Insecticide Resistance Status Research Articles

Status of Insecticide Resistance of Malaria Vector Anopheles stephensi towards Insecticides in Alwar District of Rajasthan, India

Pyrethroids have been developed as a powerful insecticide that is widely used for space spray and residual indoor spraying, with impregnated nets included in the vector control programme. Insecticide resistance reduces the effectiveness of pesticides. Therefore, the vector susceptibility condition of the Anopheles stephensi is monitored in order to select the active ones. The current study is being conducted in a malaria-ridden area in various parts of the Alwar region of Rajasthan, India, against the malaria vector An. stephensi. The Susceptibility study was conducted by the WHO standardized method using the diagnostic doses of DDT, Alpha-cypermethrin and Deltamethrin. An. stephensi showed intermediate resistance to DDT from all over the study while susceptible to Alpha-cypermethrin and Deltamethrin.

Insecticide resistance in dengue vectors from hotspots in Selangor, Malaysia.

BackgroundIn Malaysia, dengue remains a top priority disease and usage of insecticides is the main method for dengue vector control. Limited baseline insecticide resistance data in dengue hotspots has prompted us to conduct this study. The present study reports the use of a map on the insecticide susceptibility status of Aedes aegypti and Aedes albopictus to provide a quick visualization and overview of the distribution of insecticide resistance.Method and resultsThe insecticide resistance status of Aedes populations collected from 24 dengue hotspot areas from the period of December 2018 until June 2019 was proactively monitored using the World Health Organization standard protocol for adult and larval susceptibility testing was conducted, together with elucidation of the mechanisms involved in observed resistance. For resistance monitoring, susceptibility to three adulticides (permethrin, deltamethrin, and malathion) was tested, as well as susceptibility to the larvicide, temephos. Data showed significant resistance to both deltamethrin and permethrin (pyrethroid insecticides), and to malathion (organophosphate insecticide) in all sampled Aedes aegypti populations, while variable resistance patterns were found in the sampled Aedes albopictus populations. Temephos resistance was observed when larvae were tested using the diagnostic dosage of 0.012mg/L but not at the operational dosage of 1mg/L for both species.ConclusionThe present study highlights evidence of a potential threat to the effectiveness of insecticides currently used in dengue vector control, and the urgent requirement for insecticide resistance management to be integrated into the National Dengue Control Program.

A survey of insecticide resistance-conferring mutations in multiple targets in Anopheles sinensis populations across Sichuan, China

BackgroundSichuan province is located in the southwest of China, and was previously a malaria-endemic region. Although no indigenous malaria case has been reported since 2011, the number of imported cases is on the rise. Insecticide-based vector control has played a central role in the prevention of malaria epidemics. However, the efficacy of this strategy is gravely challenged by the development of insecticide resistance. Regular monitoring of insecticide resistance is essential to inform evidence-based vector control. Unfortunately, almost no information is currently available on the status of insecticide resistance and associated mechanisms in Anopheles sinensis, the dominant malaria vector in Sichuan. In this study, efforts were invested in detecting the presence and frequency of insecticide resistance-associated mutations in three genes that encode target proteins of several classes of commonly used insecticides.MethodsA total of 446 adults of An. sinensis, collected from 12 locations across Sichuan province of China, were inspected for resistance-conferring mutations in three genes that respectively encode acetylcholinesterase (AChE), voltage-gated sodium channel (VGSC), and GABA receptor (RDL) by DNA Sanger sequencing.ResultsThe G119S mutation in AChE was detected at high frequencies (0.40–0.73). The predominant ace-1 genotype was GGC/AGC (119GS) heterozygotes. Diverse variations at codon 1014 were found in VGSC, leading to three different amino acid substitutions (L1014F/C/S). The 1014F was the predominant resistance allele and was distributed in all 12 populations at varying frequencies from 0.03 to 0.86. The A296S mutation in RDL was frequently present in Sichuan, with 296SS accounting for more than 80% of individuals in six of the 12 populations. Notably, in samples collected from Chengdu (DJY) and Deyang (DYMZ), almost 30% of individuals were found to be resistant homozygotes for all three targets.ConclusionsResistance-related mutations in three target proteins of the four main classes of insecticides were prevalent in most populations. This survey reveals a worrisome situation of multiple resistance genotypes in Sichuan malaria vector. The data strengthen the need for regular monitoring of insecticide resistance and establishing a region-customized vector intervention strategy.Graphical abstract

Monitoring and mechanisms of insecticide resistance in Spodoptera exigua (Lepidoptera: Noctuidae), with special reference to diamides

The beet armyworm, Spodoptera exigua, is a major lepidopteran pest of global importance in cultivation of numerous crops including cotton, maize, soybean, onion, cabbage, and ornamentals. It has evolved resistance to different insecticides. However, the current status of insecticide resistance in S. exigua has not been well examined in China. In this study, concentration-mortality responses of S. exigua to seven insecticides, including chlorantraniliprole, tetraniliprole, methoxyfenozide, indoxacarb, chlorfenapyr, emamectin benzoate and beta-cypermethrin were evaluated. The results showed that most of the tested populations had developed moderate to high resistance to chlorantraniliprole, with resistance ratios ranging from 6.3 to 2477.3-fold. Our results also showed that chlorantraniliprole have cross-resistance with tetraniliprole in S. exigua. The AY19 population collected from Anyang in Henan Province in 2019 exhibited a high resistance level to beta-cypermethrin (RR = 277.5). Methoxyfenozide and chlorfenapyr were highly effective against all of the tested populations with resistance ratios (RR) ranging from 0.1 to 2.2-fold. One of the tested populations showed moderate resistance to indoxacarb and emamectin benzoate. We detected the known ryanodine receptor target site resistance mutation, I4743M, in the field populations of S. exigua with different levels of diamide resistance.

Influence of Pyrethroid Resistance on Vector Competency for Zika Virus by Aedes aegypti (Diptera: Culicidae).

The vector competence of mosquitoes for pathogens has been shown to be influenced by the status of insecticide resistance in the mosquito population. However, to date, only two studies has explored the impact of insecticide resistance on arbovirus transmission. The global and widespread use of pyrethroids has led to the development of insecticide resistance in many mosquito species, including Aedes aegypti (Linnaeus) (Diptera: Culicidae), the primary vector of Zika virus. Strains of Ae. aegypti that were genetically similar, but responded differently to pyrethroid exposure, were developed using backcrossing techniques. These populations were orally infected with Zika virus and susceptibility to infection, disseminated infection, and transmission potential were evaluated. Analyses revealed differences in susceptibility to infection and disseminated infection between the pyrethroid susceptible and resistant strains of Ae. aegypti during the infection period. Here, we identify an additional challenge to that of widespread pyrethroid resistance. Specifically, resistance is associated with altered phenotypic traits that influence susceptibility to arbovirus infection and progression of infection in the mosquito, factors which ultimately influence risk of arbovirus transmission. These findings support the need to 1) consider insecticide resistance status during times of arbovirus transmission and 2) to implement insecticide resistance management/ mitigation strategies in vector control programs.

Insecticide resistance status of indoor and outdoor resting malaria vectors in a highland and lowland site in Western Kenya.

Long Lasting Insecticidal Nets (LLINs) and indoor residual spraying (IRS) represent powerful tools for controlling malaria vectors in sub-Saharan Africa. The success of these interventions relies on their capability to inhibit indoor feeding and resting of malaria mosquitoes. This study sought to understand the interaction of insecticide resistance with indoor and outdoor resting behavioral responses of malaria vectors from Western Kenya. The status of insecticide resistance among indoor and outdoor resting anopheline mosquitoes was compared in Anopheles mosquitoes collected from Kisumu and Bungoma counties in Western Kenya. The level and intensity of resistance were measured using WHO-tube and CDC-bottle bioassays, respectively. The synergist piperonyl butoxide (PBO) was used to determine if metabolic activity (monooxygenase enzymes) explained the resistance observed. The mutations at the voltage-gated sodium channel (Vgsc) gene and Ace 1 gene were characterized using PCR methods. Microplate assays were used to measure levels of detoxification enzymes if present. A total of 1094 samples were discriminated within Anopheles gambiae s.l. and 289 within An. funestus s.l. In Kisian (Kisumu county), the dominant species was Anopheles arabiensis 75.2% (391/520) while in Kimaeti (Bungoma county) collections the dominant sibling species was Anopheles gambiae s.s 96.5% (554/574). The An. funestus s.l samples analysed were all An. funestus s.s from both sites. Pyrethroid resistance of An.gambiae s.l F1 progeny was observed in all sites. Lower mortality was observed against deltamethrin for the progeny of indoor resting mosquitoes compared to outdoor resting mosquitoes (Mortality rate: 37% vs 51%, P = 0.044). The intensity assays showed moderate-intensity resistance to deltamethrin in the progeny of mosquitoes collected from indoors and outdoors in both study sites. In Kisian, the frequency of vgsc-L1014S and vgsc-L1014F mutation was 0.14 and 0.19 respectively in indoor resting malaria mosquitoes while those of the outdoor resting mosquitoes were 0.12 and 0.12 respectively. The ace 1 mutation was present in higher frequency in the F1 of mosquitoes resting indoors (0.23) compared to those of mosquitoes resting outdoors (0.12). In Kimaeti, the frequencies of vgsc-L1014S and vgsc-L1014F were 0.75 and 0.05 respectively for the F1 of mosquitoes collected indoors whereas those of outdoor resting ones were 0.67 and 0.03 respectively. The ace 1 G119S mutation was present in progeny of mosquitoes from Kimaeti resting indoors (0.05) whereas it was absent in those resting outdoors. Monooxygenase activity was elevated by 1.83 folds in Kisian and by 1.33 folds in Kimaeti for mosquitoes resting indoors than those resting outdoors respectively. The study recorded high phenotypic, metabolic and genotypic insecticide resistance in indoor resting populations of malaria vectors compared to their outdoor resting counterparts. The indication of moderate resistance intensity for the indoor resting mosquitoes is alarming as it could have an operational impact on the efficacy of the existing pyrethroid based vector control tools. The use of synergist (PBO) in LLINs may be a better alternative for widespread use in these regions recording high insecticide resistance.

Insecticide resistance status and biochemical mechanisms involved in Aedes mosquitoes

Mosquitoes belonging to the genus Aedes pose a significant threat to human health on a global scenario due to their role in transmission of dengue, chikungunya, zika, and yellow fever. In absence of specific medications and vaccines against these diseases, disease prevention relies on vector control. However, in today's world, vector control is facing major challenges due to the onset of insecticide resistance in mosquitoes. There are four main mechanisms of insecticide resistance, namely, behavioral resistance, reduced penetration/cuticular resistance, metabolic detoxification, and target site resistance; however, the latter two mechanisms have been studied widely in Aedes mosquitoes. Insecticide resistance in Aedes mosquitoes is widespread throughout the world. This review compiles the degree of insecticide resistance/susceptibility prevailing among different field populations of Aedes mosquitoes worldwide. In addition, the review has detailed the mechanisms providing the resistance phenomenon observed in nature in Aedes mosquitoes.

Insecticide resistance status of malaria vectors Anopheles gambiae (s.l.) of southwest Burkina Faso and residual efficacy of indoor residual spraying with microencapsulated pirimiphos-methyl insecticide

BackgroundThe rapid spread of insecticide resistance in malaria vectors and the rebound in malaria cases observed recently in some endemic areas underscore the urgent need to evaluate and deploy new effective control interventions. A randomized control trial (RCT) was conducted with the aim to investigate the benefit of deploying complementary strategies, including indoor residual spraying (IRS) with pirimiphos-methyl in addition to long-lasting insecticidal nets (LLINs) in Diébougou, southwest Burkina Faso.MethodsWe measured the susceptibility of the Anopheles gambiae (s.l.) population from Diébougou to conventional insecticides. We further monitored the efficacy and residual activity of pirimiphos-methyl on both cement and mud walls using a laboratory susceptible strain (Kisumu) and the local An. gambiae (s.l.) population.ResultsAn. gambiae (s.l.) from Diébougou was resistant to DDT, pyrethroids (deltamethrin, permethrin and alphacypermethrin) and bendiocarb but showed susceptibility to organophosphates (pirimiphos-methyl and chlorpyrimiphos-methyl). A mixed-effect generalized linear model predicted that pirimiphos-methyl applied on cement or mud walls was effective for 210 days against the laboratory susceptible strain and 247 days against the local population. The residual efficacy of pirimiphos-methyl against the local population on walls made of mud was similar to that of cement (OR = 0.792, [0.55–1.12], Tukey’s test p-value = 0.19).ConclusionsIf data on malaria transmission and malaria cases (as measured trough the RCT) are consistent with data on residual activity of pirimiphos-methyl regardless of the type of wall, one round of IRS with pirimiphos-methyl would have the potential to control malaria in a context of multi-resistant An. gambiae (s.l.) for at least 7 months.Graphical

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

ABSTRACTThe 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.

Evaluation of Long-Lasting Insecticidal Nets (DuraNet®) Under laboratory and Semi-Field Conditions Using Experimental Huts Against Anopheles Mosquitoes in Jimma Zone, Southwestern Ethiopia

Background:Long-Lasting Insecticidal Nets (LLINs) efficacy could be compromised due to a lot of influences together with user compliance and vector population insecticide resistance status. Thus, this study was to assess the biological efficacy of DuraNet® with the help of the World Health Organization cone bioassay and field experimental hut.Methods:A laboratory and a semi-field conditions experimental huts against Anopheles Mosquitoes were conducted in southwestern Ethiopia from September 2015 to January 2016. The bio efficacy of DuraNet® was evaluated using the WHO cone bioassay test and then its field efficacy was evaluated using experimental huts against the malaria vector population.Results:World Health Organization cone bioassay tests against pyrethroid-resistant An. arabiensis led to mean percent mortality and knockdown of 78% and 93%, respectively. Washing of DuraNet® successively reduced its efficacy from 93% knockdown (0 wash) to 45% knockdown (20 washes). Similarly, mean mortality decreased from 84% (0 wash) to 47% (20 washes). A total of 1575 female mosquitoes were collected over 40 nights out of which 1373(87.8%) were An. gambiae s.l., 116 (7.4%) were Anopheles coustani and 107 (6.8%) were An. pharoensis. The mean blood-feeding rate was significantly lower (P < .001) in hut containing unwashed DuraNet® when compared to hut containing untreated DuraNet®. The mean mortality rate was significantly higher (P < .001) in hut containing DuraNet® when compared to hut containing untreated DuraNet®. Unwashed DuraNet® showed the highest personal protection 88.7% and 100% against An. Arabiensis and An. pharoensis, respectively.Conclusion:Both DuraNet® and PermaNet 2.0 moderate efficacy against a pyrethroid-resistant population of An. arabiensis from Ethiopia. The bio efficacy of DuraNet® was found below the WHO recommendation. Therefore, the real impact of the observed insecticide resistance against DuraNet® to be further studied under phase-III trials, the need for new alternative vector control tools remains critical.

VectorMap-GR: A local scale operational management tool for entomological monitoring, to support vector control activities in Greece and the Mediterranean Basin

Over the past decade, Greece and other Mediterranean countries have witnessed the emergence and resurgence of several vector-borne diseases (VBDs), posing important public health challenges and threatening the tourist industry. An essential prerequisite for the design and execution of efficient and sustainable context-specific VBD control programmes is the establishment of integrative entomological and epidemiological surveillance systems. However, the monitoring and management of surveillance datasets (often chronologically fragmented, scattered in regional health district offices and partially accessible upon requisition), as well as their transformation into actionable information, is a complex undertaking. In light of aiding and optimizing vector control efforts in the Mediterranean Basin, we developed VectorMap-GR, an online, open access, operational management tool for entomological and complementary epidemiological monitoring data. The toolʼs key components are a set of controlled vocabularies (ontologies) running throughout the system, the systemʼs database and a map interface for data querying and display. The tool supports transformation of raw data into operationally relevant information (i.e. customized maps, charts, tables and reports) in a highly interactive fashion achieved through query filters and the ArcGIS technology embedded in the system. End-users may search for and obtain information on (i) the mosquito fauna composition, abundance and spatiotemporal dynamics; (ii) the mosquito insecticide resistance status and underlying resistance mechanisms; (iii) the occurrence of VBD pathogens and infections in vectors, animals and humans; and (iv) operationally relevant physical feature georeferenced datasets (e.g. mosquito breeding sites). VectorMap-GR was pilot implemented during 2018–2020 in a mosquito control programme in the Region of Crete (southern Greece). The programmeʼs control efforts coupled with VectorMap-GR pilot implementation phase, very likely contributed to the reduction of vector population numbers and the prevention of human VBD occurrences, recorded in this period.

First report of voltage‐gated sodium channel M918V and molecular diagnostics of nicotinic acetylcholine receptor R81T in the cotton aphid

AbstractThe cotton aphid, Aphis gossypii Glover, is one of the most important agricultural insect pests. Pyrethroid and neonicotinoid insecticides have generally shown excellent control of A. gossypii, but many populations of this pest have developed resistance against these classes of insecticides. The success of insecticide resistance management strategies requires detailed knowledge of both phenotype and genotype of the target insect pest. In this study, we attempted to understand the molecular status of insecticide resistance in cotton aphid populations in Xinjiang Uygur Autonomous Region of China, the major cotton planting region of China. In addition to the previously reported M918L mutation, we discovered another substitution (M918V) in the voltage‐gated sodium channel (VGSC). Moreover, we developed a molecular assay that could be used to detect precisely the R81T mutation in the nicotinic acetylcholine receptor (nAChR). This survey revealed that 918L was the predominant VGSC allele with a frequency ranging from 50.0% to 56.7%. Notably, appreciable frequencies (between 10% and 40%) of the resistance 81T allele of the nAChR gene were detected in three investigated populations. The prevalent co‐occurrence of both VGSC 918L/V and nAchR 81T indicates a worrisome situation of multiple resistance to both pyrethroids and neonicotinoids.

Monitoring the resistance and baseline susceptibility of Plutella xylostella (L.) (Lepidoptera: Plutellidae) against spinetoram in Tamil Nadu, India

Diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae), is a destructive cosmopolitan pest that affects cruciferous crops, and insecticides are the major tool used for control. This study aimed to evaluate the insecticide resistance status of P. xylostella collected from ten different locations of Tamil Nadu, India against a diverse group of insecticides used by farmers. The results showed that spinetoram and novaluron were highly toxic to P. xylostella with a resistance ratio of 1.89- to 13.85-fold and 5.01- to 16.93-fold, respectively, compared to a susceptible laboratory population. All field populations exhibited a low to moderate level of resistance against spinosad (2.14- to 21.78-fold), emamectin benzoate (3.74- to 41.26-fold), and indoxacarb (3.42- to 29.37-fold), whereas high levels of resistance were observed against chlorantraniliprole (36.67- to 124.72-fold), flubendiamide (12.66- to 93.63-fold), fipronil (31.99- to 156.24-fold), and cypermethrin (26.97- to174.84-fold). A significant correlation was found between the LC50 values of spinetoram and spinosad (P = 0.001). However, no significant correlation (P > 0.05) was observed between spinosyn and other insecticides suggesting a lack of cross-resistance with other groups of insecticides. The synergistic assay showed that the metabolic detoxification mechanisms may not be responsible for P. xylostella resistance against spinetoram. Hence, to prevent the development of resistance in P. xylostella, a combination of insecticides having different mechanisms of action should be used in rotation.

Insecticide resistance status of Aedes aegypti in Bangladesh

BackgroundArboviral diseases, including dengue and chikungunya, are major public health concerns in Bangladesh where there have been unprecedented levels of transmission reported in recent years. The primary approach to control these diseases is to control the vector Aedes aegypti using pyrethroid insecticides. Although chemical control has long been practiced, no comprehensive analysis of Ae. aegypti susceptibility to insecticides has been conducted to date. The aim of this study was to determine the insecticide resistance status of Ae. aegypti in Bangladesh and investigate the role of detoxification enzymes and altered target site sensitivity as resistance mechanisms.MethodsEggs of Aedes mosquitoes were collected using ovitraps from five districts across Bangladesh and in eight neighborhoods of the capital city Dhaka, from August to November 2017. CDC bottle bioassays were conducted for permethrin, deltamethrin, malathion, and bendiocarb using 3- to 5-day-old F0–F2 non-blood-fed female mosquitoes. Biochemical assays were conducted to detect metabolic resistance mechanisms, and real-time PCR was performed to determine the frequencies of the knockdown resistance (kdr) mutations Gly1016, Cys1534, and Leu410.ResultsHigh levels of resistance to permethrin were detected in all Ae. aegypti populations, with mortality ranging from 0 to 14.8% at the diagnostic dose. Substantial resistance continued to be detected against higher (2×) doses of permethrin (5.1–44.4% mortality). Susceptibility to deltamethrin and malathion varied between populations while complete susceptibility to bendiocarb was observed in all populations. Significantly higher levels of esterase and oxidase activity were detected in most of the test populations as compared to the susceptible reference Rockefeller strain. A significant association was detected between permethrin resistance and the presence of Gly1016 and Cys1534 homozygotes. The frequency of kdr (knockdown resistance) alleles varied across the Dhaka Aedes populations. Leu410 was not detected in any of the tested populations.ConclusionsThe detection of widespread pyrethroid resistance and multiple resistance mechanisms highlights the urgency for implementing alternate Ae. aegypti control strategies. In addition, implementing routine monitoring of insecticide resistance in Ae. aegypti in Bangladesh will lead to a greater understanding of susceptibility trends over space and time, thereby enabling the development of improved control strategies.Graphical

A study of malaria vector surveillance as part of the Malaria Elimination Demonstration Project in Mandla, Madhya Pradesh

BackgroundUnderstanding of malaria vector density, distribution, insecticide resistance, vector incrimination, infection status, and identification of sibling species are some of the essential components of vector control measures for achieving malaria elimination goals.MethodsAs part of the malaria elimination demonstration project, entomological surveillance was carried out from October 2017 to October 2019 by collecting indoor resting mosquitoes using hand catch method. Susceptibility test was done for determining the insecticide resistance status of vector mosquito Anopheles culicifacies using standard protocols by the World Health Organization. The cone bioassay method was used for determining the efficacy and quality of insecticide sprayed. Mosquitoes collected from different ecotypes were identified and processed for parasite identification, vector incrimination and sibling species determination.ResultsThe two known malaria vector species (Anopheles culicifacies and Anopheles fluviatilis) were found in the study area, which have been previously reported in this and adjoining areas of the State of Madhya Pradesh. The prevalence of An. culicifacies was significantly higher in all study villages with peak in July while lowest number was recorded in May. Proportion of vector density was observed to be low in foothill terrains. The other anopheline species viz, Anopheles subpictus, Anopheles annularis, Anopheles vagus, Anopheles splendidus, Anopheles pallidus, Anopheles nigerrimus and Anopheles barbirostris were also recorded in the study area, although their prevalence was significantly less compared to the An. culicifacies. In 2017, An. culicifacies was found to be resistant to dichloro-diphenyl-trichloroethane (DDT) and malathion, with possible resistance to alphacypermethrin and susceptible to deltamethrin. However, in 2019, the species was found to be resistant to alphacypermethrin, DDT, malathion, with possible resistance to deltamethrin. The bioassays revealed 82 to > 98% corrected % mortality of An. culicifacies on day-one post-spraying and 35 to 62% on follow-up day-30. Anopheles culicifacies sibling species C was most prevalent (38.5%) followed by A/D and E while B was least pre-dominant (11.9%). Anopheles fluviatilis sibling species T was most prevalent (74.6%) followed by U (25.4%) while species S was not recorded. One An.culicifacies (sibling species C) was found positive for Plasmodium falciparum by PCR tests in the mosquitoes sampled from the test areas.ConclusionBased on the nine entomologic investigations conducted between 2017–2019, it was concluded that An. culicifacies was present throughout the year while An. fluviatilis had seasonal presence in the study areas. Anopheles culicifacies was resistant to alphacypermethrin and emerging resistance to deltamethrin was observed in this area. Anopheles culicifacies was confirmed as the malaria vector. This type of information on indigenous malaria vectors and insecticide resistance is important in implementation of vector control through indoor residual spraying (IRS) and use of insecticide-impregnated bed nets for achieving the malaria elimination goals.

The first implementation of allele-specific primers for detecting the knockdown and acetylcholinesterase target site mutations in malaria vector, Anopheles sacharovi

Anopheles sacharovi, a primer malaria vector species of Turkey, have a significant public health importance. It is aimed to determine the insecticide resistance status in Anopheles sacharovi populations in the Aegean and Mediterranean regions of Turkey. A total of 1638 individuals were analysed from 15 populations. Bioassay results indicated all An. sacharovi populations were resistant to DDT, malathion, fenitrothion, bendiocarb, propoxur. Many populations have begun to have resistance against permethrin and deltamethrin. Biochemical analyses results revealed that glutathione-S-transferases and P450 monooxygenases might be responsible from the mechanisms of DDT resistance; esterases and acetylcholinesterase might be responsible for organophosphate and carbamate resistance; P450 monooxygenases and esterases might be responsible for pyrethroid resistance into populations sampled from the study area. Allele-specific primers detected L1014F and L1014S mutations that provide kdr resistance against pyrethroids and DDT. Increased acetylcholinesterase insensitivity was detected while Ace-1 G119S mutations were not detected in An. sacharovi populations by using allele-specific primers. Overall results indicate the presence of multiple resistance mechanisms in Turkish An. sacharovi field populations suggesting that populations might gain resistance against all possible insecticide in the future. Therefore, insecticide resistance management strategies are urgently needed for effective vector control implementation.

Development of an Insecticide-Free Trapping Bednet to Control Mosquitoes and Manage Resistance in Malaria Vector Control: A New Way of Thinking.

Simple SummaryInsecticide resistance in mosquitoes reduces the effectiveness of malaria control interventions and has reversed the gains made in reducing malaria morbidity. Hence, new strategies are needed to mitigate the spread of resistance, preserve the efficacy of available insecticides, and restore the effectiveness of control. To combat resistance to insecticides in malaria mosquitoes, WHO recommends using long-lasting insecticide-impregnated mosquito bednets (LLINs) as well as the synergist piperonyl-butoxide (PBO). PBO enhances the insecticidal effect of the treated bednet. Unfortunately, decreases in performance of PBO-LLINs are now reported in some regions of Africa where mosquitoes are resistant to insecticides. Our objective was to develop an insecticide-free, mechanical solution that kills mosquitoes regardless of their insecticide resistance status, ultimately overcoming the problem of insecticide resistance. We designed and developed an insecticide-free mosquito trapping bednet for mass mosquito trapping and killing, the “T-Net”, and we show its efficacy compared to a conventional LLIN in Africa. Mathematical models were also developed to predict T-Net efficacy in individual homes and at the community level.Mosquito-borne malaria kills 429,000 people each year with the problem being acute in sub-Saharan Africa. The successes gained with long-lasting pyrethroid-treated bednets are now in jeopardy because of wide-spread, pyrethroid resistance in mosquitoes. Using crowd modeling theory normalized for standard bednet architecture, we were able to design an attract–trap–kill technology for mosquitoes that does not require insecticides. Using three-dimensional polyester knitting and heat fixation, trap funnels were developed with high capture efficacy with no egression under worst-case laboratory conditions. Field testing in Africa in WHO huts with Gen1-3 T (trap)-Nets validated our model, and as predicted, Gen3 had the highest efficacy with a 4.3-fold greater trap–kill rate with no deterrence or repellency compared to Permanet 2.0, the most common bednet in Africa. A T-Net population model was developed based on field data to predict community-level mosquito control compared to a pyrethroid bednet. This model showed the Gen3 non-insecticidal T-Net under field conditions in Africa against pyrethroid resistant mosquitoes was 12.7-fold more efficacious than single chemical, pyrethroid-treated nets.

New distribution record of Anopheles rivulorum-like from Sadiola, Mali, with notes on malaria vector insecticide resistance.

The SEMOS gold mine in Sadiola, southwestern Mali, has been implementing a malaria vector control programme for 15y using indoor residual house spraying and sporadic larval control. Periodic screening of the vector populations have been carried out over the years to provide information to the control programme, mainly on vector species present and their insecticide resistance status. The data from five entomological surveys, carried out in 2006, 2011, 2014, 2016 and 2018, are presented. Adult mosquitoes were collected resting on walls inside houses and on verandas. Insecticide susceptibility assays were carried out and mosquitoes subsequently identified by species using molecular assays. The major malaria vector mosquitoes, Anopheles gambiae and Anopheles arabiensis were abundant at each sampling period with Anopheles coluzzii and Anopheles funestus being rare or absent. Anopheles rivulorum was identified in 2006 and Anopheles leesoni in 2016. The presence of Anopheles rivulorum-like, identified for the first time in 2018, was not screened for in previous surveys. Insecticide susceptibility bioassays showed resistance in both A. gambiae and A. arabiensis to pyrethroids, carbamates and dichlorodiphenyltrichloroethane over the 12y. This is the first record of A. rivulorum-like west of Côte d'Ivoire. Resistance levels to the three classes of insecticides were variable but appeared to decrease after pyrethroids were discontinued for house spraying.

Species diversity and insecticide resistance within the Anopheles hyrcanus group in Ubon Ratchathani Province, Thailand

BackgroundMembers of the Anopheles hyrcanus group have been incriminated as important malaria vectors. This study aims to identify the species and explore the insecticide susceptibility profile within the Anopheles hyrcanus group in Ubon Ratchathani Province, northeastern Thailand where increasing numbers of malaria cases were reported in 2014.MethodsBetween 2013 and 2015, five rounds of mosquito collections were conducted using human landing and cattle bait techniques during both the rainy and dry seasons. Anopheles mosquitoes were morphologically identified and their insecticide susceptibility status was investigated. Synergist bioassays were carried out with An. hyrcanus (s.l.) due to their resistance to all insecticides. An ITS2-PCR assay was conducted to identify to species the Hyrcanus group specimens.ResultsOut of 10,361 Anopheles females collected, representing 18 taxa in 2 subgenera, 71.8% were morphologically identified as belonging to the Hyrcanus Group (subgenus Anopheles), followed by An. barbirostris group (7.9%), An. nivipes (6.5%), An. philippinensis (5.9%) and the other 14 Anopheles species. Specimens of the Hyrcanus Group were more prevalent during the rainy season and were found to be highly zoophilic. Anopheles hyrcanus (s.l.) was active throughout the night, with an early peak of activity between 18:00 h and 21:00 h. ITS2-PCR assay conducted on 603 DNA samples from specimens within the Hyrcanus Group showed the presence of five sisters species. Anopheles peditaeniatus was the most abundant species (90.5%, n = 546), followed by An. nitidus (4.5%, n = 27), An. nigerrimus (4.3%, n = 26), An. argyropus (0.5%, n = 3), and An. sinensis (0.2%, n = 1). All An. hyrcanus (s.l.) specimens that were found resistant to insecticides (deltamethrin 0.05%, permethrin 0.75% and DDT 4% and synergist tests) belonged to An. peditaeniatus. The degree of resistance in An. peditaeniatus to each of these three insecticides was approximately 50%. Addition of PBO (Piperonyl butoxide), but not DEF (S.S.S-tributyl phosphotritioate), seemed to restore susceptibility, indicating a potential role of oxidases as a detoxifying enzyme resistance mechanism.ConclusionsA better understanding of mosquito diversity related to host preference, biting activity and insecticide resistance status will facilitate the implementation of locally adapted vector control strategies.

Status of insecticide resistance and biochemical characterization of chlorpyrifos resistance in Sogatella furcifera (Hemiptera:Delphacidae) in Sichuan Province, China

The white-backed planthopper, Sogatella furcifera (Horváth) (Hemiptera, Delphacidae), is an energetic rice insect pest in rice production or rice-growing areas. Due to excessive use of the chemical insecticide, S. furcifera has produced the high resistance to some frequently used insecticides. In this paper, the resistance levels of S. furcifera from the eight different areas of Sichuan Province against the five chemicals were monitored by using the rice seedling dipping during 2017–2018 to understand the resistance levels. The results showed that most of all populations have developed low or moderate level of resistance for chlorpyrifos (3.4 to 44.3-fold) and thiamethoxam (3.9- to 15.5-fold), the populations in the LS (1.7 to 5.4- fold)and WS (1.6 to 5.0- fold) regions were still sensitive or low resistance levels compared with other local populations. Almost all populations displayed the susceptible to imidacloprid (0.9- to 5.0-fold), buprofezin (0.9- to 4.3-fold) or low levels of resistance to pymetrozine (1.5- to 6.8-fold). The synergism experiment indicated that P450 enzymes may be important contributed to the metabolic detoxification of chlorpyrifos. The cross-resistance bioassay showed that there was no cross-resistance between chlorpyrifos and triflumezopyrim, but for sulfoxaflor, in the XY17 population. The relative expression level of twelve insecticide resistant-related P450 genes were analyzed by using qRT-PCR and found that CYP4C77, CYP418A1, CYP418A2, CYP408A3 and CYP6ER4 were significantly more expressed in the 3rd-instar nymph of the XY17 and XY18 field populations. To determine the main resistant-related P450 gene for chlorpyrifos, the relative expression level of five P450 genes were detected by using qRT-PCR from the G2 and G4 generation of XY17 under the pressure with LC50 of chlorpyrifos. The results showed that CYP6ER4 was significantly up-regulated expression in XY17 G2 and G4 generations population over 700-fold (P < 0.01). The full length and proteins tertiary structure were also cloned and predicted. Meanwhile, the function of CYP6ER4 was analyzed by RNA interference and the results indicated that the relative expression of CYP6ER4 in the XY17 (G4) population after injected dsRNA was lower than that in the dsGFP injected group. Moreover, the mortality rates of the S. furcifera treated with the LC50 concentration of chlorpyrifos after dsRNA microinjection was significantly higher than that of the dsGFP injected group 72 h after treatment (P < 0.01). Therefore, the overexpression of CYP6ER4 may be one of the primary factors in the development of chlorpyrifos resistance in S. furcifera.