Insecticide resistance and vector control

Insecticide Resistance in Aedes aegypti Mosquitoes: Possible Detection of kdr F1534C, S989P, and V1016G Triple Mutation in Benin, West Africa

Epidemics of arboviruses in general, and dengue fever in particular, are an increasing threat in areas where Aedes (Ae.) aegypti is present. The effectiveness of chemical control of Ae. aegypti is jeopardized by the increasing frequency of insecticide resistance. The aim of this study was to determine the susceptibility status of Ae. aegypti to public health insecticides and assess the underlying mechanisms driving insecticide resistance. Ae. aegypti eggs were collected in two study sites in the vicinity of houses for two weeks using gravid Aedes traps (GATs). After rearing the mosquitoes to adulthood, female Ae. aegypti were exposed to diagnostic doses of permethrin, deltamethrin and bendiocarb, using Centers for Disease Control and Prevention (CDC) bottle bioassays. Unexposed, un-engorged female Ae. aegypti were tested individually for mixed-function oxidase (MFO), glutathione-S-transferase (GST) and α and β esterase activities. Finally, allele-specific PCR (AS-PCR) was used to detect possible kdr mutations (F1534C, S989P, and V1016G) in the voltage-gated sodium channel gene in insecticide-exposed Ae. aegypti. Most traps were oviposition positive; 93.2% and 97% of traps contained Ae. aegypti eggs in the 10ème arrondissement of Cotonou and in Godomey-Togoudo, respectively. Insecticide bioassays detected resistance to permethrin and deltamethrin in both study sites and complete susceptibility to bendiocarb. By comparison to the insecticide-susceptible Rockefeller strain, field Ae. aegypti populations had significantly higher levels of GSTs and significantly lower levels of α and β esterases; there was no significant difference between levels of MFOs. AS-PCR genotyping revealed the possible presence of 3 kdr mutations (F1534C, S989P, and V1016G) at high frequencies; 80.9% (228/282) of the Ae. aegypti tested had at least 1 mutation, while the simultaneous presence of all 3 kdr mutations was identified in 13 resistant individuals. Study findings demonstrated phenotypic pyrethroid resistance, the over-expression of key detoxification enzymes, and the possible presence of several kdr mutations in Ae. aegypti populations, emphasizing the urgent need to implement vector control strategies targeting arbovirus vector species in Benin.

Cross-infectivity of Vorticella sp. across genera of mosquitoes for development of biological mosquito control strategies

Protists in general comprise about one-third of the parasitic species infecting arthropod vectors, the role of free-living and epibiotic ciliates on mosquitoes have been insufficiently studied either due to their low pathogenicity or facultative parasites. Studies have shown that exposure of Paramecium ciliate protists, like Vorticella species, to first instar Culex nigripalpus Theobald, larvae delayed larval development and reduced biomass of emerged adults due to competition for food sources like bacteria and other microbes essential to mosquito growth and survival. Thus, we report on the capacity of a Vorticella sp. protist's ability to cross-infect host species and parasitize multiple mosquito larvae. The unique adapted behavior with the ability to remain on the exuviae in tree hole habitats provide a novel delivery system to develop products for target species-specific mosquitocides, larvicides, or viricides to be applied and sustained in aquatic systems.

Insecticide resistance of Miami-Dade Culex quinquefasciatus populations and initial field efficacy of a new resistance-breaking adulticide formulation

Sporadic outbreaks of human cases of West Nile virus (WNV), primarily vectored by Culex quinquefasciatus Say in suburban and urban areas, have been reported since introduction of the virus into Florida in 2001. Miami-Dade County, Florida is part of one of the largest metropolitan areas in the United States, supports Cx. quinquefasciatus year-round, and recently experienced over 60 human cases of WNV during one outbreak. To facilitate more effective integrated vector management and public health protection, we used the Centers for Disease Control and Prevention (CDC) bottle bioassay method to evaluate the susceptibility of adult Cx. quinquefasciatus collected from 29 locations throughout Miami-Dade County to pyrethroid and organophosphate adulticide active ingredients (AIs) used by Miami-Dade County Mosquito Control. We also determined the frequency of the 1014 knockdown resistance (kdr) mutation for Cx. quinquefasciatus from a subset of 17 locations. We detected resistance to two pyrethroid AIs in all tested locations (permethrin: 27 locations, deltamethrin: 28 locations). The 1014F allele was widely distributed throughout all 17 locations sampled; however, 29.4% of these locations lacked 1014F homozygotes even though phenotypic pyrethroid resistance was present. Organophosphate resistance was more variable; 20.7% of the locations tested were susceptible to malathion, and 33.3% of the populations were susceptible to naled. We subsequently conducted a field trial of ReMoa Tri, a recently approved multiple AI adulticide formulation labelled for resistant mosquitoes, against a mixed location field population of Miami-Dade Cx. quinquefasciatus. Average 24-hr mortality was 65.1 ± 7.2% and 48-hr mortality increased to 85.3 ± 9.1%, indicating good control of these resistant Cx. quinquefasciatus. This current study shows that insecticide resistance is common in local Cx. quinquefasciatus but effective options are available to maintain control during active disease transmission in Miami-Dade County.

Differences in excito-repellent behavior between susceptible and permethrin-resistant strains of Aedes aegypti upon exposure to insecticide-treated fabric

BACKGROUND

An important component of the biological activity of pyrethroids, when used in disease vector control, is excito-repellency. In this study, behavioral differences between insecticide susceptible (Orlando) and pyrethroid resistant (Puerto Rican) strains of Aedes aegypti were explored in a round glass arena using fabrics treated with permethrin, etofenprox, deltamethrin, or DDT. Repellency was evaluated across several variables, including the time to first flight (TFF), number of landings (NOL), total flight time (TFT), and maximum surface contact (MSC), all by video analysis.

RESULTS

Results from the Orlando strain indicated they were less likely than the Puerto Rican strain to tolerate tarsal contact with the treated fabrics. All four response variables indicated that the mosquito flight and landing behavior was most affected by pyrethroid resistance [knockdown resistance (kdr)] status. In other experiments, mosquitoes were surgically altered, with antennae ablated bilaterally, and these mosquitoes were more likely to stay on the treated surfaces for longer periods of time, irrespective of any chemical exposure. There were also differences in the responses to antennal ablation between the two strains of mosquitoes, indicating that resistance factors, probably kdr, influence the reactivity of mosquitoes to pyrethroid and DDT treatments, and that it was not completely negated by antennal ablation.

CONCLUSIONS

These findings confirm the role of antennal olfactory components in the expression of excito-repellent behaviors, and also support the hypothesis that excito-repellency from pyrethroid/DDT exposure is probably due to a combination of sublethal neurotoxic excitation and interactions with the olfactory system. © 2023 Society of Chemical Industry.

Pyrethroid susceptibility reversal in Aedes aegypti: A longitudinal study in Tapachula, Mexico

Pyrethroid resistance in Aedes aegypti has become widespread after almost two decades of frequent applications to reduce the transmission of mosquito-borne diseases. Because few insecticide classes are available for public health use, insecticide resistance management (IRM) is proposed as a strategy to retain their use. A key hypothesis of IRM assumes that negative fitness is associated with resistance, and when insecticides are removed from use, susceptibility is restored. In Tapachula, Mexico, pyrethroids (PYRs) were used exclusively by dengue control programs for 15 years, thereby contributing to selection for high PYR resistance in mosquitoes and failure in dengue control. In 2013, PYRs were replaced by organophosphates-insecticides from a class with a different mode of action. To test the hypothesis that PYR resistance is reversed in the absence of PYRs, we monitored Ae. aegypti's PYR resistance from 2016 to 2021 in Tapachula. We observed significant declining rates in the lethal concentration 50 (LC50), for permethrin and deltamethrin. For each month following the discontinuation of PYR use by vector control programs, we observed increases in the odds of mosquitoes dying by 1.5% and 8.4% for permethrin and deltamethrin, respectively. Also, knockdown-resistance mutations (kdr) in the voltage-gated sodium channel explained the variation in the permethrin LC50s, whereas variation in the deltamethrin LC50s was only explained by time. This trend was rapidly offset by application of a mixture of neonicotinoid and PYRs by vector control programs. Our results suggest that IRM strategies can be used to reverse PYR resistance in Ae. aegypti; however, long-term commitment by operational and community programs will be required for success.

Resistance and inhibitor testing on Aedes aegypti (Linnaeus) (Culicidae: Diptera) populations in the Florida Keys

Aedes aegypti is the species of greatest concern for mosquito-borne disease in the Florida Keys. Previous locally transmitted dengue outbreaks in Key West (2009-2010) and Key Largo (2020) illustrate the need for an immediate and effective response plan to maintain Ae. aegypti populations below threshold levels. An important part of the Florida Keys Mosquito Control District's vector response plan is adulticide application because it can provide an immediate reduction in Ae. aegypti adults in the community. It has become apparent that in the Florida Keys, and throughout Florida, Ae. aegypti resistance to the adulticide permethrin is prevalent. This study uses the CDC bottle bioassay method to look at resistance in Ae. aegypti collected from Key Largo, Vaca Key, and Key West, FL. Resistance was found in all three populations when exposed to permethrin and Sumithrin® but not malathion. Inhibitor testing revealed that esterase and glutathione transferase activity is involved in resistance to permethrin in Key Largo and Key West Ae. aegypti populations while oxidase activity is involved in resistance to permethrin in Ae. aegypti from Vaca Key. Lack of knockdown at the diagnostic time and previous studies detecting the presence of kdr-associated allele mutations suggest knockdown resistance in all three populations. Results from this study show that there are multiple factors involved with resistance in the Ae. aegypti populations in the Florida Keys and that resistance mechanisms vary between islands. Continued surveillance will remain important so the most effective active ingredients can be used in response to future disease transmission.

Biosynthesized silver nanoparticles (Ag NPs) from isolated actinomycetes strains and their impact on the black cutworm, Agrotis ipsilon

Nanomaterials have been produced with the use of bio-nanotechnology, which is a low-cost approach. Currently, research is being conducted to determine whether actinomycetes isolated from Egyptian soil can biosynthesize Ag nanoparticles (Ag NPs) and characterized by using the following techniques: Transmission electron microscopy (TEM), Dynamic light scattering (DLS), Fourier transforms infrared (FT-IR), Energy-dispersive X-ray spectroscopy (EDX), UV-Vis spectroscopy and X-ray diffraction (XRD). The most promising actinomycetes isolate were identified, morphologically, biochemically, and molecularly. Streptomyces avermitilis Azhar A.4 was found to be able to reduce silver metal nanoparticles from silver nitrate in nine isolates collected from Egyptian soil. Toxicity of biosynthesized against 2nd and 4th larval instar of Agrotis ipsilon (Hufn.) (Lepidoptera: Noctuidae) was estimated. In addition, activity of certain vital antioxidant and detoxifying enzymes as well as midgut histology of treated larvae were also investigated. The results showed appositive correlations between larval mortality percentage (y) and bio-AgNPs concentrations (x) with excellent (R2). The 4th larval instar was more susceptible than 2nd larval instar with LC50 (with 95% confirmed limits) =8.61 (2.76-13.89) and 26.44(13.25-35.58) ppml-1, respectively of 5 days from treatment. The initial stages of biosynthesized AgNps exposure showed significant increases in carboxylesterase (CarE) and peroxidases (PODs) activity followed by significant suppression after 5 days pos-exposure. While protease activity was significantly decreased by increasing time post-exposure. Midgut histology showed abnormality and progressive damage by increasing time post exposure leading to complete destruction of midgut cells after 5 days from exposure. These results make biosynthesized AgNPs an appropriate alternative to chemical insecticide in A. ipsilon management.

Potential key genes involved in metabolic resistance to malathion in the southern house mosquito, Culex quinquefasciatus, and functional validation of CYP325BC1 and CYP9M12 as candidate genes using RNA interference

BACKGROUND

Metabolic detoxification is one of the major mechanisms contributing to the development of resistance in mosquitoes, including the southern house mosquito, Culex quinquefasciatus. The three major detoxification supergene families, cytochrome P450s, glutathione S-transferases and general esterases, have been demonstrated to play an important role in metabolic resistance. In this study, we performed differential gene expression analysis based on high-throughput transcriptome sequencing on samples from four experimental groups to give insight into key genes involved in metabolic resistance to malathion in Cx. quinquefasciatus. We conducted a whole transcriptome analysis of field captured wild Cx. quinquefasciatus from Harris County (WI), Texas and a malathion susceptible laboratory-maintained Sebring colony (CO) to investigate metabolic insecticide resistance. Field captured mosquitoes were also phenotypically classified into the malathion resistant and malathion susceptible groups following a mortality response measure conducted using a Centers for Disease Control and Prevention (CDC) bottle assay. The live (MR) and dead (MS) specimens from the bottle assay, along with an unselected WI sample and a CO sample were processed for total RNA extraction and subjected to whole-transcriptome sequencing.

RESULTS

We demonstrated that the genes coding for detoxification enzymes, particularly cytochrome P450s, were highly up-regulated in the MR group compared to the MS group with similar up-regulation observed in the WI group compared to the CO group. A total of 1,438 genes were differentially expressed in comparison between MR and MS group, including 614 up-regulated genes and 824 down-regulated genes. Additionally, 1,871 genes were differentially expressed in comparison between WI and CO group, including 1,083 up-regulated genes and 788 down-regulated genes. Further analysis on differentially expressed genes from three major detoxification supergene families in both comparisons resulted in 16 detoxification genes as candidates potentially associated with metabolic resistance to malathion. Knockdown of CYP325BC1 and CYP9M12 using RNA interference on the laboratory-maintained Sebring strain significantly increased the mortality of Cx. quinquefasciatus after exposure to malathion.

CONCLUSION

We generated substantial transcriptomic evidence on metabolic detoxification of malathion in Cx. quinquefasciatus. We also validated the functional roles of two candidate P450 genes identified through DGE analysis. Our results are the first to demonstrate that knockdown of CYP325BC1 and CYP9M12 both significantly increased malathion susceptibility in Cx. quinquefasciatus, indicating involvement of these two genes in metabolic resistance to malathion.

Trends of insecticide resistance monitoring in mainland Tanzania, 2004-2020

BACKGROUND

Insecticide resistance is a serious threat to the continued effectiveness of insecticide-based malaria vector control measures, such as long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS). This paper describes trends and dynamics of insecticide resistance and its underlying mechanisms from annual resistance monitoring surveys on Anopheles gambiae sensu lato (s.l.) populations conducted across mainland Tanzania from 2004 to 2020.

METHODS

The World Health Organization (WHO) standard protocols were used to assess susceptibility of the wild female An. gambiae s.l. mosquitoes to insecticides, with mosquitoes exposed to diagnostic concentrations of permethrin, deltamethrin, lambdacyhalothrin, bendiocarb, and pirimiphos-methyl. WHO test papers at 5× and 10× the diagnostic concentrations were used to assess the intensity of resistance to pyrethroids; synergist tests using piperonyl butoxide (PBO) were carried out in sites where mosquitoes were found to be resistant to pyrethroids. To estimate insecticide resistance trends from 2004 to 2020, percentage mortalities from each site and time point were aggregated and regression analysis of mortality versus the Julian dates of bioassays was performed.

RESULTS

Percentage of sites with pyrethroid resistance increased from 0% in 2004 to more than 80% in the 2020, suggesting resistance has been spreading geographically. Results indicate a strong negative association (p = 0.0001) between pyrethroids susceptibility status and survey year. The regression model shows that by 2020 over 40% of An. gambiae mosquitoes survived exposure to pyrethroids at their respective diagnostic doses. A decreasing trend of An. gambiae susceptibility to bendiocarb was observed over time, but this was not statistically significant (p = 0.8413). Anopheles gambiae exhibited high level of susceptibility to the pirimiphos-methyl in sampled sites.

CONCLUSIONS

Anopheles gambiae Tanzania's major malaria vector, is now resistant to pyrethroids across the country with resistance increasing in prevalence and intensity and has been spreading geographically. This calls for urgent action for efficient malaria vector control tools to sustain the gains obtained in malaria control. Strengthening insecticide resistance monitoring is important for its management through evidence generation for effective malaria vector control decision.

Physiological selectivity and tolerance of social wasps exposed to Malathion

Insect pest infestations are a worldwide problem as a result of human actions. Among them, Aedes aegypti stands out as vector of several diseases. Like other pests, A. aegypti has become resistant to the insecticide used for its control, thus harming the local fauna of non-target insects. Therefore, the aim of this study was to study the physiological selectivity of social wasps exposed to Malathion, as well as to investigate possible resistance to this insecticide. Adults of the swarming species Polybia platycephala and Protopolybia sedula and the independent species Polistes versicolor were exposed to four Malathion concentrations. Overall, Malathion was more selective to P. versicolor and more toxic to P. platycephala, and despite the decrease in the concentration of the product recommended by the manufacturer, which in theory would be sublethal doses, social wasps still exhibited high mortality rates. In comparing the mortalities of species collected in an area where there is no application of the insecticide with an area where there is regular application, the data showed an indication that populations of non-target insects are also becoming resistant to insecticides, especially in urban environments.

Metabolic detoxification and ace-1 target site mutations associated with acetamiprid resistance in Aedes aegypti L

Despite the continuous use of chemical interventions, Aedes-borne diseases remain on the rise. Neonicotinoids are new, safer, and relatively effective pharmacological interventions against mosquitoes. Neonicotinoids interact with the postsynaptic nicotinic acetylcholine receptors (nAChRs) of the insect central nervous system, but the absence of nAChR polymorphism in resistant phenotypes makes their involvement in neonicotinoid resistance uncertain. Thus, an investigation was carried out to understand the role of metabolic detoxification and target site insensitivity in imparting acetamiprid resistance in Aedes aegypti larvae. Studies were conducted on the parent susceptible strain (PS), acetamiprid-larval selected strain for five generations (ACSF-5; 8.83-fold resistance) and 10 generations (ACSF-10; 19.74-fold resistance) of Ae. aegypti. The larval selection raised α-esterase and β-esterase activities by 1.32-fold and 1.34-fold, respectively, in ACSF-10 as compared to PS, while the corresponding glutathione-S-transferase and acetylcholinesterase activity increased by 22.5 and 2%. The ace-1 gene in PS and ACSF-10 showed four mismatches in the 1312—1511 bp region due to mutations in the Y455C codon (tyrosine to cysteine) at the 1367th position (TAC→TGC); I457V codon (isoleucine to valine) at 1372 bp and 1374 bp (ATA→GTG); and R494M codon (arginine to methionine) at 1484 bp (AGG→ATG). The R494M mutation was the novel and dominant type, observed in 70% ACSF-10 population, and has not been reported so far. The studies evidenced the combination of metabolic detoxification and target site mutation in imparting acetamiprid resistance in Ae. aegypti.

Suppression of Midgut Microbiota Impact Pyrethroid Susceptibility in Aedes aegypti

Aedes aegypti is a mosquito that transmits viral diseases such as dengue, chikungunya, Zika, and yellow fever. The insect’s microbiota is recognized for regulating several biological processes, including digestion, metabolism, egg production, development, and immune response. However, the role of the bacteria involved in insecticide susceptibility has not been established. Therefore, the objective of this study was to characterize the resident microbiota in a field population of A. aegypti to evaluate its role associated with susceptibility to the insecticides permethrin and deltamethrin. Mosquitoes were fed 10% sucrose mixed with antibiotics and then exposed to insecticides using a diagnostic dose. DNA was extracted, and sequencing of bacterial 16S rRNA was carried out on Illumina^® MiSeq™. Proteobacteria (92.4%) and Bacteroidetes (7.6%) were the phyla, which are most abundant in mosquitoes fed with sucrose 10%. After exposure to permethrin, the most abundant bacterial species were Pantoea agglomerans (38.4%) and Pseudomonas azotoformans-fluorescens-synxantha (14.2%). Elizabethkingia meningoseptica (38.4%) and Ps. azotoformans-fluorescens-synxantha (26.1%) were the most abundant after exposure to deltamethrin. Our results showed a decrease in mosquitoes’ survival when exposed to permethrin, while no difference in survival when exposed to deltamethrin when the microbiota was modified. We found that the change in microbiota modifies the response of mosquitoes to permethrin. These results are essential for a better understanding of mosquito physiology in response to insecticides.

Increased Repellent Effect of DEET on Aedes aegypti (Diptera: Culicidae) Field Population

Insecticides and repellents are routinely used in Brazil because of the high rates of arbovirus transmission and the nuisance caused by mosquitoes. However, few studies have assessed the effectiveness of repellents against mosquito populations that have been under exposure to xenobiotics, mainly insecticides and repellents. This study investigated the sensitivity of a field population of Aedes aegypti (Linnaeus, 1762) from a dengue-endemic area under high insecticide pressure to N,N-diethylmethylbenzamide (DEET), the active ingredient in common repellent products. The field (Laranjeiras, Sergipe, Brazil) and laboratory (Rockefeller) populations were characterized for the presence of the Val1016Ile kdr mutation, associated with pyrethroid resistance, and locomotor activity. Repellency bioassays were performed to assess the response of the mosquitoes to human odor by exposing them to 10% DEET applied to the skin in ethanol. Samples from the field population showed higher frequency of the kdr mutation, 21.9% homozygous and 21.9% heterozygous, greater locomotor activity and greater sensitivity to DEET than the laboratory population. These results suggest increased sensitivity to DEET in field populations and a possible interaction between insecticide exposure and sensitivity to DEET.

Circular Policy: A New Approach to Vector and Vector-Borne Diseases' Management in Line with the Global Vector Control Response (2017-2030)

Integrated Vector Management (IVM) has yielded exemplary results in combating and preventing vector-borne diseases (VBDs) and their vectors. It's success and positive outcomes depend on the sound planning, implementation, enforcement, and validation of the locally adapted vector control efforts from the involved national sectors and stakeholders. Nevertheless, current realities create several implications impeding IVM's performance. Hence, there is a need to adjust local IVM plans to several factors, such as (i) the rapidly changing and unpredictable environmental conditions (i.e., climate change, shift on species distribution, invasive species-Anopheles stephensi, Aedes aegypti and Ae. albopictus); (ii) the environmental impacts from human activities (i.e., fossil fuel use, food sources, industry, land use, urbanization and deforestation); (iii) changes in human demographics and the international movement of people (travelers and forcibly displaced persons due to conflicts and severe weather) increasing the risk of contracting and transmitting vector-borne diseases and shifting humanitarian emergencies and societal demands; (iv) the SARS-CoV2 pandemic outbreak and the implication on national public health systems; (v) the continuous flow of technological advancements and newly acquired knowledge; (vi) the realization of the strong link between planetary health and public health. Addressing these factors in IVM can become difficult, taking into consideration the numerous involved sectors, stakeholders, and fields in the management of vectors and vector-borne diseases (VBD). This document proposes and discusses the aspects and steps of a holistic approach, referenced as the Circular Policy, for national and local IVM strategies to be effective and adaptable, capable of providing the optimum outcomes.

Acetone extracts of three selected plants induce toxicological and biological effects against the house mosquito, Culex pipiens (Diptera: Culicidae)

The biological effect of acetone extracts from three selected plants, Lantana camara, Rhazya astricta, and Citrullus colocynthis, on the egg hatch rate, larvicidal activity, and larval development of Culex pipiens L. was investigated. The egg hatch rate of Cx. pipiens was significantly reduced (P<0.01) when the extracts of L. camara were used. Moreover, the used extracts significantly exhibited a variable larvicidal activity against the Cx. pipiens (P<0.001). The most toxicity was observed when the larvae were treated with the acetonic extract of L. camara, showing different toxicities with lower LC₅₀s at 140.1 ppm after two days and 51.3 ppm after ten days. In this observed time, larvae suffered chronic toxicities (increased mortality with increasing exposure time and sublethal endpoints, such as decreased larvae development) when treated with used plant extracts, leading to 96.7% mortality with L. camara and 91.5% and 85.7% mortalities with C. colocynthis and Rh. stricta, respectively. All concentrations significantly obstructed larvae development, causing significant reductions in both the proportion of pupation (P<0.001) and the emergence of adults (P<.001). The larval development reduction was observed under the L. camara extracts treatment, where only 15.2% and 9.7% of the larvae managed to reach pupal and adult stages, respectively. In conclusion, applying acetone extracts from L. camara to immature mosquito breeding sites may efficiently control mosquitoes to reduce the reliance on insecticides against these disease vectors.

Insecticide Resistance in Aedes aegypti Varies Seasonally and Geographically in Texas/Mexico Border Cities

Insecticide use is the primary method of attempting to reduce or control the spread of mosquito-borne diseases. Insecticide resistance is a major concern as resistance will limit the efficacy of vector-control efforts. The lower Rio Grande Valley region of South Texas has had autochthonous transmission of multiple mosquito-borne diseases including those caused by dengue virus, chikungunya virus, and Zika virus. However, the current status of mosquito resistance to commonly used pesticides in this region is unknown. In this study, we collected field samples from multiple municipalities in South Texas and assessed resistance using the Centers for Disease Control and Prevention bottle bioassay. All populations exhibited characteristics of resistance, and permethrin was the most effective insecticide with an average mortality rate of 44.78%. Deltamethrin and sumethrin had significantly lower mortality rates of 20.31% and 32.16%, respectively, although neither of these insecticides are commonly used for vector-control activities in this region. Depending on which insecticide was used, there was little significance between each of the 7 cities. Seasonal variation in resistance was observed among the collection sites. Both deltamethrin and sumethrin exhibited an increase in susceptibility over the course of 10 months, while permethrin exhibited a decrease in susceptibility. These data highlight the need for further studies to determine if variations in resistance observed are repeated. The data and future findings may be useful in determining the most effective strategies for pesticide use and rotation.

Organophosphate Resistance in Aedes aegypti: Study from Dengue Hemorrhagic Fever Endemic Subdistrict in Riau, Indonesia

BACKGROUND

Dengue hemorrhagic fever (DHF) is a significant health problem. The high number of cases requires preventions, including controlling the dengue vector, Aedes aegypti mosquito. One of the control methods is the use of insecticides containing organophosphate. This study aims to detect organophosphate resistance in Aedes aegypti from DHF endemic subdistrict, Riau, Indonesia by a sensitivity test of temephos and 5% malathion and measuring the activity of non-specific alpha and beta esterase enzymes.

METHODS

This observational study determined Aedes aegypti resistance from larvae to adult in one DHF endemic subdistrict in Riau, Indonesia. The bioassay was used for temephos sensitivity of Aedes aegypti larvae. The LC99 value was analyzed using probit and compared with the diagnostic value from WHO. The WHO susceptibility test was conducted to determine 5% malathion resistance from adult mosquitoes. The mortality of less than 90% was declared as resistant. Measurement of alpha and beta esterase levels used Lee's microplate assay technique based on visual identification and absorbance value (AV).

RESULTS

The results showed that Aedes aegypti were resistant to temephos. It also showed that adult mosquitoes were resistant to 5% malathion. Based on the alpha esterase activity test, it was found that most of the mosquitoes showed very sensitive meanwhile, based on the beta esterase activity test, most of the mosquitoes were moderate resistance.

CONCLUSION

This study suggests that Aedes aegypti population from DHF endemic subdistrict in Riau, Indonesia are indicated to develop resistance to organophosphate.

Green synthesis of AgNP-ligand complexes and their toxicological effects on Nilaparvata lugens

BACKGROUND

Despite developments in nanotechnology for use in the pharmaceutical field, there is still a need for implementation of this technology in agrochemistry. In this study, silver nanoparticles (AgNPs) were successfully prepared by a facile and an eco-friendly route using two different ligands, 2'-amino-1,1':4',1″-terphenyl-3,3″,5,5″-tetracarboxylic acid (H4L) and 1,3,6,8-tetrakis (p-benzoic acid)-pyrene (TBAPy), as reducing agents. The physiochemical properties of the as-obtained AgNPs were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The toxicity of H4L-AgNP and TBAPy-AgNP against the brown planthopper (BPH, Nilaparvata lugens) was also measured.

RESULTS

SEM and TEM analyses demonstrated the formation of quasi-spherical AgNP structures in the presence of H4L and TBAPy. Insecticidal assays showed that TBAPy is less effective against N. lugens, with a median lethal concentration (LC50) of 810 mg/L, while the toxicity of H4L increased and their LC50 reached 786 mg/L 168 h posttreatment at a high concentration of 2000 mg/L. H4L-AgNPs were also highly toxic at a low concentration of 20 mg/L, with LC50 =  ~ 3.9 mg/L 168 h posttreatment, while TBAPy-AgNPs exhibited less toxicity at the same concentration, with LC50 =  ~ 4.6 mg/L.

CONCLUSIONS

These results suggest that the synthesized AgNPs using the two ligands may be a safe and cheaper method compared with chemical insecticides for protection of rice plants from pests and has potential as an effective insecticide in the N. lugens pest management program.

Pyrethroid and Etofenprox Resistance in Anopheles gambiae and Anopheles coluzzii from Vegetable Farms in Yaoundé, Cameroon: Dynamics, Intensity and Molecular Basis

Previous studies have indicated widespread insecticide resistance in malaria vector populations from Cameroon. However, the intensity of this resistance and underlying mechanisms are poorly known. Therefore, we conducted three cross-sectional resistance surveys between April 2018 and October 2019, using the revised World Health Organization protocol, which includes resistance incidences and intensity assessments. Field-collected Anopheles gambiae s.l. populations from Nkolondom, Nkolbisson and Ekié vegetable farms in the city of Yaoundé were tested with deltamethrin, permethrin, alpha-cypermethrin and etofenprox, using 1× insecticide diagnostic concentrations for resistance incidence, then 5× and 10× concentrations for resistance intensity. Subsamples were analyzed for species identification and the detection of resistance-associated molecular markers using TaqMan® qPCR assays. In Nkolbisson, both An. coluzzii (96%) and An. gambiae s.s. (4%) were found together, whereas only An. gambiae s.s. was present in Nkolondom, and only An. coluzzii was present in Ekié. All three populations were resistant to the four insecticides (<75% mortality rates-MR1×), with intensity generally fluctuating over the time between mod-erate (<98%-MR5×; ≥98%-MR10×) and high (76-97%-MR10×). The kdr L995F, L995S, and N1570Y, and the Ace-1 G280S-resistant alleles were found in An. gambiae from Nkolondom, at 73%, 1%, 16% and 13% frequencies, respectively, whereas only the kdr L995F was found in An. gambiae s.s. from Nkolbisson at a 50% frequency. In An. coluzzii from Nkolbisson and Ekié, we detected only the kdr L995F allele at 65% and 60% frequencies, respectively. Furthermore, expression levels of Cyp6m2, Cyp9k1, and Gste2 metabolic genes were highly upregulated (over fivefold) in Nkolondom and Nkolbisson. Pyrethroid and etofenprox-based vector control interventions may be jeopardized in the prospected areas, due to high resistance intensity, with multiple mechanisms in An. gambiae s.s. and An. coluzzii.

Temperatures Influence Susceptibility to Insecticides in Aedes aegypti and Aedes albopictus (Diptera: Culicidae) Mosquitoes

Aedes aegypti and Aedes albopictus (Diptera: Culicidae) are vectors for several arboviruses, including dengue, Zika virus and chikungunya virus. The primary method of controlling these diseases is controlling the vector population, often with insecticides. Insecticide resistance may impact the success of these efforts. We tested the effect of variable temperature exposures on susceptibility to insecticides by exposing adult A.aegypti and A. albopictus to different temperatures and tested their susceptibility to insecticides. We hypothesized that adults maintained at high temperatures would show increased susceptibility to insecticides relative to lower temperatures. Colony mosquitoes were hatched, reared to adulthood and then maintained in three temperature regimes that reflect average seasonal temperatures in the Rio Grande Valley, TX. Susceptibility to permethrin and deltamethrin was assessed using the CDC bottle bioassay method. Overall Aedes albopictus had higher susceptibility to all insecticides than Aedes aegypti. Mosquitoes kept at different temperatures exhibited differential susceptibility to insecticides. Low temperature exposed mosquitoes had decreased susceptibility while high temperature conditions resulted in increased mortality. Our results suggest public health officials must consider temperature effects when controlling mosquitoes with insecticides.

Analyses of Insecticide Resistance Genes in Aedes aegypti and Aedes albopictus Mosquito Populations from Cameroon

The emergence of insecticide resistance in Aedes mosquitoes could pose major challenges for arboviral-borne disease control. In this paper, insecticide susceptibility level and resistance mechanisms were assessed in Aedes aegypti (Linnaeus, 1762) and Aedes albopictus (Skuse, 1894) from urban settings of Cameroon. The F1 progeny of Aedes aegypti and Aedes albopictus collected in Douala, Yaoundé and Dschang from August to December 2020 was tested using WHO tube assays with four insecticides: deltamethrin 0.05%, permethrin 0.75%, DDT 4% and bendiocarb 0.1%. TaqMan, qPCR and RT-qPCR assays were used to detect kdr mutations and the expression profiles of eight detoxification genes. Aedes aegypti mosquitoes from Douala were found to be resistant to DDT, permethrin and deltamethrin. Three kdr mutations, F1534C, V1016G and V1016I were detected in Aedes aegypti populations from Douala and Dschang. The kdr allele F1534C was predominant (90%) in Aedes aegypti and was detected for the first time in Aedes albopictus (2.08%). P450s genes, Cyp9J28 (2.23-7.03 folds), Cyp9M6 (1.49-2.59 folds), Cyp9J32 (1.29-3.75 folds) and GSTD4 (1.34-55.3 folds) were found overexpressed in the Douala and Yaoundé Aedes aegypti populations. The emergence of insecticide resistance in Aedes aegypti and Aedes albopictus calls for alternative strategies towards the control and prevention of arboviral vector-borne diseases in Cameroon.

Secondary malaria vectors in western Kenya include novel species with unexpectedly high densities and parasite infection rates

BACKGROUND

Malaria vector control has been implemented chiefly through indoor interventions targeting primary vectors resulting in population declines-pointing to a possible greater proportional contribution to transmission by secondary malaria vectors with their predominant exophagic and exophilic traits. With a historical focus on primary vectors, there is paucity of data on secondary malaria vectors in many countries in Africa. This study sought to determine the species compositions and bionomic traits, including proportions infected with Plasmodium falciparum and phenotypic insecticide resistance, of secondary vectors in three sites with high malaria transmission in Kisumu County, western Kenya.

METHODS

Cross-sectional sampling of adult Anopheles was conducted using indoor and outdoor CDC light traps (CDC-LT) and animal-baited traps (ABTs) in Kakola-Ombaka and Kisian, while larvae were sampled in Ahero. Secondary vectors captured were exposed to permethrin using WHO bioassays and then analyzed by ELISA to test for proportions infected with P. falciparum sporozoites. All Anopheles were identified to species using morphological keys with a subset being molecularly identified using ITS2 and CO1 sequencing for species identification.

RESULTS

Two morphologically identified secondary vectors captured-An. coustani and An. pharoensis-were determined to consist of four species molecularly. These included An. christyi, An. sp. 15 BSL-2014, an unidentified member of the An. coustani complex (An. cf. coustani) and a species similar to that of An. pharoensis and An. squamosus (An. cf. pharoensis). Standardized (Anopheles per trap per night) capture rates demonstrate higher proportions of secondary vectors across most trapping methods-with overall indoor and outdoor CDC-LTs and ABT captures composed of 52.2% (n = 93), 78.9% (n = 221) and 58.1% (n = 573) secondary vectors respectively. Secondary vectors were primarily caught outdoors. The overall proportion of secondary vectors with P. falciparum sporozoite was 0.63% (n = 5), with the unidentified species An. cf. pharoensis, determined to carry Plasmodium. Overall secondary vectors were susceptible to permethrin with a > 99% mortality rate.

CONCLUSIONS

Given their high densities, endophily equivalent to primary vectors, higher exophily and Plasmodium-positive proportions, secondary vectors may contribute substantially to malaria transmission. Unidentified species demonstrate the need for further morphological and molecular identification studies towards further characterization. Continued monitoring is essential for understanding their temporal contributions to transmission, the possible elevation of some to primary vectors and the development of insecticide resistance.

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

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

Permethrin Resistance in Aedes aegypti Affects Aspects of Vectorial Capacity

Aedes aegypti, as one of the vectors transmitting several arboviruses, is the main target in mosquito control programs. Permethrin is used to control mosquitoes and Aedes aegypti get exposed due to its overuse and are now resistant. The increasing percentage of permethrin resistant Aedes aegypti has become an important issue around the world and the potential influence on vectorial capacity needs to be studied. Here we selected a permethrin resistant (p-s) Aedes aegypti population from a wild Florida population and confirmed the resistance ratio to its parental population. We used allele-specific PCR genotyping of the V1016I and F1534C sites in the sodium channel gene to map mutations responsible for the resistance. Two important factors, survival rate and vector competence, that impact vectorial capacity were checked. Results indicated the p-s population had 20 times more resistance to permethrin based on LD50 compared to the parental population. In the genotyping study, the p-s population had more homozygous mutations in both mutant sites of the sodium channel gene. The p-s adults survived longer and had a higher dissemination rate for dengue virus than the parental population. These results suggest that highly permethrin resistant Aedes aegypti populations might affect the vectorial capacity, moreover, resistance increased the survival time and vector competence, which should be of concern in areas where permethrin is applied.

Computational and Experimental Approaches to Decipher the Binding Mechanism of General Odorant-Binding Protein 2 from Athetis lepigone to Chlorpyrifos and Phoxim

Insect resistance to insecticides is an increasingly serious problem, and the resistant mechanisms are complicated. The resistance research based on the chemosensory pathway is one of the hot problems at present, but the specific binding mechanism of chemosensory genes and insecticides remains elusive. The binding mechanism of AlepGOBP2 (belong to insect chemosensory gene) with two insecticides was investigated by computational and experimental approaches. Our calculation results indicated that four key residues (Phe12, Ile52, Ile94, and Phe118) could steadily interact with these two insecticides and be assigned as hotspot sites responsible for their binding affinities. The significant alkyl-π and hydrophobic interactions involved by these four hotspot residues were found to be the driving forces for their binding affinities, especially for two residues (Phe12 and Ile94) that significantly contribute to the binding of chlorpyrifos, which were also validated by our binding assay results. Furthermore, we also found that the AlepGOBP2-chlorpyrifos/phoxim complexes can be more efficiently converged in the residue-specific force field-(RSFF2C) and its higher accuracy and repeatability in protein dynamics simulation, per-residue free energy decomposition, and computational alanine scanning calculations have also been achieved in this paper. These findings provided useful insights for efficient and reliable calculation of the binding mechanism of relevant AlepGOBPs with other insecticides, facilitating to develop new and efficient insecticides targeting the key sites of AlepGOBP2.

A Review of the Control of Aedes aegypti (Diptera: Culicidae) in the Continental United States

Aedes aegypti (L) is an anthropophilic mosquito involved in the transmission of a variety of viral pathogens worldwide including dengue, chikungunya, yellow fever, and Zika viruses. This species, native to Africa, is well established in the continental U.S. (CONUS) and occasionally contributes to localized outbreaks of viral diseases. In the last seven decades, mosquito control programs in the CONUS have been focused on vectors of eastern equine encephalitis, St. Louis encephalitis, and West Nile viruses, as well as nuisance species. Aedes aegypti receives little control focus except during outbreak periods, which has led to a lack of information on appropriate and effective control options targeting Ae. aegypti in the CONUS. As such, in the event of an Ae. aegypti-borne arboviral outbreak in the CONUS, there are limited evidence-based control recommendations or protocols in place. Autochthonous outbreaks of Ae. aegypti-borne pathogens have occurred recently in the CONUS, including dengue outbreaks in 2010 and 2013, a chikungunya outbreak in 2014, and the 2016 outbreak of Zika virus. The increasing frequency of Ae. aegypti-borne outbreaks necessitates increased attention and research on control of this species to prevent and mitigate future outbreaks. This review consolidates and synthesizes the available literature on control of Ae. aegypti, specifically within the CONUS, focusing on data generated through operational applications as well as field and semifield experiments. The purpose of this review is to identify and highlight areas where additional research is needed. The review covers chemical control and insecticide resistance, biological control, source reduction, trapping, and alternative techniques.

Characterization of Pyrethroid Resistance Mechanisms in Aedes aegypti from the Florida Keys

The status of insecticide resistance in Aedes aegypti is of concern in areas where Aedes-borne arboviruses like chikungunya, dengue, and Zika occur. In recent years, outbreaks involving these arboviruses have occurred, for which vaccines do not exist; therefore, disease prevention is only through vector control and personal protection. Aedes aegypti are present on every inhabited island within the Florida Keys. The resistance status of Ae. aegypti in the Florida Keys was assessed to guide knowledge of the best choice of chemical for use during an outbreak. Mosquito eggs were collected using ovitraps placed on Key West, Stock Island, Vaca Key, Upper Matecumbe Key, Plantation Key, and Key Largo. Bottle bioassays were conducted at the Florida Keys Mosquito Control District using Biomist® 30+30 (Clarke Mosquito Control Products, Inc., Roselle, IL). Further bottle testing using malathion and permethrin occurred at the CDC, Fort Collins, CO, in addition to molecular and biochemical assays. Levels of resistance varied between islands with different underlying mechanisms present. Resistance was seen to Biomist® 30+30 but not to permethrin, indicating that piperonyl butoxide (PBO) or the inert ingredients may be involved in resistance. No study has been conducted to date examining the role of PBO in resistance. Key Largo was treated the most with adulticides and expressed the highest levels of alpha and beta esterases, oxidases, glutathione-S-transferases, and frequency of the V1016I knockdown mutation from all sites tested. Knowledge of localized resistance and underlying mechanisms helps in making rational decisions in selection of appropriate and effective insecticides.

CYP450 core involvement in multiple resistance strains of Aedes aegypti from French Guiana highlighted by proteomics, molecular and biochemical studies

Insecticide resistance is a worldwide threat for vector control around the world, and Aedes aegypti, the main vector of several arboviruses, is a particular concern. To better understand the mechanisms of resistance, four isofemale strains originally from French Guiana were isolated and analysed using combined approaches. The activity of detoxification enzymes involved in insecticide resistance was assayed, and mutations located at positions 1016 and 1534 of the sodium voltage-gated channel gene, which have been associated with pyrethroid resistance in Aedes aegypti populations in Latin America, were monitored. Resistance to other insecticide families (organophosphates and carbamates) was evaluated. A large-scale proteomic analysis was performed to identify proteins involved in insecticide resistance. Our results revealed a metabolic resistance and resistance associated with a mutation of the sodium voltage-gated channel gene at position 1016. Metabolic resistance was mediated through an increase of esterase activity in most strains but also through the shifts in the abundance of several cytochrome P450 (CYP450s). Overall, resistance to deltamethrin was linked in the isofemale strains to resistance to other class of insecticides, suggesting that cross- and multiple resistance occur through selection of mechanisms of metabolic resistance. These results give some insights into resistance to deltamethrin and into multiple resistance phenomena in populations of Ae. aegypti.

Biochemical Mechanism of Insecticide Resistance in Malaria Vector, Anopheles gambiae s.l in Nigeria

Background

Malaria is a parasitic vector-borne disease endemic in the tropical and subtropical countries of the world. The aim of this study was to investigate the current activities of the detoxification enzymes in resistant and susceptible Anopheles gambiae s.l. in northern Nigeria.

Methods

Anopheles larvae were collected from northeast and northwestern Nigeria between Aug and Nov 2018. Biochemical analyses was carried out on the mosquitoes exposed to various insecticides (deltamethrin, DDT, bendiocarb, malathion) to measure and compare the enzymatic activities of the major detoxification enzymes (P₄₅₀, GSTs, Esterase).

Results

High levels of resistance was observed; DDT 37%-53% (95%, CI: 29-61), bendiocarb 44%-55% (CI: 39-60) and deltamethrin 74%-82% (CI: 70-86). However, these mosquitoes were found to be susceptible to malathion 99%-100% (CI: 98-100). The P450 and GSTs enzymes were found to be elevated in the resistant mosquitoes exposed to deltamethrin (1.0240±0.1902); (1.3088±1.2478), DDT (1.7703±1.4528); (1.7462±0.9418) and bendiocarb (1.1814±0.0918); (1.4479±1.0083) compared to the Kisumu strain (0.764±0.4226); (0.6508±0.6542), (0.3875±0.3482); (0.4072±0.4916) and (0.6672±0.3949); (0.7126±0.7259) at P<0.05. Similarly, the resistant mosquitoes expressed increased activity to esterase (0.7606±1.1477), (0.3269±1.1957) and (2.8203±0.6488) compared to their susceptible counterpart (0.6841±0.7597), (0.7032±0.5380) and (0.6398±0.4159) at P<0.05. The enzyme ratio was found to be: P450 (1.341, 4.568 and 1.77); GSTs (2.011, 4.288 and 2.031); Esterases (1.111, 0.469 and 4.408). One way Anova and single sample t-test were also conducted to determine the effect of the enzymes on the resistant and susceptible strains.

Conclusion

High level of insecticide resistance was observed with significant elevation of detoxification enzymes activities in the resistant mosquitoes.

Community acceptance of environmental larviciding against malaria with Bacillus thuringiensis israelensis in rural Burkina Faso - A knowledge, attitudes and practices study

Background

Malaria control is based on early treatment of cases and on vector control. The current measures for malaria vector control in Africa are mainly based on long-lasting insecticidal nets (LLINs) and to a much smaller extent on indoor residual spraying (IRS). While bed net use is widely distributed and its role is intensively researched, Bti-based larviciding is a relatively novel tool in Africa. In this study, we analyze the perception and acceptability of Bti-based larval source management under different larviciding scenarios that were performed in a health district in Burkina Faso.

Objective

To research people’s perception and acceptance regarding biological larviciding interventions against malaria in their communities.

Methods

A cross-sectional study was undertaken using a total of 634 administered questionnaires. Data were collected in a total of 36 rural villages and in seven town quarters of the semi-urban town of Nouna.

Results

Respondents had basic to good knowledge regarding malaria transmission and how to protect oneself against it. More than 90% reported sleeping under a bed net, while other measures such as mosquito coils and insecticides were only used by a minority. The majority of community members reported high perceived reductions in mosquito abundance and the number of malaria episodes. There was a high willingness to contribute financially to larviciding interventions among interviewees.

Conclusions

This study showed that biological larviciding interventions are welcomed by the population that they are regarded as an effective and safe means to reduce mosquito abundance and malaria transmission. A routine implementation would, despite low intervention costs, require community ownership and contribution.

Assessment of Resistance to Organophosphates and Pyrethroids in Aedes aegypti (Diptera: Culicidae): Do Synergists Affect Mortality?

Aedes aegypti (L.) is the primary vector of Zika, dengue, yellow fever, and chikungunya viruses. Insecticides used in mosquito control can help prevent the spread of vector-borne diseases. However, it is essential to determine insecticide resistance (IR) status before control measures are undertaken. Only the most effective insecticides should be used to avoid ineffective control and/or promotion of IR. Pyrethroids and organophosphates are the most commonly used insecticides for mosquito control. Here, the efficacy of two active ingredients (AIs; permethrin [pyrethroid], chlorpyrifos [organophosphate]), two formulated products (FPs; Biomist [AI: permethrin]) and (Mosquitomist [AI: chlorpyrifos]), and three synergists (piperonyl butoxide, diethyl maleate, S-S-S-tributyl phosphorotrithioate) was evaluated in two Ae. aegypti colonies (pyrethroid resistant and susceptible). Mosquitomist was most effective against the pyrethroid-resistant colony (100% mortality at diagnostic time). Pre-exposure to synergists did not increase the efficacy of AIs against the pyrethroid-resistant colony. Further research is needed to discover how synergists may affect the efficacy of insecticides when used on pyrethroid-resistant mosquitoes.

Mechanisms associated with pyrethroid resistance in populations of Aedes aegypti (Diptera: Culicidae) from the Caribbean coast of Colombia

Aedes aegypti is the main vector of dengue, chikungunya, and Zika viruses, which are of great public health importance in Colombia. Aedes control strategies in Colombia rely heavily on the use of organophosphate and pyrethroid insecticides, providing constant selection pressure and the emergence of resistant populations. In recent years, insecticide use has increased due to the increased incidence of dengue and recent introductions of chikungunya and Zika. In the present study, pyrethroid resistance was studied across six populations of Ae. aegypti from the Caribbean coast of Colombia. Susceptibility to λ-cyhalothrin, deltamethrin, and permethrin was assessed, and resistance intensity was determined. Activity levels of enzymes associated with resistance were measured, and the frequencies of three kdr alleles (V1016I, F1534C, V410L) were calculated. Results showed variations in pyrethroid susceptibility across Ae. aegypti populations and altered enzyme activity levels were detected. The kdr alleles were detected in all populations, with high variations in frequencies: V1016I (frequency ranging from 0.15-0.70), F1534C (range 0.94-1.00), and V410L (range 0.05-0.72). In assays of phenotyped individuals, associations were observed between the presence of V1016I, F1534C, and V410L alleles and resistance to the evaluated pyrethroids, as well as between the VI1016/CC1534/VL410 tri-locus genotype and λ-cyhalothrin and permethrin resistance. The results of the present study contribute to the knowledge of the mechanisms underlying the resistance to key pyrethroids used to control Ae. aegypti along the Caribbean coast of Colombia.

Larvicidal and histopathology effect of endophytic fungal extracts of Aspergillus tamarii against Aedes aegypti and Culex quinquefasciatus

BACKGROUND

Mosquitoes biolarvicides remain the most important method for mosquito control. The previous studies have shown Aspergillus sp.-expressed larvicidal properties against mosquito species. The present study evaluated larvicidal and histopathological effect of an endophytic fungus Aspergillus tamarii isolated from theCactus stem (Opuntia ficus-indica Mill).

METHOD

The molecular identification of isolated A. tamarii was done by PCR amplification (5.8s rDNA) using a universal primer (ITS-1 and ITS-2). The secondary metabolites of A. tamarii was tested for larvicidal activity against Aedes aegypti and Culex quinquefasciatus. Larvicidal bioassay of different concentrations (- 100, 300, 500, 800 and 1000 μg/mL) isolated extracts were done according to the modified protocol. Each test included a set of control groups (i.e. DMSO and distilled water). The lethal concentrations (LC50 and LC90) were calculated by probit analysis. Experimental monitoring duration was 48 h.

RESULTS

The ethyl acetate extract from A. tamarii fungus resulted - excellent mosquitocidal effect against Ae. aegypti and Cx. quinquefasciatus mosquitoes, with least LC50 and LC90 values. -After 48 h, the Ae. aegypti expressed better results (LC50 = 29.10, 18.69, 16.76, 36.78 μg/mL and the LC90 = 45.59, 27.66, 27.50, 54.00 μg/mL) followed by Cx. quinquefaciatus (LC50 = 3.23, 24.99, 11.24, 10.95 μg/mL and the LC90 = 8.37, 8.29, 21.36, 20.28 μg/mL). The biochemical level of A. tamarii mycelium extract on both larvae was measured and the results shown a dose dependent activity on the level of AchE, α- and β-carboxylesterase assay. Gas Chromatography and Mass Spectroscopy (GC-MS) profile of A. tamarii extract reflected three compounds i.e. preg-4-en-3-one, 17. α-hydroxy-17. β-cyano- (7.39%), trans-3-undecene-1,5-diyne (45.77%) and pentane, 1,1,1,5-tetrachloro- (32.16%) which which might had attributed to larvae mortality.

CONCLUSION

The findings of - present study shows that the use of endophytic A. tamarii fungal metabolites for control of dengue and filariasis vectors is promising and needs a semifield and small scale filed trials.

Comparative Molecular Description of a Novel GST Gene in Culex pipiens (Diptera: Culicidae)

Repeated exposure to insecticides, particularly pyrethroids and organophosphates, has resulted in the development of insecticide resistance in the mosquito Culex pipiens, a primary disease vector. Glutathione S-transferase (GST) is involved in the phase II detoxification of numerous xenobiotics, including insecticides. In this study, a GST gene (CPIJ002678) was amplified, sequenced, and used in comprehensive molecular analyses ending up in development of a rapid assay to distinguish more tolerant individuals from susceptible Culex pipiens using the Restriction Fragment Length Polymorphism (RFLP) technique. Field collected Culex pipiens strains from untreated areas, organophosphates-treated areas and a lab strain reared for many generations, all were used in CDC bottle bioassays to evaluate the susceptibility status of the studied individuals to malathion insecticide. Interestingly, both field sites collected groups showed high levels of resistance at the malathion diagnostic time. Gene amplification, and bidirectional direct sequencing results were analyzed. Compared with the reference genome sequence, the pairwise alignment of the amplified sequences showed 96.6% similarity to the reference sequence in the GenBank database. The confirmed gene sequences were assembled and aligned using various bioinformatic softwares. The assembled contigs were used in NEBcutter V2.0 for constructing restriction maps and checked for the availability of differences (if present) between susceptible and more tolerant strains. Specific molecular RFLP markers were successfully recognized to differentiate the more tolerant from the susceptible Culex pipiens phenotypes.

First report of the lethal activity and synergism between deltamethrin, amitraz and piperonyl butoxide against susceptible and pyrethroid-resistant nymphs of Triatoma infestans

In South America, Triatoma infestans (Hemiptera: Reduviidae) is the main vector of the parasite Trypanosoma cruzi, etiological agent of Chagas disease. The main strategy for vector control is to spray domestic structures with pyrethroids. Reports of populations of T. infestans with varying degrees of resistance to pyrethroids have made the search for alternative molecules for vector control necessary. In the first stage of this work we investigated the lethal activity of amitraz and deltamethrin against susceptible and pyrethroid-resistant nymphs of Triatoma infestans. Lethal dose at 50% (LD₅₀) of susceptible nymphs were compared with those recorded in pyrethroid-resistant nymphs and the resistance ratio (RR₅₀) was obtained. The RR₅₀ of deltamethrin was approximately 300. In the case of amitraz, we observed similar triatomicidal activity in the two nymph populations (RR₅₀: 0.7). In a second stage of the work, we determined the synergistic effect of amitraz and piperonyl butoxide (PBO) on the lethal activity of deltamethrin. The strong synergistic effect of PBO on the lethal activity of deltamethrin in resistant nymphs produced a decrease in RR₅₀ to almost one third of the RR₅₀ reported in absence of the synergist. Amitraz plus PBO lethal activity was similarly increased in pyrethroid susceptible and resistant nymphs. Our data indicate that deltamethrin synergism by amitraz was higher against resistant than to susceptible nymphs (Synergist ratio (SR₅₀) of: 7.2- and 4.1-fold, respectively). In pyrethroid resistant nymphs, the highest level of synergism was obtained combining deltamethrin with amitraz and PBO (SR₅₀: 26.7-fold). These results indicate that this combination could be considered an effective alternative for the control of T. infestans.

Screening of insecticide resistance in Aedes aegypti populations collected from parishes in Eastern Jamaica

Owing to the increased reports in Aedes-borne diseases in the Caribbean and Latin America, the United States Agency for International Development assisted the Jamaican Ministry of Health and Wellness in conducting insecticide susceptibility tests on Aedes aegypti populations.

Sentinel sites were established in seven parishes of Jamaica (St. Catherine, Kingston and St. Andrew, St. Thomas, Portland, St. Mary and St. Ann) and Aedes aegypti eggs were collected, reared to adults per collected population and their susceptibility to varying pyrethroids and organophosphates were tested using the World Health Organization paper bioassays for these insecticides. The Centers for Disease Control and Prevention bottle bioassay was used to assess susceptibility to the carbamate, bendiocarb. The voltage gated sodium channel gene mutations V1016I and I1011V, normally associated with pyrethroid resistance, were also analysed.

The results showed that Aedes aegypti collected from all parishes exhibited resistance to pyrethroids at the following concentrations, permethrin 0.25–2.5%; deltamethrin 0.03–0.15%; lambda-cyhalothrin 0.03–0.3%; and etofenprox 0.5–2.5%. The insecticide deltamethrin at concentration 0.3% was the only pyrethroid tested that resulted in high mortality, 94.9 ± 0.34% knockdown within 1 hour of exposure and 98.95 ± 0.01% mortality (p <0.01) at 24 hours post exposure. The frequency of the voltage gated sodium channel gene mutation V1016I was high in the tested population, possibly accounting for the reduced sensitivity to pyrethroids. Organophosphate resistance was also observed in all populations tested. Mortality rates for 0.8% Malathion was 0.8 ± 0.70–60.68 ± 0.38% after 24 hour and 0.00–47.10 ± 3.02%, for pirimiphos-methyl 0.21%. Bendiocarb applied as 12.5 μg/ bottle resulted in mortality rates of 76.25 ± 4.30–100 ± 0.00% after 30 minutes of exposure.

The results showed that Ae. aegypti from the seven parishes analysed demonstrated resistance to the insecticides tested. Deltamethrin and bendiocarb at concentrations 0.3% and 12.5μg respectively, were considered most effective, causing high mortality in the local populations. Routine monitoring and evaluations of Ae. aegypti populations from the included parishes are recommended. Additionally, the study results represent the most comprehensive testing to date with local Aedes aegypti populations distributed across different parishes of Jamaica and should be useful to guide national and sub national strategies for vector control and surveillance.

The recent outbreaks of chikungunya, Zika and dengue viruses in the Caribbean and Latin America during 2013–2018, have motivated local health authorities in individual countries to seek international assistance from multiple agencies and adjust their vector management strategies in order to contain the transmission of Aedes-borne diseases. Countries within the region rely mainly on the use of commercially available insecticides to manage the mosquito populations and by extension, reduce the transmission of vector-borne diseases. However, this practice is stymied by the ability of these insects to develop resistance mechanisms to insecticides of frequent use. Many countries in the Caribbean and Latin America regions lack the facilities and supplies to conduct routine insecticide susceptibility testing. In an effort to ascertain knowledge on the presence of insecticide resistance in Aedes aegypti populations, and to determine which insecticide is more effective to reduce vector populations of Jamaica, we conducted an array of bioassays with three different types of insecticides (pyrethroid, organophosphate, carbamate) to use local evidence and inform public health authorities on vector control status and alternatives.

Pyrethroid and Carbamate Resistance in Anopheles funestus Giles along Lake Kariba in Southern Zambia

Whereas data on insecticide resistance and its underlying mechanisms exist for parts of Zambia, data remain limited in the southern part of the country. This study investigated the status of insecticide resistance, metabolic mechanisms, and parasite infection in Anopheles funestus along Lake Kariba in southern Zambia. Indoor-resting mosquitoes were collected from 20 randomly selected houses within clusters where a mass drug administration trial was conducted and raised to F1 progeny. Non–blood-fed 2- to 5-day-old female An. funestus were exposed to WHO insecticide-impregnated papers with 0.05% deltamethrin, 0.1% bendiocarb, 0.25% pirimiphos-methyl, or 4% dichloro-diphenyl-trichloroethane (DDT). In separate assays, An. funestus were pre-exposed to piperonyl butoxide (PBO) to determine the presence of monooxygenases. Wild-caught An. funestus that had laid eggs for susceptibility assays were screened for circumsporozoite protein of Plasmodium falciparum by ELISA, and sibling species were identified by polymerase chain reaction. Anopheles funestus showed resistance to deltamethrin and bendiocarb but remained susceptible to pirimiphos-methyl and DDT. The pre-exposure of An. funestus to PBO restored full susceptibility to deltamethrin but not to bendiocarb. The overall sporozoite infection rate in An. funestus populations was 5.8%. Detection of pyrethroid and carbamate resistance in An. funestus calls for increased insecticide resistance monitoring to guide planning and selection of effective insecticide resistance management strategies. To prevent the development of resistance and reduce the underlying vectorial capacity of mosquitoes in areas targeted for malaria elimination, an effective integrated vector management strategy is needed.

Insecticide Resistance Status of Aedes aegypti (Diptera: Culicidae) in California by Biochemical Assays

Insecticide resistance in Aedes aegypti mosquitoes poses a major threat to public health worldwide. There are two primary biological mechanisms that can lead to insecticide resistance, target site and metabolic resistance, both of which confer resistance to specific classes of insecticides. Due to the limited number of chemical compounds available for mosquito control, it is important to determine current enzymatic profiles among mosquito populations. This study assessed resistance profiles for three metabolic pathways, α-esterases, β-esterases, and mixed-function oxidases (MFOs), as well as insensitivity of the acetylcholinesterase (iAChE) enzyme in the presence of propoxur, among Ae. aegypti from the Central Valley and southern California. All field-collected Ae. aegypti demonstrated elevated MFOs and iAChE activity, indicating potential development of pyrethroid and organophosphate resistance, respectively. Although regional variations were found among α-esterase and β-esterase activity, levels were generally elevated, further suggesting additional mechanisms for developing organophosphate resistance. Furthermore, mosquito samples from southern California exhibited a higher expression level to all three metabolic enzymes and iAChE activity in comparison to mosquitoes from the central region. These results could help guide future mosquito control efforts, directing the effective use of insecticides while limiting the spread of resistance.

Managing plague on prairie dog colonies: insecticides as ectoparasiticides

Human health practitioners and wildlife biologists use insecticides to manage plague by suppressing fleas (Siphonaptera), but insecticides can also kill other ectoparasites. We investigated effects of deltamethrin and fipronil on ectoparasites from black-tailed prairie dogs (Cynomys ludovicianus, BTPDs). In late July, 2018, we treated three sites with 0.05% deltamethrin dust and 5 sites with host-fed 0.005% fipronil grain. Three non-treated sites functioned as experimental baselines. We collected ectoparasites before treatments (June-July, 2018) and after treatments (August-October, 2018, June-July, 2019). Both deltamethrin and fipronil suppressed fleas for at least 12 months. Deltamethrin had no detectable effect on mites (Arachnida). Fipronil suppressed mites for at least 12 months. Lice (Phthiraptera) were scarce on non-treated sites throughout the study, complicating interpretation. Concentrating on eight sites where all three ectoparasites where found in June-July, 2018 (before treatments), flea intensity was greatest on BTPDs carrying many lice and mites. These three ectoparasites co-occurred at high numbers, which might facilitate plague transmission in some cases. Lethal effects of insecticides on ectoparasite communities are potentially advantageous in the context of plague management.

Assessment the Changing Trend of Susceptibility to Two Insecticides among Field-Population Culex quinquefasciatus Compared with the Same Population Undergoing to Multiple Colonization

BACKGROUND

During the past decade, rapid development of insecticide resistance have been reported among many species of mosquito vectors against four main categories of insecticides worldwide. The aim of the research was to assess the variation trend of susceptibility levels of Culex quinquefasciatus to two insecticides separately for the field population compared with subsequent generations of the same sample after multiple colonization.

METHODS

Larvae and pupae of Cx. quinquefasciatus were collected from house sewages and reared to adult which blood-fed on roosters. Ten percent sucrose fed female mosquitoes aged 2-3 days were used for susceptibility tests with DDT and deltamethrin. Susceptibility levels was assessed in the adult stage of field stran Cx. quinquefasciatus against DDT 4.0% and deltamethrin 0.05% and continued up to next six generations undergoing multiple rearing at insectary condition.

RESULTS

The susceptibility levels to DDT 4.0% did not change compared to the field with the lab population to six generations. Regarding deltamethrin 0.05%, no significant difference was shown between field strain (58.3%) and 3rd generation (52.7%) compared to the 6th one (33.8%).

CONCLUSION

This finding may reflect the role of the kdr gene in resistance to organochlorine which has cross-resistance with pyrethroid insecticides. The results of this study clearly showed the irreversible trend of pyrethroid resistance among colonized mosquitoes. This is the first study of the resistance status of Cx. quinquefasciatus in Iran.

Impact of deltamethrin selection on kdr mutations and insecticide detoxifying enzymes in Aedes aegypti from Mexico

Background

Insecticide resistance is a serious problem for vector control programmes worldwide. Resistance is commonly attributed to mutations at the insecticide’s target site or increased activity of detoxification enzymes.

Methods

We determined the knockdown concentration (KC₅₀) and lethal concentration (LC₅₀) of deltamethrin in six natural populations of adult Aedes aegypti from southeastern Mexico. These populations were then selected over five generations using the LC₅₀ from the preceding generation that underwent selection, and the heritability of deltamethrin resistance was quantified. For each generation, we also determined the frequency of the kdr alleles L410, I1016 and C1534, and the levels of activity of three enzyme families (α- and β-esterases, mixed-function oxidases and glutathione S-transferases (GST)) associated with insecticide detoxification.

Results

There was an increase in KC₅₀ and LC₅₀ values in the subsequent generations of selection with deltamethrin (F_S5vs F_S0). According to the resistance ratios (RRs), we detected increases in LC₅₀ ranging from 1.5 to 5.6 times the values of the parental generation and in KC₅₀ ranging from 1.3–3.8 times the values of the parental generation. Triple homozygous mutant individuals (tri-locus, LL/II/CC) were present in the parental generations and increased in frequency after selection. The frequency of L410 increased from 1.18-fold to 2.63-fold after selection with deltamethrin (F_S5vs F_S0) in the populations analyzed; for I1016 an increase between 1.19-fold to 2.79-fold was observed, and C1534 was fixed in all populations after deltamethrin selection. Enzymatic activity varied significantly over the generations of selection. However, only α- esterase activity remained elevated in multiple populations after five generations of deltamethrin selection. We observed an increase in the mean activity levels of GSTs in two of the six populations analyzed.

Conclusions

The high levels of resistance and their association with high frequencies of kdr mutations (V410L, V1016I and F1534C) obtained through artificial selection, suggest an important role of these mutations in conferring resistance to deltamethrin. We highlight the need to implement strategies that involve the monitoring of kdr frequencies in insecticide resistance monitoring and management programmes.

Polymorphisms in GSTE2 is associated with temephos resistance in Aedes aegypti

The glutathione S-transferases (GSTs) are enzymes involved in several distinct biological processes. In insects, the GSTs, especially delta and epsilon classes, play a key role in the metabolism of xenobiotics used to control insect populations. Here, we investigated its potential role in temephos resistance, examining the GSTE2 gene from susceptible (RecL) and resistant (RecR) strains of the mosquito Aedes aegypti, vector for several pathogenic arboviruses. Total GST enzymatic activity and the GSTE2 gene expression profile were evaluated, with the GSTE2 cDNA and genomic loci sequenced from both strains. Recombinant GSTE2 and mutants were produced in a heterologous expression system and assayed for enzyme kinetic parameters. These proteins also had their 3D structure predicted through molecular modeling. Our results showed that RecR has a profile of total GST enzymatic activity higher than RecL, with the expression of the GSTE2 gene in resistant larvae increasing six folds. Four exclusive RecR mutations were observed (L111S, I150V, E178A and A198E), which were absent in the laboratory susceptible strains. The enzymatic activity of the recombinant GSTE2 showed different kinetic parameters, with the GSTE2 RecR showing an enhanced ability to metabolize its substrate. The I150V mutation was shown to induce significant changes in catalytic parameters and a 3D modeling of GSTE2 mapped two of the RecR changes (L111S and I150V) near the enzyme's catalytic pocket, also implying an impact on its catalytic activity. Our results reinforce a potential role for GSTE2 in the metabolic resistance phenotype while contributing to the understanding of the molecular basis for the resistance mechanism.

Oxidase, Esterase, and KDR-Associated Pyrethroid Resistance in Culex quinquefasciatus Field Collections of Collier County, Florida

In several insect species, resistance to pyrethroids and DDT (dichlorodiphenyltrichloroethane) is linked to point mutations in the voltage-gated sodium channel (VGSC) gene. Pyrethroid-based insecticides prolong the opening of sodium channels, causing paralysis known as a "knockdown" effect before mortality occurs. Point mutations in the VGSC gene result in decreased pyrethroid binding and reduced sensitivity to the insecticide-this resistance mechanism is known as knockdown resistance (kdr) as insects do not die but recover from paralysis with time. In Culex mosquito species loss of target site sensitivity to pyrethroids is linked to a number of substitutions, one of which is leucine (L) to phenylalanine (F) at residue 1014 (L1014F) in the VGSC gene. Here we report the identification of kdr-associated pyrethroid resistance and developing resistance in Cx. quinquefasciatus field collections from Collier County, FL. Evaluation of position 1014 of the VGSC in Cx. quinquefasciatus collections from 7 locations in Collier County, FL, revealed a wide range of genotypes from one part of the district to the other. Centers for Disease Control and Prevention bottle bioassay, linear regression analysis, and cage trial evaluations suggest that the L1014F mutation plays a role, at least in part, to the pyrethroid resistance status of Cx. quinquefasciatus collected in Collier County, FL. Furthermore, we identified resistance attributed to both oxidase and esterase activity, indicating that multiple mechanisms are responsible for pyrethroid resistance in Collier County Cx. quinquefasciatus.

Comparative toxicity of larvicides and growth inhibitors on Aedes aegypti from select areas in Jamaica

Insecticide resistance has become problematic in tropical and subtropical regions, where Aedes mosquitoes and Aedes-borne arboviral diseases thrive. With the recent occurrence of chikungunya and the Zika virus in Jamaica, the Ministry of Health and Wellness, Jamaica, partnered with the United States Agency for International Development to implement multiple intervention activities to reduce the Aedes aegypti populations in seven parishes across the island and to assess the susceptibility of collected samples to various concentrations of temephos, Bacillus thuringiensis subsp. israelensis, (Bti), diflubenzuron and methoprene. Of the insecticides tested, only temephos has been used in routine larviciding activities in the island. The results showed that only temephos at concentrations 0.625 ppm and Bti at concentrations 6-8 ppm were effective at causing 98-100% mortality of local Ae. aegypti at 24 h exposure. Surprisingly, the growth inhibitors diflubenzuron and methoprene had minimal effect at preventing adult emergence in Ae. aegypti larvae in the populations tested. The results demonstrate the need for insecticide resistance testing as a routine part of vector control monitoring activies in order to determine useful tools that may be incorporated to reduce the abundance of Ae. aegypti.

Voltage-gated sodium channel gene mutations and pyrethroid resistance in Rhipicephalus microplus

Pyrethroid pesticides are extensively used to manage animal and human disease vectors including the southern cattle tick Rhipicephalus microplus (Canestrini). The indiscriminate and incorrect use of pyrethroids has led to the almost ubiquitous development of resistance to this pesticide class for this tick species. Voltage-gated sodium channels (Na-channels) are the primary target-site of pyrethroids and several studies on the involvement of mutations in the coding gene among pyrethroid-resistant R. microplus populations from different parts of the world have shown that there are various single nucleotide polymorphisms (SNPs) that are associated with resistance to pyrethroids. Identification of the exact location of the mutations in the protein coding regions of the targeted gene facilitates the design of various molecular tools for genotyping the resistant populations and thus promotes the rapid detection of resistance. This review aims to provide an update on the identification of pyrethroid resistance-associated Na-channel mutations from R. microplus.The database of diverse mutations from different regions of the world helped us to develop the molecular markers for resistance monitoring in a rapid and efficient manner. Their role and the development of different forms of molecular tools for genotyping ticks for mutations in the Na-channel gene are also discussed. In this review, the word mutation is used interchangeably with SNP.

Baseline Susceptibility of Culiseta longiareolata (Diptera: Culicidae) to Different Imagicides, in Eastern Azerbaijan, Iran

BACKGROUND

Culiseta longiareolata is an important vector for many human diseases such as brucellosis, avian influenza and West Nile encephalitis. It is likely an intermediate host of avian Plasmodium that can transmit Malta fever. The aim of this study was to determine the susceptibility level of Cs. longiareolata to different classes of imagicides which are recommended by World Health Organization .

METHODS

Larval stages of the Cs. longiareolata were collected from their natural habitats in Marand County at East Azerbaijan Province, northwestern of Iran in 2017. Adult susceptibility test were carried out with using impregnated papers to insecticides including DDT 4%, Cyfluthrin 0.15%, Deltamethrin 0.05%, Propoxur 0.1% and Fenitrothion 1% by standard test kits.

RESULTS

Results showed that Cs. longiareolata adult is more susceptible to pyrethroid and carbamate insecticides. Among tested insecticides, Cyfluthrin was the most toxic against Cs. longiareolata with LT₅₀ value of 11.53 minutes and Fenitrothion had the least toxic effect (LT₅₀: 63.39 min).

CONCLUSIONS

This study provided a guideline for monitoring and evaluation of insecticide susceptibility tests against Cs. longiareolata mosquitoes for further decision making.

Insecticide resistance in Culex quinquefasciatus Say, 1823 in Brazil: a review

Culex quinquefasciatus is a successful invasive species broadly distributed in subtropical regions, including Brazil. It is an extremely annoying mosquito due to its nocturnal biting behavior, in high-density populations and it is a potential bridge between sylvatic arbovirus from birds to man in urban territories. Herein, we present a review concerning the methods of chemical control employed against Cx. quinquefasciatus in Brazil since the 1950's and insecticide resistance data registered in the literature. As there is no specific national programme for Cx. quinquefasciatus control in Brazil, the selection of insecticide resistance is likely due in part to the well-designed chemical campaigns against Aedes aegypti and the elevated employment of insecticides by households and private companies. There are very few publications about insecticide resistance in Cx. quinquefasciatus from Brazil when compared to Ae. aegypti. Nevertheless, resistance to organophosphates, carbamate, DDT, pyrethroids and biolarvicides has been registered in Cx. quinquefasciatus populations from distinct localities of the country. Concerning physiological mechanisms selected for resistance, distinct patterns of esterases, as well as mutations in the acetylcholinesterase (ace-1) and voltage-gated sodium channel (NaV) genes, have been identified in natural populations. Given environmental changes and socioeconomical issues in the cities, in recent years we have been experiencing an increase in the number of disease cases caused by arboviruses, which may involve Cx. quinquefasciatus participation as a key vector. It is urgent to better understand the efficiency and susceptibility status to insecticides, as well as the genetic background of known resistant mechanisms already present in Cx. quinquefasciatus populations for an effective and rapid chemical control when eventually required.