Permethrin Content Research Articles

Reduced effectiveness of permethrin-treated military uniforms after prolonged wear measured by contact irritancy and toxicity bioassays with Ixodes scapularis (Acari: Ixodidae) nymphs.

Factory-treated permethrin uniforms are the primary method used by the US Army to prevent arthropod bites and transmission of arthropod-borne diseases. In this study previously worn uniforms were collected from cadets at the United States Military Academy in West Point, NY to determine the amount of permethrin remaining after prolonged wear and subsequent effects on ticks. Six trousers were collected from cadets in the sophomore, junior, and senior classes. A new, unwashed uniform served as a positive control and an untreated maternity uniform served as a negative control. Fabric samples were removed from each trouser and used in bioassays with laboratory-reared Ixodes scapularis Say nymphs. Contact irritancy bioassays measured the nymphs' ability to remain in contact with fabric for a period of 5 min. Toxicity bioassays measured tick survival at 1 and 24 h after contacting uniform samples. liquid chromatography-mass spectrometry was used to quantify the permethrin content (mg/cm2) in each uniform after the bioassays were complete. The results showed significant amounts of permethrin were lost after extended wear and it was related to the cadet year group. The contact irritancy assays found uniforms with less permethrin did not irritate ticks and cause them to dislodge. Mortality was also affected by permethrin levels, with less ticks dying at 24 h on older uniforms. The results from this study show older uniforms lose most of their permethrin and no longer provide the same levels of protection.

Protective efficacy of holed and aging PBO-pyrethroid synergist-treated nets on malaria infection prevalence in north-western Tanzania.

Two billion pyrethroid long-lasting insecticidal nets (LLINs) have been distributed since 2004 for malaria prevention in Sub-Saharan Africa. Current malaria control strategies rely on an assumed effective 3-year lifespan for LLINs. PBO synergist LLINs are a newly recommended class of net but there is limited information on their life span and long-term protective efficacy in communities. To assess their operational survival, a cohort of 390 PBO LLINs (Olyset Plus) and 367 standard pyrethroid LLIN (Olyset net) from 396 households were followed for 36 months in Western Tanzania. To assess the association between the condition of the LLIN and malaria infection, nets from at least 480 randomly selected households were assessed during malaria prevalence cross-sectional surveys at 4, 9, 16, 21, 28, and 33 months post-distribution. Information on the presence and condition of nets, and demographic information from the household, were collected to evaluate factors influencing net durability. After 3 years less than 17% of nets distributed still remained in the households. The fabric condition was not associated with malaria infection in either type of net. The difference between the net types was highest when nets were between 1-2 years old, when PBO nets appeared to be similarly protective as nets less than a year old, whereas standard nets were considerably less protective as they aged, regardless of fabric condition. There was no statistical difference in the estimated median functional survival time between net types with 1.6 years (95% CI 1.38-1.87) for PBO LLIN and 1.9 years (95% CI 1.67-2.06) for standard LLINs. After 3 years, there was a loss of 55% of permethrin (pyrethroid) content for both nets, and 97% of PBO content was lost in PBO LLIN. These results highlight that functional survival is less than the recommended 3 years for both net types. However, even as the nets age, the PBO nets remained more protective than standard nets, regardless of their condition.

Evaluation of surface versus total permethrin content in permethrin-treated clothing: Implications for protection against mosquitoes

ABSTRACT Permethrin is a synthetic pyrethroid insecticide used to treat uniforms (e.g. military, foresters) and other clothing to protect people against pests (e.g., mosquitoes, ticks). Pests contacting the surface of permethrin-treated clothing (PTC) are repelled and/or killed, depending on the dose and duration of exposure. Hence, it is important to assess the amount of permethrin on the surface of clothing. Fabric swatches prepared using two commercially available permethrin treatments (Insect Shield® & Sawyer Repellant) and one laboratory created treatment (4g permethrin/L) were tested. A Martindale Abrasion and Pilling Tester (MAPT) and gas chromatography were used to assess surface permethrin content (SPC) and total permethrin content (TPC). Sawyer PTC had the highest SPC (mean ± standard error) (32.68±14.55µg/g), followed by Insect Shield® (23.35±2.71µg/g) and lab-created 4g/L permethrin (8.7±0.78µg/g). SPC (after 1000 rubs on MAPT) for Insect Shield®, Sawyer, and 4g/L permethrin groups was significantly lower than TPC (P=0.011, P<0.001, and P=0.001, respectively). The SPC/TPC relationship varied widely between permethrin treatment methods and practical implications for this are discussed. Mosquito repellency tests indicate that Insect Shield®, Sawyer, and lab-created (4g/L) permethrin-treated fabrics showed a significantly higher repellency rate than control (untreated) fabrics (P=0.001, P<0.0001, P<0.0001, respectively). While Insect Shield® had the highest repellency rate against susceptible (53%) and exposed (48%) mosquitoes, differences between groups were not significant. Repellency rates indicate SPC plus other factors (e.g. treatment method) may contribute to mosquito repellency and should be considered in risk assessments for protection against pests.

Assessing Durability and Safety of Permethrin Impregnated Uniforms Used by Outdoor Workers to Prevent Tick Bites after One Year of Use.

Long lasting permethrin-impregnated (LLPI) clothing can retain permethrin and repel ticks for up to three months and without exceeding EPA-approved safe levels; however, little is known about longer term effects of wearing LLPI clothing. Here, permethrin content was measured in new forester pants soon after initial impregnation (Insect Shield) and again one year later after being repeatedly worn by foresters in the field. Urine samples were collected from foresters for biomonitoring of permethrin metabolites at multiple time intervals (pre-use, one-month, three-to-four-months, and one-year post-use). Lethality against nymphal Ixodes scapularis Say was measured in clothing after one year of wear by foresters. Furthermore, to test potential variability in permethrin impregnation of different batches of clothing, separate sets of clothing were anonymously sent to Insect Shield for permethrin treatment over a period of three months and permethrin was quantified. Results demonstrated 33% of participants' pants had no measurable permethrin after one year of wear and permethrin content and tick mortality varied significantly between clothing. Only two of the participants' clothing resulted in ≥ 30% tick mortality after one year of wear. Significant differences were observed in 3-PBA and trans-DCCA, but not cis-DCCA metabolites in participants over the four measured time points and were higher than general United States population levels. This study provides practical information on the safety (measured by urinary metabolites) over time of LLPI clothing. It also provides snapshots (pre-washing and after one year of wear) of effectiveness of LLPI clothing as personal protective equipment against ticks for outdoor workers.

Permethrin Content in Textiles Affecting Mosquito Repellency Efficiency

Permethrin Content in Textiles Affecting Mosquito Repellency Efficiency

Assessing the impact of the addition of pyriproxyfen on the durability of permethrin-treated bed nets in Burkina Faso: a compound-randomized controlled trial

BackgroundLong-lasting insecticidal nets (LLINs) treated with pyrethroids are the foundation of malaria control in sub-Saharan Africa. Rising pyrethroid resistance in vectors, however, has driven the development of alternative net formulations. Here the durability of polyethylene nets with a novel combination of a pyrethroid, permethrin, and the insect juvenile hormone mimic, pyriproxyfen (PPF), compared to a standard permethrin LLIN, was assessed in rural Burkina Faso.MethodsA compound-randomized controlled trial was completed in two villages. In one village 326 of the PPF-permethrin nets (Olyset Duo) and 327 standard LLINs (Olyset) were distributed to assess bioefficacy. In a second village, 170 PPF-permethrin nets and 376 LLINs were distributed to assess survivorship. Nets were followed at 6-monthly intervals for 3 years. Bioefficacy was assessed by exposing permethrin-susceptible and resistant Anopheles gambiae sensu lato mosquito strains to standard World Health Organization (WHO) cone and tunnel tests with impacts on fertility measured in the resistant strain. Insecticide content was measured using high-performance liquid chromatography. LLIN survivorship was recorded with a questionnaire and assessed by comparing the physical integrity using the proportionate hole index (pHI).ResultsThe PPF-permethrin net met WHO bioefficacy criteria (≥ 80% mortality or ≥ 95% knockdown) for the first 18 months, compared to 6 months for the standard LLIN. Mean mosquito mortality for PPF-permethrin nets, across all time points, was 8.6% (CI 2.6–14.6%) higher than the standard LLIN. Fertility rates were reduced after PPF-permethrin net exposure at 1-month post distribution, but not later. Permethrin content of both types of nets remained within the target range of 20 g/kg ± 25% for 242/248 nets tested. The pyriproxyfen content of PPF-permethrin nets declined by 54%, from 10.4 g/kg (CI 10.2–10.6) to 4.7 g/kg (CI 3.5–6.0, p < 0.001) over 36 months. Net survivorship was poor, with only 13% of PPF-permethrin nets and 12% of LLINs still present in the original household after 36 months. There was no difference in the fabric integrity or survivorship between the two net types.ConclusionThe PPF-permethrin net, Olyset Duo, met or exceeded the performance of the WHO-recommended standard LLIN (Olyset) in the current study but both net types failed the 3-year WHO bioefficacy criteria.

Comparative evaluation of an improved test method for bioefficacy of insecticidal fabrics against dengue and malaria vectors

BackgroundInsecticidal fabrics are important personal protective measures against mosquitoes, ticks and other disease vectors. In the absence of internationally accepted guidelines, bioefficacy tests have been carried out using continuous exposure and three minutes exposure bioassay methods. Recently, we have reported an improved method for bioefficacy testing of insecticidal fabrics, which involves continuous exposure of mosquitoes to the test fabrics. The present paper reports the comparative evaluation of the outcomes of the continuous exposure bioassay and the three minutes bioassay on the same fabric samples.MethodsPermethrin content in the treated fabric samples was determined through HPLC analysis and NMR studies were performed to establish the stability of the analyte. Bioefficacy tests were carried out against dengue vector Aedes aegypti and malaria vector Anopheles stephensi as per the improved test method and the three minutes bioassay method.ResultsThe permethrin doses in the fabric samples ranged from 60 to 3000 mg/m2 and 36.2% of permethrin was retained after 10 washings. The extraction and chromatographic analysis were not found to affect the stability of permethrin. In continuous exposure, all fabric samples showed bioefficacy, as the mean complete knockdown time for both Ae. aegypti (10.5–34.5 min) and An. stephensi (14.5–36.8 min) was ≤ 71.5 min. The same samples were found to be not effective when tested using the three minutes bioassay method, since the knockdown and mortality percentages were well below the required bioefficacy values. The bioefficacy of the fabric samples in terms of complete knockdown time was significantly higher against Ae. aegypti in comparison to An. stephensi. The mean complete knockdown time of Ae. aegypti increased to 48.3 min after 10 washings indicating a significant reduction in bioefficacy.ConclusionsBioefficacy testing of the insecticidal fabrics using the improved method resulted in outcomes, which could be correlated better with the permethrin content in the fabric samples. The improved method is more appropriate for the testing of insecticidal fabrics than the three minutes bioassay method. Further evaluation of the improved method using different test arthropods could help in the formulation of specific guidelines for the bioefficacy testing of insecticidal fabrics.

Bioabsorption and effectiveness of long-lasting permethrin-treated uniforms over three months among North Carolina outdoor workers

BackgroundVector-borne diseases are an important cause of morbidity and mortality in the USA. Effective, convenient prevention methods are needed. Long-lasting permethrin-impregnated (LLPI) clothing can prevent tick bites, however, additional information is needed on the real-world effectiveness and safety of this preventative measure.MethodsIn this pilot study, we recruited state and county park employees from North Carolina to wear LLPI uniforms for three months during the summer of 2016. We collected spot urine samples for biomonitoring of permethrin metabolites at one week, one month and three months after first use of the LLPI uniform. Following three months of wear, we collected pants and socks and analyzed them for permethrin content and mortality to ticks and mosquitoes.ResultsThirteen park employees were included in the analysis. Bioactive amounts of permethrin remained in all clothing swatches tested, although there was great variability. Tick mortality was high, with 78% of pant and 88% of sock swatches having mean knockdown percentages ≥ 85%. In contrast, mosquito mortality was low. Over the study period, the absorbed dosage of permethrin averaged < 4 μg/kg/d of body weight based on measurements of three metabolites.ConclusionsLLPI clothing retained permethrin and bioactivity against ticks after three months of use in real-world conditions. The estimated absorbed dosage of permethrin was well below the U.S. EPA level of concern, suggesting that LLPI clothing can be used safely by outdoor workers for tick bite prevention.

ЭФФЕКТИВНОСТЬ ЭЛВЕСТИНА И МИКСОВИТА А ПРИ ОТРАВЛЕНИИ ПЕРМЕТРИНОМ

The results of the study of the action of complex drugs for animals – elvestin and mixovit A under the conditions of subchronic intoxication with permethrin are presented. The drug elvestin in a therapeutic dose in giving it to the diet of white rats showed a weak protective effect. Mixovit A did not improve the parameters (clinical and biochemical blood tests, residual permethrin content in organs and tissues), on contrary, a tendency to increase the content of residual quantities of pyrethroid in organs and tissues was marked.

Durability of Olyset campaign nets distributed between 2009 and 2011 in eight districts of Tanzania.

BackgroundLong-lasting insecticidal nets (LLINs) are the first line choice for malaria vector control in sub-Saharan Africa, with most countries adopting universal coverage campaigns. However, there is only limited information on LLIN durability under user conditions. Therefore, this study aimed to assess the durability of Olyset® LLINs distributed during campaigns between 2009 and 2011 in Tanzania.MethodsA retrospective field survey was conducted in eight districts in Tanzania mainland to assess the durability of Olyset campaign nets. Household questionnaires were used to assess attrition, i.e. net loss. All nets remaining in households were collected. A sub-sample of 198 Olyset campaign nets was examined for bio-efficacy against Anopheles gambiae s.s. mosquitoes, permethrin content and physical integrity following standard World Health Organization (WHO) methods.ResultsOf 6067 campaign nets reported to have been received between 2009 and 2011, 35 % (2145 nets) were no longer present. Most of those nets had been discarded (84 %) mainly because they were too torn (94 %). Of the 198 sub-sampled Olyset LLINs, 61 % were still in serviceable physical condition sufficient to provide personal protection while 39 % were in unserviceable physical condition according to WHO proportionate Hole Index (pHI). More than 96 % (116/120) of nets in serviceable condition passed WHO bioefficacy criteria while all nets in unserviceable condition passed WHO bioefficacy criteria. Overall mean permethrin content was 16.5 g/kg (95 % CI 16.2–16.9) with 78 % of the sub-sampled nets retaining recommended permethrin content regardless of their age or physical condition. Nets aged 4 years and above had a mean permethrin content of 14 g/kg (95 % CI 12.0–16.0). The only statistically significant predictor of reduced physical net integrity was rats in the house.ConclusionsTwo-to-four years after a mass campaign, only 39 % of distributed nets remain both present and in serviceable physical condition, a functional survival considerably below WHO assumptions of 50 % survival of a ‘three-year’ net. However, the majority of nets still retained substantial levels of permethrin and could still be bio-chemically useful against mosquitoes if their holes were repaired, adding evidence to the value of net care and repair campaigns.

Development of an Insect Repellent Spray for Textile Based on Permethrin-Loaded Lipid-Core Nanocapsules.

The aim of this study was to prepare and characterize permethrin-loaded lipid core nanocapsules (P-LNC) in order to produce a long last insect repellent spray formulation for clothes. P-LNC were prepared by self-assembling in aqueous solution showing a mean diameter of 201 +/- 4 nm with a monomodal distribution, a permethrin content of 4.6 +/- 0.1 mg/mL and zeta potential of--16.7 +/- 4 mV. P-LNC (0.46%), as well as the commercial product (0.46%) and the hydroalcoholic solution (0.50%) of permethrin were separately sprayed onto cotton or polyester, followed by successive washes of the fabric. The results showed that the fabrics treated with P-LNC are more resistant than other solutions in terms of remaining permethrin content. After twenty washes, the cotton treated with P-LNC, presented a concentration of 566 +/- 27 mg/M2 of impregnated permethrin, while for the treatment with the substance hydroalcoholic solution and with the commercial product the concentrations values were of 340 +/- 7 mg/M2 and 224 +/- 74 mg/M2, respectively. When the test was performed using polyester, this fiber was less adhesive than cotton, resulting in a final concentration of permethrin (after 20 washes) of 81 +/- 10 mg/m2 for P-LNC suspension, 94 +/- 8 mg/M2 for the substance hydroalcoolic solution and 22 +/- 3 mg/M2 for the commercial product. After impregnating cotton with the formulations and submitting to a temperature of 200 degrees C, the P-LNC also demonstrated higher adherence compared to the other formulations (407 +/- 67 mg/m2 for P-LNC, 236 +/- 72 mg/m2 for the substance hydroalcoholic solution and 158 +/- 62 mg/m2 for commercial product). These results showed that the repellent spray composed of P-LNC developed in this work is a promising and innovative product for the individual protection against insects, useful for impregnation onto cotton garments.

Bioactivity and laundering resistance of five commercially available, factory-treated permethrin-impregnated fabrics for the prevention of mosquito-borne diseases: the need for a standardized testing and licensing procedure

Personal protective measures against hematophagous vectors constitute the first line of defense against arthropod-borne diseases. In this regard, a major advance has been the development of residual insecticides that can be impregnated into clothing. Currently, however, information on specific treatment procedures, initial insecticide concentrations, arthropod toxicity, residual activity, and laundering resistance is either fragmentary or non-existent, and no World Health Organization Pesticides Evaluation Scheme or other guidelines exist for the standardized testing and licensing of insecticide-treated clothing. The aim of this study was to analyze the insecticide content, contact toxicity, laundering resistance, and residual activity of five commercially available and commonly used permethrin-treated fabrics-Insect Shield, ExOfficio, Sol's Monarch T-shirts, battle dress uniforms (BDUs), and Labonal socks-against vector-competent Aedes aegypti, Anopheles stephensi, and Culex pipiens mosquitoes under laboratory conditions. Prior to laundering, permethrin concentrations ranged from 4300 to 870 mg/m(2) whereas, after 100 defined machine launderings, the remaining permethrin content fell to between 1800 and 20 mg/m(2), a percentage permethrin loss of 58.1 to 98.5 %. The highest 99 % knockdown (KD99) efficacy of permethrin was detected in Ae. aegypti, followed by An. stephensi and Cx. pipiens demonstrating that Ae. aegypti is the most sensitive species and Cx. pipiens the least sensitive. After 100 launderings, the remaining biocidal efficacy differed markedly among the five brands, with KD99 times varying from 38.8 ± 2.9 to >360 min for Ae. aegypti, from 44 ± 3.5 to >360 min for An. stephensi, and from 98 ± 10.6 to >360 min for Cx. pipiens. Overall, the ranking of the residual biocidal efficacies within the five brands tested was as follows: BDU ≈ Labonal > Sol's Monarch > ExOfficio > Insect Shield. When applying German Armed Forces licensing conditions, none of the four products available in the civilian market would completely meet all the necessary efficacy and safety requirements fulfilled by BDUs. Therefore, we strongly recommend standardized testing and licensing procedures for insecticide-treated clothing, with defined cutoff values for initial maximum and post-laundering minimum concentrations of permethrin as well as figures for permethrin migration rates, arthropod toxicity, homogeneity on fabrics, residual activity, and laundering resistance.

Permethrin-Treated Clothing as Protection against the Dengue Vector, Aedes aegypti: Extent and Duration of Protection.

IntroductionDengue transmission by the mosquito vector, Aedes aegypti, occurs indoors and outdoors during the day. Personal protection of individuals, particularly when outside, is challenging. Here we assess the efficacy and durability of different types of insecticide-treated clothing on laboratory-reared Ae. aegypti.MethodsStandardised World Health Organisation Pesticide Evaluation Scheme (WHOPES) cone tests and arm-in-cage assays were used to assess knockdown (KD) and mortality of Ae. aegypti tested against factory-treated fabric, home-dipped fabric and microencapsulated fabric. Based on the testing of these three different treatment types, the most protective was selected for further analysis using arm-in cage assays with the effect of washing, ultra-violet light, and ironing investigated using high pressure liquid chromatography.ResultsEfficacy varied between the microencapsulated and factory dipped fabrics in cone testing. Factory-dipped clothing showed the greatest effect on KD (3 min 38.1%; 1 hour 96.5%) and mortality (97.1%) with no significant difference between this and the factory dipped school uniforms. Factory-dipped clothing was therefore selected for further testing. Factory dipped clothing provided 59% (95% CI = 49.2%– 66.9%) reduction in landing and a 100% reduction in biting in arm-in-cage tests. Washing duration and technique had a significant effect, with insecticidal longevity shown to be greater with machine washing (LW50 = 33.4) compared to simulated hand washing (LW50 = 17.6). Ironing significantly reduced permethrin content after 1 week of simulated use, with a 96.7% decrease after 3 months although UV exposure did not reduce permethrin content within clothing significantly after 3 months simulated use.ConclusionPermethrin-treated clothing may be a promising intervention in reducing dengue transmission. However, our findings also suggest that clothing may provide only short-term protection due to the effect of washing and ironing, highlighting the need for improved fabric treatment techniques.

Nanogels with High Active β-Cyclodextrin Content as Physical Coating System with Sustained Release Properties

We present the application of nanogels with high functional β-cyclodextrin (β-CD) content as new and versatile method for the modification and protection of textiles. The complexation potential of covalently embedded β-CD in nanogels is demonstrated for the common insecticide permethrin in aqueous environment. It is shown that permethrin containing β-CD nanogels can be applied easily, homogeneously and safely on keratin fibers like wool fabrics and human hairs. The permethrin concentration on fibers is directly controlled by the permethrin content in nanogels. We tested the permanence of permethrin on treated fibers with regard to washing and UV fastness. Our results show that permethrin complexed in nanogels is removed from the textile during washing, but that the complexation of permethrin by β-CD domains in the nanogels protects the active ingredient from UV degradation. Bioassay tests against the larvae of Tineola bisselliella and Anthrenocerus australis show that the activity of the ingredients does not decrease after complexation in β-CD gels and it results in protection of the wool fibers against degradation by the insect larvae.

Field evaluation of permethrin long-lasting insecticide treated nets (Olyset®) for malaria control in an endemic area, southeast of Iran

Long lasting insecticide treated nets (LLINs) have been advocated as an effective tool for prevention and control of malaria. Olyset net was the first LLINs which became commercially available and obtained WHO approval. According to the national strategic plan on evaluation of Olyset net, a field trial was conducted to determine the efficacy of these nets against malaria vectors in an endemic area in the southeast of Iran.Fourteen villages with similar topographical and epidemiological situations were selected and randomly assigned to two clusters of the study: Olyset net and untreated net. Distribution of nets was carried out to cover 100% of the population in Olyset net and untreated net cluster.Anopheline mosquitoes were collected monthly using different WHO standard methods in both areas to determine their abundance, feeding pattern and resting behaviour. Human blood index was determined using ELISA test. Additionally, Olyset nets were evaluated for their biological activity using WHO cone bioassay test by susceptible colony of Anopheles stephensi (Beech strain) and then for insecticide residues by employing high performance thin layer chromatography. Malaria incidence was measured by passive and active case detection from all study population.In total 2115 adult anopheline mosquitoes were collected and identified using morphological characters. They comprised of seven species: Anopheles dthali (Liston), A. culicifacies (Giles), A. stephensi (Liston), A. superpictus (Grassi), A.fluviatilis (James), A. moghulensis (Christophers) and A. turkhudi (Liston). A. dthali, A. culicifacies and A. stephensi were most prevalent species in both areas.In the Olyset net study area, there was a significant reduction of 41.1%, 54.4%, 59.39% and 64.1% in the indoor-resting density of A. culicifacies, A. stephensi, A. dthali and A. superpictus, respectively, with an overall reduction of 39.3% in total mosquitoes in comparison with untreated net area. A significant reduction was also observed in human blood index of vector species in the Olyset net villages. Bioefficacy test results of Olyset nets showed that the median knockdown time was 1.48 and 3.25min, while the average mortality rate was 100% and 72.3%±7.07 in baseline and after 1 year of intervention, respectively. The average permethrin content reached to 68.31% (683.1mg/m2) of the initial insecticide dose of 937±21.69mg/m2 (nearly 1000mg/m2) at the end of intervention.Malaria incidence was reduced by 96.6% and 64.8% in the village with Olyset nets and in the villages with untreated nets, respectively. During intervention period, there was a reduction of 93.2% in malaria incidence in Olyset net area as compared to the untreated area.This study indicated that Olyset nets have a major impact on malaria vectors and disease burden; therefore it could be recommended as an effective personal protection tool for malaria control in malarious areas.

Development of a Multianalyte Enzyme-Linked Immunosorbent Assay for Permethrin and Aroclors and Its Implementation for Analysis of Soil/Sediment and House Dust Extracts

Development of a multianalyte enzyme-linked immunosorbent assay (ELISA) for detection of permethrin and aroclors 1248 or 1254 and implementation of the assay for analysis of soil/sediment samples are described. The feasibility of using the multianalyte ELISA to monitor aroclors 1254 and permethrin simultaneously was tested with permethrin and aroclor standards and with aroclor- and permethrin-containing soil/sediment and house dust samples. Comparison of the I₅₀ and I₂₀ values of the multianalyte with those of a single-analyte assay revealed similar results, and multianalyte ELISA determination of analyte amounts in soil/sediment dust samples yielded similar results to those of a single-analyte assay. A single-analyte assay of permethrin content in permethrin-containing dust samples showed that the ELISA can determine the analyte accurately in samples with dust matrix contents ranging from 6.25 to 100 mg as indicated by the good correlation between the results of the immunoassay and those of the gas chromatography analysis.

Screen-printed acetylcholinesterase-based biosensors for inhibitive determination of permethrin

An amperometric assay based on acetylcholinesterase (AChE) inactivation has been developed for the monitoring of permethrin using a screen-printed three-electrode system. The enzyme AChE catalyzes the hydrolysis of acetylthiocholine to thiocholine, which can be electrochemically oxidized. The presence of permethrin inhibits the AChE activity, resulting in a lower thiocholine production and thus, a decrease in the amperometric oxidation current. Immobilization of AChE was performed by cross-linking giving a capability of detection of 8.1±0.4μM. Repeatability and reproducibility of the developed AChE biosensor were also calculated, yielding values of 9.6% (n=4) and 5.4% (n=5), respectively related to the slopes of the calibration curves performed in the range from 6.2 up to 41μM. The method was successfully applied to the determination of permethrin content in a commercial lice gel.

The impact of permethrin-impregnated bednets on malaria vectors of the Kenyan coast.

The effects of introducing permethrin-impregnated bednets on local populations of the malaria vector mosquitoes Anopheles funestus and the An.gambiae complex was monitored during a randomized controlled trial at Kilifi on the Kenyan coast. Pyrethrum spray collections: inside 762 households were conducted between May 1994 and April 1995 after the introduction of bednets in half of the study area. All-night human bait collections were performed in two zones (one control and one intervention) for two nights each month during the same period. PCR identifications of An.gambiae sensu lato showed that proportions of sibling species were An.gambiae sensu stricto > An.merus > An.arabiensis. Indoor-resting densities of An.gambiae s.l. and the proportion of engorged females decreased significantly in intervention zones as compared to control zones. However, the human blood index and Plasmodium falciparum sporozoite rate remained unaffected. Also vector parous rates were unaltered by the intervention, implying that survival rates of malaria vectors were not affected. The human-biting density of An.gambiae s.l., the predominant vector, was consistently higher in the intervention zone compared to the control zone, but showed 8% reduction compared to pre-intervention biting rates-versus 94% increase in the control zone. Bioassay, susceptibility and high-performance liquid chromatography results all indicated that the permethrin content applied to the nets was sufficient to maintain high mortality of susceptible vectors throughout the trial. Increased rates of early outdoor-biting, as opposed to indoor-biting later during the night, were behavioural or vector composition changes associated with this intervention, which would require further monitoring during control programmes employing insecticide-treated bednets.

Observations on Anopheles gambiae Giles s.l. (Diptera: Culicidae) during a trial of permethrin-treated bed nets in The Gambia

AbstractIn a Gambian village, the peak collections of females of the complex of Anopheles gambiae Giles occurred three months after the onset of the heaviest rains; 32% of these were A. melas Theobald, and 54% of blood-meals were identified as originating from man. Counts of A. gambiae s.l. in rooms containing permethrin-treated bed nets were compared with those in rooms containing placebo-treated nets. The numbers in the permethrin-treated nets were far lower than in placebo-treated nets. A higher rate of exophily was noted in rooms containing permethrin-treated nets. The numbers of unfed A. gambiae s.l. found inside the rooms with placebo-treated nets were significantly higher than those with permethrin-treated nets. However, the proportion fed and the mortality in the exit traps were not significantly affected by permethrin treatment. Three-minute bioassays conducted on four different fabric types impregnated at the same concentration showed that the toxicity varied between the fabrics. Handwashing severely reduced the toxicity and approximately halved the permethrin content. Bed nets are frequently washed in Gambian villages, and this could be a problem in the application of permethrin impregnation of bed nets for vector control. Methods are discussed to overcome this problem at the village level.

LEAF RESIDUE COMPARTMENTALIZATION AND EFFICACY OF PERMETHRIN APPLIED TO SOYBEAN

Permethrin (EC, 0.084 kg AI/ha) was applied to soybean by backpack sprayer and eight determinations of leaf residue compartmentalization and insect mortality were made during the 27 days following application. After 6 days, 40% of the initial surface permethrin residue remained; after 27 days, 8% of the initial residue was left. Below-surface residues almost tripled in the first 4 days after application and then remained at about the same level thereafter. The surface residues disappeared with a half life of 7.7 days, whereas total leaf permethrin content persisted with a half life of 13.9 days. The observed insect control correlated with the known feeding habits of the insects. Velvetbean caterpillar, Anticarsia gemmatalis Hübner, which by feeding on foliage is exposed to total leaf insecticide content, was controlled for the entire investigation. Threecornered alfalfa hopper, Spissistilus festinus (Say), which feeds on petioles and peduncles, was controlled for at least the first 4 days after application. The number of southern green, Nezara viridula (L.), and green, Acrosternum hilare (Say), stink bugs, which feed on pods, also stayed below the check for at least 4 days after treatment. Thus the leaf permethrin content appeared to be available for effective control of threecornered alfalfa hopper and the stink bugs for ca. 0.5 half life of the residues on the surface, even though after this time surface residues were still measurable.