Levels Of Insecticide Resistance Research Articles

Spatio-temporal characterization of phenotypic resistance in malaria vector species.

Malaria, a deadly disease caused by Plasmodium protozoa parasite and transmitted through bites of infected female Anopheles mosquitoes, remains a significant public health challenge in sub-Saharan Africa. Efforts to eliminate malaria have increasingly focused on vector control using insecticides. However, the emergence of insecticide resistance (IR) in malaria vectors pose a formidable obstacle, and the current IR mapping models remain static, relying on fixed coefficients. This study introduces a dynamic spatio-temporal approach to characterize phenotypic resistance in Anopheles gambiae complex and Anopheles arabiensis. We developed a cellular automata (CA) model and applied it to data collected from Ethiopia, Nigeria, Cameroon, Chad, and Burkina Faso. The data encompasses georeferenced records detailing IR levels in mosquito vector populations across various classes of insecticides. In characterizing the dynamic patterns of confirmed resistance, we identified key driving factors through correlation analysis, chi-square tests, and extensive literature review. The CA model demonstrated robustness in capturing the spatio-temporal dynamics of confirmed IR states in the vector populations. In our model, the key driving factors included insecticide usage, agricultural activities, human population density, Land Use and Land Cover (LULC) characteristics, and environmental variables. The CA model developed offers a robust tool for countries that have limited data on confirmed IR in malaria vectors. The embrace of a dynamical modeling approach and accounting for evolving conditions and influences, contribute to deeper understanding of IR dynamics, and can inform effective strategies for malaria vector control, and prevention in regions facing this critical health challenge.

Metabolic Resistance and Not Voltage-Gated Sodium Channel Gene Mutation Is Associated with Pyrethroid Resistance of Aedes albopictus (Skuse, 1894) from Cambodia.

(1) Background: In Cambodia, Aedes albopictus is an important vector of the dengue virus. Vector control using insecticides is a major strategy implemented in managing mosquito-borne diseases. Resistance, however, threatens to undermine the use of insecticides. In this study, we present the levels of insecticide resistance of Ae. albopictus in Cambodia and the mechanisms involved. (2) Methods: Two Ae. albopictus populations were collected from the capital, Phnom Penh city, and from rural Pailin province. Adults were tested with diagnostic doses of malathion (0.8%), deltamethrin (0.03%), permethrin (0.25%), and DDT (4%) using WHO tube assays. Synergist assays using piperonyl butoxide (PBO) were implemented before the pyrethroid assays to detect the potential involvement of metabolic resistance mechanisms. Adult female mosquitoes collected from Phnom Penh and Pailin were tested for voltage-gated sodium channel (VGSC) kdr (knockdown resistance) mutations commonly found in Aedes sp.-resistant populations throughout Asia (S989P, V1016G, and F1534C), as well as for other mutations (V410L, L982W, A1007G, I1011M, T1520I, and D1763Y). (3) Results: The two populations showed resistance against all the insecticides tested (<90% mortality). The use of PBO (an inhibitor of P450s) strongly restored the efficacy of deltamethrin and permethrin against the two resistant populations. Sequences of regions of the vgsc gene showed a lack of kdr mutations known to be associated with pyrethroid resistance. However, four novel non-synonymous mutations (L412P/S, C983S, Q1554STOP, and R1718L) and twenty-nine synonymous mutations were detected. It remains to be determined whether these mutations contribute to pyrethroid resistance. (4) Conclusions: Pyrethroid resistance is occurring in two Ae. albopictus populations originating from urban and rural areas of Cambodia. The resistance is likely due to metabolic resistance specifically involving P450s monooxygenases. The levels of resistance against different insecticide classes are a cause for concern in Cambodia. Alternative tools and insecticides for controlling dengue vectors should be used to minimize disease prevalence in the country.

The G932C mutation of chitin synthase 1 gene (CHS1) mediates buprofezin resistance as confirmed by CRISPR/Cas9-mediated knock-in approach in the brown planthopper, Nilaparvata lugens

The brown planthopper (Nilaparvata lugens) is a major destructive rice pest in Asia. High levels of insecticide resistance have been frequently reported, and the G932C mutation in the chitin synthase 1 (CHS1) gene has been found to mediate buprofezin resistance. However, there has been no direct evidence to confirm the functional significance of the single G932C substitution mutation leading to buprofezin resistance in N. lugens. Here, we successfully constructed a knock-in homozygous strain (Nl-G932C) of N. lugens using CRISPR/Cas9 coupled with homology-directed repair (HDR). Compared with the background strain susceptible to buprofezin (Nl-SS), the knock-in strain (Nl-G932C) showed a 94.9-fold resistance to buprofezin. Furthermore, resistant strains (Nl-932C) isolated from the field exhibited a 2078.8-fold resistance to buprofezin, indicating that there are other mechanisms contributing to buprofezin resistance in the field. Inheritance analysis showed that the resistance trait is incomplete dominance. In addition, the Nl-G932C strain had a relative fitness of 0.33 with a substantially decreased survival rate, emergence rate, and fecundity. This study provided in vivo functional evidence for the causality of G932C substitution mutation of CHS1 with buprofezin resistance and valuable information for facilitating the development of resistance management strategies in N. lugens. This is the first example of using CRISPR/Cas9 gene-editing technology in a hemipteran insect to directly confirm the role of a candidate target site mutation in insecticide resistance.

Stability of Resistance to Permethrin and Malathion in Mexican Populations of Aedes aegypti (Diptera: Culicidae) with Recommendations for Rotational Use1

Abstract Aedes aegypti (L.) (Diptera: Culicidae) management in Mexico primarily involves destruction of breeding sites and application of insecticides. There are many cases of field resistance and few studies on the instability of this phenomenon, despite its usefulness in management of this pest. The goal of this research was to estimate, under laboratory conditions, the stability of resistance to permethrin and malathion in 3 field-collected Mexican populations of Ae. aegypti. Early fourth-instar larvae were used for the bioassays according to the methodology of the World Health Organization (WHO). Initially, we estimated the level of insecticide resistance in F1 larvae. Then, each population was individually reared without selection pressure through 7 generations, and the insecticide response was monitored and compared with the susceptible New Orleans strain. The resistance response (RR95) to permethrin in the F1 generation varied from 53.8 to 267.9X at the LC95 level. In malathion, the RR95 of the F1 generation ranged from 5.6 to 10.5X. In most cases, the highest rate of resistance decline occurred from F1 to F2. The response to permethrin and malathion after 7 generations without selection pressure was similar to that observed in the susceptible reference strain.

Insecticide resistance level of Aedes aegypti L. (Diptera: Culicidae) in northern Mexico

Objective: To determine the response of the larvae of three Ae. aegypti populations from the Mexican North Pacific region to insecticides with different mode of action.&#x0D; Design/Methodology/Approach: Three colonies were obtained placing ovitramps in peridomestic sites in Guadalajara (Jalisco), Culiacan (Sinaloa), and La Paz (Baja California Sur). Based on the methodology proposed by WHO, the bioassays were carried out with F1 larvae in the early fourth instar.&#x0D; Results: The larvae from the three field colonies had high resistance to permethrin and low resistance to deltamethrin; however, they were susceptible to Spinosad and Bacillus thuringiensis var. Israelensis. The Culiacan strain showed a high resistance to the malathion and propoxur insecticides.&#x0D; Study Limitations/Implications: The results provided valuable information about the response of these populations to insecticides, which are useful to establish resistance in the lab. Consequently, further studies should be carried out to complement the information obtained in these field tests.&#x0D; Findings/Conclusions: The data indicated resistance levels to pyrethroid insecticides (mainly permethrin), as well as to organophosphates and carbamates.

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%.

Lygus Bug and Alfalfa Weevil Insecticide Resistance in the Pacific Northwest

AbstractIn Washington State, east of the Cascade Mountains, alfalfa is grown for seed and forage. Alfalfa weevils are the primary defoliators of alfalfa grown for forage and seed, and Lygus bugs are the key direct pest in alfalfa seed production in the Pacific Northwest. Both alfalfa weevil and Lygus bugs are controlled by insecticide applications. Some levels of insecticide resistance have been observed in recent years. This article reports on a series of experiments that were conducted to quantify the resistance status of Lygus bugs and alfalfa weevils to several insecticides in Washington State. Earn 1.5 CEUs in Integrated Pest Management by reading this article and taking the quiz at https://web.sciencesocieties.org/Learning‐Center/Courses.

Transposable elements differ between geographic populations of the Colorado potato beetle, Leptinotarsa decemlineata (Coleoptera: Chrysomelidae).

Agricultural insect herbivores show a remarkable ability to adapt to modern agroecosystems, making them ideal for the study of the mechanisms underlying rapid evolution. The mobilization of transposable elements is one mechanism that may help explain this ability. The Colorado potato beetle, Leptinotarsa decemlineata, is a highly adaptable species, as shown by its wide host range, broad geographic distribution, and tolerance to insecticides. However, beetle populations vary in insecticide tolerance, with Eastern US beetle populations being more adaptable than Western US ones. Here, we use a community ecology approach to examine how the abundance and diversity of transposable elements differs in 88 resequenced genomes of L. decemlineata collected throughout North America. We tested if assemblages and mobilization of transposable elements differed between populations of L. decemlineata based on the beetle's geography, host plant, and neonicotinoid insecticide resistance. Among populations of North American L. decemlineata, individuals collected in Mexico host more transposable elements than individuals collected in the United States. Transposable element insertion locations differ among geographic populations, reflecting the evolutionary history of this species. Total transposable element diversity between L. decemlineata individuals is enough to distinguish between populations, with more TEs found in beetles collected in Mexico than in the United States. Transposable element diversity does not appear to differ between beetles found on different host plants, or relate to different levels of insecticide resistance.

Rapid test to detect insecticide resistance in field populations of Spodoptera frugiperda (Lepidoptera: Noctuidae).

Introduction: The development of insecticide resistance in Spodoptera frugiperda populations is a serious threat to the crop industry. Given the spread of invasive resistant populations, prospective monitoring should be accelerated, and the development of diagnostic tools for rapid and accurate assessments of insecticide resistance is essential. Methods: First, the discriminating dose and diagnostic time of the kit were determined by the glass vial method based on a susceptible strain. Then, pests that were collected from field populations were used to determine their susceptibility to seven insecticides by using the diagnostic kit. Finally, the accuracy of the kit was verified based on correlation analyses and the likelihood of insecticide control failure was assessed. Results: Here, we describe a diagnostic kit that enables the rapid detection of resistance to chlorpyrifos, bifenthrin, deltamethrin, lambda-cyhalothrin, phoxim, chlorantraniliprole and chlorfenapyr within 1-2h in S. frugiperda at diagnostic doses of 0.98, 0.84, 0.38, 1.64, 0.0082, 1.75 and 0.65μg/cm2, respectively. The linear equation between mortalities under diagnostic doses and actual resistance ratios measured by the diet-overlay bioassay was determined. The high correlation indicates that the insecticide resistance levels diagnosed by the kit were consistent with the results of the diet-overlay bioassay. Moreover, we found a significant negative correlation between diagnostic mortality and the likelihood of control failure for bifenthrin (r = -0.899, p = 0.001), deltamethrin (r = -0.737, p = 0.024) and lambda-cyhalothrin (r = -0.871, p = 0.002). Discussion: The insecticide resistance diagnostic kit for S. frugiperda is a user-friendly tool (portable, short detection time). Its excellent performance qualifies the kit as a reliable screening tool for identifying effective insecticides in sustainable resistance management.

Exaptation of I4760M mutation in ryanodine receptor of Spodoptera exigua (Lepidoptera: Noctuidae): Lessons from museum and field samples

Since 2007, diamide insecticides have been widely used in Korea to control various types of lepidopteran pests including Spodoptera exigua. For nearly a decade, diamide resistance in field populations of S. exigua across 18 localities has been monitored using bioassays. Despite their short history of use, resistance to diamide insecticides has emerged. Based on the LC50 values, some field populations showed a higher level of resistance to chlorantraniliprole, a diamide insecticide, compared to that of the susceptible strain, although regional and temporal variations were observed. To investigate resistance at a molecular level, we examined three mutations (Y4701C, I4790M, and G4946E) in the ryanodine receptor (RyR), which is the primary mechanism underlying diamide insecticide resistance. DNA sequencing showed that only the I4790M mutation was found in most field populations. As resistance levels varied significantly despite the uniform presence of the I4790M mutation, we considered the presence of another resistance factor. Further, the I4790M mutation was also found in S. exigua specimens collected prior to the commercialization of diamide insecticides in Korea as well as in other countries, such as the USA. This finding led us to hypothesize that the I4790M mutation were predisposed in field populations owing to selection factors other than diamide use. For further clarification, we conducted whole-genome sequencing of S. exigua (449.83 Mb) and re-sequencing of 18 individual whole genomes. However, no additional non-synonymous mutations were detected in the RyR-coding region. Therefore, we concluded that the high level of diamide insecticide resistance in Korean S. exigua is not caused by mutations at the target site, RyR, but is attributed to other factors that need to be investigated in future studies.

SITUATION OF RESISTANCE TO INSECTICIDES OF MAJOR MALARIA VECTORS IN VIETNAM, PERIOD 2012 – 2022

Surveys were conducted from 2012 to 2022 with the goal of determining the level ofinsecticide resistance of the primary malaria vector in Vietnam in the period 2011 - 2022.The results showed that An. minimus detected in 1 of 28 study sites (3.57%) was possiblyresistant to alphacypermethrin, 1 of 22 sites (4.55%) was possibly resistant tolambdacyhalothrin and 1 of 6 sites (16.67%) was possibly resistant to deltamethrin. An.dirus detected at 3 of 11 sites (27.27%) were possibly resistant to alphacypermethrin and1 of 9 sites (11.11%) was possible resistant to lambdacyhalothrin. An. epiroticus detectedin 7 of 18 sites (38.89%) were possible resistant and 10 of 18 sites (55.56%) wereresistant to alphacypermethrin, 4 of 16 sites (25.00%) were possible resistant and 11 of 16sites (44.44%) were resistant to lambdacyhalothrin, 3 of 7 sites (42.86%) were possibleresistant and 2 of 7 sites (28.57%) were resistant to permethrin, with 1 of 9 sites(11.11%)was possible resistant and 4 of 9 sites (44.44%) were resistant to deltamethrin.

Resistance development, cross-resistance, and fitness costs associated with Aphis gossypii resistance towards sulfoxaflor and acetamiprid in different geographical regions1

Aphis gossypii has become increasingly difficult to manage due to its very strong insecticide resistance. In the laboratory, we established sulfoxaflor-resistant and acetamiprid-resistant strains in two A. gossypii populations with different basal insecticide resistance levels, and evaluated the effects of basal insecticide resistance on the resistance development and cross-resistance, as well as differences in fitness. Under the same selection pressure, Yarkant A. gossypii (with low basal insecticide resistance) evolved resistance to sulfoxaflor and acetamiprid more quickly than Jinghe A. gossypii (with high basal insecticide resistance), and the evolution of A. gossypii resistance to sulfoxaflor developed faster than acetamiprid in both Yarkant and Jinghe, Xingjiang, China. The sulfoxaflor-resistant strains selected from Yarkant and Jinghe developed significant cross-resistance to acetamiprid, imidacloprid, thiamethoxam and pymetrozine; while the acetamiprid-resistant strains developed significant cross-resistance to sulfoxaflor, imidacloprid, thiamethoxam, pymetrozine, and chlorpyrifos. The relative fitness of A. gossypii decreased as the resistance to sulfoxaflor and acetamiprid developed. The relative fitness levels of the sulfoxaflor-resistant strains (Yarkant-SulR and Jinghe-SulR) were lower than those of the acetamiprid-resistant strains (Yarkant-AceR and Jinghe-AceR). In addition, the relative fitness levels of sulfoxaflor- and acetamiprid-resistant strains were lower in Jinghe than in Yarkant. In summary, basal insecticide resistance of A. gossypii and insecticide type affected the evolution of resistance to insecticides in A. gossypii, as well as cross-resistance to other insecticides. The sulfoxaflor- and acetamiprid-resistant A. gossypii strains had obvious fitness costs. The results of this work will contribute to the insecticide resistance management and integrated management of A. gossypii.

Insecticide Resistance Development and Detoxification Enzyme Activities of Spodoptera litura (Fabricius) in Soybean from Kumaon Himalayas

Background: Soybean is an important crop of Uttarakhand both in hills as well as in plains and Spodoptera litura is an important pest of soybean in Uttarakhand. Several insecticides have been in use for its management and resistance has been observed against different group of insecticides. Thus, to study the level of infestation and insecticide resistance from soybean fields of hill farmers of Kumaon Himalaya, survey and experiments were conducted. Methods: Survey was conducted and scale of infestation was determined. Chemical and biochemical assay were conducted to study insecticide resistance. For chemical assay IRAC Method No. 7 using insecticides indoxacarb 14.5% SC, chlorantraniliprole 18.5% Sc, fipronil 5% SC, chlorpyriphos 50%+cypermethrin 5% EC and profenofos 40%+cypermethrin 4% EC and for biochemical assay the specific activity of Carboxylesterase, Acetyl choline esterase, Mono-oxygenase and Glutathione-S-transferase was studied. Result: The infestation level from different regions showed the presence of S. litura, ranging from mild to severe infestation. The resistance ratio of different insecticides used ranged from a low to an extremely high resistance level with LC50 ranging from 0.37 µg/ml to 1648.84 µg/ml. The biochemical analysis of carboxylesterase, acetylcholinesterase, monooxygenase and gluthione-s-transferase showed an overproduction of these detoxification enzymes in the resistant population.

Development of Insecticide Resistance in Field Populations of Onion Thrips, Thrips tabaci (Thysanoptera: Thripidae).

The present study evaluated insecticide resistance in field populations of onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), collected from eight different onion-growing regions of Punjab, Pakistan. These field-collected populations were assessed for resistance development against eight commonly used active ingredients including deltamethrin, lambda-cyhalothrin, imidacloprid, acetamiprid, spinosad, spinetoram, cypermethrin, and abamectin. In leaf dip bioassays, T. tabaci adults showed varied levels of resistance towards different insecticides. Moderate or high levels of resistance to deltamethrin (58-86 fold), lambda-cyhalothrin (20-63 fold), and cypermethrin (22-54 fold) were observed in T. tabaci field populations. There were very low to moderate resistance levels to imidacloprid (10-38 fold), acetamiprid (5-29 fold), and abamectin (10-30 fold). The lowest levels of resistance were detected in thrips exposed to spinosad (3-13 fold) and spinetoram (3-8 fold). Insecticide resistance levels varied among populations collected from various geographic locations, but all populations exhibited elevated levels of resistance to deltamethrin. Thrips tabaci populations with higher resistance levels were most commonly found from the southern part of Punjab, Pakistan. Our findings revealed that spinosyns could be used as alternatives to conventional insecticides for the successful management of T. tabaci in onion fields.

Insecticide resistance management strategies for public health control of mosquitoes exhibiting polygenic resistance: Acomparison of sequences, rotations, and mixtures.

Malaria control uses insecticides to kill Anopheles mosquitoes. Recent successes in malaria control are threatened by increasing levels of insecticide resistance (IR), requiring insecticide resistance management (IRM) strategies to mitigate this problem. Field trials of IRM strategies are usually prohibitively expensive with long timeframes, and mathematical modeling is often used to evaluate alternative options. Previous IRM models in the context of malaria control assumed IR to have a simple (monogenic) basis, whereas in natural populations, IR will often be a complex polygenic trait determined by multiple genetic variants. A quantitative genetics model was developed to model IR as a polygenic trait. The model allows insecticides to be deployed as sequences (continuous deployment until a defined withdrawal threshold, termed "insecticide lifespan", as indicated by resistance diagnosis in bioassays), rotations (periodic switching of insecticides), or full-dose mixtures (two insecticides in one formulation). These IRM strategies were compared based on their "strategy lifespan" (capped at 500 generations). Partial rank correlation and generalized linear modeling was used to identify and quantify parameters driving the evolution of resistance. Random forest models were used to identify parameters offering predictive value for decision-making. Deploying single insecticides as sequences or rotations usually made little overall difference to their "strategy lifespan", though rotations displayed lower mean and peak resistances. Deploying two insecticides in a full-dose mixture formulation was found to extend the "strategy lifespan" when compared to deploying each in sequence or rotation. This pattern was observed regardless of the level of cross resistance between the insecticides or the starting level of resistance. Statistical analysis highlighted the importance of insecticide coverage, cross resistance, heritability, and fitness costs for selecting an appropriate IRM strategy. Full-dose mixtures appear the most promising of the strategies evaluated, with the longest "strategy lifespans". These conclusions broadly corroborate previous results from monogenic models.

Mosquito Larval Bioassays.

Insecticide bioassays are frequently used to measure levels of insecticide resistance in mosquito populations, examining the ability of mosquitoes to survive exposure to insecticides. Laboratory bioassays measure insects' responses to insecticides in resistant (field) populations and laboratory susceptible strains using serial doses or concentrations across the range of >0 and <100% mortality. This protocol measures the toxicity of insecticides to mosquito larvae and determines the level of insecticide resistance. Generally, laboratory-reared mosquito larvae of known age or instar are exposed to H2O containing various concentrations of an insecticide, and the response (mortality) is recorded 24 h after the test. Larval bioassay tests can (1) identify the lethal concentrations of larvicide that cause 50% and 90% mortality (LC50 and LC90, respectively); (2) determine the diagnostic concentration needed to monitor susceptibility in mosquito larvae in the field; and (3) investigate the resistance status and the mechanisms governing insecticide resistance to a specific insecticide.

CRISPR/Cas9-mediated knockout of NlCYP6CS1 gene reveals its role in detoxification of insecticides in Nilaparvata lugens (Hemiptera: Delphacidae).

The brown planthopper (Nilaparvata lugens) is one of the major rice insect pests in Asia. Recently, high levels of insecticide resistance have been frequently reported and cytochrome P450 monooxygenase (P450)-mediated metabolic detoxification is a common resistance mechanism in N. lugens. However, there has been no persuasive genetic method to prove the role of P450s in insecticide resistance in N. lugens. Here, CRISPR/Cas9 system was used to disrupt the P450 gene NlCYP6CS1 to elucidate its role in insecticide resistance in field populations of N. lugens. We successfully constructed a homozygous strain (Nl6CS1-KO) with a 5-bp deletion and 1-bp insertion mutation of NlCYP6CS1. Compared with a background resistant strain (Nl-R), the susceptibility of knockout strain Nl6CS1-KO to imidacloprid, nitenpyram, thiamethoxam, dinotefuran, and pymetrozine was increased by 2.3-, 3.4-, 7.0-, 4.2- and 3.9-fold, respectively, but not significantly changed to triflumezopyrim, chlorpyrifos and buprofezin. Life table analysis demonstrated that the Nl6CS1-KO strain resembled the Nl-R strain in terms of egg and nymph developmental duration and adult lifespan, but differed from the Nl-R strain in the survival rate of eggs and nymphs, reproduction, and body weight. Our study demonstrates the effect of functional deletion of NlCYP6CS1 on multiple insecticide resistance in N. lugens. For the first time, we applied CRISPR/Cas9 system to reveal the mechanism of insecticide resistance in N. lugens, which may shed light on similar studies in other hemipteran insects. © 2023 Society of Chemical Industry.

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.

Distribution of Insecticide Resistance Genetic Markers in the West Nile Virus Vector Culex pipiens from South-Eastern Romania.

Culex pipiens pipiens and Culex pipiens molestus mosquitoes are the vectors of West Nile virus in south-eastern Romania, an area of intense circulation and human transmission of this virus. The level of insecticide resistance for the mosquito populations in the region has not been previously assessed. Culex pipiens mosquitoes collected between 2018 and 2019 in south-eastern Romania from different habitats were subjected to biotype identification by real-time PCR. Substitutions causing resistance to organophosphates and carbamates (F290V and G119S in acetylcholinesterase 1) and to pyrethroids (L1014F in voltage gated Na+ channel) were screened by PCR or sequencing. Substitutions F290V and G119S were detected at very low frequencies and only in heterozygous state in Culex pipiens molestus biotype specimens collected in urban areas. The molestus biotype population analysed was entirely homozygous for L1014F, and high frequencies of this substitution were also found for pipiens biotype and hybrid mosquitoes collected in urban and in intensive agriculture areas. Reducing the selective pressure by limiting the use of pyrethroid insecticides only for regions where it is absolutely necessary and monitoring L1014F mutation should be taken into consideration when implementing vector control strategies.

Brazilian Populations of Aedes aegypti Resistant to Pyriproxyfen Exhibit Lower Susceptibility to Infection with Zika Virus.

Zika virus (ZIKV) infection has caused devastating consequences in Brazil as infections were associated with neurological complications in neonates. Aedes aegypti is the primary vector of ZIKV, and the evolution of insecticide resistance (IR) in this species can compromise control efforts. Although relative levels of phenotypic IR in mosquitoes can change considerably over time, its influence on vector competence for arboviruses is unclear. Pyriproxyfen (PPF)-resistant populations of Ae. aegypti were collected from five municipalities located in Northeast of Brazil, which demonstrated different resistance levels; low (Serrinha, Brumado), moderate (Juazeiro do Norte, Itabuna), and high (Quixadá). Experimental per os infection using ZIKV were performed with individuals from these populations and with an insecticide susceptible strain (Rockefeller) to determine their relative vector competence for ZIKV. Although all populations were competent to transmit ZIKV, mosquitoes derived from populations with moderate to high levels of IR exhibited similar or lower susceptibility to ZIKV infection than those from populations with low IR or the susceptible strain. These observations suggest an association between IR and arbovirus infection, which may be attributable to genetic hitchhiking. The use of PPF to control Brazilian Ae. aegypti may be associated with an indirect benefit of reduced susceptibility to infection, but no changes in disseminated infection and transmission of ZIKV among PPF-resistant phenotypes.