Voltage-sensitive Sodium Channels Research Articles

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

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. 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. 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.

Frequency of kdr mutations in the voltage-sensitive sodium channel (VSSC) gene in Aedes aegypti from Yogyakarta and implications for Wolbachia-infected mosquito trials

BackgroundIn the inner city of Yogyakarta, Indonesia, insecticide resistance is expected in the main dengue vector, Aedes aegypti, because of the intensive local application of pyrethroid insecticides. However, detailed information about the nature of resistance in this species is required to assist the release of Wolbachia mosquitoes in a dengue control program, so that we can ensure that insecticide resistance in the strain of Ae. aegypti being released matches that of the background population.MethodsHigh-resolution melt genotyping was used to screen for kdr mutations associated with pyrethroid resistance in the voltage-sensitive sodium channel (VSSC) gene in Ae. aegypti of some areas in the inner city of Yogyakarta.ResultsThe results show that the V1016G mutation predominated, with individuals homozygous for the 1016G allele at a frequency of 82.1% and the mutant allele G at a frequency of 92%. Two patterns of co-occurrence of mutations were detected in this study, homozygous individuals V1016G/S989P; and heterozygous individuals V1016G/F1534C/S989P. We found the simultaneous occurrence of kdr mutations V1016G and F1534C at all collection sites, but not within individual mosquitoes. Homozygous mutants at locus 1016 were homozygous wild-type at locus 1534 and vice versa, and heterozygous V1016G were also heterozygous for F1534C. The most common tri-locus genotype co-occurrences were homozygous mutant 1016GG and homozygous wild-type FF1534, combined with homozygous mutant 989PP (GG/FF/PP) at a frequency of 38.28%.ConclusionsGiven the relatively small differences in frequency of resistance alleles across the city area, locality variations in resistance should have minor implications for the success of Wolbachia mosquito trials being undertaken in the Yogyakarta area.

Characterization of Sodium Channel Mutations in the Dengue Vector Mosquitoes Aedes aegypti and Aedes albopictus within the Context of Ongoing Wolbachia Releases in Kuala Lumpur, Malaysia.

Specific sodium channel gene mutations confer target site resistance to pyrethroid insecticides in mosquitoes and other insects. In Aedes mosquito species, multiple mutations that contribute to resistance vary in their importance around the world. Here, we characterize voltage sensitive sodium channel (Vssc) mutations in populations of Aedesaegypti from Kuala Lumpur, Malaysia, and look at their persistence in populations affected by ongoing Wolbachia releases (a dengue control measure). We also describe a Vssc mutation in Aedesalbopictus (F1534L) found for the first time in Malaysia. We show that there are three predominant Vssc haplotypes in Aedesaegypti in this region, which all persist with regular backcrossing, thereby maintaining the original genetic composition of the populations. We identify changes in genotype frequency in closed populations of Ae. aegypti maintained for multiple generations in laboratory culture, suggesting different fitness costs associated with the genotypes, some of which may be associated with the sex of the mosquito. Following population replacement of Ae. aegypti by Wolbachia in the target area, however, we find that the Vssc mutations have persisted at pre-release levels. Mosquitoes in two genotype classes demonstrate a type I pyrethroid resistance advantage over wildtype mosquitoes when exposed to 0.25% permethrin. This resistance advantage is even more pronounced with a type II pyrethroid, deltamethrin (0.03%). The results point to the importance of these mutations in pyrethroid resistance in mosquito populations and the need for regular backcrossing with male mosquitoes from the field to maintain similarity of genetic background and population integrity during Wolbachia releases.

Synthesis, Anticonvulsant and Antinociceptive Activity of New Hybrid Compounds: Derivatives of 3-(3-Methylthiophen-2-yl)-pyrrolidine-2,5-dione.

The present study aimed to design and synthesize a new series of hybrid compounds with pyrrolidine-2,5-dione and thiophene rings in the structure as potential anticonvulsant and antinociceptive agents. For this purpose, we obtained a series of new compounds and evaluated their anticonvulsant activity in animal models of epilepsy (maximal electroshock (MES), psychomotor (6 Hz), and subcutaneous pentylenetetrazole (scPTZ) seizure tests). To determine the mechanism of action of the most active anticonvulsant compounds (3, 4, 6, 9), their influence on the voltage-gated sodium and calcium channels as well as GABA transporter (GAT) was assessed. The most promising compound 3-(3-methylthiophen-2-yl)-1-(3-morpholinopropyl)pyrrolidine-2,5-dione hydrochloride (4) showed higher ED50 value than those of the reference drugs: valproic acid (VPA) and ethosuximide (ETX) (62.14 mg/kg vs. 252.7 mg/kg (VPA) in the MES test, and 75.59 mg/kg vs. 130.6 mg/kg (VPA) and 221.7 mg/kg (ETX) in the 6 Hz test, respectively). Moreover, in vitro studies of compound 4 showed moderate but balanced inhibition of the neuronal voltage-sensitive sodium (site 2) and L-type calcium channels. Additionally, the antinociceptive activity of the most active compounds (3, 4, 6, 9) was also evaluated in the hot plate test and writhing tests, and their hepatotoxic properties in HepG2 cells were also investigated. To determine the possible mechanism of the analgesic effect of compounds 3, 6, and 9, the affinity for the TRPV1 receptor was investigated.

Bed bugs, Cimex lectularius L., exhibiting metabolic and target site deltamethrin resistance are susceptible to plant essential oils

Pyrethroid resistance has been a major hurdle limiting the effective control of bed bugs (Cimex lectularius L.). Alternative approaches that include the use of plant essential oils (EOs) have been proposed for effective management of bed bugs. However, EO resistance level comparisons between pyrethroid susceptible and resistant bed bug populations have not been previously conducted. The goal of this study was twofold: (i) determine deltamethrin resistance levels and associated resistance mechanisms in the field-collected Knoxville strain and (ii) quantify resistance levels of the Knoxville strain to five EOs (thyme, oregano, clove, geranium and coriander), their major insecticidal constituents (thymol, carvacrol, eugenol, geraniol and linalool) and an EO-based product (EcoRaider®). First, we found that the Knoxville strain was 72,893 and 291,626 fold more resistant to topically applied deltamethrin in comparison to the susceptible Harlan strain at the LD25 and LD50 lethal dose levels, respectively. Synergist bioassays and detoxification enzyme assays revealed significantly higher activity of cytochrome P450 and esterase enzymes in the resistant Knoxville strain. Further, Sanger sequencing revealed the presence of the L925I mutation in the voltage-sensitive sodium channel α subunit gene. The Knoxville strain that possesses both enzymatic and target site deltamethrin resistance, however, did not show any resistance to EOs, their major insecticidal constituents and EcoRaider® in topical bioassays (resistance ratio of ~1). In conclusion, this study demonstrated that a deltamethrin-resistant strain of bed bugs is susceptible to EOs and their insecticidal constituents.

First evidence of the mutations associated with pyrethroid resistance in head lice (Phthiraptera: Pediculidae) from Honduras

BackgroundThe human head louse, Pediculus humanus capitis, is a cosmopolitan blood-sucking ectoparasite affecting mostly schoolchildren in both developed and developing countries. In Honduras, chemical pediculicides are the first line of treatment, with permethrin as their main active ingredient. Despite the extended use of these products, there is currently no research investigating insecticide resistance in Honduran head lice. In head lice, the most common mechanism is knockdown resistance (kdr), which is the result of two point mutations and the associated amino acid substitutions, T917I and L920F, within the voltage-sensitive sodium channel (VSSC).MethodsGenomic DNA was extracted from 83 head lice collected in the localities of San Buenaventura and La Hicaca, Honduras. Polymerase chain reaction (PCR) was used to amplify a 332-bp fragment of the VSSC gene that contains a site affected by C/T mutation which results in a T917I amino acid substitution on each human head louse genomic DNA fragments.ResultsThe C/T non-synonymous mutation which results in the T917I kdr amino acid substitution was detected in both head lice populations at frequencies ranging between 0.45–0.5. Globally, the frequency of this substitution was 0.47. Of these, 5 (6.1%) were homozygous susceptible and 78 (93.9%) were heterozygotes. The kdr-resistant homozygote (RR) was not detected in the studied populations. Thus, 93.9% of the head lice collected in Honduras harbored only one T917I allele. Exact test for the Hardy-Weinberg equilibrium for both localities showed that genotype frequencies differed significantly from expectation. In addition, San Buenaventura and La Hicaca populations had an inbreeding coefficient (Fis) < 0, suggesting an excess of heterozygotes.ConclusionsTo our knowledge, this is the first study showing the presence of the C/T mutation responsible of the T917I kdr allele associated with pyrethroid resistance in P. h. capitis from Honduras. The PCR-restriction fragment length polymorphism (RFLP) employed here has demonstrated to be a reliable, economic, and reproducible assay that can be used to accurately genotype individual head lice for the mutation encoding the resistance-conferring T917I amino acid substitution. This highlights the necessity of proactive resistance management programmes designed to detect pyrethroid mutations before they become established within populations of head lice.

Intercellular communication and ion channels in neuropathic pain chronicization.

Neuropathic pain is caused by primary lesion or dysfunction of either peripheral or central nervous system. Due to its complex pathogenesis, often related to a number of comorbidities, such as cancer, neurodegenerative and neurovascular diseases, neuropathic pain still represents an unmet clinical need, lacking long-term effective treatment and complex case-by-case approach. We analyzed the recent literature on the role of selective voltage-sensitive sodium, calcium and potassium permeable channels and non-selective gap junctions (GJs) and hemichannels (HCs) in establishing and maintaining chronic neuropathic conditions. We finally focussed our review on the role of extracellular microenvironment modifications induced by resident glial cells and on the recent advances in cell-to-cell and cell-to-extracellular environment communication in chronic neuropathies. In this review, we provide an update on the current knowledge of neuropathy chronicization processes with a focus on both neuronal and glial ion channels, as well as on channel-mediated intercellular communication.

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

BackgroundAedes 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 findingsWe 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/SignificanceOur 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.

Tracking the Increase of Acaricide Resistance in an Invasive Population of Cattle Fever Ticks (Acari: Ixodidae) and Implementation of Real-Time PCR Assays to Rapidly Genotype Resistance Mutations

AbstractThe invasive cattle fever tick, Rhipicephalus (Boophilus) microplus (Canestrini) (Acari: Ixodidae), occurs in the United States only along the Texas border as incursions from Mexico. Intensive acaricide treatment of cattle herds in Mexico to reduce tick populations has resulted in the development of resistance to an array of acaricides. Resistance to permethrin has increased both in incidence and level in Texas over the last decade, even though permethrin is not used to control fever ticks on the U.S. side of the border. From 3 to 4% of submittals in 2008 to over 50% in 2016 and 2017 showed resistance based on standardized pesticide bioassays. Moreover, by 2017, the highly resistant ticks had spread to include all five of the southmost Texas counties and were found on both cattle and sylvatic hosts. Improved diagnostic tools developed by our group include a panel of DNA-based real-time PCR assays to detect mutations within the voltage-sensitive sodium channel (Vssc) that are involved in permethrin resistance. Further, a positive correlation between the presence of multiple Vssc mutations and phenotypic resistance was validated. These assays can be completed within days of receiving field collected ticks providing timely, valuable information to program managers. Microsatellite marker analysis of these pyrethroid resistant tick populations provided evidence that separate incursions of resistant ticks had entered Texas independently.

Pyrethroid-Derived Acids and Alcohols: Bioactivity and Synergistic Effects on Mosquito Repellency and Toxicity.

Pyrethroids are one of the most commonly used classes of insecticides, and their acid and alcohol components are esterase degradation products, usually considered to be biologically inactive. In this study, it was found that several pyrethroid acids had a spatial repellent activity that was greater than DEET, often more active than the parent pyrethroids, and showed little cross resistance in a pyrethroid-resistant Puerto Rico strain of Aedes aegypti mosquitoes. Further investigation revealed that the acids can synergize not only contact repellent standards but also other pyrethroid components as well as the parent pyrethroids themselves. Synergism by the pyrethroid acids is expressed as both increased spatial repellency and vapor toxicity as well as human bite protection. Electrophysiological studies confirmed that pyrethroid acids (100 μM) had no effect on neuronal discharge in larval Drosophila melanogaster CNS and were detected by electroantennography, and there was little resistance to olfactory sensing of these acids in antennae from Puerto Rico strain mosquitoes carrying kdr mutations. Thus, the data suggest that the pyrethroid acids have a different mode of action than the parent pyrethroids, unrelated to the voltage-sensitive sodium channel. The results highlight the potential of pyrethroid acids to be useful in future repellent formulations.

Evaluation of resistance to permethrin, cypermethrin and deltamethrin in different populations of Musca domestica (L.), collected from the Iranian dairy cattle farms

Abstract The house fly, Musca domestica (Linnaeus) (Diptera: Muscidae), is a major pest for human and livestock health and is also resistant to different insecticides. Herein, six M. domestica populations were collected, five of them from industrial cattle farms and the Koohrang population from a remote area as a susceptible population. The resistance/susceptibility of populations to three pyrethroids was evaluated. High levels of permethrin resistance were observed in all field populations and the resistance ratios (RRs) were estimated to vary from 52- to 129-fold. Resistant populations also exhibited resistance to other pyrethroids (cypermethrin and deltamethrin), with RRs ranging between 45- and 180-fold. According to synergistic (piperonyl butoxide, diethyl maleate and triphenyl phosphate) and enzymatic assays, resistant populations exhibited multiple resistance phenotypes. Cytochrome P450 monooxygenases (P450s), glutathione S-transferases (GSTs), and carboxylesterases (CarEs) were found to be involved in pyrethroid resistance in Isfahan population, P450s and GSTs in Mobarake population and CarEs detoxified pyrethroids in Natanz and Alavijeh populations. As substitution of Leucine (CTT) with Phenylalanine (TTT) at position 1014 of the voltage sensitive sodium channel (VSSC) gene is the most common mutation conferring resistance to pyrethroids in M. domestica, we sequenced a partial fragment of IIS6 and L1014F mutation was detected in all resistant populations. The present study provides valuable information for early detection of pyrethroid resistance and developing resistance management strategies in the house fly populations.

Monitoring of Pyrethroid Resistance Allele Frequency in the Common Bed Bug (Cimex lectularius) in the Republic of Korea.

Two-point mutations (V419L and L925I) on the voltage-sensitive sodium channel of bed bugs (Cimex lectularius) are known to confer pyrethroid resistance. To determine the status of pyrethroid resistance in bed bugs in Korea, resistance allele frequencies of bed bug strains collected from several US military installations in Korea and Mokpo, Jeollanam-do, from 2009–2019 were monitored using a quantitative sequencing. Most bed bugs were determined to have both of the point mutations except a few specimens, collected in 2009, 2012 and 2014, having only a single point mutation (L925I). No susceptible allele was observed in any of the bed bugs examined, suggesting that pyrethroid resistance in bed bug populations in Korea has reached a serious level. Large scale monitoring is required to increase our knowledge on the distribution and prevalence of pyrethroid resistance in bed bug populations in Korea. Based on present study, it is urgent to restrict the use of pyrethroids and to introduce effective alternative insecticides. A nation-wide monitoring program to determine the pyrethroid resistance level in bed bugs and to select alternative insecticides should be implemented.

Comprehensive engineering of the tarantula venom peptide huwentoxin-IV to inhibit the human voltage-gated sodium channel hNav1.7

Comprehensive engineering of the tarantula venom peptide huwentoxin-IV to inhibit the human voltage-gated sodium channel hNav1.7

Regional and seasonal detection of resistance mutation frequencies in field populations of Anopheles Hyrcanus Group and Culex pipiens complex in Korea

Pyrethroid (PYR) and organophosphate (OP) insecticides have been extensively used for mosquito control for several decades in South Korea, and has resulted in the rapid development of resistance in the field. In this study, quantitative sequencing (QS) protocols were developed for the frequency prediction of insecticide resistance alleles [e.g., the L1014F/C mutation on the voltage sensitive sodium channel as a PYR resistance allele and the G119S mutation on the acetylcholinesterase 1 as OP resistance alleles] in four regional populations of Anopheles Hyrcanus Group and Culex pipiens complex. Both of the L1014F/C and G119S mutations were observed in all examined regional populations of An. Hyrcanus Group, suggesting a wide distribution of both PYR and OP resistance. In contrast, populations of the Cx. pipiens complex were determined to possess almost no G119S mutation, but relatively higher frequencies of the L1014F mutation, showing differential resistance patterns between different mosquito groups. The mutation frequencies were also monitored throughout a mosquito season (May–October) at one collection site to determine the seasonal changes of resistance mutation frequency in mosquito populations. Dramatic decreases of both L1014F/C and G119S mutation frequencies were observed in the An. Hyrcanus Group toward the fall, with no mutations observed in the early spring, suggesting a connection between the fitness costs of overwintering and insecticide resistance. However, no apparent trends were detectable in the Cx. pipiens complex populations due to low or zero mutation frequencies.

Surveillance of a kdr Resistance Mutation in Culex pipiens (Diptera: Culicidae) and Culex quinquefasciatus in California.

Culex pipiens Linnaeus and Culex quinquefasciatus Say are the primary vectors of West Nile and St. Louis encephalitis viruses in California. Pyrethrins and pyrethroids (synthetic pyrethrins) are the most widely used insecticides to control adult stage mosquitoes to prevent disease transmission. The most abundant and widespread mutation associated with pyrethroid resistance is the L1014F mutation of the voltage-sensitive sodium channel gene. Statewide, based on the testing of almost 2,000 mosquitoes from 14 counties, the resistant allele frequency was 71%. Although the L1014F mutation was found in all counties assessed, the resistance allele profiles differed between regions of California. The highest resistant allele frequency occurred in the Central region and lowest frequencies were from the Northern and Southern regions. Resistance allele frequencies observed in 2014–2016 are nearly 1.5 times higher than those from pre-2012, indicating that resistance profiles can change over time. Regular monitoring of the L1014F kdr mutation will help aid in operational decisions.

Different Generations of Type-B Monoamine Oxidase Inhibitors in Parkinson's Disease: From Bench to Bedside.

Three inhibitors of type-B monoamine oxidase (MAOB), selegiline, rasagiline, and safinamide, are used for the treatment of Parkinson’s disease (PD). All three drugs improve motor signs of PD, and are effective in reducing motor fluc-tuations in patients undergoing long-term L-DOPA treatment. The effect of MAOB inhibitors on non-motor symptoms is not uniform and may not be class-related. Selegiline and rasagiline are irreversible inhibitors forming a covalent bond within the active site of MAOB. In contrast, safinamide is a reversible MAOB inhibitor, and also inhibits voltage-sensitive sodium channels and glutamate release. Safinamide is the prototype of a new generation of multi-active MAOB inhibitors, which in-cludes the antiepileptic drug, zonisamide. Inhibition of MAOB-mediated dopamine metabolism largely accounts for the an-tiparkinsonian effect of the three drugs. Dopamine metabolism by MAOB generates reactive oxygen species, which contrib-ute to nigro-striatal degeneration. Among all antiparkinsonian agents, MAOB inhibitors are those with the greatest neuropro-tective potential because of inhibition of dopamine metabolism, induction of neurotrophic factors, and, in the case of safina-mide, inhibition of glutamate release. The recent development of new experimental animal models that more closely mimic the progressive neurodegeneration associated with PD will allow to test the hypothesis that MAOB inhibitors may slow the progression of PD.

CYP-mediated resistance and cross-resistance to pyrethroids and organophosphates in Aedes aegypti in the presence and absence of kdr

Aedes aegypti thrives in urban environments and transmits several debilitating human viral diseases. Thus, our ability to control this mosquito species in endemic areas is of utmost importance. The use of insecticides, mostly pyrethroids and organophosphates (OPs), has long been the primary means of controlling A. aegypti, but widespread insecticide resistance has emerged. The two main mechanisms of pyrethroid resistance in A. aegypti are CYP-mediated detoxification and mutations in the target site, voltage-sensitive sodium channel (Vssc), referred to as knockdown resistance (kdr). Knowledge about the contributions and interactions of these mechanisms to resistance is important for the understanding of the molecular and evolutionary basis of insecticide resistance, and to determine the effectiveness of insecticides. In this study, we address two aims: 1) determine the patterns of CYP-mediated cross-resistance to pyrethroid and OP insecticides, both in the presence and absence of kdr (S989P + V1016G), and 2) determine whether the interaction between the two mechanisms yields a greater than, less than, or additive effect on resistance. We tested seven pyrethroids and four OPs against three congenic strains of A. aegypti: ROCK (susceptible), CYP:ROCK (CR) (resistant due to CYP-mediated detoxification without kdr), and CYP + KDR:ROCK (CKR) (resistant due to both CYPs and kdr), and compared these to the congenic KDR:ROCK strain that was previously reported. We found that resistance ratios (RRs) were variable between pyrethroids and strains, ranging from 6.2- to 42-fold for CR, and 70- to 261-fold for CKR. In general, we found that CYP-mediated resistance alone contributes less to resistance than kdr. The effect of the combined mechanisms on resistance was significantly greater than additive for all pyrethroids except (1R)-trans-fenfluthrin. CYP-mediated pyrethroid resistance conferred cross-resistance to both methyl paraoxon and fenitrothion, and negative cross-resistance to methyl parathion and naled. Based on our results, we recommend that etofenprox and cyfluthrin be avoided for A. aegypti control in areas where these two resistance mechanisms are prevalent.

Insecticide resistance status of Aedes aegypti and Aedes albopictus mosquitoes in Papua New Guinea

BackgroundAedes aegypti and Ae. albopictus are important vectors of infectious diseases, especially those caused by arboviruses such as dengue, chikungunya and Zika. Aedes aegypti is very well adapted to urban environments, whereas Ae. albopictus inhabits more rural settings. Pyrethroid resistance is widespread in these vectors, but limited data exist from the Southwest Pacific Region, especially from Melanesia. While Aedes vector ecology is well documented in Australia, where incursion of Ae. albopictus and pyrethroid resistance have so far been prevented, almost nothing is known about Aedes populations in neighbouring Papua New Guinea (PNG). With pyrethroid resistance documented in parts of Indonesia but not in Australia, it is important to determine the distribution of susceptible and resistant Aedes populations in this region.MethodsThe present study was aimed at assessing Aedes populations for insecticide resistance in Madang and Port Moresby, located on the north and south coasts of PNG, respectively. Mosquitoes were collected using ovitraps and reared in an insectary. Standard WHO bioassays using insecticide-treated filter papers were conducted on a total of 253 Ae. aegypti and 768 Ae. albopictus adult mosquitoes. Subsets of samples from both species (55 Ae. aegypti and 48 Ae. albopictus) were screened for knockdown resistance mutations in the voltage-sensitive sodium channel (Vssc) gene, the target site of pyrethroid insecticides.ResultsHigh levels of resistance against pyrethroids were identified in Ae. aegypti from Madang and Port Moresby. Aedes albopictus exhibited susceptibility to pyrethroids, but moderate levels of resistance to DDT. Mutations associated with pyrethroid resistance were detected in all Ae. aegypti samples screened. Some genotypes found in the present study had been observed previously in Indonesia. No Vssc mutations associated with pyrethroid resistance were found in the Ae. albopictus samples.ConclusionsTo our knowledge, this is the first report of pyrethroid resistance in Ae. aegypti mosquitoes in PNG. Interestingly, usage of insecticides in PNG is low, apart from long-lasting insecticidal nets distributed for malaria control. Further investigations on how these resistant Ae. aegypti mosquito populations arose in PNG and how they are being sustained are warranted.

First Determination of Pyrethroid Knockdown Resistance Alleles in Human Head Lice (Phthiraptera: Pediculidae) From Chile.

The infestation with the human ectoparasite, Pediculus humanus capitis (De Geer), is a common public health problem affecting schoolchildren worldwide. In Chile, the main active ingredients present in the over-the-counter pediculicides contain pyrethroids. Despite the extended use of these products, there is no evidence of the insecticide resistance status of the head lice geographically located in Chile. The most extended resistant mechanism of pyrethroids consists of the target site insensitivity (Kdr) determined by the presence of mutations linked to insecticide-binding sites in the voltage-sensitive sodium channel. T917I is recognized as the main mutation in head lice, and detection is considered to be a biomarker of resistance. The goal of the present study was to detect the presence and distribution of T917I mutation in five geographic locations of Chile. All five geographically selected louse populations had a frequency of pyrethroid resistance genes that ranged from 36 to 77%, and 94.9% of the collected head lice had one or two T917I mutant alleles. Moreover, the frequency of the aggregate resistant alleles was 50.5%. This is the first evidence that head lice in Chile had the mutations commonly associated with the resistance to pyrethroids. Moreover, the overrepresentation of heterozygotes in the studied populations suggests that head lice in Chile are currently under active selective pressure.

Insecticide resistance monitoring of house fly populations from the United States

Insecticide resistance in house fly populations is a major problem faced by livestock producers worldwide. A survey of insecticide resistance levels and pyrethroid resistance allele frequencies in the United States was conducted in 2008–09, but little is known about how resistance levels have changed over the last 10 years. In addition, new target-site pyrethroid resistance alleles that confer high levels of resistance have been recently identified in the voltage-sensitive sodium channel, and their frequencies in field populations are unknown. Our aim in this study was to reassess the resistance status of house flies from select locations in the United States by examining resistance levels against commonly used insecticides and frequencies of known resistance alleles. House flies were collected from animal production facilities in five different states between 2016 and 2018. Resistance levels to three insecticides (permethrin, tetrachlorvinphos, and methomyl), representing three classes of insecticides (pyrethroids, organophosphates and carbamates) varied geographically and were lowest in the population collected from New Mexico, intermediate in the population collected from Utah, and greatest in the population from Kansas. The recently identified 1B pyrethroid resistance allele increased dramatically in frequency compared to previous reports, most notably in populations from Kansas and Maryland, indicating that it may already be widespread around the United States. Based on comparison with historical data, the population collected from Kansas represents one of the most highly permethrin resistant populations ever sampled. If the alleles responsible for this level of resistance spread, pyrethroids may be of limited use for house fly control in the United States in the near future.