Resistant Aedes Research Articles

Insecticide Resistance in Aedes aegypti from the National Capital Region of the Philippines.

Human arboviral diseases such as dengue, chikungunya, and Zika can be transmitted by the mosquito Aedes aegypti. The insecticide-based vector control strategy is critical in reducing transmission of these Aedes-borne diseases but is threatened mainly by the emergence of insecticide resistance. Adult Ae. aegypti from the National Capital Region (NCR), Philippines, were subjected to bioassays to determine their susceptibility to diagnostic doses of pyrethroid, organochlorine, and organophosphate insecticides following the standard World Health Organization insecticide susceptibility test. This study reports the detection of insecticide resistance to pyrethroids and organochlorine in Ae. aegypti from the Philippines for the first time. Most of the Ae. aegypti populations from NCR exhibited phenotypic resistance to permethrin, etofenprox, and DDT. Varying resistance levels to deltamethrin, cyfluthrin, and lambda-cyhalothrin were observed in the different mosquito populations, while all populations tested to malathion were susceptible to this organophosphate. This finding should alert public health authorities to consider modifying the existing vector management package for greater control efficacy. Best practices proven to prevent or delay the development of insecticide resistance, such as insecticide rotation, should also be implemented, while alternative chemicals with a different mode of action should be explored to ensure the continuing efficacy of program interventions.

Detection of Insecticide Resistance in Aedes aegypti from Dengue Endemic Areas of Northern India

Detection of Insecticide Resistance in Aedes aegypti from Dengue Endemic Areas of Northern India

Boric acid toxic sugar bait suppresses male Aedes aegypti (Diptera: Culicidae): wing beat frequency and amplitude, flight activity, fecundity, insemination, and mate-finding Allee effect.

Controlling the spread of arboviral diseases remains a considerable challenge due to the rapid development of insecticide resistance in Aedes mosquitoes. This study evaluated the effects of boric acid-containing toxic sugar bait (TSB) on field populations of resistant Aedes aegypti mosquitoes. In addition, this study examined the flight activity and wing beat frequency and amplitude of males and the flight activity, fecundity, and insemination of females after pairing with males exposed to TSB. The population dynamics of Aedes mosquitoes under imbalanced sex ratios were examined to simulate realistic field conditions for male suppression under the effect of TSB. The mortality of male mosquitoes was consistently high within 24 h after exposure. By contrast, the mortality of female mosquitoes was inconsistent, with over 70% mortality observed at 168 h. The flight activity and wing beat amplitude of treated males were significantly lower than those of controls, but no significant difference in wing beat frequency was detected. The fecundity and insemination of treated female mosquitoes were lower than those of controls. A simulation study indicated that considerably low male population densities led to mating failures, triggering a mate-finding Allee effect and resulting in persistently low population levels. Boric acid-containing TSB could effectively complement current chemical intervention approaches to control resistant mosquito populations. TSB is effective in reducing field male populations and impairing male flight activity and female-seeking behavior, resulting in decreased fecundity and insemination. Male suppression due to TSB potentially results in a small mosquito population. © 2024 Society of Chemical Industry.

Entomological assessment of hessian fabric transfluthrin vapour emanators as a means to protect against outdoor-biting Aedes after providing them to households for routine use in Port-au-Prince, Haiti.

A simple treated fabric device for passively emanating the volatile pyrethroid transfluthrin was recently developed in Tanzania that protected against nocturnal Anopheles and Culex mosquitoes for several months. Here these transfluthrin emanators were assessed in Port-au-Prince, Haiti against outdoor-biting Aedes. Transfluthrin emanators were distributed to participating households in poor-to-middle class urban neighbourhoods and evaluated once every two months in terms of their effects on human landing rates of wild Aedes populations. A series of three such entomological assessment experiments were conducted, to examine the influence of changing weather conditions, various transfluthrin formulations and emanator placement on protective efficacy measurements. Laboratory experiments assessed resistance of local Aedes aegypti to transfluthrin and deltamethrin, and the irritancy and repellency of the transfluthrin-treated fabric used in the field. Across all three entomological field assessments, little evidence of protection against wild Ae. aegypti was observed, regardless of weather conditions, transfluthrin formulation or emanator placement: A generalized linear mixed model fitted to the pooled data from all three assessment rounds (921 females caught over 5129 hours) estimated a relative landing rate [95% Confidence interval] of 0.87 [0.73, 1.04] for users of treated versus untreated emanators (P = 0.1241). Wild Ae. aegypti in this setting were clearly resistant to transfluthrin when compared to a fully susceptible colony. Transfluthrin emanators had little if any apparent effect upon Aedes landing rates by wild Ae. aegypti in urban Haiti, and similar results have been obtained by comparable studies in Tanzania, Brazil and Peru. In stark contrast, however, parallel sociological assessments of perspectives among these same end-users in urban Haitian communities indicate strong satisfaction in terms of perceived protection against mosquitoes. It remains unclear why the results obtained from these complementary entomological and sociological assessments in Haiti differ so much, as do those from a similar set of studies in Brazil. It is encouraging, however, that similar contrasts between the entomological and epidemiological results of a recent large-scale assessment of another transfluthrin emanator product in Peru, which indicate they provide useful protection against Aedes-borne arboviral infections, despite apparently providing only modest protection against Aedes mosquito bites.

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.

Assessing pyrethroid resistance in Aedes aegypti from Cordoba Colombia: Implications of kdr mutations.

Resistance to insecticides is one of the great challenges that vector control programs must face. The constant use of pyrethroid-type insecticides worldwide has caused selection pressure in populations of the Aedes aegypti vector, which has promoted the emergence of resistant populations. The resistance mechanism to pyrethroid insecticides most studied to date is target-site mutations that desensitize the voltage-gated sodium channel (VGSC) of the insect to the action of pyrethroids. In the present study, susceptibility to the pyrethroid insecticides permethrin, lambda-cyhalothrin, and deltamethrin was evaluated in fourteen populations from the department of Córdoba, Colombia. The CDC bottle bioassay and WHO tube methods were used. Additionally, the frequencies of the F1534C, V1016I, and V410L mutations were determined, and the association of resistance with the tri-locus haplotypes was examined. The results varied between the two techniques used, with resistance to permethrin observed in thirteen of the fourteen populations, resistance to lambda-cyhalothrin in two populations, and susceptibility to deltamethrin in all the populations under study with the CDC method. In contrast, the WHO method showed resistance to the three insecticides evaluated in all populations. The frequencies of the mutated alleles ranged from 0.05-0.43 for 1016I, 0.94-1.0 for 1534C, and 0.01-0.59 for 410L. The triple homozygous mutant CIL haplotype was associated with resistance to all three pyrethroids evaluated with the WHO bioassay, while with the CDC bioassay, it was only associated with resistance to permethrin. This study highlights the importance of implementing systematic monitoring of kdr mutations, allowing resistance management strategies to be dynamically adjusted to achieve effective control of Aedes aegypti.

Study of Resistance of Aedes aegypti Mosquitoes to Pyrethroids by Free-flight Method

Efforts to combat dengue hemorrhagic fever (DHF) in Bali are focused on controlling the vector of Aedes aegypti Mosquitoes. One method is fumigation (fogging) with insecticides. The use of insecticides for a long time and improper doses can trigger resistance. Many countries including Indonesia have reported incidents of insecticide resistance. Methods for determining the level of insecticide resistance are bioassay, biochemistry, and gene mutation. The method does not describe the actual environmental conditions of Mosquitoes. Queensland Institute of Medical Research (QIMR) Berghofer developed a free-flight test procedure to evaluate insecticide resistance in free-flying mosquito conditions. The study, which was conducted in June 2019-January 2020, aimed to measure the level of insecticide resistance with the free-flight method in the A. aegypti population in North Denpasar. A total of 20 female A. aegypti aged 5-10 days were released in the free-flight room for 24 hours with permethrin or cypermethrin insecticide boards. The level of resistance is determined based on the mosquito mortality rate using WHO standards. The results showed permethrin and cypermethrin resistance in the A. aegypti population of North Denpasar, with mortality of less than 80%.

Effects of transfluthrin-treated jute and cotton clothing against resistant and susceptible Aedes aegypti (Diptera: Culicidae) in a semifield system.

Volatile pyrethroids exert a range of both lethal and behavioral effects on mosquitoes through the passive release of insecticides into the atmosphere. We investigated the protective efficacy (PE) of transfluthrin-treated jute (TI-jute) and cotton (TI-cotton) fabrics, worn at the back of a protective black vest, against laboratory-reared pyrethroid susceptible and resistant strains of Aedes aegypti (L.) in a semifield system (SFS). Each fabric (1,029 cm2) was treated with 1.79 mg/cm2 of transfluthrin as the intervention. Human landing collections were conducted by 2 collectors seated in designated treatment and control compartments of the SFS. The trials were conducted for 41 days, with 16 days partitioned into morning and evening phases. Furthermore, we examined blood feeding behavior and fecundity of the surviving mosquitoes post-exposure. Results showed that in the morning, the PE of TI-jute (49.4%) was higher than that of TI-cotton (36.8%). TI-jute demonstrated a lower PE of 9.6% against the transfluthrin-resistant strain. Remarkably, a significantly higher number of eggs were laid by the transfluthrin-resistant mosquitoes that survived the intervention (36.5 eggs/female) compared to the control group (11.8 eggs/female). These findings suggest that TI-jute can help protect against bites and alter the life traits of Ae. aegypti. The study highlights that the timing of the intervention during the day affected the efficacy of TI-jute and TI-cotton, while sublethal exposure to transfluthrin stimulated egg production in the resistant strain. These are critical challenges that warrant attention in vector control strategies. Investigating this phenomenon in mosquito reproduction necessitates future research at a molecular level.

The Key Associated Factor of the Emergence of the Dengue Vector in Peri-Urban and Rural Settlements

Introduction: The population density of Aedes mosquitoes is a risk factor for dengue in endemic areas. Therefore, it is necessary to understand the risk factors for mosquito vector emergence in settlements. This study aimed to determine the key factors associated with the occurrence and population density of dengue vectors in peri-urban and rural settlements. Methods: A cross-sectional study was conducted in two dengue-endemic villages, Bergas-Kidul and Gebugan, representing peri-urban and rural settlements, respectively. A cluster-based larval survey was conducted in the dengue-case house and in 18–20 houses around a radius of 100 m. All water containers and their characteristics and mosquito larvae emergence were recorded in each house to calculate Aedes indices. The geographic coordinates, altitude, air temperature, and humidity were mapped and analyzed using GIS and SPSS software. Results and Discussion: Dengue vectors were found in peri-urban and rural with HI, CI, BI, and DF indices of 29.3%, 32.2%, 35.4, 6.0; then 12.2%, 14.3%, 14.6, and 3.0, respectively. In peri-urban areas, larval occurrence was associated with air temperature, air humidity, container type, and open microhabitat, whereas in rural areas, it was associated with only open microhabitat. Conclusion: The Aedes indices represent a high density of mosquito populations, and the existence of open microhabitats is the key factor for larval occurrence in both peri-urban and rural settlements. Community participation in vector control needs to be increased in addition to studying the resistance of Aedes mosquitoes to a number of insecticide groups.

Genetic structure and kdr mutations in Aedes aegypti populations along a road crossing the Amazon Forest in Amapá State, Brazil

Insecticide resistance in Aedes aegypti poses a significant threat to disease control. One form of resistance, caused by kdr mutations in the NaV gene, hinders vector control efforts in Brazil. Despite genetic differences typically accumulating among isolated populations, this mosquito can actively and passively disperse through human transportation. Our study investigated the genetic structure and spread of kdr mutations in Ae. aegypti populations across six localities in Amapá State, Brazil, within the Amazonian Forest. Using 12 microsatellite loci and qPCR methods, we assessed genetic structure and identified three common kdr mutations (V410L, V1016I, and F1534C). High prevalence of kdr alleles was observed in all localities, indicating widespread distribution in Amapá State. Microsatellite analysis revealed differentiation among mosquito populations, dividing them into two distinct clusters supported by Bayesian and DAPC analyses. Oiapoque, located along the northern border with French Guiana, exhibited the highest kdr frequencies and genetic differentiation compared to other localities. Our findings suggest genetic structure in Ae. aegypti populations in Amapá State, with some passive gene flow between clusters. The study underscores the need for continuous surveillance of Ae. aegypti populations to monitor the spread of insecticide resistance and inform effective vector control strategies.

Insecticide Resistance and Metabolic Mechanisms in Aedes aegypti from Two Agrosystems (Vegetable and Cotton Crops) in Côte d'Ivoire.

Background: The emergence of insecticide resistance in Aedes vectors mosquitoes poses a real challenge for arboviral-borne disease control. In Côte d'Ivoire, data are available on phenotypic resistance and the presence of kdr mutations in Aedes aegypti. Therefore, information on metabolic resistance in Aedes populations is very scarce. Here, we assessed the insecticide resistance status of Ae. aegypti in periurban and rural areas of Côte d'Ivoire, and we investigated the role of detoxification enzymes as possible resistance mechanisms. Materials and Methods: Aedes mosquito eggs were collected between June 2019 to April 2021 in two agricultural sites. Adults of Ae. aegypti were tested using World Health Organization tube assays, with seven insecticides belonging to pyrethroids, organochlorines, carbamates, and organophosphates classes. We determined the knockdown times (KdT50, KdT95) and resistance ratios of pyrethroids in natural populations. The synergist piperonyl butoxide (PBO) was used to investigate the role of enzymes in resistance. Biochemical assays were performed to detect potential increased activities in mixed-function oxidase levels, nonspecific esterases (NSEs), and glutathione S-transferases. Results: The results showed that Ae. aegypti populations were resistant to five insecticides with mortality of 46% and 89% for 0.75% permethrin, 68% and 92% for 0.05% deltamethrin, 57% and 89% for lambda-cyhalothrin, 41% and 47% for dichlorodiphenyltrichloroethane (DDT), 82% and 91% for chlorpyrifos-methyl in Songon-Agban and Kaforo, respectively. Susceptibility to carbamates was observed in our study sites. After exposure to PBO, the susceptibility of Ae. aegypti to pyrethroids and DDT was partially restored in Songon-Agban. Whereas in Kaforo, none increase of the mortality rates of Ae. aegypti for these four insecticides was observed after exposure to PBO. Increased activity of NSE (α-esterases) was found in Songon-Agban compared with the reference susceptible strain. Conclusion: These findings provide valuable information to support decisions for vector control strategies in Cote d'Ivoire. Also, we highlight the need for the monitoring of insecticide resistance management in Aedes vectors.

Insecticidal and Repellent Properties of Rapid-Acting Fluorine-Containing Compounds against Aedes aegypti Mosquitoes.

The development of safe and potent insecticides remains an integral part of a multifaceted strategy to effectively control human-disease-transmitting insect vectors. Incorporating fluorine can dramatically alter the physiochemical properties and bioavailability of insecticides. For example, 1,1,1-trichloro-2,2-bis(4-fluorophenyl)ethane (DFDT)─a difluoro congener of trichloro-2,2-bis(4-chlorophenyl)ethane (DDT)─was demonstrated previously to be 10-fold less toxic to mosquitoes than DDT in terms of LD50 values, but it exhibited a 4-fold faster knockdown. Described herein is the discovery of fluorine-containing 1-aryl-2,2,2-trichloro-ethan-1-ols (FTEs, for fluorophenyl-trichloromethyl-ethanols). FTEs, particularly per-fluorophenyl-trichloromethyl-ethanol (PFTE), exhibited rapid knockdown not only against Drosophila melanogaster but also against susceptible and resistant Aedes aegypti mosquitoes, major vectors of Dengue, Zika, yellow fever, and Chikungunya viruses. The R enantiomer of any chiral FTE, synthesized enantioselectively, exhibited faster knockdown than its corresponding S enantiomer. PFTE does not prolong the opening of mosquito sodium channels that are characteristic of the action of DDT and pyrethroid insecticides. In addition, pyrethroid/DDT-resistant Ae. aegypti strains having enhanced P450-mediated detoxification and/or carrying sodium channel mutations that confer knockdown resistance were not cross-resistant to PFTE. These results indicate a mechanism of PFTE insecticidal action distinct from that of pyrethroids or DDT. Furthermore, PFTE elicited spatial repellency at concentrations as low as 10 ppm in a hand-in-cage assay. PFTE and MFTE were found to possess low mammalian toxicity. These results suggest the substantial potential of FTEs as a new class of compounds for controlling insect vectors, including pyrethroid/DDT-resistant mosquitoes. Further investigations of FTE insecticidal and repellency mechanisms could provide important insights into how incorporation of fluorine influences the rapid lethality and mosquito sensing.

Bioinsecticidal activity of cajeput oil to pyrethroid-susceptible and -resistant mosquitoes

Mosquito-borne diseases are a significant threat to human health. The frequent and repetitive application of insecticides can result in the selection of resistant mosquito populations leading to product failures for reducing community disease transmission. It is important that new interventions are discovered and developed for reducing mosquito populations and, in turn, protecting human health. Plant essential oils are promising chemical interventions for reducing mosquito populations. The myrtle family, Myrtaceae, has numerous species to be studied as potential bioinsecticides. Here, we combined toxicological, biochemical, and neurophysiological approaches to provide evidence for cajeput oil and terpene constituents to elicit bioinsecticidal activity to pyrethroid-susceptible and -resistant Aedes aegypti. We show cajeput oil terpenes to enhance cAMP production, increase ACh levels, inhibit in vivo and in vitro AChE activity, and disrupt spike discharge frequencies of the mosquito CNS. This study presents the first report on the bioinsecticidal activity of cajeput oil terpenes to pyrethroid-susceptible and -resistant mosquitoes and provides comparative data for the octopaminergic system as a putative molecular target for the bioinsecticides with implications for resistance management.

Association of 410L, 1016I and 1534C kdr mutations with pyrethroid resistance in Aedes aegypti from Ouagadougou, Burkina Faso, and development of a one-step multiplex PCR method for the simultaneous detection of 1534C and 1016I kdr mutations

BackgroundSince 2000, Burkina Faso has experienced regular dengue cases and outbreaks, making dengue an increasingly important health concern for the country. Previous studies in Burkina Faso reported that resistance of Aedes aegypti to pyrethroid insecticides was associated with the F1534C and V1016I kdr mutations. The current study reports high resistance of Ae. aegypti populations to pyrethroid insecticides, likely supported by mutations in the voltage-gated sodium channel, here evidenced by genotyping the kdr SNPs V410L, V1016I and F1534C. We also describe a new multiplex PCR-based diagnostic of F1534C and V1016I kdr SNPs.MethodsLarvae of Ae. aegypti were collected from three health districts of Ouagadougou in 2018. The resistance status of Ae. aegypti to permethrin (15 μg/ml) and deltamethrin (10 μg/ml) was tested using bottles and to malathion (5%) using WHO tube tests. All bioassays used 1-h exposure and mortality recorded 24 h post-exposure. Bioassay results were interpreted according to WHO thresholds for resistance diagnosis. The kdr mutations were screened using AS-PCR and TaqMan methods in exposed and non-exposed Aedes mosquitoes.ResultsFemales from all health districts were resistant to permethrin and deltamethrin (< 20% mortality) but were fully susceptible to 5% malathion. The F1534C and V1016I kdr mutations were successfully detected using a newly developed multiplex PCR in perfect agreement with TaqMan method. The 1534C/1016I/410L haplotype was correlated with permethrin resistance but not with deltamethrin resistance; however, the test power was limited by a low frequency of dead individuals in deltamethrin exposure.ConclusionsResistance to pyrethroid insecticides is associated with kdr mutant haplotypes, while the absence of substantial resistance to malathion suggests that it remains a viable option for dengue vector control in Ouagadougou.

Improving the efficiency of aerosolized insecticide testing against mosquitoes

Developing robust and standardised approaches for testing mosquito populations against insecticides is vital for understanding the effectiveness of new active ingredients or formulations. Methods for testing mosquito susceptibility against contact insecticides or products, such as those delivered through public health programmes, are well-established and standardised. Nevertheless, approaches for testing volatile or aerosolized insecticides used in household products can be challenging to implement efficiently. We adapted WHO guidelines for household insecticides to develop a standardised and higher-throughput methodology for testing aerosolized products in a Peet Grady test chamber (PG-chamber) using caged mosquitoes and an efficient decontamination method. The new approach was validated using insecticide resistant and susceptible Aedes and Anopheles mosquito colonies. An added feature is the inclusion of cage-facing cameras to allow real-time quantification of knockdown following insecticide exposure. The wipe-based decontamination method was highly effective for removing pyrethroids' aerosolized oil-based residues from chamber surfaces, with < 2% mortality recorded for susceptible mosquitoes tested directly on the surfaces. There was no spatial heterogeneity for knockdown or mortality of caged mosquitoes within the PG chamber. The dual-cage approach we implement yields eight-times the throughput compared to a free-flight protocol, allows simultaneous testing of different mosquito strains and effectively discriminates susceptible and resistant mosquito colonies tested side-by-side.

Current enzyme-mediated insecticide resistance status of Aedes aegypti populations from a dengue-endemic city in southern Mexico.

To identify the enzyme-mediated insecticide resistance in Aedes aegypti in Tapachula, Mexico. Biochemical assays were undertaken to determine the enzyme levels in mosquitoes from 22 sites collected in 2018 and 2020 in Tapachula. Results of 2018 were correlated with the resistance to insecticides pub-lished. Mosquitoes had higher levels than those of the susceptible strain in 2018 and 2020 respectively of α-esterases in 15 and 12 sites; β-esterases in 7 and 6 sites; glutathione-S-transferases in 11 and 19 sites; ρNPA-esterases in 21 and 17 sites; and cytochromes P450 in 20 and 22 sites. In mosquitoes of 2018, there was a moderate correlation between previously documented Malathion resistance ratios and the insensitive acetylcholinesterase (r=0.459, p= 0.03). The elevated enzyme levels found indicate its contribution to the resistance to pyrethroids and organo-phosphates already published in mosquitoes from Tapachula. Bioassays using enzyme inhibitors resulted in greater mor-tality, confirming that metabolism contributes to resistance.

Susceptibility status of Aedes aegypti (Diptera: Culicidae) against insecticides of public health use in Delhi and NCR region, India.

Aedes (Stegomyia) aegypti is a primary vector responsible for the transmission of various arboviral diseases in India. Without an effective drug or vaccine against these diseases, chemical insecticide-based vector control supplemented with source reduction remains the best option for their effective management. The development of insecticide resistance due to the continuous use of insecticides might affect the control operations. Adults and larvae of Aedes aegypti were collected from different localities in Delhi. Larvae were exposed to discriminating (0.02mg/l) and application (1mg/l) doses of temephos. WHO tube assay was conducted for F1 adults using impregnated insecticide papers of dichlorodiphenyltrichloroethane (DDT), malathion, deltamethrin, permethrin, cyfluthrin, and lambda-cyhalothrin. Larvae of Ae. aegypti were found resistant (76.0%) to the discriminating dose of temephos, whereas suscep-tible (100.0%) to the application dose of the temephos. Adult Aedes (Fl) mosquitoes were resistant to DDT (23.7%), malathion (90.5%), deltamethrin (76.0%), permethrin (96.2 %) cyfluthrin (85.5%), and lambda-cyhalothrin (94.0%). Indoor residual spray is not used in Delhi for vector control. Resistance in Aedes might be due to pesticide usage for agricultural activities in peripheral regions of Delhi. There is a need to investigate more on the insecticide resistance mechanisms for indirect resistance development. Understanding the insecticide susceptibility status of urban vectors is critical for planning effective control strategies.

Insecticide resistance levels and associated mechanisms in three Aedes aegypti populations from Venezuela.

The massive use of insecticides in public health has exerted selective pressure resulting in the development of resistance in Aedes aegypti to different insecticides in Venezuela. Between 2010 and 2020, the only insecticides available for vector control were the organophosphates (Ops) fenitrothion and temephos which were focally applied. To determine the state of insecticide resistance and to identify the possible biochemical and molecular mechanisms involved in three populations of Ae. aegypti from Venezuela. CDC bottle bioassays were conducted on Ae. aegypti collected between October 2019 and February 2020 in two hyperendemic localities for dengue in Aragua State and in a malaria endemic area in Bolívar State. Insecticide resistance mechanisms were studied using biochemical assays and polymerase chain reaction (PCR) to detect kdr mutations. Bioassays showed contrasting results among populations; Las Brisas was resistant to malathion, permethrin and deltamethrin, Urbanización 19 de Abril was resistant to permethrin and Nacupay to malathion. All populations showed significantly higher activity of mixed function oxidases and glutathione-S-transferases (GSTs) in comparison with the susceptible strain. The kdr mutations V410L, F1534C, and V1016I were detected in all populations, with F1534C at higher frequencies. Insecticide resistance persists in three Ae. aegypti populations from Venezuela even in the relative absence of insecticide application.

Spatial Distribution of Pyrethroid Resistance and kdr Mutations in Aedes aegypti from La Guajira, Colombia.

Dengue, chikungunya, and Zika are of great concern to the public health of Colombia. One of the main control strategies for these diseases is the application of insecticides directed at the Aedes aegypti vector. However, insecticide resistance has been increasingly recorded in the country, making control measures difficult. Here, we evaluated the resistance profiles for pyrethroids in populations of Ae. aegypti from La Guajira, Colombia. The frequency (diagnostic dose, DD) and intensity (2×, 5×, and 10× DD) of resistance to permethrin, deltamethrin, and lambda-cyhalothrin were determined in 15 populations of Ae. aegypti from La Guajira, Colombia, using the bottle bioassay. The kdr mutations V1016I, F1534C, and V410L, were identified, and their allele and genotype frequencies were calculated. Finally, the mortality values for the analyzed pyrethroids were interpolated following the IDW method for predicting pyrethroid resistance. The populations of Ae. aegypti showed a high frequency of resistance to permethrin with a low to moderate intensity, which was associated with the triple-resistant haplotype LL410/II1016/CC1534. They remain susceptible to deltamethrin and, in some populations, expressed the risk of developing resistance to lambda-cyhalothrin.

Association of Midgut Bacteria and Their Metabolic Pathways with Zika Infection and Insecticide Resistance in Colombian Aedes aegypti Populations.

Introduction: Aedes aegypti is the vector of several arboviruses such as dengue, Zika, and chikungunya. In 2015–16, Zika virus (ZIKV) had an outbreak in South America associated with prenatal microcephaly and Guillain-Barré syndrome. This mosquito’s viral transmission is influenced by microbiota abundance and diversity and its interactions with the vector. The conditions of cocirculation of these three arboviruses, failure in vector control due to insecticide resistance, limitations in dengue management during the COVID-19 pandemic, and lack of effective treatment or vaccines make it necessary to identify changes in mosquito midgut bacterial composition and predict its functions through the infection. Its study is fundamental because it generates knowledge for surveillance of transmission and the risk of outbreaks of these diseases at the local level. Methods: Midgut bacterial compositions of females of Colombian Ae. aegypti populations were analyzed using DADA2 Pipeline, and their functions were predicted with PICRUSt2 analysis. These analyses were done under the condition of natural ZIKV infection and resistance to lambda–cyhalothrin, alone and in combination. One-step RT-PCR determined the percentage of ZIKV-infected females. We also measured the susceptibility to the pyrethroid lambda–cyhalothrin and evaluated the presence of the V1016I mutation in the sodium channel gene. Results: We found high ZIKV infection rates in Ae. aegypti females from Colombian rural municipalities with deficient water supply, such as Honda with 63.6%. In the face of natural infection with an arbovirus such as Zika, the diversity between an infective and non-infective form was significantly different. Bacteria associated with a state of infection with ZIKV and lambda–cyhalothrin resistance were detected, such as the genus Bacteroides, which was related to functions of pathogenicity, antimicrobial resistance, and bioremediation of insecticides. We hypothesize that it is a vehicle for virus entry, as it is in human intestinal infections. On the other hand, Bello, the only mosquito population classified as susceptible to lambda–cyhalothrin, was associated with bacteria related to mucin degradation functions in the intestine, belonging to the Lachnospiraceae family, with the genus Dorea being increased in ZIKV-infected females. The Serratia genus presented significantly decreased functions related to phenazine production, potentially associated with infection control, and control mechanism functions for host defense and quorum sensing. Additionally, Pseudomonas was the genus principally associated with functions of the degradation of insecticides related to tryptophan metabolism, ABC transporters with a two-component system, efflux pumps, and alginate synthesis. Conclusions: Microbiota composition may be modulated by ZIKV infection and insecticide resistance in Ae. aegypti Colombian populations. The condition of resistance to lambda–cyhalothrin could be inducing a phenome of dysbiosis in field Ae. aegypti affecting the transmission of arboviruses.