Deltamethrin Resistance Research Articles

First detection of voltage-gated sodium channel mutations in Phlebotomus argentipes collected from Bangladesh

Phlebotomus argentipes is the main vector of visceral leishmaniasis in Bangladesh and is controlled using deltamethrin, a synthetic pyrethroid, through indoor residual spraying (IRS). A mutation at L1014 (leucine at codon 1014) of the voltage-gated sodium channel (VGSC), known as a knockdown resistance (kdr) gene, is thought to be an important pyrethroid resistance mechanism. This study detected mutations at codon 1014, and at codons 1011, 1016, and 1020, which are kdr sites in other insects. The kdr relationship with deltamethrin resistance in P. argentipes from an IRS-targeted site in Bangladesh was also evaluated. Sand flies were collected from Magurjora village, Mymensingh district, Bangladesh in November 2012. A WHO cone bioassay test using deltamethrin was conducted and specimens were grouped as 'live' or 'dead'. After morphological identification, genomic DNA was used to genotype a partial VGSC gene from P. argentipes. The kdr/ pyrethroid resistance relationship was evaluated using Fisher's exact test. Targeted codons were genotyped from 8 'live' and 63 'dead' P. argentipes. All 'live' specimens had mutant alleles (L1014F and L1014S) at codon 1014. The mutant allele rate was 94% for 'live' specimens and 55% for 'dead' specimens. The mutant allele survival odds were higher for the wild-type L1014L allele, and L1014F odds were lower for L1014S. There were no mutations at codons 1011, 1016, and 1020. The L1014 mutations suggested that pyrethroid resistance had appeared in Bangladesh. Further research on kdr mutations in P. argentipes is important for the appropriate IRS.

Deltamethrin resistance status of Rhipicephalus (Boophilus) Microplus ticks in gaddi goats of north-western Himalayas, India

In this study, adult immersion test (AIT) and larval packet test (LPT) were employed for the evaluation of deltamethrin resistance status in Rhipicephalus (Boophilus) microplus ticks collected from organised and unorganised goat farms of Palampur (Himachal Pradesh). On AIT, the mean mortality varied significantly (P<0.05) fromnil (controland upto 200 ppm delta methrin) to 40.0±0.24% (800 ppm delta methrin). The inhibition of oviposition varied significantly (P<0.05) from nil (control) to 28.83% (800 ppm deltamethrin). The RF (resistance factor) values on AIT and LPT were 23.98 and 10.2, respectively, suggesting level II of resistance (moderate) against deltamethrin in Rhipicephalus (Boophilus) microplus ticks from Gaddi goats of north-western Himalayas.

Adaptation by copy number variation increases insecticide resistance in the fall armyworm

Understanding the genetic basis of insecticide resistance is a key topic in agricultural ecology. The adaptive evolution of multi-copy detoxification genes has been interpreted as a cause of insecticide resistance, yet the same pattern can also be generated by the adaptation to host-plant defense toxins. In this study, we tested in the fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae), if adaptation by copy number variation caused insecticide resistance in two geographically distinct populations with different levels of resistance and the two host-plant strains. We observed a significant allelic differentiation of genomic copy number variations between the two geographic populations, but not between host-plant strains. A locus with positively selected copy number variation included a CYP gene cluster. Toxicological tests supported a central role for CYP enzymes in deltamethrin resistance. Our results indicate that copy number variation of detoxification genes might be responsible for insecticide resistance in fall armyworm and that evolutionary forces causing insecticide resistance could be independent of host-plant adaptation.

Investigation of deltamethrin resistance in salmon lice (Lepeophtheirus salmonis) provides no evidence for roles of mutations in voltage-gated sodium channels.

The pyrethroid deltamethrin is used to treat infestations of farmed salmon by parasitic salmon lice, Lepeophtheirus salmonis (Krøyer). However, the efficacy of deltamethrin for salmon delousing is threatened by resistance development. In terrestrial arthropods, knockdown resistance (kdr) mutations of the voltage-gated sodium channel (Nav ), the molecular target for pyrethroids, can cause deltamethrin resistance. A putative kdr mutation of an L. salmonis sodium channel homologue (LsNav 1.3 I936V) has been identified previously. At the same time, deltamethrin resistance of L. salmonis has been shown to be inherited maternally and to be associated with mitochondrial DNA (mtDNA) mutations. This study assessed potential roles of the above putative kdr mutation as a determinant of deltamethrin resistance in laboratory strains and field populations of L. salmonis. The deltamethrin-resistant L. salmonis strain IoA-02 expresses the LsNav 1.3 I936V mutation but was susceptible to the non-ester pyrethroid etofenprox, a compound against which pyrethroid-resistant arthropods are usually cross-resistant if resistance is caused by Nav mutations. In a family derived from a cross between an IoA-02 male and a drug-susceptible female lacking the kdr mutation, deltamethrin resistance was not associated with the genotype at the LsNav 1.3 locus (P > 0.05). Similarly, in Scottish field populations of L. salmonis, LsNav 1.3 I936V showed no association with deltamethrin resistance. By contrast, genotypes at the mtDNA loci A14013G and A9030G were significantly associated with deltamethrin resistance (P < 0.001). In the studied L. salmonis isolates, deltamethrin resistance was unrelated to the LsNav 1.3 I936V mutation, but showed close association with mtDNA mutations.

Ran participates in deltamethrin stress through regulating the nuclear import of Nrf2

The small GTPase Ran has a variety of biological functions, one of the most prominent of which is to regulate nucleocytoplasmic transport. In our previous study, it was suggested that Ran is involved in the deltamethrin (DM) stress. In addition, Keap1-Nrf2-ARE pathway was also confirmed to be associated with DM stress. We report here that under DM stress, interfering Ran or nuclear transport factor Ntf2 by RNAi could suppress the nuclear import of nuclear transcription factor Nrf2 which then down-regulates the expressions of detoxification enzyme genes (Cyp4d20, Cyp4ae1, GstD5, Sod3, etc.), ultimately resulting in a significant apoptosis of Drosophila Kc cells. In contrast, after overexpressing Ran in Kc cells, Nrf2 has a higher concentration in the nucleus, and the expressions of detoxification enzyme genes are up-regulated, while the DM-induced apoptosis is significantly lower than that of the control group. Additionally, we preliminary found silencing Ntf2 or Ran could prevent the nuclear import of transcription factor Dif under DM stress, subsequently decreased expressions of antimicrobial peptide genes (Drsl1). In summary, our data mainly indicates that Ran may participate in DM stress through regulating the nuclear import of Nrf2, which could help to study the mechanism of deltamethrin resistance.

Transcription factor FTZ-F1 regulates mosquito cuticular protein CPLCG5 conferring resistance to pyrethroids in Culex pipiens pallens

BackgroundCulex pipiens pallens poses a serious threat to human health because of its widespread distribution, high carrier capacity for several arboviruses, frequent human-biting, and growth in urban environments. Pyrethroid insecticides have been mainly used to control adult Cx. pipiens pallens during outbreaks of mosquito-borne diseases. Unfortunately, mosquitoes have developed resistance, rendering the insecticides ineffective. Cuticular resistance is the primary mechanism of pyrethroid resistance. Previously, we revealed that cuticular protein of low complexity CPLCG5 is a major cuticular protein associated with deltamethrin resistance in Cx. pipiens pallens, which is enriched in the cuticle of mosquitoes’ legs and participates in pyrethroid resistance by forming a rigid matrix. However, the regulatory mechanisms of its transcription remain unknown.ResultsFirst, qRT-PCR analysis revealed that the expression of FTZ-F1 (encoding Fushi tarazu-Factor 1) was ~ 1.8-fold higher in the deltamethrin-resistant (DR) than deltamethrin-susceptible (DS) strains at 24 h post-eclosion (PE) and ~ 2.2-fold higher in the DR strain than in the DS strain at 48 h PE. CPLCG5 and FTZ-F1 were co-expressed in the legs, indicating that they might play an essential role in the legs. Dual luciferase reporter assays and EMSA (electrophoretic mobility shift experiments) revealed that FTZ-F1 regulates the transcription of CPLCG5 by binding to the FTZ-F1 response element (− 870/− 864). Lastly, knockdown of FTZ-F1 not only affected CPLCG5 expression but also altered the cuticle thickness and structure of the legs, increasing the susceptibility of the mosquitoes to deltamethrin in vivo.ConclusionsThe results revealed that FTZ-F1 regulates the expression of CPLCG5 by binding to the CPLCG5 promoter region, altering cuticle thickness and structure, and increasing the susceptibility of mosquitoes to deltamethrin in vivo. This study revealed part of the mechanism of cuticular resistance, providing a deeper understanding of insecticide resistance.

Cypermethrin resistance in Hyalomma anatolicum and Rhipicephalus microplus ticks of arid and semi-arid zone of Haryana, a northern state of India

Regular monitoring of the status of acaricide resistance in field ticks is the need of the hour. Synthetic pyrethroids (cypermethrin and deltamethrin) are most commonly used acaricides against field ticks. There is bulk of literature on development of deltamethrin resistance; however, scarce information is available regarding current status of cypermethrin efficacy against field ticks. In the present study, the cypermethrin resistance status in Rhipicephalus microplus and Hyalomma anatolicum ticks infesting cattle and buffaloes of five districts located in the Northern Indian state, Haryana was determined using larval packet test. The linear regression graphs of probit mortality of tick larvae were plotted against log concentrations of cypermethrin to determine the slope of mortality, LC50, LC95 and the resistance factor (RF).Seven isolates of R. microplus were found resistant with their RF ranges from 1.83 to 25.35, whereas, 5 isolates of H. anatolicum were recorded as resistant with their RF ranging from 1.54 to 2.56 indicating a slower pace of development of cypermethrin resistance in multi-host ticks. Jarwa isolate of R. microplus and Dhangar isolate of H. anatolicum was found susceptible (RF < 1.5) to cypermethrin. The RF values of Agroha and Siwani isolate of R. microplus (10.73 and 25.35) were much higher as compared to other isolates indicating an urgency to address the growing cypermethrin resistance problem at grassroots level. Data generated in the present technical program could be of enormous help in formulating a suitable strategy against ticks and tick-borne infections of humans and animals.

Cuticular thickening associated with insecticide resistance in dengue vector, Aedes aegypti L.

Aedes aegypti is a globally spread disease vector of supreme concern, primarily controlled by chemical insecticides. Current study investigates the comparative rate of acetamiprid and deltamethrin resistance development in Ae. aegypti larvae and; possible correlation between resistance and cuticular thickening. The larvae were selected with LC90 level of the respective insecticide for 10 successive generations and the level of resistance induced was estimated. The larvae of parent (PS), acetamiprid-selected (ACSF-10) and deltamethrin-selected (DLSF-10) strains were sectioned through first abdominal segment to elucidate the variation in cuticular thickness. The PS larvae of Ae. aegypti were 229.26-fold higher susceptible to deltamethrin as compared to acetamiprid, exhibiting corresponding LC50 values of 0.00082 mg/L and 0.18799 mg/L. Larval selections induced 9.91-fold and 19.74-fold resistance to deltamethrin and acetamiprid, respectively; indicating multifactorial and heterozygous pattern. Cuticular analysis of the larval sections demonstrated a significantly thicker cuticle in selected strains, the mean thickness in PS, ACSF-10 and DLSF-10 was 2.891 ± 0.243, 4.288 ± 0.508 and 5.695 ± 0.437 μm, respectively revealing 1.48-fold and 1.97-fold thicker cuticle in the ACSF-10 and DLSF-10 strains, respectively in comparison to PS strain. The increased cuticular thickness possibly inhibited the insecticide penetration in selected larvae resulting in the resistance development. This is the first such report which demonstrates the association between acetamiprid/deltamethrin resistance in Ae. aegypti larvae with the cuticular thickness.

Fine scale spatial investigation of multiple insecticide resistance and underlying target-site and metabolic mechanisms in Anopheles gambiae in central C\xf4te d\u2019Ivoire

Routine monitoring of occurrence, levels and mechanisms of insecticide resistance informs effective management strategies, and should be used to assess the effect of new tools on resistance. As part of a cluster randomised controlled trial evaluating a novel insecticide-based intervention in central Côte d’Ivoire, we assessed resistance and its underlying mechanisms in Anopheles gambiae populations from a subset of trial villages. Resistance to multiple insecticides in An. gambiae s.s. and An. coluzzii was detected across villages, with dose–response assays demonstrating extremely high resistance intensity to the pyrethroid deltamethrin (> 1,500-fold), and mortality following exposure to pyrethroid-treated bednets was low (< 30% mortality in cone bioassays). The 1014F kdr mutation was almost fixed (≥ 90%) in all villages but the 1575Y kdr-amplifying mutation was relatively rare (< 15%). The carbamate and organophosphate resistance-associated Ace-1 G119S mutation was also detected at moderate frequencies (22–43%). Transcriptome analysis identified overexpression of P450 genes known to confer pyrethroid resistance (Cyp9K1, Cyp6P3, and Cyp6M2), and also a carboxylesterase (COEAE1F) as major candidates. Cyp6P3 expression was high but variable (up to 33-fold) and correlated positively with deltamethrin resistance intensity across villages (r2 = 0.78, P = 0.02). Tools and strategies to mitigate the extreme and multiple resistance provided by these mechanisms are required in this area to avoid future control failures.

Multiple insecticide resistance in Aedes aegypti (Diptera: Culicidae) from Boyeros municipality, Cuba and associated mechanisms

In this study, insecticide resistance and the mechanisms responsible were characterized in Ae. aegypti of Boyeros municipality from Havana, Cuba. Boyeros represents a high epidemiological risk because it is located near the Havana International Airport, it is highly urbanized, and it has a large influx of people from endemic countries so that it qualifies as a sentinel site for surveillance. The larvae collected from five areas of this municipality showed resistance to temephos associated with metabolic enzymes. The adult mosquitoes displayed a deltamethrin resistance and less distinctly to other pyrethroids associated with a high frequency of sodium channel gene mutations (F1534C and V1016I), detected for the first time in a field population from Cuba. The presence in the field populations of two insecticide resistance mechanisms represents a limiting factor in the success of the control operations of this vector, so other strategies should be considered to preserve the effectiveness of the insecticides available in public health for vector control in Cuba.

Corrigendum.

Insect Molecular BiologyVolume 29, Issue 5 p. 498-498 CorrigendumFree Access Corrigendum This article corrects the following: Exome-wide association of deltamethrin resistance in Aedes aegypti from Mexico K. Saavedra-Rodriguez, C. L. Campbell, A. Lenhart, P. Penilla, S. Lozano-Fuentes, W. C. Black, Volume 28Issue 5Insect Molecular Biology pages: 591-604 First Published online: March 13, 2019 First published: 23 August 2020 https://doi.org/10.1111/imb.12660AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat In the article “Exome-wide association of deltamethrin resistance in Aedes aegypti from Mexico”, by K. Saavedra-Rodriguez et al. [1], the affiliation of coauthor P. Penilla was incorrectly published as “Division of Parasitic Diseases and Malaria, Center for Global Health, Centers for Disease Control and Prevention, Atlanta, GA, USA”. The correct affiliation should have been “Centro Regional de Investigación en Salud Pública, Instituto Nacional de Salud Pública, Tapachula, Chiapas, México”. The authors apologize for the error. Reference 1Saavedra-Rodriguez, K., Campbell, C.L., Lenhart, A., Penilla, P., Lozano-Fuentes, S. and Black, W.C.,.I.V. (2019) Exome-wide association of deltamethrin resistance in Aedes aegypti from Mexico. Insect Mol Biol, 28, 591– 604. https://doi.org/10.1111/imb.12575. Volume29, Issue5October 2020Pages 498-498 ReferencesRelatedInformation

Bed bugs, Cimex lectularius L., exhibiting metabolic and target site deltamethrin resistance are susceptible to plant essential oils

Pyrethroid resistance has been a major hurdle limiting the effective control of bed bugs (Cimex lectularius L.). Alternative approaches that include the use of plant essential oils (EOs) have been proposed for effective management of bed bugs. However, EO resistance level comparisons between pyrethroid susceptible and resistant bed bug populations have not been previously conducted. The goal of this study was twofold: (i) determine deltamethrin resistance levels and associated resistance mechanisms in the field-collected Knoxville strain and (ii) quantify resistance levels of the Knoxville strain to five EOs (thyme, oregano, clove, geranium and coriander), their major insecticidal constituents (thymol, carvacrol, eugenol, geraniol and linalool) and an EO-based product (EcoRaider®). First, we found that the Knoxville strain was 72,893 and 291,626 fold more resistant to topically applied deltamethrin in comparison to the susceptible Harlan strain at the LD25 and LD50 lethal dose levels, respectively. Synergist bioassays and detoxification enzyme assays revealed significantly higher activity of cytochrome P450 and esterase enzymes in the resistant Knoxville strain. Further, Sanger sequencing revealed the presence of the L925I mutation in the voltage-sensitive sodium channel α subunit gene. The Knoxville strain that possesses both enzymatic and target site deltamethrin resistance, however, did not show any resistance to EOs, their major insecticidal constituents and EcoRaider® in topical bioassays (resistance ratio of ~1). In conclusion, this study demonstrated that a deltamethrin-resistant strain of bed bugs is susceptible to EOs and their insecticidal constituents.

Genetic structure of deltamethrin-resistant populations of Triatoma infestans (Hemiptera: Reduviidae) in the Gran Chaco.

The genetic structure of natural populations offers insight into the complexities of their dynamics, information that can be relevant to vector control strategies. Microsatellites are useful neutral markers to investigate the genetic structure and gene flow in Triatoma infestans, one of the main vectors of Chagas disease in South America. Recently, a heterogeneous pyrethroid-resistant hotspot was found in the Argentine Gran Chaco, characterized by the highest levels of deltamethrin resistance found at the present time. We applied population genetics analyses to microsatellite and village data and search for associations between the genetic variability and the heterogeneous toxicological pattern previously found. We genotyped 10 microsatellite loci in 67 T. infestans from 6 villages with no, low, and high pyrethroid resistance. The most genetically diverse populations were those susceptible or with low values of resistance. In contrast, high-resistance populations had lower herozygosity and some monomorphic loci. A negative association was found between variability and resistant ratios. Global and pairwise FSTs indicated significant differentiation between populations. The only susceptible population was discriminated in all the performed studies. Low-resistance populations were also differentiated by a discriminant analysis of principal components (DAPC) and were composed mostly by the same two genetic clusters according to STRUCTURE Bayesian algorithm. Individuals from the high-resistance populations were overlapped in the DAPC and shared significant proportions of a genetic cluster. These observations suggest that the resistant populations might have a common origin, although more genetic markers and samples are required to test this hypothesis more rigorously.

Aerobic Metabolism Alterations as an Evidence of Underlying Deltamethrin Resistance Mechanisms in Triatoma infestans (Hemiptera: Reduviidae)

Triatoma infestans (Klug, 1834), the main vector of Chagas disease in Latin America, is regularly controlled by spraying the pyrethroid deltamethrin, to which some populations have developed resistance. The three main mechanisms of resistance are 1) metabolic resistance by overexpression or increased activity of detoxifying enzymes, 2) target site mutations, and 3) cuticle thickening/modification. We use open-flow respirometry to measure real-time H2O loss rate (V˙H2O) and CO2 production rate (V˙CO2), on nymphs from susceptible and resistant populations before and after exposure to the insecticide to understand the underlying mechanisms of resistance in live insects. Lack of differences in V˙H2O between populations suggested that cuticular thickness/composition is not acting as a relevant resistance mechanism. Similarly, there was no difference in resting V˙CO2, suggesting a trade-off between resistance mechanisms and other physiological processes. The increment in V˙CO2 after application of deltamethrin was similar in both populations, which suggested that while enhanced enzymatic detoxification may play a role in resistance expression in this population, the main mechanism involved should be a passive one such as target site mutations. Open-flow respirometry provided useful evidence for evaluating the mechanisms involved in deltamethrin resistance. Using this technique could improve efficiency of scientific research in the area of insecticide resistance management, leading to a faster decision making and hence improved control results.

Detection of single nucleotide polymorphism in the para-sodium channel gene of Rhipicephalus annulatus populations from Egypt resistant to deltamethrin

Rhipicephalus annulatus field populations collected from small cattle farms in Beni-Suef province in Egypt were evaluated for deltamethrin resistance by toxicological in vitro bioassays (adult immersion test-AIT and larval packet test-LPT). Moreover, a quantitative PCR high resolution melting (PCR-HRM) technique was used to detect nucleotide substitutions in the voltage-gated sodium channel (Na-channel) gene. By the in vitro bioassays, the examined ticks were phenotypically categorized as deltamethrin susceptible (populations El-Wasta - A, and El-Hakamna - C) or resistant (populations El-Wasta - B, El-Hakamna - D, EL-Halabia - E, and Kom-abokhalad - F). Based on LPT findings, the phenotypic resistant populations were found to have a resistance ratio between 6.5 – 10.8. The PCR-HRM genotyping of the ticks showed variable melting curves among the populations in domain II of the Na-channel gene. Analysis of the curves showed the presence of wild type, mutant homozygous, and mutant heterozygous tick individuals. By sequencing the PCR amplified fragments, the C190A mutation was the only detected nucleotide polymorphism of domain II among the phenotypically resistant populations, which was present in 39.5 % (34/86) of the ticks tested. On the other hand, the phenotypically susceptible populations A and C did not show C190A mutant homozygous (RR) individuals. Meanwhile, in domain III all of the examined populations revealed melting curves like the wild type. Furthermore, the sequence analysis of these populations confirmed the absence of SNPs in domain III. The C190A single point mutation was detected for the first time in domain II of the Na-channel gene of deltamethrin-resistant R. annulatus in Egypt using PCR-HRM. Screening for efficacy of chemical compounds used by farmers to control ticks on cattle should be considered as part of animal health programs to manage the emerging resistance to acaricides in R. annulatus populations.

Preliminary Selection and Analysis of Deltamethrin-Resistant Strains ofAedes albopictusin the Laboratory

Background: Aedes albopictus is a major vector for transmission of many viral pathogens. Deltamethrin resistance was analyzed by catching A. albopictus in the field; the analysis effect is affected by many insecticides that often interact with A. albopictus in the field environment. Materials and Methods: This study examined the development of deltamethrin resistance in A. albopictus mosquitoes under controlled laboratory conditions, focusing on morphological changes, reproductive fitness, and mutation of the knockdown resistance (kdr) gene. Deltamethrin-resistant strains were selected up to the 20th generation. To determine the level of resistance, the lethal concentration 50 (LC50) of deltamethrin in the larvae was obtained, followed by the resistance ratio (RR), and in adult mosquitoes, mortality rates were calculated using the contact tube method. Results: An increase in the LC50 from 0.0070 to 0.0563 mg/L was observed in resistant versus sensitive strains, with an increase of 11.26 in the RR. Overall, the results of the larval resistance bioassay showed that resistant larvae had medium resistance; however, by the 20th generation, adult mosquitoes showed strong resistance. PCR amplification, cloning, and sequencing of sodium channel domain III gene fragments were subsequently carried out using selected resistant and sensitive female mosquitoes. As a result, a number of base mutations were observed in the kdr gene in the resistant strain; however, no amino acid sequence mutations were observed, suggesting that base sequence changes did not affect protein expression. Results of morphological changes between resistant and sensitive strains showed that significant differences in the body, foreleg, mid leg, and hind leg length, as well as wing length and width, antenna length, and proboscis length were observed between 18th-generation resistant and sensitive strains of A. albopictus. On analysis of reproductive fitness associated with deltamethrin resistance in selection of mosquitoes, observation results showed differences between resistant and sensitive strains; the female/male ratio of mosquitoes decreased after pupa hatching, with more females and fewer males. Conclusions: The model of deltamethrin-resistant selection of A. albopictus was successfully established in the laboratory. The morphological phenotypes of the deltamethrin-resistant population of A. albopictus mosquitoes had changed. The kdr gene of the 19th and 20th generations of deltamethrin-resistant A. albopictus mosquitoes had silent mutations at several sites. After deltamethrin resistance selection, the female/male ratio of mosquitoes increased after pupa hatching, with more females and fewer males, hinting at increased chances of more female mosquitoes transmitting diseases.

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

BackgroundInsecticide resistance is a serious problem for vector control programmes worldwide. Resistance is commonly attributed to mutations at the insecticide’s target site or increased activity of detoxification enzymes.MethodsWe determined the knockdown concentration (KC50) and lethal concentration (LC50) of deltamethrin in six natural populations of adult Aedes aegypti from southeastern Mexico. These populations were then selected over five generations using the LC50 from the preceding generation that underwent selection, and the heritability of deltamethrin resistance was quantified. For each generation, we also determined the frequency of the kdr alleles L410, I1016 and C1534, and the levels of activity of three enzyme families (α- and β-esterases, mixed-function oxidases and glutathione S-transferases (GST)) associated with insecticide detoxification.ResultsThere was an increase in KC50 and LC50 values in the subsequent generations of selection with deltamethrin (FS5vs FS0). According to the resistance ratios (RRs), we detected increases in LC50 ranging from 1.5 to 5.6 times the values of the parental generation and in KC50 ranging from 1.3–3.8 times the values of the parental generation. Triple homozygous mutant individuals (tri-locus, LL/II/CC) were present in the parental generations and increased in frequency after selection. The frequency of L410 increased from 1.18-fold to 2.63-fold after selection with deltamethrin (FS5vs FS0) in the populations analyzed; for I1016 an increase between 1.19-fold to 2.79-fold was observed, and C1534 was fixed in all populations after deltamethrin selection. Enzymatic activity varied significantly over the generations of selection. However, only α- esterase activity remained elevated in multiple populations after five generations of deltamethrin selection. We observed an increase in the mean activity levels of GSTs in two of the six populations analyzed.ConclusionsThe high levels of resistance and their association with high frequencies of kdr mutations (V410L, V1016I and F1534C) obtained through artificial selection, suggest an important role of these mutations in conferring resistance to deltamethrin. We highlight the need to implement strategies that involve the monitoring of kdr frequencies in insecticide resistance monitoring and management programmes.

Mutations in the voltage-gated sodium channel gene associated with deltamethrin resistance in commercially sourced Phytoseiulus persimilis.

The implementation of Integrated Pest Management in current agricultural practice is a convenient and very effective strategy to keep pest populations under control. The use of biological control agents, such as Phytoseiulus persimilis, is key for the success of such an approach. This predatory mite is widely used as it is very effective for controlling Tetranychus urticae, one of the most devastating crop pests. Here, we identify several mutations located in the voltage-gated sodium channel (VGSC) of commercially sourced P. persimilis that correlate with a reduced susceptibility to the pyrethroid deltamethrin. We found that the mites sourced from two different biocontrol product companies have intrinsic genotypic differences that correlate with their phenotype when tested with different concentrations of deltamethrin. Mites from Syngenta Bioline, carrying the mutations M918L and A1536T, were able to survive deltamethrin concentrations of up to 10 ppm, while the mites from Koppert Biological Systems, with the combination M918L, L925V and S1539T, survived treatment with 40 ppm. All of the point mutations identified in the predatory mite samples are located in a particular region of the VGSC, previously proposed as the binding site for this family of pesticides and identified as a 'hot spot' for resistance.

Efficacy and cytotoxic potential of deltamethrin, essential oils of Cymbopogon citratus and Cinnamonum camphora and their synergistic combinations against stored product pest, Trogoderma granarium (Everts)

Residual film method was followed to analyze the toxicity of deltamethrin, essential oils (EOs) of Cymbopogon citratus and Cinnamonum camphora in separate and form of various combinations against LHR1 and LHR2 populations of fifth instar larvae of Trogoderma granarium. The cytotoxic potential of LC50s of both EOs, deltamethrin and their various combinations was as well investigated. The LHR2 population showed 23.73 fold deltamethrin resistance with respect to LHR1 population. Both EOs had high insecticidal activity than deltamethrin but C. citratus EO was less toxic than C. camphora EO against both populations. Based on strength of synergism and dose reduction index, the order of insecticidal activity of combinations in LHR1 population was: C. citratus EO: deltamethrin < C. camphora EO: deltamethrin < C. citratus EO: C. camphora EO < C. citratus EO: C. camphora EO: deltamethrin. In LHR2 population the order was: C. citratus EO: C. camphora EO < C. citratus EO: deltamethrin < C. camphora EO: deltamethrin < C. citratus EO: C. camphora EO: deltamethrin. Following to exposure of LC50 of each treatment various markers of cytotoxicity viz., haemocyte viability, cell proliferation rate and mitochondrial dehydrogenase activity were decreased significantly with respect to control in both populations. Except for deltamethrin, each treatment significantly increased the lactate dehydrogenase activity. Phenoloxidase activity was reduced significantly in LHR1 population following to exposure of each treatment. Likewise, LHR2 population also showed significantly reduced activity of phenoloxidase following to exposure of each treatment except deltamethrin as it increased the activity. Furthermore, each marker of cytotoxicity was fluctuated in relation to the toxicity of LC50 of treatments and combination contained both EOs and deltamethrin produced highest cytotoxicity. Findings of this study should be used in granaries for the effective control of insecticide resistance in T. granarium1.

Deltamethrin resistance in Chagas disease vectors colonizing oil palm plantations: implications for vector control strategies in a public health-agriculture interface

BackgroundTriatomine bugs are responsible for the vectorial transmission of the parasite Trypanosoma cruzi, etiological agent of Chagas disease, a zoonosis affecting 10 million people and with 25 million at risk of infection. Several triatomine species of the genus Rhodnius have been found inhabiting palm crowns where insects can find shelter in leaves axils and blood from palm-associated vertebrates. Rhodnius prolixus insects have been collected in oil palms in Colombia, and high T. cruzi infection rates were found. Since pest control is carried out in oil palm plantations, continuous exposure to insecticides could be occurring in these triatomines. Some insecticides suggested for pest control in oil palm plantations are also recommended for triatomine control in human dwellings. In this study, our objective was to assess if triatomines inhabiting oil palms exhibit resistance to deltamethrin, an insecticide used for vector control.MethodsRhodnius prolixus nymphs were sampled in oil palms located in Tauramena, Colombia. To determine deltamethrin resistance, biological and biochemical assays were carried out on fifth-instar nymphs from the F1 generation. For biological assays, pure and commercial deltamethrin were used, and in biochemical assays, activities of detoxifying enzymes related to pyrethroid resistance, such as oxidases, esterases and transferases, were quantified.ResultsDeltamethrin lethal dosage 50 and 90 in R. prolixus from oil palms was significantly higher than in those from a susceptible colony suggesting possible deltamethrin resistance. Moreover, mortality with commercial deltamethrin was very low in insects from oil palms. In biochemical assays, the activity of evaluated detoxifying enzymes was significantly higher in R. prolixus from oil palms than in those from the susceptible colony.ConclusionsPossible deltamethrin resistance found in R. prolixus insects from oil palms could threaten traditional vector control strategies in urban settings if insecticide-resistant triatomines can migrate from oil palms plantations. In palm oil producer countries such as Colombia, the oil palm plantations are growing constantly during the last years. We suggest that pest control strategies in oil palm crops should include triatomine surveillance and toxicological monitoring, especially in zones with several Chagas disease cases.