. © 2020 Society of Chemical Industry.

A survey of insecticide resistance-conferring mutations in multiple targets in Anopheles sinensis populations across Sichuan, China

Background

Sichuan province is located in the southwest of China, and was previously a malaria-endemic region. Although no indigenous malaria case has been reported since 2011, the number of imported cases is on the rise. Insecticide-based vector control has played a central role in the prevention of malaria epidemics. However, the efficacy of this strategy is gravely challenged by the development of insecticide resistance. Regular monitoring of insecticide resistance is essential to inform evidence-based vector control. Unfortunately, almost no information is currently available on the status of insecticide resistance and associated mechanisms in Anopheles sinensis, the dominant malaria vector in Sichuan. In this study, efforts were invested in detecting the presence and frequency of insecticide resistance-associated mutations in three genes that encode target proteins of several classes of commonly used insecticides.

Methods

A total of 446 adults of An. sinensis, collected from 12 locations across Sichuan province of China, were inspected for resistance-conferring mutations in three genes that respectively encode acetylcholinesterase (AChE), voltage-gated sodium channel (VGSC), and GABA receptor (RDL) by DNA Sanger sequencing.

Results

The G119S mutation in AChE was detected at high frequencies (0.40–0.73). The predominant ace-1 genotype was GGC/AGC (119GS) heterozygotes. Diverse variations at codon 1014 were found in VGSC, leading to three different amino acid substitutions (L1014F/C/S). The 1014F was the predominant resistance allele and was distributed in all 12 populations at varying frequencies from 0.03 to 0.86. The A296S mutation in RDL was frequently present in Sichuan, with 296SS accounting for more than 80% of individuals in six of the 12 populations. Notably, in samples collected from Chengdu (DJY) and Deyang (DYMZ), almost 30% of individuals were found to be resistant homozygotes for all three targets.

Conclusions

Resistance-related mutations in three target proteins of the four main classes of insecticides were prevalent in most populations. This survey reveals a worrisome situation of multiple resistance genotypes in Sichuan malaria vector. The data strengthen the need for regular monitoring of insecticide resistance and establishing a region-customized vector intervention strategy.

Graphical abstract

Recessivity of pyrethroid resistance and limited interspecies hybridization across Hyalella clades supports rapid and independent origins of resistance

Several populations of the amphipod, Hyalella azteca, have developed resistance to pyrethroid insecticides due to non-target exposure, but the dominance of the resistance trait is unknown. The current study investigated the dominance level of point mutations in natural populations of insecticide-resistant H. azteca and determined whether H. azteca from different clades with and without resistant alleles can hybridize and produce viable offspring. A parent generation (P₀) of non-resistant homozygous wild type H. azteca was crossbred with pyrethroid-resistant homozygous mutant animals and the tolerance of the filial 1 (F₁) generation to the pyrethroid insecticide, permethrin, was measured. Then the genotypes of the F₁ generation was examined to assure heterozygosity. The resistant parents had permethrin LC₅₀ values that ranged from 52 to 82 times higher than the non-resistant animals and both crossbreeding experiments produced heterozygous hybrid offspring that had LC₅₀ values similar to the non-resistant H. azteca parent. Dominance levels calculated for each of the crosses showed values close to 0, confirming that the L925I and L925V mutations were completely recessive. The lack of reproduction by hybrids of the C x D breeding confirmed that these clades are reproductively isolated and therefore introgression of adaptive alleles across these clades is unlikely. Potential evolutionary consequences of this selection include development of population bottlenecks, which may arise leading to fitness costs and reduced genetic diversity of H. azteca.

Sequence and transcript expression of the super-kdr locus of the horn fly, Haematobia irritans

In horn flies, Haematobia irritans irritans (Diptera: Muscidae) (Linnaeus, 1758), target site resistance to pyrethroids can be diagnosed by an allele-specific PCR that genotypes individual flies at both the super-kdr (skdr) and the knock down resistance (kdr) associated loci. When this technique uses genomic DNA as template, modifications, such as alternative RNA splicing and RNA editing are not specifically detected. Alternative splicing at the skdr locus has been reported in Dipterans; thus, the genomic DNA-based allele-specific PCR may not accurately reflect the frequency of the skdr mutation in horn fly field populations. To investigate if alternative splicing occurs at the skdr locus of horn flies, genomic DNA and cDNA sequences isolated from two wild populations and two laboratory-reared colonies with varying degrees of pyrethroid resistance were compared. There was no indication of alternative splicing at the super-kdr locus neither in the wild populations nor in the laboratory-reared colonies.

Impact of deltamethrin selection on kdr mutations and insecticide detoxifying enzymes in Aedes aegypti from Mexico

Background

Insecticide resistance is a serious problem for vector control programmes worldwide. Resistance is commonly attributed to mutations at the insecticide’s target site or increased activity of detoxification enzymes.

Methods

We determined the knockdown concentration (KC₅₀) and lethal concentration (LC₅₀) of deltamethrin in six natural populations of adult Aedes aegypti from southeastern Mexico. These populations were then selected over five generations using the LC₅₀ from the preceding generation that underwent selection, and the heritability of deltamethrin resistance was quantified. For each generation, we also determined the frequency of the kdr alleles L410, I1016 and C1534, and the levels of activity of three enzyme families (α- and β-esterases, mixed-function oxidases and glutathione S-transferases (GST)) associated with insecticide detoxification.

Results

There was an increase in KC₅₀ and LC₅₀ values in the subsequent generations of selection with deltamethrin (F_S5vs F_S0). According to the resistance ratios (RRs), we detected increases in LC₅₀ ranging from 1.5 to 5.6 times the values of the parental generation and in KC₅₀ ranging from 1.3–3.8 times the values of the parental generation. Triple homozygous mutant individuals (tri-locus, LL/II/CC) were present in the parental generations and increased in frequency after selection. The frequency of L410 increased from 1.18-fold to 2.63-fold after selection with deltamethrin (F_S5vs F_S0) in the populations analyzed; for I1016 an increase between 1.19-fold to 2.79-fold was observed, and C1534 was fixed in all populations after deltamethrin selection. Enzymatic activity varied significantly over the generations of selection. However, only α- esterase activity remained elevated in multiple populations after five generations of deltamethrin selection. We observed an increase in the mean activity levels of GSTs in two of the six populations analyzed.

Conclusions

The high levels of resistance and their association with high frequencies of kdr mutations (V410L, V1016I and F1534C) obtained through artificial selection, suggest an important role of these mutations in conferring resistance to deltamethrin. We highlight the need to implement strategies that involve the monitoring of kdr frequencies in insecticide resistance monitoring and management programmes.

Evidence for both sequential mutations and recombination in the evolution of kdr alleles in Aedes aegypti

BACKGROUND

Aedes aegypti is a globally distributed vector of human diseases including dengue, yellow fever, chikungunya, and Zika. Pyrethroid insecticides are the primary means of controlling adult A. aegypti populations to suppress arbovirus outbreaks, but resistance to pyrethroid insecticides has become a global problem. Mutations in the voltage-sensitive sodium channel (Vssc) gene are a major mechanism of pyrethroid resistance in A. aegypti. Vssc resistance alleles in A. aegypti commonly have more than one mutation. However, our understanding of the evolutionary dynamics of how alleles with multiple mutations arose is poorly understood.

METHODOLOGY/PRINCIPAL FINDINGS

We examined the geographic distribution and association between the common Vssc mutations (V410L, S989P, V1016G/I and F1534C) in A. aegypti by analyzing the relevant Vssc fragments in 25 collections, mainly from Asia and the Americas. Our results showed all 11 Asian populations had two types of resistance alleles: 1534C and 989P+1016G. The 1534C allele was more common with frequencies ranging from 0.31 to 0.88, while the 989P+1016G frequency ranged from 0.13 to 0.50. Four distinct alleles (410L, 1534C, 410L+1534C and 410L+1016I+1534C) were detected in populations from the Americas. The most common was 410L+1016I+1534C with frequencies ranging from 0.50 to 1.00, followed by 1534C with frequencies ranging from 0.13 to 0.50. Our phylogenetic analysis of Vssc supported multiple independent origins of the F1534C mutation. Our results indicated the 410L+1534C allele may have arisen by addition of the V410L mutation to the 1534C allele, or by a crossover event. The 410L+1016I+1534C allele was the result of one or two mutational steps from a 1534C background.

CONCLUSIONS/SIGNIFICANCE

Our data corroborated previous geographic distributions of resistance mutations and provided evidence for both recombination and sequential accumulation of mutations contributing to the molecular evolution of resistance alleles in A. aegypti.

Evolution of kdr haplotypes in worldwide populations of Aedes aegypti: Independent origins of the F1534C kdr mutation

Aedes aegypti is the primary vector of dengue, chikungunya, Zika, and urban yellow fever. Insecticides are often the most effective tools to rapidly decrease the density of vector populations, especially during arbovirus disease outbreaks. However, the intense use of insecticides, particularly pyrethroids, has selected for resistant mosquito populations worldwide. Mutations in the voltage gated sodium channel (Na_V) are among the principal mechanisms of resistance to pyrethroids and DDT, also known as “knockdown resistance,” kdr. Here we report studies on the origin and dispersion of kdr haplotypes in samples of Ae. aegypti from its worldwide distribution. We amplified the IIS6 and IIIS6 Na_V segments from pools of Ae. aegypti populations from 15 countries, in South and North America, Africa, Asia, Pacific, and Australia. The amplicons were barcoded and sequenced using NGS Ion Torrent. Output data were filtered and analyzed using the bioinformatic pipeline Seekdeep to determine frequencies of the IIS6 and IIIS6 haplotypes per population. Phylogenetic relationships among the haplotypes were used to infer whether the kdr mutations have a single or multiple origin. We found 26 and 18 haplotypes, respectively for the IIS6 and IIIS6 segments, among which were the known kdr mutations 989P, 1011M, 1016I and 1016G (IIS6), 1520I, and 1534C (IIIS6). The highest diversity of haplotypes was found in African samples. Kdr mutations 1011M and 1016I were found only in American and African populations, 989P + 1016G and 1520I + 1534C in Asia, while 1534C was present in samples from all continents, except Australia. Based primarily on the intron sequence, IIS6 haplotypes were subdivided into two well-defined clades (A and B). Subsequent phasing of the IIS6 + IIIS6 haplotypes indicates two distinct origins for the 1534C kdr mutation. These results provide evidence of kdr mutations arising de novo at specific locations within the Ae. aegypti geographic distribution. In addition, our results suggest that the 1534C kdr mutation had at least two independent origins. We can thus conclude that insecticide selection pressure with DDT and more recently with pyrethroids is selecting for independent convergent mutations in Na_V.

Insecticide resistance is a global threat for the control of Aedes aegypti, the mosquito vector of aboviruses such as dengue, chikungunya and Zika. Mutations in the voltage gated sodium channel (Na_V), known as kdr, are one of the principal mechanisms related to resistance to pyrethroids, the class of insecticide most employed worldwide inside and around residences. We investigate whether the same kdr mutations found in Ae. aegypti populations from distinct regions of the world have a common origin and subsequently dispersed or if they emerged in unrelated populations at distinct moments. By evaluating the sequences of two fragments of the Na_V gene, obtained from DNA collections of Ae. aegypti from several countries, we found at least two independent origins for the F1534C kdr mutation in American, African and Asian populations. There was no evidence for multiple origins of the common kdr mutations V1016I and P989S + V1016G, which were exclusive to American and Asian populations. Our results increase our knowledge of insecticide resistance evolution in one of the main arboviral mosquito vectors of major global diseases.

Detection of amitraz resistance and reduced treatment efficacy in the Varroa Mite, Varroa destructor, within commercial beekeeping operations

The parasitic mite Varroa destructor and the associated viruses it transmits are responsible for most instances of honey bee colony losses in the United States. As such, beekeepers utilize miticides to control Varroa populations. Widespread resistance has developed to the miticides fluvalinate and coumaphos. However, Varroa has largely maintained susceptibility to amitraz despite a long and extensive use history. Anecdotal reports of reduced amitraz effectiveness have been a widely discussed contemporary issue among commercial beekeepers. Amitraz resistance was measured by in vitro bioassays with technical amitraz as well as Apivar® efficacy tests. Amitraz resistance was evaluated in commercial beekeeping operations in Louisiana, New York, and South Dakota with a long history of amitraz use. This research shows that amitraz remains an effective Varroa control product in many operations. However, apiaries across operations displayed a wide range of amitraz resistance from no resistance to high resistance that resulted in Varroa control failure. The resistance ratios from in vitro amitraz bioassays were correlated with reduced Apivar® efficacy, demonstrating bona fide cases of Varroa control failures due to amitraz resistance. Therefore, amitraz resistance monitoring protocols need to be developed. A resistance monitoring network should be established to ensure the sustainability of miticide use for Varroa control.

First detection of the kdr mutation (L1014F) in the plague vector Xenopsylla cheopis (Siphonaptera: Pulicidae)

BACKGROUND

The oriental rat flea, Xenopsylla cheopis, is the most efficient vector of the plague. Pyrethroid insecticides such as cypermethrin, cyhalothrin and deltamethrin have been often used to limit plague transmission via controlling the vector during outbreaks. However, this strategy is threatened by the development of insecticide resistance. Understanding the mechanisms underlying pyrethroid resistance is the prerequisite for successful flea control.

METHODS

Partial DNA sequences of X. cheopis voltage gated sodium channel (VGSC) gene were amplified from a total of 111 individuals, collected from a natural plague epidemic foci in Baise City, Guangxi Zhuang Autonomous Region of China. These DNA fragments were sequenced. The frequency and distribution of kdr mutations were assessed in four X. cheopis populations. The origin of kdr mutations was investigated by phylogenetic and network analysis.

RESULTS

The classical knockdown resistance (kdr) mutation (L1014F) was detected in four field populations at frequencies ranging between 0.021-0.241. The mutant homozygote was observed only in one of the four populations. Seven haplotypes were identified, with two of them carrying the resistance L1014F mutation. Phylogenetic tree and network analysis indicated that the L1014F allele was not singly originated. Based on polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) profiling, an easy-to-use and accurate molecular assay for screening individual fleas for the L1014F mutation was developed.

CONCLUSIONS

To our knowledge, this work represents the first report of the L1014F mutation in the plague vector X. cheopis. The incidence of the L1014F allele highlights the need of further studies on the phenotypic effect of this mutation in this plague vector. Early detection and monitoring of insecticide resistance is suggested in order to make effective control strategies in case of plague outbreaks in this region.

Low Frequency of Knockdown Resistance Mutations in Musca domestica (Muscidae: Diptera) Collected From Northwestern Iran

Musca domestica L., the common housefly, is a very important mechanical vector of pathogens. Continuous exposure to pyrethroid insecticides has led to insecticide resistance in houseflies. Some mutations in the voltage-gated sodium channel gene (vgsc) reduce the binding affinity of pyrethroids target site insensitivity. We collected houseflies from the Urmia district of Northwestern Iran. Following DNA extraction, 580 bp regions of the vgsc known to contain knockdown resistance (kdr) mutations were amplified and sequenced using specific primers. The amplified region contained two exons (211-bp and 248-bp) and three introns. There were eight polymorphic sites between M. domestica insecticide-susceptible (MDU38813), super-kdr (NW_004774263) and aabys (KT897924) strains from GenBank in comparison with our sequences. Two amino acid substitutions were detected, N967Y (% polymorphism = 9.5%) and L1014H (% polymorphism = 4.7%) that can be associated with resistance. The common and previously reported mutations L1014F and M918T+L1014F were not detected. Diagnosis based on sequence analysis is useful for monitoring the frequency of pyrethroid resistance mutations, which will be helpful in avoiding overuse of this class of insecticides in house fly control.

Target-site mutations (AChE-G119S and kdr) in Guangxi Anopheles sinensis populations along the China-Vietnam border

Background

In South Asia, the epidemiology of malaria is complex, and transmission mainly occurs in remote areas near international borders. Vector control has been implemented as a key strategy in malaria prevention for decades. A rising threat to the efficacy of vector control efforts is the development of insecticide resistance, thus it is important to monitor the type and frequency of insecticide resistant alleles in the disease vectors such as An. sinensis along the China-Vietnam border. Such information is needed to synthesize effective malaria vector control strategies.

Methods

A total of 208 adults of An. sinensis, collected from seven sites in southwest Guangxi along the China-Vietnam border, were inspected for the resistance-conferring G119S mutation in acetylcholinesterase (AChE) by PCR-RFLP (polymerase chain reaction restriction fragment length polymorphism) and kdr mutations in the voltage-gated sodium channel (VGSC) by sequencing. In addition, the evolutionary origin of An. sinensis vgsc gene haplotypes was analyzed using Network 5.0.

Results

The frequencies of mutant 119S of AChE were between 0.61–0.85 in the seven An. sinensis populations. No susceptible homozygote (119GG) was detected in three of the seven sites (DXEC, LZSK and FCGDX). Very low frequencies of kdr (0.00–0.01) were detected in the seven populations, with most individuals being susceptible homozygote (1014LL). The 1014F mutation was detected only in the southeast part (FCGDX) at a low frequency of 0.03. The 1014S mutation was distributed in six of the seven populations with frequencies ranging from 0.04 to 0.08, but absent in JXXW. Diverse haplotypes of 1014L and 1014S were found in An. sinensis along the China-Vietnam border, while only one 1014F haplotype was detected in this study. Consistent with a previous report, resistant 1014S haplotypes did not have a single origin.

Conclusions

The G119S mutation of AChE was present at high frequencies (0.61–0.85) in the An. sinensis populations along the China-Vietnam border, suggesting that the vector control authorities should be cautious when considering carbamates and organophosphates as chemicals for vector control. The low frequencies (0.00–0.11) of kdr in these populations suggest that pyrethroids remain suitable for use against An. sinensis in these regions.

Life and Death at the Voltage-Sensitive Sodium Channel: Evolution in Response to Insecticide Use

The voltage-sensitive sodium channel (VSSC) is a critical component of the insect nervous system. Pyrethroids and DDT are insecticides that have been widely used, and they kill insects by perturbations of the VSSC. Decades of insecticide use selected for mutations in Vssc that give rise to resistance in almost all pest insects. However, the mutations responsible for the resistance are not always the same, and some unusual patterns have emerged. This review focuses on what pyrethroid/DDT selection has done, in terms of Vssc changes that have occurred, using four well-studied species as examples of the differences that have evolved. Information is provided about the mutations that occur, potential pathways by which alleles with multiple mutations arose, the relative fitness of the alleles, the levels of resistance conferred, and the geographic distribution of the mutations. The lessons learned and exciting new areas of research are discussed.

Multiple recombination events between two cytochrome P450 loci contribute to global pyrethroid resistance in Helicoverpa armigera

The cotton bollworm, Helicoverpa armigera (Hübner) is one of the most serious insect pest species to evolve resistance against many insecticides from different chemical classes. This species has evolved resistance to the pyrethroid insecticides across its native range and is becoming a truly global pest after establishing in South America and having been recently recorded in North America. A chimeric cytochrome P450 gene, CYP337B3, has been identified as a resistance mechanism for resistance to fenvalerate and cypermethrin. Here we show that this resistance mechanism is common around the world with at least eight different alleles. It is present in South America and has probably introgressed into its closely related native sibling species, Helicoverpa zea. The different alleles of CYP337B3 are likely to have arisen independently in different geographic locations from selection on existing diversity. The alleles found in Brazil are those most commonly found in Asia, suggesting a potential origin for the incursion of H. armigera into the Americas.

Levels of Resistance to Pyrethroid among Distinct kdr Alleles in Aedes aegypti Laboratory Lines and Frequency of kdr Alleles in 27 Natural Populations from Rio de Janeiro, Brazil

Background

Several mutations in voltage gated sodium channel (Na_V) have been identified in Aedes aegypti populations worldwide. However, only few are related to knockdown resistance to pyrethroids, most of which with variations in the 1016 and 1534 Na_V sites. In Brazil, at least two Na_V alleles are known: Na_VR1, with a substitution in the 1534 (1016 Val⁺ + 1534 Ile^kdr) and Na_VR2, with substitutions in both 1016 and sites (1016Ile^kdr + 1534Cys^kdr). There is also the duplication in the Na_V gene, with one copy carrying the substitution Ile1011Met, although its effects on pyrethroid resistance remain to be clarified. Our goals in this study were (1) to determine the role of each kdr Na_V allele and the duplication on pyrethroid resistance and (2) to screen the frequency of the kdr alleles in 27 several natural Ae. aegypti populations from the metropolitan region of Rio de Janeiro.

Methods

Pyrethroid resistance was evaluated by a knockdown time (KdT) assay, an adaptation of the WHO test tubes with paper impregnated with deltamethrin. We used laboratory-selected Ae. aegypti lineages: R1R1 and R2R2 (homozygous for the kdr Na_VR1 and Na_VR2 alleles, respectively), Dup (with duplication in the Na_V gene), Rockefeller (the susceptibility reference control), and F1 hybrids among them. Genotyping of both 1016 and 1534 Na_V sites was performed in 811 Ae. aegypti sampled from 27 localities from Rio de Janeiro (17), Niterói (6) and Nova Iguaçu (4) cities, Rio de Janeiro State, Brazil, with a TaqMan real time PCR approach.

Results

The laboratory lineages R1R1, R2R2, and R1R2 were the only ones that needed more than 60 minutes to knock down all the insects exposed to the pyrethroid, being the KdT R2R2 > R1R2 > R1R1, corroborating the recessive nature of the kdr mutations. Frequency of kdr alleles Na_VR1 and Na_VR2 in field-caught mosquitoes varied from 0 to 52% and 43 to 86%, respectively, evidencing high levels of “resistant genotypes” (R1R1, R1R2, and R2R2), which together summed 60 to 100% in Ae. aegypti populations from Rio de Janeiro.

Conclusions

The Na_VR1 and Na_VR2 kdr alleles confer resistance to the pyrethroid deltamethrin in homozygotes and R1R2 heterozygotes, being the R2R2 most resistant genotype. The allele containing duplication in the Na_V gene, with a mutation in the 1011 site, did not confer resistance under the tested conditions. The frequencies of the “resistant genotypes” are elevated in Ae. aegypti natural populations from Rio de Janeiro.

Novel cytochrome P450 (CYP6D1) and voltage sensitive sodium channel (Vssc) alleles of the house fly (Musca domestica) and their roles in pyrethroid resistance

BACKGROUND

The house fly Musca domestica is an important disease vector. Point mutation-mediated target-site insensitivity of the voltage sensitive sodium channel (VSSC) and increased detoxification mediated by cytochrome P450 (CYP6D1) overexpression have been characterized as two major mechanisms of pyrethroid resistance. In this study, genetic mutations in the Vssc and CYP6D1 genes and their contribution to pyrethroid resistance were investigated.

RESULTS

Twelve lines of house flies homozygous for four genotypes were established. House flies carrying the VSSC 1014F mutation and overexpressing CYP6D1 had higher resistance to pyrethroids than those carrying 1014F alone. The presence of the 15-bp insert in the promoter region of the CYP6D1 gene did not necessarily result in a significant increase in CYP6D1 mRNA and pyrethroid resistance levels. A novel Vssc allele carrying two mutations (G1924D and G2004S) in combination with the classic 1014F and a novel CYP6D1 allele that is very similar to CYP6D1v1 were identified in Chinese house flies.

CONCLUSION

This work demonstrates the effect of genetic mutations in CYP6D1 and Vssc on the susceptibility of house flies to pyrethroids, and verifies that 15-bp insert-containing CYP6D1 alleles have a single origin. These findings offer insights into the evolution of insecticide resistance and have implications for house fly control. © 2017 Society of Chemical Industry.

Species Diversity Hinders Adaptation to Toxicants

Environmental toxicants such as pesticides exert strong selection pressure on many species. While the resulting development of pesticide resistance in agricultural pest species is well-known, reports on the extent of adaptation in exposed nontarget species are contradictory. These contradictory reports highlight a continuing challenge in understanding the relevant ecological mechanisms that facilitate or hinder adaptation to toxicants in the field. Here we show that species diversity hinders the adaptation to toxicants. In agricultural streams with low diversity, we observed an up to 8-fold increase in insecticide tolerance in a total of 17 macroinvertebrate species that was not observed in more diverse communities under similar contamination. High species diversity occurred independently from adjacent nonpolluted refuge areas. Therefore, the low level of adaptation in diverse streams cannot be explained by an increased recolonization of sensitive individuals from refuge areas. Instead, high intraspecific competition may facilitate the selection for increased tolerance in low-diverse communities. In diverse communities, by contrast, species interactions may reduce intraspecific competition and, thus, the potential for developing toxicant resistance. We suggest that this mechanism may be the general case in adaptation to environmental stressors. Additionally, we conclude that the current framework for risk assessment of pesticides is not protective against selection for tolerant organisms and the associated risk of genetic erosion.

Biochemical and Molecular Mechanisms Associated With the Resistance of the European Corn Borer (Lepidoptera: Crambidae) to Lambda-Cyhalothrin and First Monitoring Tool

The European corn borer (Ostrinia nubilalis (Hübner)) is one of the most serious corn pest in Europe where it is controlled with pesticides, in particular, pyrethroids. First control failures with this chemical family occurred on the field in 2008 in the center of France, and the first resistance case was described in 2012. In the present study, we investigate resistance mechanisms involved in seven French populations of O. nubilalis collected in the field. Resistances to deltamethrin and lambda-cyhalothrin were confirmed, with a higher resistance ratio for lambda-cyhalothrin (63.79 compared to 7.67). Resistance to the two active compounds was correlated except for one population, indicating a high probability of cross-resistance. Analyses of the activity of three major families of detoxification enzymes in resistant individuals showed a significant increase of the average MFO activity in males of four populations (activity ratios of 2.76-5.73) and higher GST activity in females of two other populations (activity ratios 4.48 and 5.21). Molecular investigation of the sodium channel gene sequence showed the presence of the kdr mutation in a highly resistant individual. We designed a PCR-RFLP screening tool to search for this mutation in the field, and we found it in five populations but not in the susceptible one. The resistance of O. nubilalis to pyrethroids in France seems to result from a combination of resistance mechanisms, possibly as a consequence of a selection pressure with an exceptional duration (almost 40 yr old).

Qualitative Sybr Green real-time detection of single nucleotide polymorphisms responsible for target-site resistance in insect pests: the example of Myzus persicae and Musca domestica

Chemical insecticides have been widely used to control insect pests, leading to the selection of resistant populations. To date, several single nucleotide polymorphisms (SNPs) have already been associated with insecticide resistance, causing reduced sensitivity to many classes of products. Monitoring and detection of target-site resistance is currently one of the most important factors for insect pest management strategies. Several methods are available for this purpose: automated and high-throughput techniques (i.e. TaqMan or pyrosequencing) are very costly; cheaper alternatives (i.e. RFLP or PASA-PCRs) are time-consuming and limited by the necessity of a final visualization step. This work presents a new approach (QSGG, Qualitative Sybr Green Genotyping) which combines the specificity of PASA-PCR with the rapidity of real-time PCR analysis. The specific real-time detection of Cq values of wild-type or mutant alleles (amplified used allele-specific primers) allows the calculation of ΔCqW-M values and the consequent identification of the genotypes of unknown samples, on the basis of ranges previously defined with reference clones. The methodology is applied here to characterize mutations described in Myzus persicae and Musca domestica and we demonstrate it represents a valid, rapid and cost-effective technique that can be adopted for monitoring target-site resistance in field populations of these and other insect species.

Diversity of knockdown resistance alleles in a single house fly population facilitates adaptation to pyrethroid insecticides

Insecticide use exerts a tremendous selection force on house fly populations, but the frequencies of the initial resistance mutations may not reach high levels if they have a significant fitness cost in the absence of insecticides. However, with the continued use of the same (or similar) insecticides, it is expected that new mutations (conferring equal or greater resistance, but less of a fitness cost) will evolve. Pyrethroid insecticides target the insect voltage sensitive sodium channel (VSSC) and have been widely used for control of house flies at animal production facilities for more than three decades. There are three Vssc mutations known that cause resistance to pyrethroids in house flies: knockdown resistance (kdr, L1014F), kdr-his (L1014H) and super-kdr (M918T + L1014F). Whether or not there are any new mutations in house fly populations has not been examined for decades. We collected house flies from a dairy in Kansas (USA) and selected this population for three generations. We discovered multiple new Vssc alleles, including two that give very high levels of resistance to most pyrethroids. The importance of these findings to understanding the evolution of insecticide resistance, designing appropriate resistance monitoring and management schemes, and the future of pyrethroids for house fly control are discussed.

Diversity and frequency of kdr mutations within Anopheles sinensis populations from Guangxi, China

BACKGROUND

Anopheles sinensis is a major vector of malaria in China and its control is under great threat as the development of insecticide resistance. Voltage-gated sodium channel (VGSC) is the target of several classes of insecticides. Genetic mutations of VGSC have been documented to confer knockdown resistance (kdr) to dichlorodiphenyltrichloroethane (DDT) and pyrethroids in mosquitoes. To control this vector efficiently, it is important to know the resistance-associated genetic mutations, their distribution frequencies and genealogical relations.

METHODS

Three hundreds and thirteen (313) adults of An. sinensis collected from nine locations across Guangxi Zhuang Autonomous Region were used. The partial sequence of the An. sinensis voltage gated sodium channel gene (AS-VGSC) containing codon 1014 was sequenced. PHASE2.1 was used to construct the haplotypes of each individual, and the accuracy of haplotypes was further confirmed by clone sequencing. The genealogical relations of kdr mutations in AS-VGSC was analysed using TCS 2.1 and Network 5.0.

RESULTS

Sixteen AS-VGSC haplotypes including seven haplotypes carrying non-synonymous mutations at codon 1014, and fifty-five AS-VGSC genotypes were identified from 313 mosquitoes collected from nine geographical locations across Guangxi. The number of haplotypes in each of the nine populations ranged from 5 to 13. The frequency of haplotypes carrying kdr mutations ranged from 2.7 to 80.0 % within the nine populations, of which 1014C was unexpectedly high in the northeast of Guangxi. Genealogical analysis suggested multiple origins of kdr mutations in An. sinensis.

CONCLUSION

Diverse haplotypes of AS-VGSC are distributed in Guangxi. The presence of haplotypes carrying mutations at codon 1014 indicates a risk of pyrethroid and DDT resistance. The kdr mutations show differential distribution geographically, with high frequencies occurred in the northeast of Guangxi. Genealogical analysis suggests multiple origins of kdr mutations in An. sinensis populations in Guangxi. These findings have important practical implications for the sustainability of An. sinensis control programmes.

Landscape genetic structure and evolutionary genetics of insecticide resistance gene mutations in Anopheles sinensis

Background

Anopheles sinensis is one of the most abundant vectors of malaria and other diseases in Asia. Vector control through the use of insecticides is the front line control method of vector-borne diseases. Pyrethroids are the most commonly used insecticides due to their low toxicity to vertebrates and low repellency. However, the extensive use of insecticides has imposed strong selection pressure on mosquito populations for resistance. High levels of resistance to pyrethroid insecticides and various mutations and haplotypes in the para sodium channel gene that confers knockdown resistance (kdr) have been detected in An. sinensis. Despite the importance of kdr mutations in pyrethroid resistance, the evolutionary origin of the kdr mutations is unknown. This study aims to examine the evolutionary genetics of kdr mutations in relation to spatial population genetic structure of An. sinensis.

Methods

Adults or larvae of Anopheles sinensis were collected from various geographic locations in China. DNA was extracted from individual mosquitoes. PCR amplification and DNA sequencing of the para-type sodium channel gene were conducted to analyse kdr allele frequency distribution, kdr codon upstream and downstream intron polymorphism, population genetic diversity and kdr codon evolution. The mitochondrial cytochrome c oxidase COI and COII genes were amplified and sequenced to examine population variations, genetic differentiation, spatial population structure, population expansion and gene flow patterns.

Results

Three non-synonymous mutations (L1014F, L1014C, and L1014S) were detected at the kdr codon L1014 of para-type sodium channel gene. A patchy distribution of kdr mutation allele frequencies from southern to central China was found. Near fixation of kdr mutation was detected in populations from central China, but no kdr mutations were found in populations from southwestern China. More than eight independent mutation events were detected in the three kdr alleles, and at least one of them evolved multiple times subsequent to their first divergence. Based on sequence analysis of the mitochondrial COI and COII genes, significant and large genetic differentiation was detected between populations from southwestern China and central China. The patchy distribution of kdr mutation frequencies is likely a consequence of geographic isolation in the mosquito populations and the long-term insecticide selection.

Conclusion

Our results indicate multiple origins of the kdr insecticide-resistant alleles in An. sinensis from southern and central China. Local selection related to intense and prolonged use of insecticide for agricultural purposes, as well as frequent migrations among populations are likely the explanations for the patchy distribution of kdr mutations in China. On the contrary, the lack of kdr mutations in Yunnan and Sichuan is likely a consequence of genetic isolation and absence of strong selection pressure. The present study compares the genetic patterns revealed by a functional gene with a neutral marker and demonstrates the combined impact of demographic and selection factors on population structure.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1513-6) contains supplementary material, which is available to authorized users.

Overcoming super-knock down resistance (super-kdr) mediated resistance: multi-halogenated benzyl pyrethroids are more toxic to super-kdr than kdr house flies

Target site insensitivity because of mutations in the voltage-sensitive sodium channel gene (Vssc) is a major mechanism of resistance to pyrethroid insecticides in the house fly, Musca domestica. There are three known Vssc alleles that confer resistance to pyrethroids in the house fly: knock down resistance (kdr; L1014F), super-kdr (M918T + L1014F) and kdr-his (L1014H), but there has been no side-by-side comparison of the resistance levels that they confer. We compared the levels of resistance conferred by the three Vssc alleles in congenic strains to 19 structurally diverse pyrethroids, and compared the full-length Vssc cDNA sequences from each strain. Generally, the levels of resistance conferred were kdr-his < kdr < super-kdr. However, there was significant variation in this pattern, especially for super-kdr, for which both high and low resistance ratios were observed for several pyrethroids. We also examined the levels of resistance in heterozygotes. Resistance in each of the hybrids was generally inherited as an incompletely recessive trait, except for the kdr-his/kdr hybrids, which showed incompletely to completely dominant resistance (ie had resistance levels comparable to kdr homozygotes). The importance of these results to understanding the frequencies of these resistance alleles in natural populations, the evolution of insecticide resistance and resistance management strategies are discussed.

L1014F-kdr Mutation in Indian Anopheles subpictus (Diptera: Culicidae) Arising From Two Alternative Transversions in the Voltage-Gated Sodium Channel and a Single PIRA-PCR for Their Detection

Leucine-to-phenylalanine substitution at residue L1014 in the voltage-gated sodium channel, target site of action for dichlorodiphenyltrichloroethane (DDT) and pyrethroids, is the most common knockdown resistance (kdr) mutation reported in several insects conferring resistance against DDT and pyrethroids. Here, we report presence of two coexisting alternative transversions, A>T and A>C, on the third codon position of L1014 residue in malaria vector Anopheles subpictus Grassi (species A) from Jamshedpur (India), both leading to the same amino acid substitution of Leu-to-Phe with allelic frequencies of 19 and 67%, respectively. A single primer-introduced restriction analysis-polymerase chain reaction (PIRA-PCR) was devised for the identification of L1014F-kdr mutation in An. subpictus resulting from either type of point mutation. Genotyping of samples with PIRA-PCR revealed high frequency (82%) of L1014F-kdr mutation in the study area.

Genetic structure of Bemisia tabaci Med populations from home-range countries, inferred by nuclear and cytoplasmic markers: impact on the distribution of the insecticide resistance genes

BACKGROUND

Insecticide resistance management in Bemisia tabaci is one of the main issues facing agricultural production today. An extensive survey was undertaken in five Mediterranean countries to examine the resistance status of Med B. tabaci species in its range of geographic origin and the relationship between population genetic structure and the distribution of resistance genes. The investigation combined molecular diagnostic tests, sequence and microsatellite polymorphism studies and monitoring of endosymbionts.

RESULTS

High frequencies of pyrethroid (L925I and T929V, VGSC gene) and organophosphate (F331W, ace1 gene) resistance mutations were found in France, Spain and Greece, but not in Morocco or Tunisia. Sequence analyses of the COI gene delineated two closely related mitochondrial groups (Q1 and Q2), which were found either sympatrically (Spain) or separately (France). Only Q1 was observed in Greece, Morocco and Tunisia. Bayesian analyses based on microsatellite loci revealed three geographically delineated genetic groups (France, Spain, Morocco/Greece/Tunisia) and high levels of genetic differentiation even between neighbouring samples. Evidence was also found for hybridisation and asymmetrical gene flow between Q1 and Q2.

CONCLUSIONS

Med B. tabaci is more diverse and structured than reported so far. On a large geographic scale, resistance is affected by population genetic structure, whereas on a local scale, agricultural practices appear to play a major role.

An independent occurrence of the chimeric P450 enzyme CYP337B3 of Helicoverpa armigera confers cypermethrin resistance in Pakistan

The increasing resistance level of insect pest species is a major concern to agriculture worldwide. The cotton bollworm, Helicoverpa armigera, is one of the most important pest species due to being highly polyphagous, geographically widespread, and resistant towards many chemical classes of insecticides. We previously described the mechanism of fenvalerate resistance in Australian populations conferred by the chimeric cytochrome P450 monooxygenase CYP337B3, which arose by unequal crossing-over between CYP337B1 and CYP337B2. Here, we show that this mechanism is also present in the cypermethrin-resistant FSD strain from Pakistan. The Pakistani and the Australian CYP337B3 alleles differ by 18 synonymous and three nonsynonymous SNPs and additionally in the length and sequence of the intron. Nevertheless, the activity of both CYP337B3 proteins is comparable. We demonstrate that CYP337B3 is capable of metabolizing cypermethrin (trans- and especially cis-isomers) to the main metabolite 4'-hydroxycypermethrin, which exhibits no intrinsic toxicity towards susceptible larvae. In a bioassay, CYP337B3 confers a 7-fold resistance towards cypermethrin in FSD larvae compared to susceptible larvae from the Australian TWB strain lacking CYP337B3. Linkage analysis shows that presence of CYP337B3 accounts for most of the cypermethrin resistance in the FSD strain; up-regulation of other P450s in FSD plays no detectable role in resistance. The presence or absence of CYP337B3 can be easily detected by a simple PCR screen, providing a powerful tool to rapidly distinguish resistant from susceptible individuals in the field and to determine the geographical distribution of this resistance gene. Our results suggest that CYP337B3 evolved twice independently by unequal crossing-over between CYP337B2 and two different CYP337B1 alleles.

Global distribution and origin of target site insecticide resistance mutations in Tetranychus urticae

The control of Tetranychus urticae, a worldwide agricultural pest, is largely dependent on pesticides. However, their efficacy is often compromised by the development of resistance. Recent molecular studies identified a number of target site resistance mutations, such as G119S, A201S, T280A, G328A, F331W in the acetylcholinesterase gene, L1024V, A1215D, F1538I in the voltage-gated sodium channel gene, G314D and G326E in glutamate-gated chloride channel genes, G126S, I136T, S141F, D161G, P262T in the cytochrome b and the I1017F in the chitin synthase 1 gene. We examined their distribution, by sequencing the relevant gene fragments in a large number of T. urticae collections from a wide geographic range. Our study revealed that most of the resistance mutations are spread worldwide, with remarkably variable frequencies. Furthermore, we analyzed the variability of the ace locus, which has been subjected to longer periods of selection pressure historically, to investigate the evolutionary origin of ace resistant alleles and determine whether they resulted from single or multiple mutation events. By sequencing a 1540 bp ace fragment, encompassing the resistance mutations and downstream introns in 139 T. urticae individuals from 27 countries, we identified 6 susceptible and 31 resistant alleles which have arisen from at least three independent mutation events. The frequency and distribution of these ace haplotypes varied geographically, suggesting an interplay between different mutational events, gene flow and local selection.

Administration of Brevibacillus laterosporus spores as a poultry feed additive to inhibit house fly development in feces: a new eco-sustainable concept

The success of a microbial pesticide application against house flies developing in manure should accomplish the uniform mixing of active ingredients with this breeding medium, thus enhancing residual effects. The oral administration of the entomopathogenic bacterium Brevibacillus laterosporus to caged poultry species allows the homogeneous incorporation of its active ingredients with fly breeding media. Feces from treated broilers or hens show toxicity against exposed fly adults and larvae. Insecticidal effects are concentration-dependent with a lethal median concentration (LC50) value of 1.34 × 10(8) and 0.61 × 10(8) spores/g of feces for adults and larvae, respectively. Manure toxicity against flies was maintained as long as chickens were fed a diet containing adequate concentrations of B. laterosporus spores. Toxicity significantly decreased after spore administration to birds was interrupted. When poultry diet contained 10(10) spores/g, mortality of flies reared on feces exceeded 80%. The use of B. lateroporus spores as a feed additive in poultry production systems fostering a more integrated approach to farming is discussed.

Livestock bedding effects on two species of parasitoid wasps of filth flies

Choice of livestock bedding has been shown to affect density of filth fly maggots. Here, laboratory experiments indicate that bedding type can also affect natural enemies of the flies, specifically the parasitoid wasps Spalangia endius Walker and Urolepis rufipes (Ashmead) (Hymenoptera: Pteromalidae) parasitizing a natural host, the house fly Musca domestica L. (Diptera: Muscidae). For both parasitoid species, when females parasitized hosts under bedding, cedar shavings resulted in fewer parasitoids compared with pine shavings, but pine shavings did not differ from wood pellets and corn cob pellets. In the absence of exposure to hosts, longevity of adult females was reduced in cedar shavings compared with pine shavings and pellets. In contrast to the effects on parasitization and on adult survival, shavings treatment had no significant effect on the number of parasitoids or flies that emerged when hosts were not exposed to shavings until after parasitization.

Insecticide resistance in house flies from the United States: resistance levels and frequency of pyrethroid resistance alleles

Although insecticide resistance is a widespread problem for most insect pests, frequently the assessment of resistance occurs over a limited geographic range. Herein, we report the first widespread survey of insecticide resistance in the USA ever undertaken for the house fly, Musca domestica, a major pest in animal production facilities. The levels of resistance to six different insecticides were determined (using discriminating concentration bioassays) in 10 collections of house flies from dairies in nine different states. In addition, the frequencies of Vssc and CYP6D1 alleles that confer resistance to pyrethroid insecticides were determined for each fly population. Levels of resistance to the six insecticides varied among states and insecticides. Resistance to permethrin was highest overall and most consistent across the states. Resistance to methomyl was relatively consistent, with 65-91% survival in nine of the ten collections. In contrast, resistance to cyfluthrin and pyrethrins + piperonyl butoxide varied considerably (2.9-76% survival). Resistance to imidacloprid was overall modest and showed no signs of increasing relative to collections made in 2004, despite increasing use of this insecticide. The frequency of Vssc alleles that confer pyrethroid resistance was variable between locations. The highest frequencies of kdr, kdr-his and super-kdr were found in Minnesota, North Carolina and Kansas, respectively. In contrast, the New Mexico population had the highest frequency (0.67) of the susceptible allele. The implications of these results to resistance management and to the understanding of the evolution of insecticide resistance are discussed.