Use Of Pyrethroids Research Articles

Assessment of pyrethroid contamination and potential mitigation strategies in California Central Coast surface waters

Increased use of pyrethroids in the Central Coast of California since 2011 has resulted in a dramatic increase in the number and proportion of surface water samples with detectable concentrations at levels of concern to the public and state regulators. The goals of this study were to investigate the relationships between pyrethroid usage and environmental contamination, quantify and assess the potential risks, and recommend mitigation strategies. This study compiled the available pyrethroid use and surface water sampling data for the region, and then applied GIS methods to dynamic simulation modeling and usage-restriction buffer analyses. The results showed that in Monterey County alone, the agricultural usages of bifenthrin and permethrin each increased by ~50%, and the positive detection frequencies of both also increased around 2011–2013. County-wide, bifenthrin positive detections in surface water samples increased precipitously from 8.2% (7/85) for 2008–2012 up to 36.4% (106/291) for 2013–2017, and detections above its crustacean LC50 concentration went from 7.1% (6/85) to 35.7% (104/291). Despite its higher usage by mass, comparable figures for permethrin were more modest for the same time-periods, with positive detections going from 10.6% (9/85) to 14.4% (64/444), and detections above its crustacean LC50 going from 3.5% (3/85) to 7.2% (32/444). The seasonal lag between high bifenthrin usage in spring/summer and high detections in fall/winter samples showed the best correlations with 128- to 182-day lag times. This timing suggests that fallow season rain is likely the main driver of pyrethroid off-site movement into surface waters. SWAT modeling indicated that significant reductions in surface water permethrin concentrations only occurred with buffer distances of 1.6–3.2 km, but not with narrower buffers. However, if those wider buffers were implemented, permethrin could no longer be used on the majority of land where it is currently applied. Specifically, a 1.6-km buffer reduced the instream concentration by 8% but impacted 50% of the cropland, and a 3.2-km buffer reduced the concentration by 50% while impacting 76% of cropland. This study suggested that more promising alternative management practices could include an overall reduction in pyrethroid usage back to 2011 levels or other active mitigation strategies, like planting cover crops during the fallow winter wet season, or installing either vegetated buffer strips and/or sediment check dams on small tributaries to minimize sediment runoff.

Malaria vector species composition and entomological indices following indoor residual spraying in regions bordering Lake Victoria, Tanzania

BackgroundVector control through long-lasting insecticidal nets (LLINs) and focal indoor residual spraying (IRS) is a major component of the Tanzania national malaria control strategy. In mainland Tanzania, IRS has been conducted annually around Lake Victoria basin since 2007. Due to pyrethroid resistance in malaria vectors, use of pyrethroids for IRS was phased out and from 2014 to 2017 pirimiphos-methyl (Actellic® 300CS) was sprayed in regions of Kagera, Geita, Mwanza, and Mara. Entomological surveillance was conducted in 10 sprayed and 4 unsprayed sites to determine the impact of IRS on entomological indices related to malaria transmission risk.MethodsWHO cone bioassays were conducted monthly on interior house walls to determine residual efficacy of pirimiphos-methyl CS. Indoor CDC light traps with or without bottle rotator were hung next to protected sleepers indoors and also set outdoors (unbaited) as a proxy measure for indoor and outdoor biting rate and time of biting. Prokopack aspirators were used indoors to capture resting malaria vectors. A sub-sample of Anopheles was tested by PCR to determine species identity and ELISA for sporozoite rate.ResultsAnnual IRS with Actellic® 300CS from 2015 to 2017 was effective on sprayed walls for a mean of 7 months in cone bioassay. PCR of 2016 and 2017 samples showed vector populations were predominantly Anopheles arabiensis (58.1%, n = 4,403 IRS sites, 58%, n = 2,441 unsprayed sites). There was a greater proportion of Anopheles funestus sensu stricto in unsprayed sites (20.4%, n = 858) than in sprayed sites (7.9%, n = 595) and fewer Anopheles parensis (2%, n = 85 unsprayed, 7.8%, n = 591 sprayed). Biting peaks of Anopheles gambiae sensu lato (s.l.) followed periods of rainfall occurring between October and April, but were generally lower in sprayed sites than unsprayed. In most sprayed sites, An. gambiae s.l. indoor densities increased between January and February, i.e., 10–12 months after IRS. The predominant species An. arabiensis had a sporozoite rate in 2017 of 2.0% (95% CI 1.4–2.9) in unsprayed sites compared to 0.8% (95% CI 0.5–1.3) in sprayed sites (p = 0.003). Sporozoite rates were also lower for An. funestus collected in sprayed sites.ConclusionThis study contributes to the understanding of malaria vector species composition, behaviour and transmission risk following IRS around Lake Victoria and can be used to guide malaria vector control strategies in Tanzania.

Longitudinal exposure to pyrethroids 3-PBA, trans-TCC & 2,4 D herbicides in rural schoolchildren, Maule, Chile.

Background: Several studies show that early exposure to pesticides and during the preschool and school stage affects the development and health of children. In Maule, a series of studies have shown the exposure of organophosphate pesticides(OP), however, there are no studies assessing exposure to pyrethroids and herbicide 2,4 D. Objetive: To evaluate exposure to pyrethroids 3-phenoxybenzoic acid 3-PBA, trans-2,2-(dichloro)-2-dimethylvinylcyclopropane carboxylic acid trans-DCCA(Trans-TCC) and 2,4 D herbicides in schoolchildren. Method: Longitudinal study, 48 schoolchildren from 5 to 13 years old from two rural schools in the Maule. Specific metabolites of pyrethroids 3-PBA, Trans-TCC and 2.4 D in the urine of the school children were evaluated. The data were correlated with an earlier study that evaluated the exposure of OP metabolites. Two samples were taken in September and 2 samples in November, a total of 384 urine samples were obtained during 2016 and 2017. Data analysis: descriptive, U Mann Whitney for repeated measurements, Spearman and GEE. Results: The 100% of schoolchildren have more than two pesticide metabolites in their urine in both years, with the 3-PBA metabolite being the most frequent. 3-PBA in November 2017 increases its presence in urine compared to 2016(from 0.69 μg/L in 2016 to 1.90μg/L in 2017). In 2016, the specific metabolites of 3-PBA correlate with TCC, 2,4 D, chlorpyrifos, diazinon, paration. In 2017, 3-PBA was correlated with 2,4 D and TCC. Importantly, the concentrations of 3-PBA pesticide metabolites in urine found in Chilean children was higher than studies in the USA where there is an association of exposure from prenatal stage to these metabolites with difficulties in emotional control and attention. Conclusions: Promote the monitoring, training and active epidemiological surveillance of agricultural communities. The increased use of pyrethroids is worrying. Promote the intervention of school communities, involving government agencies and agricultural companies, considering preventing to the population.

Permethrin Resistance Status and Associated Mechanisms in Aedes albopictus (Diptera: Culicidae) From Chiapas, Mexico.

There are major public health concerns regarding the spread of mosquito-borne diseases such as dengue, Zika, and chikungunya, which are mainly controlled by using insecticides against the vectors, Aedes aegypti (Linnaeus) and Aedes albopictus (Skuse). Pyrethroids are the primary class of insecticides used for vector control, due to their rapid knockdown effect and low toxicity to vertebrates. Unfortunately, continued use of pyrethroids has led to widespread insecticide resistance in Ae. aegypti; however, we lack information for Ae. albopictus-a sympatric species in Chiapas since 2002. In this study, we evaluated the permethrin resistance status of Ae. albopictus collected from Mexico and Texas. We also selected for permethrin resistance in the laboratory and investigated the potential mechanisms conferring resistance in this species. Knockdown resistance mutations, specifically F1534C, in the voltage-gated sodium channel gene, and increased activity of detoxifying enzymes were evaluated. Low levels of permethrin resistance (<2.4-fold) were observed in our field populations of Ae. albopictus and the F1534C mutation was not detected in any of the sites. Low levels of resistance were also observed in the artificially selected strain. There was significantly higher cytochrome P450 activity in our permethrin-selected and nonselected strains from Mexico compared to the control strain. Our results suggest the Ae. albopictus sampled from 2016 are mostly susceptible to pyrethroids. These results contrast with the high levels of permethrin resistance (>58-fold) found in Ae. aegypti from the same sites in Mexico. This research indicates the importance of continued monitoring of Ae. albopictus populations to prevent resistance from developing in the future.

Prevalence and distribution of pathogen infection and permethrin resistance in tropical and temperate populations of Rhipicephalus sanguineus s.l. collected worldwide.

The brown dog tick, Rhipicephalus sanguineus sensu lato (s.l.) Latreille (Acari: Ixodidae), is a peridomestic, cosmopolitan parasite of dogs known to vector numerous pathogens of veterinary and medical importance. Recent phylogenetic analyses separate this tick into temperate and tropical lineages. Populations of Rh. sanguineus s.l. have been reported to exhibit sodium channel target site insensitivity to permethrin and etofenprox, which is likely due to the prolonged use of pyrethroids against many pests in and around the home. In this study, populations collected in the Caribbean, Africa, Asia, Europe and North America, were tested to identify the distribution of a known resistance mechanism, pathogen-vector interactions and phylogeny in relation to latitude. Using molecular assays, populations from 29 distinct locations were simultaneously geographically typed and screened for bacterial infection by Rickettsia, Ehrlichia, Babesia and Hepatozoon species, and for the presence of a sodium channel single nucleotide polymorphism known to confer permethrin resistance. Implications of these results on Rh. sanguineus s.l. management in association with geographical distribution will be discussed.

Low Levels of Pyrethroid Resistance in Hybrid Offspring of a Highly Resistant and a More Susceptible Mosquito Strain.

The use of insecticides has been a central approach to control disease-transmitting mosquitoes for the last century. The high prevalence of pyrethroid use as public health insecticides has resulted in the evolution of pyrethroid resistance in many populations of Aedes aegypti (Linnaeus) (Diptera: Culicidae), throughout its global distribution range. Insecticide resistance is often correlated with an associated fitness cost. In this project, we studied the phenotypes of hybrid mosquitoes derived from crossing a pyrethroid-resistant strain of Ae. aegypti (Puerto Rico [PR]) with a more susceptible one (Rockefeller [ROCK]). We first sequenced and compared the para gene of both original strains. We then crossed males from one strain with females of the other, creating two hybrids (Puertofeller, Rockorico). We used a Y-tube choice assay to measure the attraction of these strains towards a human host. We then compared the levels of pyrethroid resistance in the different strains. We found three known resistance mutations in the para gene sequence of the PR strain. In our attraction assays, PR females showed lower attraction to humans, than the ROCK females. Both hybrid strains showed strong attraction to a human host. In the insecticide resistance bottle assays, both hybrid strains showed marginal increases in resistance to permethrin compared to the more susceptible ROCK strain. These results suggest that hybrids of sensitive and permethrin-resistant mosquitoes have an incremental advantage compared to more susceptible mosquitoes when challenged with permethrin. This explains the rapid spread of permethrin resistance that was observed many times in the field.

High frequency of knockdown resistance mutations in the para gene of cat flea (Ctenocephalides felis) samples collected from goats.

Fleas are ectoparasites of mammals and birds. In livestock such as sheep and goat, flea bites cause many clinical signs. Several types of insecticides including pyrethroids are used to struggle against fleas. The widespread use of these insecticides causes an increase in the number of resistant individuals in flea populations. T929V and L1014F mutations corresponding to pyrethroid resistance have been found in the para gene of cat fleas. We aimed to investigate T929V and L1014F mutations in flea samples (n:162) collected from goats in seven different farms where cypermethrin, a synthetic pyrethroid, had been used intensively. To achieve this aim, collected flea samples were morphologically identified under a stereo microscope and DNA isolation was conducted by HotSHOT method. Later, a bi-PASA targeting the para gene was applied to identify both mutations in corresponding samples. According to the results obtained, all fleas were Ctenocephalides felis. Frequencies of T929V and L1014F mutations in fleas were 92.6% (150/162) and 95.7% (155/162), respectively. In conclusion, the frequency of mutations related to pyrethroid resistance was very high in the fleas collected from all the farms and it was thought that the high frequency of these mutations can be attributed to intensive use of pyrethroids.

Spatial variation in the frequency of knockdown resistance genotypes in Florida Aedes aegypti populations

BackgroundThe development of insecticide resistance in disease-vectoring mosquito species can lead to vector control failure and disease resurgence. However, insecticide applications remain an essential public health intervention. In Florida, insecticide resistance in Aedes aegypti, an anthropophilic mosquito species capable of transmitting dengue, chikungunya, and Zika virus, is a major concern. Understanding the location, scale, and driving factors of insecticide resistance can enhance the ability of vector control organizations to target populations effectively.MethodsWe used previously collected data on frequencies of mutations that confer resistance to commonly used pyrethroid insecticides in Ae. aegypti specimens from 62 sites distributed across 18 counties in Florida. To determine the scale of clustering for the most resistant variant, we used a Ripley’s K function. We also used a spatial scanning statistic technique to identify locations of clusters where higher than expected frequencies of susceptible or resistant mosquitoes occurred. We then tested for associations between landscape, demographic, and insecticide-use factors using a beta regression modelling approach and evaluated the effect of spatial lag and spatial error terms on overall explanatory power of these models.ResultsThe scale at which maximum clustering of the most resistant variant occurs is approximately 20 kilometers. We identified statistically significant clusters of genotypes associated with resistance in several coastal cities, although some of these clusters were near significant clusters of susceptible mosquitoes, indicating selection pressures vary at the local scale. Vegetation density, distance from roads, and pyrethroid-use by vector control districts were consistently significant predictors of knockdown resistance genotype frequency in the top-performing beta regression models, although pyrethroid use surprisingly had a negatively associated with resistance. The incorporation of spatial lags resulted in improvements to the fit and explanatory power of the models, indicating an underlying diffusion process likely explains some of the spatial patterns observed.ConclusionsThe genetic mutations that confer resistance to pyrethroids in Ae. aegypti mosquitoes in Florida exhibit spatial autocorrelation and patterns that can be partially explained by landscape and insecticide-use factors. Further work at local scales should be able to identify the mechanisms by which these variables influence selection for alleles associated with resistance.

Chronology of sodium channel mutations associated with pyrethroid resistance in Aedes aegypti.

Aedes aegypti is the primary mosquito vector of dengue, yellow fever, Zika and chikungunya. Current strategies to control Ae. aegypti rely heavily on insecticide interventions. Pyrethroids are a major class of insecticides used for mosquito control because of their fast acting, highly insecticidal activities and low mammalian toxicity. However, Ae. aegypti populations around the world have begun to develop resistance to pyrethroids. So far, more than a dozen mutations in the sodium channel gene have been reported to be associated with pyrethroid resistance in Ae. aegypti. Co-occurrence of resistance-associated mutations is common in pyrethroid-resistant Ae. aegypti populations. As global use of pyrethroids in mosquito control continues, new pyrethroid-resistant mutations keep emerging. In this microreview, we compile pyrethroid resistance-associated mutations in Ae. aegypti in a chronological order, as they were reported, and summarize findings from functional evaluation of these mutations in an in vitro sodium channel expression system. We hope that the information will be useful for tracing possible evolution of pyrethroid resistance in this important human disease vector, in addition to the development of methods for global monitoring and management of pyrethroid resistance in Ae. aegypti.

Aquaculture-driven evolution: distribution of pyrethroid resistance in the salmon louse throughout the North Atlantic in the years 2000–2017

Abstract The parasitic salmon louse, and its documented resistance to chemotherapeutants, represents the most persistent environmental challenge to global salmonid aquaculture. We used a genetic marker associated with pyrethroid resistance to analyse ∼15 000 lice collected from the North Atlantic in the period 2000–2017. The genotype associated with resistance was not detected in lice collected from throughout the North Atlantic in the year 2000 or 2002. However, by the year 2009 onwards, it was found in lice from fish farms throughout much of the North Atlantic. It was also found in modest frequencies in lice collected from wild Atlantic salmon captured off Greenland. The most recent samples displayed very high frequencies of the genotype associated with resistance, particularly in intensive aquaculture regions of Norway (&amp;gt;90%) and Scotland (&amp;gt;70%). These results closely align with observations from the field. We suggest that pyrethroid resistance first emerged in Europe just before or around the year 2000 and was thereafter dispersed throughout much of the North Atlantic where its increased frequency was driven by extensive pyrethroid use. Although the resistant genotype was not detected in lice from Canada, it is likely to occur in very low frequencies that would quickly increase if pyrethroids were to be used in that region.

Loss of pyrethroid resistance in newly established laboratory colonies of Aedes aegypti.

BackgroundResistance to pyrethroid insecticides in Aedes aegypti has become widespread after almost two decades of the frequent use of these pesticides to reduce arbovirus transmission. Despite this resistance, pyrethroids continue to be used because they are relatively inexpensive and have low human toxicity. Resistance management has been proposed as a way to retain the use of pyrethroids in natural populations. A key component of resistance management is the assumption that negative fitness is associated with resistance alleles such that resistance alleles will decline in frequency when the insecticides are removed. At least three studies in Ae. aegypti have demonstrated a decrease in pyrethroid resistance once the insecticide has been removed.Methods/Principal findingsThe present study aims to evaluate variation in the loss of pyrethroid resistance among newly established laboratory populations of Ae. aegypti from Mexico. Eight field collections were maintained for up to eight generations, and we recorded changes in the frequencies of the mutations at the V1,016I locus and at the F1,534C locus in the voltage-gated sodium channel gene (VGSC). I1,016 and C1,534 confer resistance. We also examined resistance ratios (RR) with type 1 and 2 pyrethroids.Conclusions/SignificanceWe demonstrate that, in general, the frequency of the Ae. aegypti pyrethroid-resistance alleles I1,016 and C1,534 decline when they are freed from pyrethroid pressure in the laboratory. However, the pattern of decline is strain dependent. In agreement with earlier studies, the RR was positively correlated with the frequencies of the resistance allele I1,016 and showed significant protection against permethrin, and deltamethrin, whereas F1,534C showed protection against permethrin but not against deltamethrin.

Transcriptome analysis of hepatopancreas of Eriocheir sinensis with hepatopancreatic necrosis disease (HPND).

Hepatopancreatic necrosis disease (HPND) is a newly emerging disease in the Chinese mitten crab, Eriocheir sinensis, which has resulted in large economic losses. However, the underlying cause of this disease remains unclear. To better understand the pathogenesis and pathogenic mechanism of HPND, we compared the transcriptome differences of the hepatopancreas of E. sinensis with and without HPND. The analysis yielded > 30 million reads for each sample of three test (with HPND) and three control groups (without HPND). We observed 978 downregulated genes and 644 upregulated genes. Among the gene ontology categories “biological process,” “cellular component,” and “molecular function”, the subcategories cellular process, single-organism process, biological regulation, metabolic process, cell part, organelle, organelle part, binding, and catalytic were enriched. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that “metabolism of xenobiotics by cytochrome P450,” “drug metabolism—cytochrome P450,” “chemical carcinogenesis,” and “material metabolism” were the “five” most significantly enriched pathways in the hepatopancreas of E. sinensis with HPND. The results revealed that material metabolic abnormalities and drug effects from the external environment might be associated with HPND in the Chinese mitten crab. Considering the wide use of pyrethroids for pond cleaning in Xinghua city, we speculated that pyrethroids might cause HPND in the Chinese mitten crab. Our study provided useful information about the cause and pathogenetic mechanisms of HPND and could help to prevent this disease in production practice.

Chronic cypermethrin exposure alters mouse embryonic stem cell growth kinetics, induces Phase II detoxification response and affects pluripotency and differentiation gene expression

Worldwide uncontrolled use of synthetic pyrethroids contaminates water and soil leading to health hazards. Cypermethrin (CYP), the most used pyrethroid, induces detrimental effects on adults and embryos at different stages of development of several vertebrate species. In Mammals, CYP-induced alterations have been previously described in adult somatic cells and in post-implantation embryos. It remains unknown whether CYP has effects during pre-implantation development. Studies to access pre-implantation embryo toxicity are complicated by the restricted number of blastocysts that may be obtained, either in vivo or in vitro. Embryonic stem cells (ESCs) are an in vitro model study that overcomes these limitations, as millions of pluripotent cells are available to the analysis. Also, ESCs maintain the same pluripotency characteristics and differentiation capacity of the inner cell mass (ICM) present in the blastocyst, from which they derive. In this work, using mouse R1 ESCs, we studied CYP-induced cell death, ROS production, the activation of oxidative stress-related and detoxification responses and the population growth kinetics following 72 h exposure at the 0.3 mM LD50 dose. Also, the expression levels of pluripotency genes in exposed ESCs and of markers of the three germ layers after their differentiation into embryoid bodies (EBs) were determined. Two apoptotic waves were observed at 12-24 h and at 72 h. The increase of ROS production, at 24 h until the end of the culture period, was accompanied by the induction, at 48 h, of redox-related Cat, Sod1, Sod2, Gpx1 and Gpx4 genes. Up-regulation of Cyp1b1, but not of Cyp1a1, phase I gene was detected at 72 h and induction of Nqo1, Gsta1 and Ugt1a6 phase II genes began at 24 h exposure. The results show that exposed R1 ESCs activate oxidative stress-related and detoxification responses, although not sufficient, during the culture period tested, to warrant recovery of the growth rate observed in untreated cells. Also, CYP exposure altered the expression of Oct-4 and Nanog pluripotency genes in ESCs and, when differentiated into EBs, the expression of Fgf5, Brachyury and Foxa2, early markers of the ectoderm, mesoderm and endoderm germ layers, respectively. NIH/3T3 cells, a differentiated cell line of embryonic origin, were used for comparison.

The double-mutation（M918I + L1014F）kdr allele is fixed in Cimex hemipterus populations in Guangxi, China.

Four putative knockdown resistance (kdr) mutations have been documented in the voltage-gated sodium channel (VGSC) gene of Cimex hemipterus from several countries. However, no information regarding kdr mutations in any Chinese tropical bed bug population is available to date. In this study, a double-mutation（M918I + L1014F）kdr allele was identified in six C. hemipterus populations across Guangxi Zhuang Autonomous Region of China. The frequency of this allele was 100% in all the six examined populations. In addition, only two cytochrome c oxidase I (COI) gene haplotypes, with one synonymous nucleotide variation, were identified in a total of 48 individuals from six locations. The fixation and broad geographic distribution of this resistant allele questions the continued use of pyrethroids in the treatment of tropical bed bug infestations. The very low genetic diversity within and among these populations indicates that these bed bugs may have a single origin.

Distribution of Anopheles mosquito species, their vectorial role and profiling of knock-down resistance mutations in Botswana.

Knowledge of vector species composition and monitoring their change over time is critical to evaluate malaria transmission and assess control interventions. This is especially important in countries such as Botswana, where malaria transmission is subjected to fluctuations due to climate variability. Another important aspect that impacts vector populations is the insecticide resistance. In order to assess species composition and the presence of mutations associated with insecticide resistance, Anopheles specimens from larval samplings and indoor pyrethrum spray sheet collections were analysed. A total of 349 Anopheles were screened by morphology and PCR as belonging to the An. gambiae complex and An. funestus group. Specimens were subsequently analysed for human blood meal and Plasmodium index. Finally, knock-down resistance polymorphisms were assessed. Anopheles arabiensis accounted for the majority of specimens collected through larval (96.7%) and pyrethrum spray sheet collection (87.4%) across all sampling sites, and this species was the only one found positive for human blood and for P. falciparum. Other Anopheles species were collected in small numbers by pyrethrum spray catches, namely An. quadriannulatus, An. longipalpis type C and An. parensis. The authors speculate on changing climate patterns and their possible impact on species composition. The kdr assay revealed that Anopheles mosquitoes were homozygous wild type for both L1014F (kdr-w) and L1014S (kdr-e) mutations. These results highlight the unique vectorial role of An. arabiensis in Botswana and indicated that even with prolonged use of pyrethroids and DDT, the mosquito population has not developed kdr mutations, despite some in vivo evidence of insecticide resistance.

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.

Molecular analysis of pyrethroid resistance in Cimex hemipterus (Hemiptera: Cimicidae) collected from different parts of Iran.

The present study was aimed to assess the bedbugs susceptibility to pyrethroid insecticides using molecular analysis. With the aid of pest control companies, adult bedbugs were collected from various places such as hotels, residential houses, and industrial buildings in seven cities highly crowded with domestic and foreign tourists in Iran from May 2016 to August 2017. Bedbugs were colonized in the laboratory to evaluate their resistance to pyrethroid using insecticide resistance bioassay. Genomic DNA was extracted from susceptible and resistant bedbugs. At first, specie specific primers targeting cytochrome oxidase subunit I (COI) gene was performed to confirm Cimex hemipterus species. Then, kdr-like gene was examined for point mutation using PCR and nucleotide sequencing. Bioassay showed that 11 out of 35 examined bedbugs were resistant to pyrethroids (31.43%; 95.00% confidence interval: 29.48-33.08%). The DNA sequencing showed that all examined bedbugs collected from Tehran province had homozygous V419L kdr-like gene mutations. The level of pyrethroid resistance found in the collected bugs from Tehran province indicated that this phenomenon has already been prevailed in the site and prompts the need to reevaluate the large use of pyrethroids to control the bedbugs.

Farmers\u2019 pesticide usage practices in the malaria endemic region of North-Western Tanzania: implications to the control of malaria vectors

BackgroundPesticides remain the mainstay for the control of agricultural pests and disease vectors. However, their indiscriminate use in agriculture has led to development of resistance to both crop pests and disease vectors. This threatens to undermine the success gained through the implementation of chemical based vector control programs. We investigated the practices of farmers with regard to pesticide usage in the vegetable growing areas and their impact on susceptibility status of An. gambiae s.l.MethodsA stratified multistage sampling technique using the administrative structure of the Tanzanian districts as sampling frame was used. Wards, villages and then participants with farms where pesticides are applied were purposively recruited at different stages of the process, 100 participants were enrolled in the study. The same villages were used for mosquito larvae sampling from the farms and the surveys were complimented by the entomological study. Larvae were reared in the insectary and the emerging 2–3 days old female adults of Anopheles gambiae s.l were subjected to susceptibility test.ResultsForty eight pesticides of different formulations were used for control of crop and Livestock pests. Pyrethroids were the mostly used class of pesticides (50%) while organophosphates and carbamates were of secondary importance. Over 80% of all farmers applied pesticides in mixed form. Susceptibility test results confirmed high phenotypic resistance among An. gambiae populations against DDT and the pyrethroids (Permethrin-0.75%, Cyfluthrin-0.15%, Deltametrin-0.05% and Lambdacyhalothrin-0.05%) with mortality rates 54, 61, 76 and 71%, respectively. Molecular analysis showed An. arabiensis as a dominant species (86%) while An. gambiae s.s constituted only 6%. The kdr genes were not detected in all of the specimens that survived insecticide exposures.ConclusionThe study found out that there is a common use of pyrethroids in farms, Livestocks as well as in public health. The study also reports high phenotypic resistance among An. gambiae s.l against most of the pyrethroids tested. The preponderance of pyrethroids in agriculture is of public health concern because this is the class of insecticides widely used in vector control programs and this calls for combined integrated pest and vector management (IPVM).

Hypospadias in boys born to mothers exposed to dichlorodiphenyltrichloroethane and pyrethroid insecticides

PDS 72: Environmental health issues in LMIC, Exhibition Hall (PDS), Ground floor, August 28, 2019, 10:30 AM - 12:00 PM Background: Hypospadias is the ectopic opening of the male urethra and related in vivo to maternal estrogenic and/or anti-androgenic exposures. We examined the relationship between maternal exposure to DDT and pyrethroids and hypospadias in a malaria endemic area. Dichlorodiphenyltrichloroethane (DDT) and the pyrethroids cypermethrin and deltamethrin are used to control malaria. In vitro, DDT is estrogenic and its breakdown product, dichlorodiphenyldichloroethylene (DDE) is anti-androgenic. Cypermethrin, and permethrin are metabolized to cis-3-and trans-3-(2,2-dichlorovinyl)-2,2-dimethyl-cyclopropane carboxylic acid (cis- and trans-DCCA) and the most common pyrethroid metabolite 3-phenoxybenzoic acid (3-PBA). Deltamethrin breaks down to the metabolites 3-PBA and cis-(2,2-dibromovinyl)-2,2-dimethylcyclopropane-1-carboxylic acid (cis-DBCA). DCCA and 3-PBA are anti-androgenic. Methods: We measured peripartum levels of DDT and DDE in maternal blood and the pyrethroid metabolites cis- and trans-DCCA, 3-PBA and cis-DBCA in maternal urine in a birth cohort and examined boys at age one year for hypospadias (n=359). Due to the high prevalence of phimosis (n=291, 81.1%), which prevented examination for hypospadias, we restricted analyses to boys without phimosis (n= 68). Results: Hypospadias was observed in 32 boys. Maternal cis-DCCA, trans-DCCA and 3-PBA urinary concentrations were significantly associated with increased relative risks (RR) of having a boy with hypospadias (RR 1.90 (95% CI: 1.31, 2.75), 1.82 (95% CI: 1.27, 2.63) and 1.85 (95% CI: 1.06, 3.22), respectively). There were no significant associations between DDT, DDE and DBCA and hypospadias. Conclusions: Boys examined had very high prevalence of phimosis and hypospadias. Mothers with high urinary concentrations of 3-PBA and DCCA had significantly greater risks of having a son with hypospadias. This is the first study to report associations between maternal pyrethroid exposure and hypospadias. Hormonal mechanisms might be involved in the etiology. Given the extensive global use of pyrethroids, our findings raise health concerns for other populations with high usage for malaria control, home use or agricultural purposes.

Reproductive sublethal effects of macrocyclic lactones and synthetic pyrethroids on the dung beetle Onthophagus similis.

Dung-colonizing beetles provide a range of ecosystem services in farmland pasture systems. However, such beetles are declining in Northern temperate regions. This may, in part, be due to the widespread use of macrocyclic lactones (MLs) and synthetic pyrethroids (SPs) in livestock farming. These chemicals are used to control pests and parasites of cattle; the residues of which are excreted in dung at concentrations toxic to insects. While the lethal effects of such residues are well known, sublethal effects are less understood. Any effects, however, may have important consequences for beetle populations, particularly if they affect reproduction. To investigate, the impact of ML and SP exposure on the reproductive output of Onthophagus similis (Scriba), a Northern temperate dung beetle species, was examined. In laboratory trials, field-collected adult O. similis exposed to the ML ivermectin at 1 ppm (wet weight) over a period of 3 weeks had smaller oocytes (p = 0.016), smaller fat bodies and reduced motility compared to the control. In a farm-level investigation, cattle dung-baited pitfall trapping was undertaken on 23 beef cattle farms in SW England, which either used MLs (n = 9), SPs (n = 7) or neither chemical (n = 7). On farms that used no MLs or SPs, 24.2% of females caught were gravid. However, on farms that used MLs no gravid females were caught, and only 1% of the beetles caught on farms using SPs were gravid (p < 0.001). The association between ML and SP use and impaired reproductive output suggests that the use of such chemicals is likely to be ecologically damaging.