Synergist Piperonyl Butoxide Research Articles

Mobility of Stored Product Beetles after Exposure to a Combination Insecticide Containing Deltamethrin, Methoprene, and a Piperonyl Butoxide Synergist Depends on Species, Concentration, and Exposure Time.

Adults of Rhyzopertha dominica (F.), the lesser grain borer, Cryptolestes ferrugineus (Stephens), the rusty grain beetle, and Sitophilus oryzae (L.), the rice weevil, were exposed for 1, 24, and 72 h on wheat treated with concentrations of 0% (untreated controls) to 100% of the proposed label rate of an experimental formulation of deltamethrin + Methoprene + piperonyl butoxide synergist. Movement and velocity of movement were assessed after each exposure time using a camera-based monitoring system (Ethovision®). Movement of R. dominica decreased with increasing concentration and exposure time, so that movement had virtually ceased at the 48 and 72 h exposures. Cryptolestes ferrugineus was less susceptible compared to R. dominica, but there was still a general pattern of decreased movement and velocity of movement with increasing concentration and exposure time. Sitophilus oryzae was the least susceptible species, with less differences at the 1 h exposure interval compared to the other two species, but after 24–72 h, the patterns of declining movement and velocity were apparent as the concentration increased. Data were analyzed using curve-fit equations to show the relationship between concentration and exposure time for each species. Results show that the Ethovison system can be used to assess the sub-lethal effects of exposure to grain protectant insecticides and elucidate behavioral variation between different stored product insects.

Dietary exposure to pesticide residues and associated health risks in infants and young children – Results of the French infant total diet study

A total diet study (TDS) was undertaken to estimate the chronic dietary exposure to pesticide residues and health risks for the French infants and young children below 3 years old. As a whole, 516 pesticides and metabolites were analysed in 309 food composite samples including 219 manufactured baby foods and 90 common foods, which cover 97% of infants and young children's diet. These composite samples were prepared using 5,484 food products purchased during all seasons from 2011 to 2012 and processed as consumed. Pesticide residues were detected in 67% of the samples and quantified in 27% of the baby food samples and in 60% of the common foods. Seventy-eight different pesticides were detected and 37 of these quantified at levels ranging from 0.02 to 594 µg/kg. The most frequently detected pesticides (greater than 5% samples) were (1) the fungicides 2-phenylphenol, azoxystrobin, boscalid, captan and its metabolite tetrahydrophthalimide, carbendazim, cyprodinil, difenoconazole, dodine, imazalil, metalaxyl, tebuconazole, thiabendazole, (2) the insecticides acetamiprid, pirimiphos-methyl and thiacloprid, (3) the herbicide metribuzin and (4) the synergist piperonyl butoxide. Dietary intakes were estimated for each of the 705 individuals studied and for 431 pesticides incl. 281 with a toxicological reference value (TRV). In the lower-bound scenario, which tends to underestimate the exposure, the TRV were never exceeded. In the upper-bound scenario that overestimates exposure, the estimated intakes exceeded the TRV for dieldrin and lindane (two persistent organic pollutants) and propylene thiourea, a metabolite of propineb. For these three substances, more sensitive analyses are needed to refine the assessment. For 17 other detected and/or prioritised pesticides, the risk could not be characterised due to the lack of a valid TRV, of certain food analyses or the absence of analytical standards for their metabolites.

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.

A survey of Anopheles species composition and insecticide resistance on the island of Bubaque, Bijagos Archipelago, Guinea-Bissau

BackgroundBubaque is the most populous island of the Bijagos archipelago, a group of malaria-endemic islands situated off the coast of Guinea-Bissau, West Africa. Malaria vector control on Bubaque relies almost exclusively on the use of long-lasting insecticidal nets (LLINs). However, there is little information on local vector bionomics and insecticide resistance.MethodsA survey of mosquito species composition was performed at the onset of the wet season (June/July) and the beginning of the dry season (November/December). Sampling was performed using indoor adult light-traps and larval dipping. Anopheles mosquitoes were identified to species level and assessed for kdr allele frequency by TaqMan PCR. Females were analysed for sporozoite positivity by CSP-ELISA. Resistance to permethrin and α-cypermethrin was measured using the CDC-bottle bioassay incorporating the synergist piperonyl-butoxide.ResultsSeveral Anopheles species were found on the island, all belonging to the Anopheles gambiae sensu lato (s.l.) complex, including An. gambiae sensu stricto, Anopheles coluzzii, Anopheles melas, and An. gambiae/An. coluzzii hybrids. Endophagic Anopheles species composition and abundance showed strong seasonal variation, with a majority of An. gambiae (50% of adults collected) caught in June/July, while An. melas was dominant in November/December (83.9% of adults collected). Anopheles gambiae had the highest sporozoite rate in both seasons, with infection rates of 13.9% and 20% in June/July and November/December, respectively. Moderate frequencies of the West African kdr allele were found in An. gambiae (36%), An. coluzzii (35%), An. gambiae/An. coluzzii hybrids (42%). Bioassays suggest moderate resistance to α-cypermethrin, but full susceptibility to permethrin.ConclusionsThe island of Bubaque maintained an An. gambiae s.l. population in both June/July and November/December. Anopheles gambiae was the primary vector at the onset of the wet season, while An. melas is likely to be responsible for most dry season transmission. There was moderate kdr allele frequency and synergist assays suggest likely metabolic resistance, which could reduce the efficacy of LLINs. Future control of malaria on the islands should consider the seasonal shift in mosquito species, and should employ continuous monitoring for insecticide resistance.

Evaluation of an alpha-cypermethrin\u2009+\u2009PBO mixture long-lasting insecticidal net VEERALIN\xae LN against pyrethroid resistant Anopheles gambiae s.s.: an experimental hut trial in M\u2019b\xe9, central C\xf4te d\u2019Ivoire

BackgroundLong-lasting insecticidal nets (LLINs) are the primary method of malaria prevention. However, the widespread resistance to pyrethroids among major malaria vector species represents a significant threat to the continued efficacy of pyrethroid LLIN. Piperonyl butoxide (PBO) is a synergist that inhibits the activity of metabolic enzymes of the cytochrome P450 family known to detoxify insecticides including pyrethroids. Synergist LLIN incorporating PBO and a pyrethroid may provide improved control compared to pyrethroid-only LLIN.MethodsThe efficacy of VEERALIN® LN (VKA polymers Pvt Ltd, India), an alpha-cypermethrin PBO synergist net was evaluated in experimental huts in M’bé, central Côte d’Ivoire against wild pyrethroid resistant Anopheles gambiae s.s. Comparison was made with a standard alpha-cypermethrin-treated net (MAGNet® LN, VKA polymers Pvt Ltd, India). Nets were tested unwashed and after 20 standardized washes.ResultsVEERALIN® LN demonstrated improved efficacy compared to MAGNet® LN against wild free-flying pyrethroid-resistant An. gambiae s.s. Before washing, VEERALIN® LN produced mortality of An. gambiae s.s. (51%) significantly higher than the standard pyrethroid-only net (29%) (P < 0.0001). Although there was a significant reduction in mortality with both LLINs after 20 washes, VEERALIN® LN remained superior in efficacy to MAGNet® LN (38 vs 17%) (P < 0.0001). Blood-feeding was significantly inhibited with both types of insecticide-treated nets relative to the untreated control net (P < 0.0001). Unwashed VEERALIN® LN induced significantly higher blood-feeding inhibition of An. gambiae s.s. (62.6%) compared to MAGNet® LN (35.4%) (P < 0.001). The difference persisted after washing, as there was no indication that either LLIN lost protection against biting or blood-feeding. The level of personal protection derived from the use of VEERALIN® LN was high (87%) compared to MAGNet® LN (66–69%) whether unwashed or washed. The AI content of VEERALIN® LN after 20 washes decreased from 6.75 to 6.03 g/kg for alpha-cypermethrin and from 2.95 to 2.64 g/kg for PBO, corresponding to an overall retention of 89% for each compound.ConclusionsThe addition of the synergist PBO to pyrethroid net greatly improved protection and control of pyrethroid-resistant An. gambiae s.s. The pyrethroid-PBO VEERALIN® LN has the potential to reduce transmission in areas compromised by pyrethroid resistance.

Characterisation of Anopheles strains used for laboratory screening of new vector control products

BackgroundInsecticides formulated into products that target Anopheles mosquitos have had an immense impact on reducing malaria cases in Africa. However, resistance to currently used insecticides is spreading rapidly and there is an urgent need for alternative public health insecticides. Potential new insecticides must be screened against a range of characterized mosquito strains to identify potential resistance liabilities. The Liverpool School of Tropical Medicine maintains three susceptible and four resistant Anopheles strains that are widely used for screening for new insecticides. The properties of these strains are described in this paper.MethodsWHO tube susceptibility bioassays were used for colony selection and to screen for resistance to the major classes of public health insecticides. Topical and tarsal contact bioassays were used to produce dose response curves to assess resistance intensity. Bioassays with the synergist piperonyl butoxide were also performed. Taqman™ assays were used to screen for known target site resistance alleles (kdr and ace-1). RT-qPCR was used to quantify expression of genes associated with pyrethroid resistance.ResultsPyrethroid selection pressure has maintained resistance to this class in all four resistant strains. Some carbamate and organophosphate resistance has been lost through lack of exposure to these insecticide classes. The Anopheles gambiae (sensu lato) strains, VK7 2014, Banfora M and Tiassalé 13 have higher levels of pyrethroid resistance than the An. funestus FUMOZ-R strain. Elevated expression of P450s is found in all four strains and the 1014F kdr mutation is present in all three An. gambiae strains at varying frequencies. Tarsal contact data and overexpression of CYP4G16 and SAP2 suggest penetration barriers and/or sequestration also confer resistance in Banfora M.ConclusionsContinual selection with deltamethrin has maintained a stable pyrethroid-resistant phenotype over many generations. In conjunction with a standardized rearing regime, this ensures quality control of strains over time allowing for robust product comparison and selection of optimal products for further development. The identification of multiple mechanisms underpinning insecticide resistance highlights the importance of screening new compounds against a range of mosquito strains.

Fast emerging insecticide resistance in Aedes albopictus in Guangzhou, China: Alarm to the dengue epidemic.

Dengue is one of the most serious mosquito-borne infectious diseases in the world. Aedes albopictus is the most invasive mosquito and one of the primary vectors of dengue. Vector control using insecticides is the only viable strategy to prevent dengue virus transmission. In Guangzhou, after the 2014 pandemic, massive insecticides have been implemented. Massive insecticide use may lead to the development of resistance, but few reports are available on the status of insecticide resistance in Guangzhou after 2014. In this study, Ae. albopictus were collected from four districts with varied dengue virus transmission intensity in Guangzhou from 2015 to 2017. Adult Ae. albopictus insecticide susceptibility to deltamethrin (0.03%), permethrin(0.25%), DDT(4%), malathion (0.8%) and bendiocarb (0.1%) was determined by the standard WHO tube test, and larval resistance bioassays were conducted using temephos, Bacillus thuringiensis israelensis (Bti), pyriproxyfen (PPF) and hexaflumuron. Mutations at the voltage-gated sodium channel (VGSC) gene and acetylcholinesterase (AChE) gene were analyzed. The effect of cytochrome P450s on the resistance of Ae. albopictus to deltamethrin was tested using the synergistic agent piperonyl butoxide (PBO). The results showed that Ae. albopictus populations have rapidly developed very high resistances to multiple commonly used insecticides at all study areas except malathion, Bti and hexaflumuron. We found 1534 codon mutations in the VGSC gene that were significantly correlated with the resistance to pyrethroids and DDT, and 11 synonymous mutations were also found in the gene. The resistance to deltamethrin can be significantly reduced by PBO but may generated cross-resistance to PPF. Fast emerging resistance in Ae. albopictus may affect mosquito management and threaten the prevention and control of dengue, similar to the resistance in Anopheles mosquitoes has prevented the elimination of malaria and call for timely and guided insecticide management.

Knockdown of NADPH-cytochrome P450 reductase and CYP6MS1 increases the susceptibility of Sitophilus zeamais to terpinen-4-ol

Terpinen-4-ol showed highly insecticidal activity to stored-grain pest Sitophilus zeamais, and cytochrome P450s were strongly induced in response to terpinen-4-ol fumigation. Understanding of the function of P450 enzyme system in the susceptibility to terpinen-4-ol in S. zeamais will benefit the potential application of terpinen-4-ol in controlling stored-grain pests. In the present study, the synergist piperonyl butoxide increased the toxicity of terpinen-4-ol to S. zeamais, with a synergism ratio of 3.5-fold. Two isoforms of NADPH-cytochrome P450 reductase (SzCPR) were identified, with the difference at the N-terminal. SzCPR contained an N-terminal membrane anchor, FMN, FAD, and NADP binding domains. Expression levels of SzCPR were upregulated by tea tree oil (TTO) and its main constituent terpinen-4-ol under different concentrations and time periods. RNAi was generated for S. zeamais by feeding adults dsRNA and the knockdown of SzCPR increased the susceptibility of S. zeamais to terpinen-4-ol, with higher mortality of adults than control under terpinen-4-ol fumigation. Further RNAi analysis showed that P450 gene CYP6MS1 mediated the susceptibility of S. zeamais to terpinen-4-ol. These results revealed that cytochrome P450 enzyme system, especially CYP6MS1 participated in the susceptibility of S. zeamais to terpinen-4-ol. The findings provided a foundation to clarify the metabolic mechanisms of terpinen-4-ol in stored-grain pests.

Bio-efficacy and physical integrity of piperonylbutoxide coated combination net (PermaNet\xae 3.0) against pyrethroid resistant population of Anopheles gambiae s.l. and Culex quinquefasciatus mosquitoes in Ethiopia

BackgroundPermaNet® 3.0 is a deltamethrin-treated combination long-lasting insecticidal net with the addition of synergist piperonylbutoxide (PBO) on its roof section. It is designed to overcome the challenge posed by pyrethroid resistant vector populations against mainstream long-lasting insecticidal nets impregnated with pyrethroids only. The objective of this study was to determine insecticide resistance status of Anopheline and Culicine mosquitoes, to evaluate the bio-efficacy of PermaNet® 3.0 nets and to assess household factors affecting the physical integrity of PermaNet® 3.0 after 3 years of use.MethodsInsecticide susceptibility test was conducted using the WHO tube test. Bio-activity of PermaNet® 3.0 samples was evaluated using the WHO cone bioassay. Cross-sectional survey was conducted on 150 randomly selected households from two districts to determine household factors affecting net utilization. One hundred fifty PermaNet® 3.0 nets were randomly collected from the community with replacement after 3 years of deployment and physical integrity of each net was assessed.ResultsBoth Anopheles gambiae sensu lato and Culex quinquefasciatus developed resistance against permethrin and deltamethrin. However, following pre-exposure to synergist PBO the susceptibility of mosquito population increased to both permethrin (from 39% without to 92% with PBO against An. gambiae and from 28% without to 94% with PBO against Culex quinquefasciatus) and deltamethrin (from 52% without to 99% with PBO against An. gambiae and from 43% without to 98% with PBO against Culex quinquefasciatus). Eighty percent (80%) mortality was recorded in wild population of An. gambiae s.l. exposed to unused PermaNet® 3.0, but its bioactivity subsequently declined as washing frequency increased from 0 to 20. The PBO coated roof section of unused PermaNet® 3.0 resulted in higher mosquito mortality (100%) compared to the side panels without PBO (85%). House structure, cooking and washing habits, and damage due to household pests were cited as determinants associated with bed net deterioration. Bed net proportionate hole index (pHI) was ranged from 0 to 6064. Of the 150 PermaNet® 3.0 nets assessed 80, 29 and 41 were considered as ‘good’, ‘acceptable’ and ‘too torn’, respectively.ConclusionsThe bio-efficacy evaluation of PermaNet® 3.0 from Jimma area, southwestern Ethiopia showed moderate efficacy against pyrethroid resistant population of An. gambiae and Culex quinquefasciatus. Thus, NMCPs in parallel to deployment of LLINs, should implement timely insecticide resistance management and integrated vector management strategies to slowdown the evolution and further spread of insecticide resistance. Household factors such as, housing conditions, open flame fire used for cooking and rodent attack were identified as factors contributing to the observed reduced bed net physical integrity in the study area. Universal coverage of bed nets should be accompanied with community awareness creation and training on net utilization and handling.

Bioassays and Methodologies for Insecticide Tests with Larvae of Trogoderma granarium (Everts), the Khapra Beetle.

New insecticide treatment options would be beneficial for control programs for Trogoderma granarium Everts, the khapra beetle, in the United States. Two insecticides were evaluated, the Polyzone® formulation of deltamethrin and a formulation of the insect growth regulator methoprene combined with deltamethrin and the synergist piperonyl butoxide. In the test with Polyzone® deltamethrin, concrete arenas were treated with a low and high rate, and held outside, inside a shed, or inside a lab. Compared to storage in the lab, residue degradation increased slightly in the shed, and then further outside, as evidenced by greater larval survival and adult emergence. Across all environmental treatments, the high rate was more effective than the lower rate. For the combination methoprene product, the effect of food contact with treated surfaces was examined. When treating arenas with food and transferring the food to clean dishes, there was no immediate effect on larval survival, but there was a reduction in survival and emergence to the adult stage after one month. For both tests, larvae apparently often went into diapause after they were introduced onto the treatment arenas. Both treatments could be utilized in management programs if T. granarium infestations are detected.

Escalation of Pyrethroid Resistance in the Malaria Vector Anopheles funestus Induces a Loss of Efficacy of Piperonyl Butoxide-Based Insecticide-Treated Nets in Mozambique.

BackgroundInsecticide resistance poses a serious threat to insecticide-based interventions in Africa. There is a fear that resistance escalation could jeopardize malaria control efforts. Monitoring of cases of aggravation of resistance intensity and its impact on the efficacy of control tools is crucial to predict consequences of resistance.MethodsThe resistance levels of an Anopheles funestus population from Palmeira, southern Mozambique, were characterized and their impact on the efficacy of various insecticide-treated nets established.ResultsA dramatic loss of efficacy of all long-lasting insecticidal nets (LLINs), including piperonyl butoxide (PBO)–based nets (Olyset Plus), was observed. This An. funestus population consistently (2016, 2017, and 2018) exhibited a high degree of pyrethroid resistance. Molecular analyses revealed that this resistance escalation was associated with a massive overexpression of the duplicated cytochrome P450 genes CYP6P9a and CYP6P9b, and also the fixation of the resistance CYP6P9a_R allele in this population in 2016 (100%) in contrast to 2002 (5%). However, the low recovery of susceptibility after PBO synergist assay suggests that other resistance mechanisms could be involved.ConclusionsThe loss of efficacy of pyrethroid-based LLINs with and without PBO is a concern for the effectiveness of insecticide-based interventions, and action should be taken to prevent the spread of such super-resistance.

Acequinocyl Resistance Associated With I256V and N321S Mutations in the Two-Spotted Spider Mite (Acari: Tetranychidae).

The two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), is one of the most important pest species, because it devastates many horticultural and ornamental crops and fruit trees. In the present study, we explored a field strain that was collected in January 2001 and then selected for 16 years for acequinocyl resistance. The resistance ratios calculated for the LC50 value in the laboratory-selected acequinocyl-resistant (LSAR16) strain was 4,237-fold higher than that of the susceptible strain. Pretreatment with the synergists piperonyl butoxide and S,S,S-tributyl-phosphorotrithioate significantly increased the toxicity of acequinocyl to the LSAR16 strain. Crossing experiments revealed that the resistance in the LSAR16 strain was maternally inherited, dominant, and monogenic. Furthermore, among individuals in the LSAR16 strain, 85.5-98.5% had the I256V mutation and 98-99% had the N321S mutation in mitochondrial cytochrome b. These results suggest that these two new point mutations contribute to acequinocyl resistance in T. urticae.

Determination of Insecticide Susceptibility of Field Populations of Tomato Leaf Miner (Tuta absoluta) in Northern Nigeria

In 2016, northern Nigeria experienced a devastating infestation by the tomato leaf miner, leading to soaring in prices of tomatoes across the country. Unfortunately, information on the resistance status of this pest is lacking in northern Nigeria, hampering appropriate control measures. Here, we identified to species level and, using bioassays, characterised insecticide susceptibility profile of a field population of a tomato leaf miner from northern Nigeria. Highest resistance was observed with λ-cyhalothrin (a Type II pyrethroid) with a low mortality (18.52% at 56 h) and LD50 of 7461.474 ppm. Resistance was also established toward propoxur and chlorpyrifos-methyl with average mortalities each of 56% and LD50s of 1023.51 ppm and 106.351 ppm, respectively. Highest susceptibility was observed from abamectin with mortality of 86% and LD50 of 0.034 ppm. Pre-exposure to the synergist piperonylbutoxide significantly recovered λ–cyhalothrin susceptibility ((mortality~90%, χ2 = 98.35, p &lt; 0.0001) and LD50 = 0.92 ppm) implicating P450 monoxygenases. No significant changes were observed on pre-exposure to diethyl maleate and triphenylphosphate-inhibitors of glutathione S-transferases and carboxylesterases, respectively. Sequencing of domain II of the voltage-gated sodium channel established 1014F kdr mutation 100% fixed in both λ-cyhalothrin-alive and dead larvae. These findings highlight the challenges for control of this invasive agricultural pest in northern Nigeria.

Insecticide resistance status, frequency of L1014F Kdr and G119S Ace-1 mutations, and expression of detoxification enzymes in Anopheles gambiae (s.l.) in two regions of northern Benin in preparation for indoor residual spraying

BackgroundThis study aims to provide baseline data on the resistance status to insecticides, the frequency of mechanisms involved and the impact of the association with the synergist piperonyl butoxide (PBO) on resistant Anopheles gambiae (s.l.) populations in two regions of northern Benin, prior to an indoor residual spraying campaign and introduction of next generation long-lasting insecticidal nets (LLINs) incorporating PBO.MethodsAdult Anopheles gambiae (s.l.) originating from larvae collected in two study regions (Alibori within the Kandi-Gogounou-Segbana districts and Donga within the Djougou-Copargo-Ouake districts) were tested with impregnated papers (bendiocarb 0.1%, pirimiphos-methyl 0.25%, permethrin 0.75% and deltamethrin 0.05%). The synergist PBO was used to check for the involvement of detoxification enzymes in pyrethroid resistant populations. Molecular analyses were performed for the identification of species within the Anopheles gambiae (s.l.) complex and kdr L1014F and G119S Ace-1 mutations. Biochemical assays assessed the activity of detoxification enzymes.ResultsAnopheles gambiae (s.l.) was resistant to pyrethroids, with a mortality range of 25–83% with deltamethrin and 6–55% with permethrin. A significant increase in mortality was observed after pre-exposure to PBO for both deltamethrin (63–99%) and permethrin (56–99%). With bendiocarb, An. gambiae (s.l.) were susceptible in Kandi (99% mortality), with possible resistance (92–95%) recorded in Djougou, Copargo, Gogounou, Ouake and Segbana. All study populations were fully susceptible to pirimiphos-methyl. The frequencies of resistant mutations varied according to species and sites: 0.67–0.88 for L1014F kdr and 0–0.06 for G119S Ace-1. Three study locations (Djougou, Gogounou and Kandi) showed high oxidase activity and four sites (Djougou, Ouake, Copargo and Kandi) showed elevated esterase activity.ConclusionsThis study confirms resistance to pyrethroids and suggests emerging bendiocarb resistance in An. gambiae (s.l.) populations in northern Benin. However, recovery of susceptibility to pyrethroids after PBO exposure, and susceptibility to organophosphates in the An. gambiae (s.l.) populations indicate that next generation LLINs incorporating PBO synergist combined with an indoor residual spraying (IRS) campaign with organophosphate insecticides may be regarded as alternative control tools.

Molecular basis of permethrin and DDT resistance in an Anopheles funestus population from Benin

BackgroundInsecticide resistance in Anopheles mosquitoes is threatening the success of malaria control programmes. In order to implement suitable insecticide resistance management strategies, it is necessary to understand the underlying mechanisms involved. To achieve this, the molecular basis of permethrin and DDT resistance in the principal malaria vector, Anopheles funestus from inland Benin (Kpome), was investigated.ResultsHere, using a microarray-based genome-wide transcription and qRT-PCR analysis, we showed that metabolic resistance mechanisms through over-expression of cytochrome P450 and glutathione S-transferase genes (GSTs) are a major contributor to DDT and permethrin resistance in Anopheles funestus from Kpome. The GSTe2 gene was the most upregulated detoxification gene in both DDT- [fold-change (FC: 16.0)] and permethrin-resistant (FC: 18.1) mosquitoes suggesting that upregulation of this gene could contribute to DDT resistance and cross-resistance to permethrin. CYP6P9a and CYP6P9b genes that have been previously associated with pyrethroid resistance were also significantly overexpressed with FC 5.4 and 4.8, respectively, in a permethrin resistant population. Noticeably, the GSTs, GSTd1-5 and GSTd3, were more upregulated in DDT-resistant than in permethrin-resistant Anopheles funestus suggesting these genes are more implicated in DDT resistance. The absence of the L1014F or L1014S kdr mutations in the voltage-gated sodium channel gene coupled with the lack of directional selection at the gene further supported that knockdown resistance plays little role in this resistance.ConclusionsThe major role played by metabolic resistance to pyrethroids in this An. funestus population in Benin suggests that using novel control tools combining the P450 synergist piperonyl butoxide (PBO), such as PBO-based bednets, could help manage the growing pyrethroid resistance in this malaria vector in Benin.

Residual efficacy of deltamethrin applied on porous and non-porous surfaces against Sitophilus granarius (L.), Plodia interpunctella (Hübner) and Blattella germanica (L.):

Residual efficacy of the insecticide deltamethrin, EC formulation with 25 g/L AI + 225 g/L PBO (synergist piperonyl butoxide), against lab populations of S. granarius and P. interpunctella by applying product water solutions (12.5 mg AI/m2) to porous surface, and against B. germanica by applying them to non-porous surface, was investigated in laboratory (at 25±1°C and 55-60% r.h.). The mortality of cockroach adults on deposits aged 0, 14, 30 and 45 days was estimated after 30 minutes of their contact with the treated surfaces, and additional 24 h and 48 h of recovery, while the mortality of stored-product insects (adults or larvae) on 0, 7, 14 and 30 days old deposits was estimated after 2, 7 and 14 days of exposure to treated surfaces and additional 7 days of recovery. Mortality of cockroaches in all variants was 100%, except on 45 days old deposit and after 24 h of recovery, when it was 97%. Deltamethrin caused 0% weevil mortality after 2 days of exposure to deposits of all ages (0-30 days), while P. interpunctella larval mortality was 87-93%. However, mortality was 100% after 7 and 14 days of weevil/moth exposure in all variants of deposit ages and/or additional 7 days of recovery. The results show that deltamethrin applied to porous and non-porous surfaces is a highly effective insecticide for weevil/moth and cockroach control, and it showed a good residual activity for up to 30 and 45 days, respectively.

Carbamate resistance in a UK population of the halophilic mosquito Ochlerotatus detritus implicates selection by agricultural usage of insecticide

The salt marsh mosquito Ochlerotatus detritus Haliday, 1833 (Diptera: Culicidae) is locally abundant in some areas of the UK, can be a pernicious summer nuisance biter and is one of eleven British mosquitoes considered as a potential bridge vector of West Nile Virus. WHO bioassays of insecticide susceptibility were performed on O. detritus from Parkgate Marshes, Little Neston, Wirral, UK using three insecticides, the pyrethroid permethrin, the carbamate bendiocarb and the organophosphate fenitrothion. O. detritus were fully susceptible to permethrin and fenitrothion but exhibited strong resistance to bendiocarb (66% of females alive following 1–hr exposure; LT50 of 116 minutes). Sequencing of the known resistance-causing mutations in the acetylcholinesterase target site of carbamate/organophosphates, and of pyrethroids, the voltage-gated sodium channel, revealed no known target-site mutations indicating the carbamate resistance is not target-site mediated. Pre-exposure to the synergist piperonyl butoxide recovered full bendiocarb susceptibility further implicating metabolic resistance. We show that UK mosquitoes have the potential to develop resistance to insecticides and suggest that the carbamate resistance detected could be a result of exposure to agricultural insecticides.

Characterizing Permethrin and Etofenprox Resistance in Two Common Laboratory Strains of Anopheles gambiae (Diptera: Culicidae).

Anopheles gambiae Giles (Diptera: Culicidae) is the most prolific malaria vector in sub-Saharan Africa, where widespread insecticide resistance has been reported. An. gambiae laboratory strains are commonly used to study the basic biology of this important mosquito vector, and also in new insecticide discovery programs, where insecticide-susceptible and -resistant strains are often used to screen new molecules for potency and cross-resistance, respectively. This study investigated the toxicity of permethrin, a Type-I pyrethroid insecticide, and etofenprox, a non-ester containing pyrethroid insecticide, against An. gambiae at three life stages. This characterization was performed with susceptible (G3; MRA-112) and resistant (Akdr; MRA-1280) An. gambiae strains; the Akdr strain is known to contain the L1014F mutation in the voltage-sensitive sodium channel. Surprisingly, etofenprox displays a lower level of resistance than permethrin against all stages of mosquitoes, except in a headless larval paralysis assay designed to minimize penetration factors. In first-instar An. gambiae larvae, permethrin had significant resistance, determined by the resistance ratio (RR50 = 5), but etofenprox was not significantly different (RR50 = 3.4) from the wild-type strain. Fourth-instar larvae displayed the highest level of resistance for permethrin (RR50 = 108) and etofenprox (RR50 = 35). Permethrin (PC50 = 2 ppb) and etofenprox (PC50 = 9 ppb) resulted in headless larval paralysis (5-h), but resistance, albeit lower, was still present for permethrin (RR50 = 5) and etofenprox (RR50 = 6.9). In adult female mosquitoes, permethrin displayed higher resistance (RR50 = 14) compared to etofenprox (RR50 = 4.3). The level of etofenprox resistance was different from that previously reported for a similar Akron An. gambiae laboratory strain (MRA-913). The chemical synergists piperonyl butoxide (PBO) and diethyl maleate (DEM) were able to synergize permethrin, but not etofenprox in the resistant strain (Akdr). In conclusion, multiple mechanisms are likely involved in pyrethroid resistance, but resistance profiles are dependent upon selection. Etofenprox is an effective insecticide against An. gambiae in the lab but will likely suffer from resistance in the field.

Biodegradation of chlorpyrifos and 3,5,6-trichloro-2-pyridinol by the epiphytic yeasts Rhodotorula glutinis and Rhodotorula rubra.

The possible involvement of the epiphytic yeasts Rhodotorula glutinis and Rhodotorula rubra in the biodegradation of the insecticide chlorpyrifos and its metabolite 3,5,6-trichloro-2-pyridinol (TCP), in pure cultures and in plant surfaces (tomato fruits) was investigated. Higher biodegradation rates were observed as the concentration of chlorpyrifos and the inoculum of the microorganisms were increased, while the yeasts proved to be more active at 25 and 15 °C. The presence of glucose in the mineral nutrient medium, as an extra source of carbon, delayed the biodegradation by Rhodotorula glutinis, while Rhodotorula rubra proved to be more active. The detection and quantification of the parent compound and TCP was successfully achieved using a LC/MS/MS chromatographic system. The in vitro enzymatic assays applied suggested that esterases may be involved in the biodegradation of chlorpyrifos, a fact that was further enhanced after the addition of the synergists triphenyl phosphate, diethyl maleate and piperonyl butoxide in the biodegradation trials. The decrease of chlorpyrifos residues on tomato fruits confirmed the corresponding on pure cultures, resulting in the suggestion that the yeasts R. glutinis and R. rubra can possibly be used successfully for the removal or detoxification of chlorpyrifos residues on tomatoes.

Evidence of Insecticide Resistance to Pyrethroids and Bendiocarb in Anopheles funestus from Tsararano, Marovoay District, Madagascar.

Introduction In Madagascar, malaria control relies on the countrywide use of long lasting insecticide treated bed nets (LLINs) and on indoor residual spraying (IRS) in the central highland area as well as a small area on the eastern coast. We tested insecticide resistance mechanisms of Anopheles funestus from Tsararano, a malaria endemic village in the coastal health district of Marovoay. Methods Insecticide susceptibility bioassays were done in July 2017 on first-generation Anopheles funestus (F1) to assess (i) the susceptibility to permethrin (0.05%), deltamethrin (0.05%), DDT (4%), malathion (5%), fenitrothion (1%), and bendiocarb (0.1%); (ii) the effect of preexposure to the piperonyl butoxide (PBO) synergist; and (iii) the enzymatic activities of cytochrome P450, esterases, and glutathione S-transferases (GST). Results Our results demonstrated that An. funestus was phenotypically resistant to pyrethroids and bendiocarb, with a mortality rate (MR) of 33.6% (95%CI: 24.5-43.7%) and 86% (95%CI: 77.6-92.1%), respectively. In contrast, An. funestus were 100% susceptible to DDT and organophosphates (malathion and fenitrothion). Preexposure of An. funestus to PBO synergist significantly restored the susceptibility to bendiocarb (MR=100%) and increased the MR in the pyrethroid group, from 96% (95%CI: 90.0-98.9%) to 100% for deltamethrin and permethrin, respectively (χ2 = 43, df = 3, P< 0.0001). Enzymatic activities of cytochrome P450 and α-esterases were significantly elevated among An. funestus compared with the IPM reference strain (Mann-Whitney U= 30, P<0.0001; U = 145.5, P <0.0001, respectively). No significant differences of β-esterases activities compared to the IPM reference strain were observed (Mann-Whitney U = 392.5, P = 0.08). Conclusion In Tsararano, despite the absence of an IRS programme, there is evidence of high levels of insecticide resistance to pyrethroids and bendiocarb in An.