Metabolic Resistance in Permethrin-Resistant Florida Aedes aegypti (Diptera: Culicidae)

First report of V1016I, F1534C and V410L kdr mutations associated with pyrethroid resistance in Aedes aegypti populations from Niamey, Niger

BACKGROUND

Ae. aegypti is the vector of important μ arboviruses, including dengue, Zika, chikungunya and yellow fever. Despite not being specifically targeted by insecticide-based control programs in West Africa, resistance to insecticides in Ae. aegypti has been reported in countries within this region. In this study, we investigated the status and mechanisms of Ae. aegypti resistance in Niamey, the capital of Niger. This research aims to provide baseline data necessary for arbovirus outbreak prevention and preparedness in the country.

METHODS

Ovitraps were used to collect Ae. aegypti eggs, which were subsequently hatched in the insectary for bioassay tests. The hatched larvae were then reared to 3-5-day-old adults for WHO tube and CDC bottle bioassays, including synergist tests. The kdr mutations F1534C, V1016I, and V410L were genotyped using allele-specific PCR and TaqMan qPCR methods.

RESULTS

Ae. aegypti from Niamey exhibited moderate resistance to pyrethroids but susceptibility to organophosphates and carbamates. The kdr mutations, F1534C, V1016I and V410L were detected with the resistant tri-locus haplotype 1534C+1016L+410L associated with both permethrin and deltamethrin resistance. Whereas the homozygote tri-locus resistant genotype 1534CC+1016LL+410LL was linked only to permethrin resistance. The involvement of oxidase and esterase enzymes in resistance mechanisms was suggested by partial restoration of mosquitoes' susceptibility to pyrethroids in synergist bioassays.

CONCLUSION

This study is the first report of Ae. aegypti resistance to pyrethroid insecticides in Niamey. The resistance is underpinned by target site mutations and potentially involves metabolic enzymes. The observed resistance to pyrethroids coupled with susceptibility to other insecticides, provides data to support evidence-based decision-making for Ae. aegypti control in Niger.

Evaluation of a novel triple-action adulticide containing a pyrethroid, macrocyclic lactone, and fatty acid against pyrethroid-resistant Aedes aegypti and Culex quinquefasciatus (Diptera: Culicidae)

Insecticide resistance in mosquito populations has long been recognized as a significant global public health challenge, motivating the development of new control chemistries. ReMoa Tri is a novel triple-action space spray that employs a different mode of action than traditional adult mosquito control formulations. It combines 3 components: fenpropathrin, a mixed-type I/II pyrethroid; abamectin, a macrocyclic lactone; and C8910, a patented fatty acid chain. As an ultra-low volume adulticide, ReMoa Tri has the potential to target mosquito species that are resistant to pyrethroid and organophosphate-based control materials. To determine whether ReMoa Tri effectively targets resistant mosquito species in Florida's Collier County, United States, we conducted ground-based field cage trials using field-caught pyrethroid-resistant Culex quinquefasciatus (Say) and Aedes aegypti (L.), of which the latter also displayed developing resistance to organophosphates. Trials were also conducted against the same mosquito populations with Merus 3.0, a pyrethrin-based adulticide used by the Collier Mosquito Control District. ReMoa Tri was effective against Collier's pyrethroid-resistant Cx. quinquefasciatus, resulting in more than 95% mortality in semifield cage trials by 24 h postapplication. Similarly, ReMoa Tri applications against Collier's pyrethroid-resistant Ae. aegypti resulted in 72%-89% mortality at 24 h postapplication and 74%-97% mortality at 48 h postapplication. This study represents the first field data on this novel space spray, and its findings shed light on the performance of ReMoa Tri against local mosquito populations that have developed resistance to currently available adulticides.

Transcription factor B-H2 regulates CYP9J34 expression conveying deltamethrin resistance in Culex pipiens pallens

BACKGROUND

Mosquitoes are vectors of various diseases, posing significant health threats worldwide. Chemical pesticides, particularly pyrethroids like deltamethrin, are commonly used for mosquito control, but the emergence of resistant mosquito populations has become a concern. In the deltamethrin-resistant (DR) strain of Culex pipiens pallens, the highly expressed cytochrome P450 9 J34 (CYP9J34) gene is believed to play a role in resistance, yet the underlying mechanism remains unclear.

RESULTS

Quantitative polymerase chain reaction with reverse transcription (qRT-PCR) analysis revealed that the expression of CYP9J34 was 14.6-fold higher in DR strains than in deltamethrin-susceptible (DS) strains. The recombinant production of CYP9J34 protein of Cx. pipiens pallens showed that the protein could directly metabolize deltamethrin, yielding the major metabolite 4'-OH deltamethrin. Through dual luciferase reporter assays and RNA interference, the transcription factor homeobox protein B-H2-like (B-H2) was identified to modulate the expression of the CYP9J34 gene, contributing to mosquito resistance to deltamethrin.

CONCLUSIONS

Our findings demonstrate that the CYP9J34 protein could directly degrade deltamethrin, and the transcription factor B-H2 could regulate CYP9J34 expression, influencing the resistance of mosquitoes to deltamethrin. © 2023 Society of Chemical Industry.

Changes in mosquito species and blood meal composition associated with adulticide applications

Although adulticide application is a pillar in the integrated management of nuisance and vector mosquitoes, non-target effects of adulticide applications within ecosystems are a substantial concern. However, the impacts of adulticide applications on non-target organisms are not necessarily detrimental, and in some cases, may provide benefits to certain organisms or wildlife. Here, we hypothesized that adulticide applications have beneficial non-target impacts on vertebrate wildlife through reduced biting pressure. To test this, we collected mosquitoes from ultra-low volume Permanone-treated (intervention) and untreated (reference) areas and assessed mosquito abundance and diversity, and abundance of blood-engorged female mosquitoes. We performed DNA barcoding analysis on mosquito blood meals to identify host species. Our results demonstrated a significant reduction in mosquito abundance by 58.9% in the intervention areas, taking into account the reduction in reference areas. Consequently, this decline led to a 64.5% reduction in the abundance of blood-engorged females. We also found a temporal dynamic of mosquito composition driven by mosquito control actions in which different mosquito species became dominant at treated sites while composition at reference areas remained similar during the same period. The present study suggests that the beneficial effects of mosquito control treatments for humans extend to other vertebrates, which represents an unstudied and rarely recognized non-target impact.

Baseline Susceptibility and Effectiveness of Adulticides to Local Aedes Taeniorhynchus From Collier County, Florida

The black salt marsh mosquito, Aedes taeniorhynchus, is the primary nuisance mosquito in the coastal regions of Florida. This study aimed to establish the baseline susceptibility of Ae. taeniorhynchus to adulticide products used for mosquito control by the Collier Mosquito Control District (CMCD). The Centers for Disease Control and Prevention bottle bioassay was used to test technical-grade and formulated products, and Merus 3.0® was evaluated in semifield cage trials through aerial applications. The results revealed the baseline susceptibility of Ae. taeniorhynchus to the tested materials and the effectiveness of Merus 3.0 to effectively control the Ae. taeniorhynchus. The study provides important information for the development of an integrated mosquito management strategy for controlling Ae. taeniorhynchus mosquito populations in southwest Florida.

Insecticide resistance: Status and potential mechanisms in Aedes aegypti

Aedes aegypti, an important vector in the transmission of human diseases, has developed resistance to two commonly used classes of insecticides, pyrethroids and organophosphates, in populations worldwide. This study examined sensitivity/resistance to chlorpyrifos, fenitrothion, malathion, deltamethrin, permethrin, and β-cyfluthrin, along with possible metabolic detoxification and target site insensitivity, in three Aedes aegypti mosquito strains. The resistant strain (PR) had developed high levels of resistance to all three pyrethroid insecticides compared to a susceptible population, with 6, 500-, 3200- and 17,000-fold resistance to permethrin, β-cyfluthrin, and deltamethrin, respectively. A newly emerged Ae. aegypti population collected from St. Augustine, Florida (AeStA) showed elevated levels of resistance to malathion (12-fold) and permethrin (25-fold). Synergists DEF (S,S,S,-tributyl phosphorotrithioate) and DEM (diethyl maleate) showed no or minor effects on insecticide resistance in both the AeStA and PRG20strains, but PBO (piperonyl butoxide) completely abolished resistance to both malathion and permethrin in AeStA and partially suppressed resistance in PR. The voltage-gated sodium channel sequences were examined to explore the mechanism that only partially inhibited the suppression of resistance to PBO in PR. Two mutations, V1016G/I and F1534C substitutions, both of which are associated with the development of pyrethroid resistance, were identified in the PRG20 strain but not in AeStA. These results suggest that while cytochrome P450 mediated detoxification may not be solely responsible, it is the major mechanism governing the development of resistance in AeStA. Both P450 mediated detoxification and target site insensitivity through the mutations in the voltage-gated sodium channel contribute to the high levels of resistance in the PRG20 strain.

Comparative Transcriptomic Analysis of Insecticide-Resistant Aedes aegypti from Puerto Rico Reveals Insecticide-Specific Patterns of Gene Expression

Aedes aegypti transmits major arboviruses of public health importance, including dengue, chikungunya, Zika, and yellow fever. The use of insecticides represents the cornerstone of vector control; however, insecticide resistance in Ae. aegypti has become widespread. Understanding the molecular basis of insecticide resistance in this species is crucial to design effective resistance management strategies. Here, we applied Illumina RNA-Seq to study the gene expression patterns associated with resistance to three widely used insecticides (malathion, alphacypermethrin, and lambda-cyhalothrin) in Ae. aegypti populations from two sites (Manatí and Isabela) in Puerto Rico (PR). Cytochrome P450s were the most overexpressed detoxification genes across all resistant phenotypes. Some detoxification genes (CYP6Z7, CYP28A5, CYP9J2, CYP6Z6, CYP6BB2, CYP6M9, and two CYP9F2 orthologs) were commonly overexpressed in mosquitoes that survived exposure to all three insecticides (independent of geographical origin) while others including CYP6BY1 (malathion), GSTD1 (alpha-cypermethrin), CYP4H29 and GSTE6 (lambda-cyhalothrin) were uniquely overexpressed in mosquitoes that survived exposure to specific insecticides. The gene ontology (GO) terms associated with monooxygenase, iron binding, and passive transmembrane transporter activities were significantly enriched in four out of six resistant vs. susceptible comparisons while serine protease activity was elevated in all insecticide-resistant groups relative to the susceptible strain. Interestingly, cuticular-related protein genes (chinase and chitin) were predominantly downregulated, which was also confirmed in the functional enrichment analysis. This RNA-Seq analysis presents a detailed picture of the candidate detoxification genes and other pathways that are potentially associated with pyrethroid and organophosphate resistance in Ae. aegypti populations from PR. These results could inform development of novel molecular tools for detection of resistance-associated gene expression in this important arbovirus vector and guide the design and implementation of resistance management strategies.

Impact of the V410L kdr mutation and co-occurring genotypes at kdr sites 1016 and 1534 in the VGSC on the probability of survival of the mosquito Aedes aegypti (L.) to Permanone in Harris County, TX, USA

Harris County, TX, is the third most populous county in the USA and upon detection of arboviruses Harris County Public Health applies insecticides (e.g., pyrethroid-based Permanone 31-66) against adults of Culex quinquefasciatus to prevent disease transmission. Populations of Aedes aegypti, while not yet a target of public health control, are likely affected by pyrethroid exposure. As this species is a vector of emerging arboviruses, its resistance status to Permanone and the kdr mutations in the voltage-gated sodium channel (VGSC) associated with pyrethroid resistance were investigated. We examined females of known genotype at the V1016I and F1534C sites (N = 716) for their genotype at the 410 amino acid position in the VGSC, and for the influence of their kdr genotype on survival to Permanone at three different distances from the insecticide source in field tests. Most females (81.8%) had at least one resistant L allele at the 410 position, being the first report of the V410L mutation in Ae. aegypti for Texas. When only genotypes at the 410 position were analyzed, the LL genotype exhibited higher survivorship than VL or VV. Out of 27 possible tri-locus kdr genotypes only 23 were found. Analyses of the probability of survival of tri-locus genotypes and for the V410L genotype using a multivariate logistic regression model including area, distance, and genotype found significant interactions between distance and genotype. When only the most common tri-locus genotypes were analyzed (LL/II/CC, 48.2%; VL/II/CC, 19.1%; and VV/II/CC, 10.1%) genotype had no effect on survival, but significant interactions of distance and genotype were found. This indicated that the V410L kdr allele increased survival probability at certain distances. Genotypes did not differ in survivorship at 7.62-m, but LL/II/CC had higher survivorship than VL/II/CC at 15.24- and 22.86-m. The model also identified differences in survivorship among the operational areas investigated.

Impacts of differential mosquito control treatment regimens on insecticide susceptibility status of Aedes aegypti (Diptera: Culicidae)

Abstract

Aedes aegypti (Linnaeus) is an invasive mosquito species and notable vector of several pathogens in the USA. Their cryptic and anthropophilic nature puts this species in close association with humans, where they can also be a nuisance. Mosquito control programs are the front line of defense for protecting the community from nuisance-biting and disease. However, the occurrence and prevalence of insecticide resistance in mosquitoes is a well-documented phenomenon that directly impacts the efficacy of insecticide applications. In Florida specifically, widespread resistance in Ae. aegypti has created a need for operational strategies that combat and, ideally, reverse resistance. Laboratory studies and the association between fitness costs and insecticide resistance indicate that this reversion is possible under the right conditions. For a 2.5-year period, the impact of varying operational treatment regimens on insecticide resistance in Ae. aegypti is evaluated using kdr genotyping and the CDC bottle bioassay. In an organophosphate treatment area, a decrease in frequency of a double homozygous resistant genotype was observed. CDC bottle bioassays did not reveal any clear trends in the data to indicate a reversion to insecticide susceptibility. However, the changes in genotype could indicate the first step back to insecticide susceptibility. This study provides preliminary data that has implications for resistance management in mosquito control operations.

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