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Pyrethroid resistance in Aedes aegypti is widespread in southern Vietnam because the photostable 2nd generation pyrethroids have been used in large amounts over extensive areas for malaria and dengue vector control. In our previous report in 2009, F1534C, one of the point mutations in the voltage-sensitive sodium channel (VSSC) in Ae. aegypti, was widespread at high frequency in south and central area. However, no significant correlation between the frequency of F1534C and pyrethroid susceptibility was detected primarily because the F1534C mutation frequency in the southern highland area was very low, despite that the bioassay indicated high pyrethroid resistance. The point mutation in the VSSC, L982W, which was not the target mutation in our previous study, was recently determined to be an important mutation causing high-pyrethroid resistance in Vietnamese Ae. aegypti. In the present study, a re-investigation of L982W in the mosquito samples collected in 2006-2008 revealed a greater distribution of this mutation (allelic percentage 59.2%) than F1534C (21.7%) and the greater proportion of homozygous L982W as compared to F1534C provided a plausible answer to the question concerning the unknown resistance factor in the southern highland area. L982W frequencies were uniformly higher in the southern part of Vietnam, including the highland area with a significantly high positive correlation with pyrethroid resistance in Ae. aegypti.

Insecticides are widely used to control pests in agriculture and insect vectors that transmit human diseases. However, these chemicals can have a negative effect on nontarget, beneficial organisms including bees. Discovery and deployment of selective insecticides is a major mission of modern toxicology and pest management. Pyrethroids exert their toxic action by acting on insect voltage-gated sodium channels. Honeybees and bumblebees are highly sensitive to most pyrethroids, but are resistant to a particular pyrethroid, taufluvalinate (τ-FVL). Because of its unique selectivity, τ-FVL is widely used to control not only agricultural pests but also varroa mites, the principal ectoparasite of honeybees. However, the mechanism of bee resistance to τ-FVL largely remains elusive. In this study, we functionally characterized the sodium channel BiNav1–1 from the common eastern bumblebee (Bombus impatiens) in Xenopus oocytes and found that the BiNav1–1 channel is highly sensitive to six commonly used pyrethroids, but resistant to τ-FVL. Phylogenetic and mutational analyses revealed that three residues, which are conserved in sodium channels from 12 bee species, underlie resistance to τ-FVL or sensitivity to the other pyrethroids. Further computer modeling and mutagenesis uncovered four additional residues in the pyrethroid receptor sites that contribute to the unique selectivity of the bumblebee sodium channel to τ-FVL versus other pyrethroids. Our data contribute to understanding a long-standing enigma of selective pyrethroid toxicity in bees and may be used to guide future modification of pyrethroids to achieve highly selective control of pests with minimal effects on nontarget organisms.

Culex pipiens complex is an important vector of epizootic and zoonotic pathogens, including West Nile virus. Chicago, Illinois and its suburbs have suffered high incidence of human West Nile virus infections in the past. This makes abatement programs in and around the Chicago area an essential service. The control of Cx. pipiens is often complicated by rapidly evolving resistance to pyrethroids, which are the most widely used chemical class in US mosquito abatement programs. The present study assessed Sumithrin® resistance in Cx. pipiens collected from five locations around Cook County, Illinois, neighboring the city limits of Chicago. According to CDC guidelines, samples from all five locations demonstrated some resistance to Sumithrin®. When assessed with Anvil®, a formulated product made of Sumithrin® synergized with piperonyl butoxide, susceptibility was rescued in mosquitoes from three out of the five locations, suggesting involvement of mixed-function oxidases and/or carboxylesterases in Sumithrin® resistance at these locations. Not all locations had susceptibility rescued by Anvil®, but these locations had relatively low knockdown resistance allele frequencies, suggesting that mechanisms other than knockdown resistance may be involved. Enzyme activities did not reveal any marked trends that could be related back to mortality in the bottle bioassays, which highlights the need for multiple types of assays to infer enzymatic involvement in resistance. Future directions in pyrethroid resistance management in Chicago area Cx. pipiens are discussed.

Control of dengue vectors with synthetic pyrethroids is employed worldwide but development of pyrethroid resistance in Aedes mosquitoes is a big challenge for successful prevention of dengue. Pyrethroids are of two types: type I (devoid of α-cyano group) and type II (contain α-cyano group) which differ in their toxic effect. Therefore, this study investigated potential difference in the cytochrome P450 monooxygenase (CYP) mediated resistance status against two types of synthetic pyrethroids in wild Aedes ( Ae. ) albopictus populations from dengue endemic sub-Himalayan West Bengal. The role of CYPs in resistance development was studied through synergist assay and gene expression studies. Widespread resistance was observed against permethrin (type I) and lambdacyhalothrin (type II) in studied populations. Use of Piperonyl Butoxide (PBO) in synergist assay restored susceptibility to both the insecticides and confirmed involvement of CYP in observed resistance. Differential overexpression of three CYP genes, CYP6P12 , CYP6A8 and CYP6N3 was observed in all populations and population specific differential induction of CYP6P12 and CYP6A8 upon permethrin and lambdacyhalothrin exposure was also noted. These findings indicate occurrence of monooxygenase mediated pyrethroid resistance in Ae. albopictus populations from this region. Use of monooxygenase blockers can improve the efficacy of pyrethroids for control of this vector.

House flies (Musca domestica) are a significant nuisance and vector species. Currently, few technologies are available to adequately control their populations, and insecticide resistance threatens the efficacy of some approaches currently utilized. Transfluthrin is a promising volatile pyrethroid that has been successful in controlling mosquitoes and other pest insects, offering the potential as an alternative or future chemical control tool for the abatement of diverse arthropod pests. For this study, we tested whether transfluthrin could prevent fly capture at an attractant source compared to the control when placed on the exterior of the attractant device. Our results indicate that transfluthrin significantly reduced fly capture for both a pyrethroid-susceptible and pyrethroid-resistant strain of house fly compared to the untreated controls. These results indicate the potential of using transfluthrin in future integrated pest management programs for the control of house flies. House flies are notoriously difficult to control, owing to their tendency to live in close relationships with humans and their livestock, and their rapid development of resistance to chemical controls. With this in mind, we explored an alternative chemical control, a spatial repellent to deter Musca domestica L. from points we wanted to protect (i.e., a baited trap). Our results demonstrated that the synthetic spatial repellent, transfluthrin, is effective in preventing M. domestica adults from entering protected traps for both a susceptible strain (CAR21) and a field-acquired permethrin-resistant strain (WHF; 24 h LD[sub.50] resistance ratio of 150), comprising 22% and 28% of the total number of flies collected, respectively. These results are promising and demonstrate that transfluthrin can be an effective spatial repellent to protect points of interest where needed.

Malaria vector control may be compromised by resistance to insecticides in vector populations. Actions to mitigate against resistance rely on surveillance using standard susceptibility tests, but there are large gaps in the monitoring data across Africa. Using a published geostatistical ensemble model, we have generated maps that bridge these gaps and consider the likelihood that resistance exceeds recommended thresholds. Our results show that this model provides more accurate next-year predictions than two simpler approaches. We have used the model to generate district-level maps for the probability that pyrethroid resistance in Anopheles gambiae s.l. exceeds the World Health Organization thresholds for susceptibility and confirmed resistance. In addition, we have mapped the three criteria for the deployment of piperonyl butoxide-treated nets that mitigate against the effects of metabolic resistance to pyrethroids. This includes a critical review of the evidence for presence of cytochrome P450-mediated metabolic resistance mechanisms across Africa. The maps for pyrethroid resistance are available on the IR Mapper website, where they can be viewed alongside the latest survey data.

Insecticide resistance in malaria vectors remains a global public health problem; however, little is known about resistance levels in Osun State, despite relatively high rates of malaria and distribution of insecticide-treated nets in the area. This study evaluates the resistance status of adult female Anopheles gambiae s.l to pyrethroids (permethrin, deltamethrin and alpha-cypermethrin) and an organophosphate (pirimiphos-methyl) insecticides and knockdown resistant (KDR) gene detection in six locations (Ido-Osun, Ipetumodu, Inisa, Ejigbo, Ijebu-Jesha and Ila) across the three senatorial districts in Osun State, Nigeria. Larval sampling was done between 0700hr and 1100hrs weekly between January and December 2022. Collected larvae were reared to the adult stage in the Department of Animal and Environmental Biology laboratory of Osun State University, Osogbo, Nigeria and then identified morphologically using morphological keys. Insecticide bioassay was conducted with permethrin (0.75%), deltamethrin (0.05%), alpha-cypermethrin (0.05%) and pirimiphos-methyl (0.25%) using WHO procedure. The mosquitoes were subjected to molecular analysis to detect the KDR gene. Pirimiphos-methyl showed significantly higher knockdown at 60 minutes (KD60) and achieved 100% mortality compared with the pyrethroids tested (p < 0.05), with no resistance detected across the study areas. Overall, pyrethroid mortality ranged from 40% to 97% across the study sites, indicating suspected to confirmed resistance. The lowest mortality was recorded at Ila for permethrin (86%) and at Ejigbo for alpha-cypermethrin (60%) and deltamethrin (40%)\". In addition, there was the detection of the KDR gene across the study areas. The present study reveals the insecticidal efficacy of pirimiphos-methyl against female Anopheles gambiae s.l as compared to pyrethroids. Therefore, there is a need to intensify insecticide resistance surveillance of Anopheles in Osun State to plan indoor residual spraying with pirimiphos-methyl and explore the use of PBO or dual active ingredient insecticides treated nets (ITNs) to address the potential impacts of pyrethroid resistance.