Insecticide Resistance Mechanisms Research Articles

Insecticide resistance levels and mechanisms in Aedes aegypti populations in and around Ouagadougou, Burkina Faso.

BackgroundRecent outbreaks of dengue and other Aedes aegypti-borne arboviruses highlight the importance of a rapid response for effective vector control. Data on insecticide resistance and underlying mechanisms are essential for outbreak preparedness, but are sparse in much of Africa. We investigated the levels and heterogeneity of insecticide resistance and mechanisms of Ae. aegypti from contrasting settings within and around Ouagadougou, Burkina Faso.Methodology/Principal findingsBioassays were performed on larvae and adults to diagnose prevalence of resistance, and to assess levels where resistance was detected. Investigation of resistance mechanisms was performed using synergist bioassays, knockdown resistance (kdr) target site mutation genotyping and quantitative PCR expression analysis of candidate P450 genes.Larval dose-response assays indicated susceptibility to the organophosphates tested. Adult females were also susceptible to organophosphates, but resistance to carbamates was suspected in urban and semi-urban localities. Females from all localities showed resistance to pyrethroids but resistance prevalence and level were higher in urban and especially in semi-urban areas, compared to the rural population. Environment was also associated with susceptibility: adults reared from larvae collected in tires from the semi-urban site were significantly less resistant to pyrethroids than those collected from large outdoor drinking water containers (‘drums’). Susceptibility to both pyrethroids tested was largely restored by pre-exposure to Piperonyl Butoxide (PBO), suggesting a strong metabolic basis to resistance.The 1534C kdr mutation was nearly fixed in semi-urban and urban areas but was far less common in the rural area, where the 1016I kdr mutation frequency was also significantly lower. P450 gene analysis detected limited over-expression of single candidates but significantly elevated average expression in the semi-urban site compared to both a susceptible laboratory colony, and females from the other collection sites.Conclusions/SignificanceOur results reveal pyrethroid resistance and paired kdr mutations in both urban and semi-urban sites at levels that are unprecedented for mainland Africa. The combination of target site and metabolic mechanisms is common in Ae. aegypti populations from other continents but is a worrying finding for African populations. However, organophosphate insecticides are still active against both larvae and adults of Ae. aegypti, providing useful insecticidal options for control and resistance management.

Enzymatic and molecular characterization of insecticide resistance mechanisms in field populations of Aedes aegypti from Selangor, Malaysia

BackgroundDengue is a serious public health problem worldwide, including in Selangor, Malaysia. Being an important vector of dengue virus, Aedes aegypti are subjected to control measures which rely heavily on the usage of insecticides. Evidently, insecticide resistance in Ae. aegypti, which arise from several different point mutations within the voltage-gated sodium channel genes, has been documented in many countries. Thus, this robust study was conducted in all nine districts of Selangor to understand the mechanisms of resistance to various insecticides in Ae. aegypti. Mosquitoes were collected from dengue epidemic and non-dengue outbreak areas in Selangor.MethodsUsing the Center for Disease Control and Prevention (CDC) bottle assays, the insecticide resistance status of nine different Ae. aegypti strains from Selangor was accessed. Synergism tests and biochemical assays were conducted to further understand the metabolic mechanisms of insecticide resistance. Polymerase chain reaction (PCR) amplification and sequencing of the IIP-IIS6 as well as IIIS4-IIIS6 regions of the sodium channel gene were performed to enable comparisons between susceptible and resistant mosquito strains. Additionally, genomic DNA was used for allele-specific PCR (AS-PCR) genotyping of the gene to detect the presence of F1534C, V1016G and S989P mutations.ResultsAdult female Ae. aegypti from various locations were susceptible to malathion and propoxur. However, they exhibited different levels of resistance against dichlorodiphenyltrichloroethane (DDT) and pyrethroids. The results of synergism tests and biochemical assays indicated that the mixed functions of oxidases and glutathione S-transferases contributed to the DDT and pyrethroid resistance observed in the present study. Besides detecting three single kdr mutations, namely F1534C, V1016G and S989P, co-occurrence of homozygous V1016G/S989P (double allele) and F1534C/V1016G/S989P (triple allele) mutations were also found in Ae. aegypti. As per the results, the three kdr mutations had positive correlations with the expressions of resistance to DDT and pyrethroids.ConclusionsIn view of the above outcomes, it is important to seek new tools for vector management instead of merely relying on insecticides. If the latter must be used, regular monitoring of insecticide resistance should also be carried out at all dengue epidemic areas. Since the eggs of Ae. aegypti can be easily transferred from one location to another, it is probable that insecticide-resistant Ae. aegypti can be found at non-dengue outbreak sites as well.

Resistance Status to Deltamethrin, Permethrin, and Temephos Along With Preliminary Resistance Mechanism in Aedes aegypti (Diptera: Culicidae) From Punjab, Pakistan.

The use of insecticides such as deltamethrin, permethrin, and temephos has been a primary tool to manage Aedes aegypti (Linnaeus) in Punjab province, Pakistan; however, recent reports of control failure necessitate monitoring insecticide resistance. For this reason, we evaluated 12 field strains of Ae. aegypti from Punjab for resistance against deltamethrin, permethrin, and temephos along with underlying resistance mechanisms. For deltamethrin, high level of resistance was observed in Rawalpindi, Faisalabad, Sheikhupura, Lahore, Pattoki, and Kasur strains (RRLC50 > 10-fold); moderate level of resistance in Sargodha, Gujranwala, and Sialkot strains (RRLC50 = 5- to 10-fold), and low level of resistance in Okara, Multan, and Sahiwal strains (RRLC50 < 5-fold). In the case of permethrin, high level of resistance was found in all the field strains, except the Okara strain that exhibited moderate resistance. For temephos, five field strains, viz. Faisalabad, Rawalpindi, Kasur, Lahore, and Gujranwala, showed high level of resistance; five strains, viz. Sheikhupura, Sialkot, Pattoki, Sahiwal, and Okara, showed moderate resistance, and two strains from Multan and Sargodha showed low resistance to temephos. Synergism bioassays implementing piperonyl butoxide and S,S,S-tributylphosphorotrithioate exhibited a nonsignificant effect on synergizing toxicity of deltamethrin and permethrin in all field strains except the Lahore strain, suggesting the possible role of target-site resistance mechanism. However, both synergists had a significant effect on synergizing toxicity of temephos in all field strains, suggesting the possibility of metabolic-based mechanism of insecticide resistance. In conclusion, the study confirmed the presence of resistance to deltamethrin, permethrin, and temephos in the studied field strains of Ae. aegypti from Punjab, Pakistan.

Status of insecticide resistance in Bemisia tabaci: resistance, cross-resistance, stability of resistance, genetics and fitness costs

The whitefly, Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) is a worldwide pest of major crops. It is a highly adaptable insect pest and resists almost all chemical compounds used for its control. It resists at a 7–30 fold, 7–4931-, 20–80-, and 12–2461 fold to various compounds of cyclodiene, organophosphates, carbamates and pyrethroid, respectively. It also resists up to 2000 fold to neonicotinoids and buprofezin. However, B. tabaci resists to some level to pyradabin, spiromesifen, pymetrozine, fipronil, diafenthuron and spinosaid. Resistance in B. tabaci is quite unstable in the absence of selection pressure, and cross-resistance within and between chemical groups is an established phenomenon. Further, inheritance of insecticide resistance in B. tabaci exclusively appears autosomal and partially recessive but resistance to pyriproxyfen and bifenthrin in Q-and B-type varies from incomplete to complete dominance. Furthermore, resistance to imidacloprid, bifenthrin, fenvelerate and pyriproxyfen is controlled by more than one gene (factor). However, resistance to pyriproxyfen in Q-type appears to be under the control of one factor. Mechanism of insecticide resistance and cost of fitness in this insect has also been discussed.

Dynamics and monitoring of insecticide resistance in malaria vectors across mainland Tanzania from 1997 to 2017: a systematic review

BackgroundMalaria still claims substantial lives of individuals in Tanzania. Insecticide-treated nets (ITNs) and indoor residual spray (IRS) are used as major malaria vector control tools. These tools are facing great challenges from the rapid escalating insecticide resistance in malaria vector populations. This review presents the information on the dynamics and monitoring of insecticide resistance in malaria vectors in mainland Tanzania since 1997. The information is important to policy-makers and other vector control stakeholders to reflect and formulate new resistance management plans in the country.MethodsReviewed articles on susceptibility and mechanisms of resistance in malaria vectors to insecticides across mainland Tanzania were systematically searched from the following databases: PubMed, Google scholar, HINARI and AGORA. The inclusion criteria were articles published between 2000 and 2017, reporting susceptibility of malaria vectors to insecticides, mechanisms of resistance in the mainland Tanzania, involving field collected adult mosquitoes, and mosquitoes raised from the field collected larvae. Exclusion criteria were articles reporting insecticide resistance in larval bio-assays, laboratory strains, and unpublished data. Reviewed information include year of study, malaria vectors, insecticides, and study sites. This information was entered in the excel sheet and analysed.ResultsA total of 30 articles met the selection criteria. The rapid increase of insecticide resistance in the malaria vectors across the country was reported since year 2006 onwards. Insecticide resistance in Anopheles gambiae sensu lato (s.l.) was detected in at least one compound in each class of all recommended insecticide classes. However, the Anopheles funestus s.l. is highly resistant to pyrethroids and DDT. Knockdown resistance (kdr) mechanism in An. gambiae s.l. is widely studied in the country. Biochemical resistance by detoxification enzymes (P450s, NSE and GSTs) in An. gambiae s.l. was also recorded. Numerous P450s genes associated with metabolic resistance were over transcribed in An. gambiae s.l. collected from agricultural areas. However, no study has reported mechanisms of insecticide resistance in the An. funestus s.l. in the country.ConclusionThis review has shown the dynamics and monitoring of insecticide resistance in malaria vector populations across mainland Tanzanian. This highlights the need for devising improved control approaches of the malaria vectors in the country.

Identification and classification of differentially expressed genes in pyrethroid-resistant Culex pipiens pallens.

Culex pipiens pallens is an important vector that transmits Bancroftian filariasis, Japanese encephalitis and other diseases that pose a serious threat to human health. Extensive and improper use of insecticides has caused insecticide resistance in mosquitoes, which has become an important obstacle to the control of mosquito-borne diseases. It is crucial to investigate the underlying mechanism of insecticide resistance. The aims of this study were to identify genes involved in insecticide resistance based on the resistance phenotype, gene expression profile and single-nucleotide polymorphisms (SNPs) and to screen for major genes controlling insecticide resistance. Using a combination of SNP and transcriptome data, gene expression quantitative trait loci (eQTLs) were studied in deltamethrin-resistant mosquitoes. The most differentially expressed pathway in the resistant group was identified, and a regulatory network was built using these SNPs and the differentially expressed genes (DEGs) in this pathway. The major candidate genes involved in the control of insecticide resistance were analyzed by qPCR, siRNA microinjection and CDC bottle bioassays. A total of 85 DEGs that encoded putative detoxification enzymes (including 61 P450s) were identified in this pathway. The resistance regulatory network was built using SNPs, and these metabolic genes, and a major gene, CYP9AL1, were identified. The functional role of CYP9AL1 in insecticide resistance was confirmed by siRNA microinjection and CDC bottle bioassays. Using the eQTL approach, we identified important genes in pyrethroid resistance that may aid in understanding the mechanism underlying insecticide resistance and in targeting new measures for resistance monitoring and management.

LLIN Evaluation in Uganda Project (LLINEUP): a cross-sectional survey of species diversity and insecticide resistance in 48 districts of Uganda

BackgroundLong-lasting insecticidal nets (LLINs) are the principal tool for malaria control in Africa and are presently treated with a single class of insecticide; however, increasing levels of insecticide resistance threaten their success. In response to this threat nets have been developed that incorporate the synergist, piperonyl butoxide (PBO), which inhibits the activity of cytochrome P450s which is one main mechanisms of insecticide resistance, allowing resistance to pyrethroids to be reversed. However, data on the value and cost effectiveness of these nets is lacking. A large-scale cluster randomised trial of conventional LLINs and PBO-LLINs was conducted in Uganda in 104 health sub-districts (HSDs) in 2017–2019. Prior to the mass distribution of LLINs, a baseline entomological survey was carried out, the results of which are reported herein. Ten households from each HSD were randomly selected for entomological surveillance at baseline which included household mosquito collections.ResultsPrior to LLIN distribution entomological collections were carried out in 1029 houses across the 104 HSDs. Anopheles gambiae (s.l.) was the principal vector in all but 9 of the 71 HSDs that yielded vector species. Molecular analysis found An. gambiae (s.s.) to be the predominant vector collected. Plasmodium falciparum was detected in 5.5% of An. gambiae (s.s.) and in 4.0% of An. funestus (s.s.) examined. Infection rates of other plasmodium species (P. vivax, P. ovale and P. malariae) were lower with infection rates of 1.2% and 1.7% for An. gambiae (s.s.) and An. funestus (s.s.), respectively. The knockdown resistance (kdr) mutation Vgsc-L1014S was found at very high frequency in An. gambiae (s.s.) with the Vgsc-L1014F mutation at low frequency and the wild-type allele virtually absent. In An. arabiensis the wild-type allele was predominant. The resistance-associated alleles, Cyp4j5-L43F and Coeae1d were found at moderate frequencies which varied across the study site. Vgsc-N1575Y mutation was not found in any samples examined.ConclusionsNo significant differences between planned intervention arms was observed in vector densities, sporozoite infection rate or insecticide resistance marker frequency across the study site prior to the distribution of LLINs. Very high levels of kdr resistance were observed in all areas; however, the resistance-associated markers Cyp4j5-L43F and Coeae1d were found at varying frequencies across the study site which may have implications for the effectiveness of standard LLINs.Trial registration This study is registered with ISRCTN, ISRCTN17516395. Registered 14 February 2017, http://www.isrctn.com/ISRCTN17516395

Biochemical Resistance Mechanisms to Fenvalerate in Plutella xylostella (Lepidoptera: Plutellidae).

The diamondback moth, Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae), is one of the most important pests of cruciferous crops in Iran and is controlled mostly by fenvalerate. The susceptibility to fenvalerate was investigated for four populations of P. xylostella. Bioassay results indicated significant differences among the populations tested. The highest level of resistance to fenvalerate was obtained for the Khuzestan (Khz) population (resistance ratio = 9.5). Survival was suppressed by diethyl maleate, piperonylbutoxide, and triphenyl phosphate, which confirmed that resistance to fenvalerate is caused by glutathione S-transferases (GSTs), mixed function oxidases, and esterases, respectively. Up to 8.6-, 2-, 2.7-, and 1.75-fold increases in GSTs, esterase (α-naphthylacerate and β-naphthyl acetate as substrate), and cytochrome P450 monooxygenases activities in resistant strains when compared with the susceptible one, were observed, respectively. The expression of six GST genes of P. xylostella including GSTs1, GSTe2, GSTe4, GSTo4, GSTd4, and GSTd5 were analyzed. The quantitative PCR analysis showed that three of the PxGSTs had the highest expression levels in the Khz population. Two of the GSTs (GSTd4 and PxGSTe2) exhibited highest expression level in both Khz and Alborz (Alb) populations. Therefore, PxGST genes were involved in fenvalerate resistance in P. xylostella. Overall, the mechanisms of insecticide resistance in diamondback moth populations in four regions of Iran were related to GST, esterase, and cytochrome P450 monooxygenase activities.

Modulation in Activity Profiles in Insecticide-Resistant Population of Tobacco Caterpillar, &lt;i&gt;Spodoptera Litura&lt;/i&gt; (Fabricius)

Activity spectrum of detoxification enzymes was systematically assessed in tobacco caterpillar, Spodoptera litura collected from four locations in Kerala, India, to decipher the mechanism of insecticide resistance. Using the susceptible check ICAR-NBAIR strain, specific activity profiles of acetylcholine esterase (AChE) were found to be 16.16-, 10.71- and 4.88-fold higher in the Kovilnada, Palappur and Kanjikuzhi populations respectively. Specific activities of mixed function oxidase (MFO) were also found to be 19.24-, 17.11-, 6.08-fold higher in the same populations respectively, indicating the predominance of AChE and MFO towards imparting resistance. Carboxylesterase (CarE) and glutathion-S-transferase (GST) specific activity profiles were 3.62- and 3.37-fold higher in the Kovilnada population, followed by 2.89- and 2.98-fold higher in the Palappur population and as 2.10- and 1.15-fold higher in the Kanjikuzhi population, indicating their partial role in resistance development. Suppression of specific activities in synergism bioassays with AChE in chlorpyriphos + TPP treatment (9.32-fold), GST in chlorpyriphos + DEM (4.78-fold) and CarE in quinalphos + TPP (5.15-fold) highlighted the involvement of multiple detoxification enzymes conferring resistance to organophosphates. Reduced activity of MFO in case of lambda-cyhalothrin + PBO (5.35-fold), CarE in case of cypermethrin + TPP (7.36-fold) and 3.60-fold reduction in MFO in case of cypermethrin + PBO highlighted the role of esterases and MFOs towards resistance development against synthetic pyrethroids.

Insecticide resistance in Aedes albopictus Skuse from sub-Himalayan districts of West Bengal, India

Dengue is one of the most rapidly spreading infectious diseases prevalent throughout the tropical and sub-tropical regions of the world. In absence of specific medications and vaccines, the sole method of disease prevention relies on vector control mainly using insecticides. But with the advent of Insecticide resistance, worldwide vector control programs are facing failure. In this study, eleven different Ae. albopictus population from sub-Himalayan districts of West Bengal, India were investigated as per WHO protocols to find out the current status of insecticide susceptibility against DDT, permethrin and propoxur. Also the role of three insecticide detoxifying enzymes underlying observed resistance was investigated through quantitative and synergistic assays to unveil the mechanism of insecticide resistance. It was found that majority of studied populations were resistant to 4% DDT. Two populations, namely Alipurduar (APD) and Jalpaiguri (JPG) were severely resistant to 0.75% permethrin, whereas only JPG population was found to exhibit severe resistance against 0.1% propoxur. Moreover, the involvement of detoxifying enzymes was also noted in conferring resistance against DDT and Permethrin. This study indicates the inefficacy of DDT in controlling Ae. albopictus populations in the study region. This study may help in implementation of an efficient vector control and insecticide resistance management strategies.

“Armed to the teeth”: The multiple ways to survive insecticidal and predatory challenges in Aedes aegypti larvae

Environmental pollutants, such as insecticides, can alter the equilibrium of aquatic ecosystems, particularly those closely located to human occupations. The use of such anthropogenic compounds frequently results in the selection of resistant individuals. However, how the underlying insecticide resistance mechanisms interplay with the abilities of the resistant individuals to cope with other environmental challenges (e.g., predators) has not received adequate attention. Here, we evaluated whether resistance to pyrethroid insecticides in larvae of the yellow fever mosquito, Aedes aegypti (Diptera: Culicidae), would affect their abilities to survive other environmental challenges. We assessed the susceptibilities of the pyrethroid-resistant larvae to other insecticides (i.e., the oxadiazine indoxacarb and juvenile hormone mimic pyriproxyfen) and determined the activities of potential detoxification enzymes. Finally, we also recorded potential alterations in larva swimming behavior in the presence of predators, such as the water bug Belostoma anurum (Hemiptera: Belostomatidae). Our results revealed that high pyrethroid resistance was associated with moderate resistance to the other two insecticides. Furthermore, this multiple resistance was associated with higher detoxification activity by glutathione-S-transferases and general esterases. Interestingly, in comparison with insecticide-susceptible larvae, the pyrethroid-resistant larvae not only swam for longer periods and distances, but also took longer to be captured by B. anurum nymphs. Collectively, our findings revealed increased abilities to survive natural environmental challenges (e.g., predatory attacks) in mosquito larvae that express physiological and behavioral changes associated with multiple resistance to insecticides.

High-throughput analysis of insecticides on malaria vectors using liquid chromatography tandem mass spectrometry.

BackgroundDifferent setups and protocols have been developed for investigating insecticide effects on Anopheles (An.) mosquitoes, vectors of malaria. However, chemical uptake resulting from their tarsal contact with insecticide-treated material has seldom been investigated. To address the challenges encountered in the interpretation of bioassay data, a high throughput method for chemical analysis on malaria vectors was developed and validated for five selected insecticides including alpha-cypermethrin (aCYP), deltamethrin (DM), etofenprox (EPX), permethrin (PM), pirimiphos-methyl (PPM).MethodsThe method includes a single chemical extraction step via an ultrasound probe on mosquito samples and analysis via liquid chromatography coupled to high-resolution tandem mass spectrometry (UHPLC-MS/MS). The protocol was established for two malaria vector species, Anopheles gambiae senso stricto (s.s.) and An. stephensi, both males and females. Recovery rates ranged from 70 to 100% without any influence of sex or species. The method was efficiently applied to female An. gambiae s.s. of the KISUMU1 reference strain, after susceptibility tests using the World Health Organization’s standard protocol.ResultsSusceptibility tests revealed 13.4–18.4 minutes knockdown times for 50% mosquitoes during exposure to EPX and pyrethroids. The mortality rates 24 hours post-exposure to insecticides were mostly 99–100%, except in two PM and three PPM assays suggesting possible or confirmed resistance to these insecticides. The mean insecticide uptake in dead mosquitoes ranged from 23 pg (aCYP) to 1812 pg (EPX) per specimen. However, the mean uptake in survivors to PM and PPM was reduced by at least 25%, suggesting that acute doses were not achieved in these specimens during bioassays.ConclusionsThe developed and validated UHPLC-MS/MS method could be used to address some limitations of bioassays or to assess the penetration of insecticides in mosquito matrix with reference to cuticle thickness and other insecticide resistance mechanisms.

Bed bugs (Cimex lectularius L.) exhibit limited ability to develop heat resistance.

The global population growth of the bed bug, Cimex lectularius (L.), is attributed to their cryptic behavior, diverse insecticide resistance mechanisms, and lack of public awareness. Bed bug control can be challenging and typically requires chemical and non-chemical treatments. One common non-chemical method for bed bug management is thermal remediation. However, in certain instances, bed bugs are known to survive heat treatments. Bed bugs may be present after a heat treatment due to (i) abiotic factors associated with the inability to achieve lethal temperatures in harborage areas for a sufficient time period, (ii) re-infestation from insects that escaped to cooler areas during a heat treatment or (iii) development of physiological resistance that allows them to survive heat exposure. Previous research has investigated the optimal temperature and exposure time required for either achieving complete mortality or sublethally affecting their growth and development. However, no research has examined bed bug populations for their ability to develop resistance to heat exposure and variation in thermo-tolerance between different bed bug strains. The goals of this study were: i) to determine if bed bugs could be selected for heat resistance under a laboratory selection regime, and ii) to determine if bed bug populations with various heat exposure histories, insecticide resistance profiles, and geographic origins have differential temperature tolerances using two heat exposure techniques (step-function and ramp-function). Selection experiments found an initial increase in bed bug survivorship; however, survivorship did not increase past the fourth generation. Sublethal exposure to heat significantly reduced bed bug feeding and, in some cases, inhibited development. The step-function exposure technique revealed non-significant variation in heat tolerance between populations and the ramp-function exposure technique provided similar results. Based on these study outcomes, the ability of bed bugs to develop heat resistance appears to be limited.

Insecticide resistance in the tomato pinworm Tuta absoluta: patterns, spread, mechanisms, management and outlook

The South American tomato pinworm, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), is an invasive pest difficult to control. Insecticide application is quite common and remains the prevalent control method particularly in open-field cultivation systems. As a result, insecticide resistance to many chemical classes of insecticides has been described both in South America and in Europe. The development of insecticide resistance is relatively fast in this species, and the main mechanisms involved are altered target-site sensitivity and/or enhanced detoxification, depending on the chemical class. However, insecticide resistance mechanisms do not differ between South America and Europe and are mainly due to simple genotype variations leading to high levels of resistance. The presence of resistance alleles at low frequency, especially against newer chemistry, is of major concern, as they tend to spread with the invasions making tomato pinworm particularly difficult to control. The monitoring methods and management programmes developed for the species benefited from the pro-activity of the Insecticide Resistance Action Committee and its country groups, particularly in Brazil and Spain. Bioassay methods were developed, resistance monitoring activities initiated and resistance management guidance was provided. The implementation of integrated control programmes and appropriate resistance management strategies as part of such programs is of utmost importance to keep tomato pinworm infestations under economic damage thresholds, thus guaranteeing sustainable yields.

First detection of a Vssc allele V1016G conferring a high level of insecticide resistance in Aedes albopictus collected from Europe (Italy) and Asia (Vietnam), 2016: a new emerging threat to controlling arboviral diseases.

Introduction Aedes albopictus (Skuse) is an important vector of arboviral diseases, including dengue, chikungunya and Zika virus disease. Monitoring insecticide resistance and mechanisms by which the mosquito develops resistance is crucial to minimise disease transmission.AimTo determine insecticide resistance status and mechanisms in Ae. albopictus from different geographical regions.MethodsWe sampled 33 populations of Ae. albopictus from Asia, Europe and South America, and tested these for susceptibility to permethrin, a pyrethroid insecticide. In resistant populations, the target site for pyrethroids, a voltage-sensitive sodium channel (Vssc) was genotyped. Three resistant sub-strains, each harbouring a resistance allele homozygously, were established and susceptibilities to three different pyrethroids (with and without a cytochrome P450 inhibitor) were assayed.ResultsMost populations of Ae. albopictus tested were highly susceptible to permethrin but a few from Italy and Vietnam (4/33), exhibited high-level resistance. Genotyping studies detected a knockdown resistance (kdr) allele V1016G in Vssc for the first time in Ae. albopictus. Two previously reported kdr alleles, F1534C and F1534S, were also detected. The bioassays indicated that the strain homozygous for the V1016G allele showed much greater levels of pyrethroid resistance than other strains harbouring F1534C or F1534S.ConclusionThe V1016G allele was detected in bothAsian and Italian Ae. albopictus populations, thus a spread of this allele beyond Italy in Europe cannot be ruled out. This study emphasises the necessity to frequently and regularly monitor the V1016G allele in Ae. albopictus, particularly where this mosquito species is the main vector of arboviruses.

Insecticide resistance genes affect Culex quinquefasciatus vector competence for West Nile virus.

Insecticide resistance has been reported to impact the interactions between mosquitoes and the pathogens they transmit. However, the effect on vector competence for arboviruses still remained to be investigated. We examined the influence of two insecticide resistance mechanisms on vector competence of the mosquito Culex quinquefasciatus for two arboviruses, Rift Valley Fever virus (RVFV) and West Nile virus (WNV). Three Cx. quinquefasciatus lines sharing a common genetic background were used: two insecticide-resistant lines, one homozygous for amplification of the Ester2 locus (SA2), the other homozygous for the acetylcholinesterase ace-1 G119S mutation (SR) and the insecticide-susceptible reference line Slab. Statistical analyses revealed no significant effect of insecticide-resistant mechanisms on vector competence for RVFV. However, both insecticide resistance mechanisms significantly influenced the outcome of WNV infections by increasing the dissemination of WNV in the mosquito body, therefore leading to an increase in transmission efficiency by resistant mosquitoes. These results showed that insecticide resistance mechanisms enhanced vector competence for WNV and may have a significant impact on transmission dynamics of arboviruses. Our findings highlight the importance of understanding the impacts of insecticide resistance on the vectorial capacity parameters to assess the overall consequence on transmission.

Susceptibility to common insecticides and detoxifying enzyme activities in Anopheles sundaicus (sensu lato) after cessation of indoor residual spraying of insecticides in the Jaffna Peninsula and its surroundings in northern Sri Lanka

BackgroundSri Lanka has been malaria-free since 2013 but re-introduction of malaria transmission by infected overseas travelers is possible due to a prevalence of potent malaria vectors. Knowledge of the insecticide resistance status among Anopheles vectors is important if vector control has to be reintroduced in the island. The present study investigated the insecticide susceptibility levels and resistance mechanisms of Anopheles sundaicus (sensu lato) (previously classified as Anopheles subpictus species B) an important malaria vector in the Jaffna Peninsula and it surroundings in northern Sri Lanka after indoor residual spraying of insecticides was terminated in 2013.ResultsSpecies-specific PCR assays identified An. sundaicus (s.l.) in four locations in the Jaffna and adjacent Kilinochchi districts. Bioassays confirmed that An. sundaicus (s.l.) collected in Kilinochchi were completely susceptible to 0.05% deltamethrin and 5% malathion and resistant to 4% dichlorodiphenyltrichloroethane (DDT), whereas those from Jaffna were relatively susceptible to all three insecticides. Kilinochchi populations of An. sundaicus (s.l.) showed significantly higher glutathione S-transferase activity than population from Jaffna. However, Jaffna An. sundaicus (s.l.) had significantly higher Propoxur-resistant acetylcholinesterase activity. Activities of non-specific esterases and monooxygenases were not significantly elevated in An. sundaicus (s.l.) collected in both districts.ConclusionsThe susceptibility to malathion and deltamethrin in An. sundaicus (s.l.) suggests that they can be still used for controlling this potential malaria vector in the Jaffna Peninsula and adjacent areas. Continuing country-wide studies on other malaria vectors and their insecticide susceptibilities are important in this regard.

Transcription factor FTZ-F1 and cis-acting elements mediate expression of CYP6BG1 conferring resistance to chlorantraniliprole inPlutella xylostella.

Cytochrome P450-mediated detoxification plays an important role in the development of insecticide resistance. Previous studies have demonstrated that overexpression of CYP6BG1 was responsible for permethrin resistance in Plutella xylostella, and our experiments also showed that upregulation of this gene is associated with chlorantraniliprole resistance in P.xylostella. However, the transcriptional regulation involved in the expression of CYP6BG1 remains unknown. To further investigate the regulation of CYP6BG1 expression, the promoters of this gene were cloned and analyzed from one susceptible and four different resistant populations of P. xylostella. First, the promoter region of P. xylostella CYP6BG1 was compared in five populations, and three types of 5'-flanking region were found. Second, the region between -562 and +49 of CYP6BG1 in a field population (TH) of P. xylostella showed the highest promoter activity and could be induced by chlorantraniliprole. Third, the transcriptional factor FTZ-F1, which is an orphan nuclear receptor and binds to the fushi tarazu (ftz) gene, was predicted by the online software Alggen and Jaspar. It was proved to regulate the expression of CYP6BG1 by RNAi. The expression levels of FTZ-F1 and CYP6BG1 could be induced by chlorantraniliprole and were significantly higher in the resistant populations. These data give a better understanding of the transcriptional regulation of an important insecticide detoxification enzyme gene, and therefore will help in understanding the molecular mechanisms of insecticide resistance in P. xylostella. © 2018 Society of Chemical Industry.

Transcript-Level Analysis of Detoxification Gene Mutation-Mediated Chlorpyrifos Resistance in Laodelphax striatellus (Hemiptera: Delphacidae).

Enhanced detoxification and target mutations that weaken insecticide binding ability are major mechanisms of insecticide resistance. Among these, over-expression or site mutations of carboxylesterase (CarE), cytochrome P450s (CYP450), and glutathione-S-transferase (GST) were the main form responsible for insecticide detoxification; however, transcript-level analysis of the relationship of detoxification gene mutations with chlorpyrifos (an organophosphorus insecticide) resistance is scarce thus far. In this study, multiple sites exhibiting polymorphisms within three detoxification genes were firstly examined via sequencing among different chlorpyrifos-resistant and susceptible individuals of Laodelphax striatellus. For example, the mutation frequencies of A374V in LsCarE16 were 83, 33, and 3%, S277A in LsCarE24 were 88, 28, and 3%, E36K in LsCYP426A1 were 100, 65, and 0% for chlorpyrifos-resistant, resistant decay, and susceptible individuals, respectively. Analysis also found expression levels of GSTd1, GSTt1, GSTs2, CYP4DE1U1, and CYP425B1 are coordinated with chlorpyrifos resistance levels; moreover, we found the deficiencies of 43S and 44A as well as two point mutations of E60D and Q61H at N-terminal region of the OP potential target acetylcholinesterase (AChE) in high resistant but not in low-chlorpyrifos resistant individuals. The results above all demonstrated the dynamic evolutionary process of insecticide resistance and revealed some resistance factors that only played roles at certain resistance level; high insecticide resistance in this example is the result of synergistic impact from multiple resistance factors.

Anopheles bionomics, insecticide resistance mechanisms, and malaria transmission in the Korhogo area, northern Côte d'Ivoire: a pre-intervention study.

A better understanding of malaria transmission at a local scale is essential for developing and implementing effective control strategies. In the framework of a randomized controlled trial (RCT), we aimed to provide an updated description of malaria transmission in the Korhogo area, northern Côte d’Ivoire, and to obtain baseline data for the trial. We performed human landing collections (HLCs) in 26 villages in the Korhogo area during the rainy season (September–October 2016, April–May 2017) and the dry season (November–December 2016, February–March 2017). We used PCR techniques to ascertain the species of the Anopheles gambiae complex, Plasmodium falciparum sporozoite infection, and insecticide resistance mechanisms in a subset of Anopheles vectors. Anopheles gambiae s.l. was the predominant malaria vector in the Korhogo area. Overall, more vectors were collected outdoors than indoors (p < 0.001). Of the 774 An. gambiae s.l. tested in the laboratory, 89.65% were An. gambiae s.s. and 10.35% were An. coluzzii. The frequencies of the kdr allele were very high in An. gambiae s.s. but the ace-1 allele was found at moderate frequencies. An unprotected individual living in the Korhogo area received an average of 9.04, 0.63, 0.06 and 0.12 infected bites per night in September–October, November–December, February–March, and April–May, respectively. These results demonstrate that the intensity of malaria transmission is extremely high in the Korhogo area, especially during the rainy season. Malaria control in highly endemic areas such as Korhogo needs to be strengthened with complementary tools in order to reduce the burden of the disease.